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Duc Tung Nguyen

Artificial and factitious foods for the production and

population enhancement of phytoseiid predatory mites

2015D

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ISBN 978-90-5989-764-9

To my family

Promoter: Prof. dr. ir. Patrick De Clercq

Department of Crop Protection,

Faculty of Bioscience Engineering,

Ghent University, Belgium

Chair of the examination committee: Prof. dr. ir. Geert Haesaert

Department of Applied Biosciences



Members of the examination committee: Prof. dr. Gilbert Van Stappen

Department of Animal Production



Prof. dr. ir. Luc Tirry

Department of Crop Protection,



Prof. dr. ir. Stefaan De Smet

Department of Animal Production



Prof. dr. Felix Wäckers

Lancaster Environment Centre

University of Lancaster, United Kingdom

Prof. dr. Nguyen Van Dinh

Department of Entomology

Faculty of Agronomy

Vietnam National University of Agriculture, Vietnam

Dean:

Prof. dr. ir. Guido Van Huylenbroeck

Rector:

Prof. dr. Anne De Paepe

Artificial and factitious foods for the

production and population enhancement of

phytoseiid predatory mites

by

Duc Tung Nguyen

Thesis submitted in the fulfillment of the requirements for the Degree of Doctor (PhD) in

Applied Biological Sciences

Dutch translation:

Artificiële en onnatuurlijke voedselbronnen voor de productie en de populatie-ondersteuning

van roofmijten uit de familie Phytoseiidae

Please refer to this work as follows:

Nguyen, D.T. 2015. Artificial and factitious foods for the production and population

enhancement of phytoseiid predatory mites. PhD Thesis, Ghent University, Ghent, Belgium

Frontcover: A female Amblyseius swirskii

Backcover: Top: dry decapsulated cysts of A. franciscana. Middle left: prepupae of black

soldier fly, Hermetia illucens. Middle right: Ephestia kuehniella eggs. Bottom:

pupae of Chinese oak silkworm Antheraea pernyi

ISBN-number: 978-90-5989-764-9

The research was conducted at the Laboratory of Agrozoology, Department of Crop

Protection, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000

Ghent, Belgium.

The author and promoter give the permission to use this study for consultation and to copy

parts of it for personal use only. Every other use is subject to copyright laws. Permission to

reproduce any material should be obtained from the author.

Acknowledgement

Undertaking this PhD has been a truly life-changing experience for me and it would not have

been obtained without the support and guidance that I received from many people. So many

people I would like to acknowledge, however, it might not be simple to express it enough.

First of all, I would like to thank my promoter, Prof. dr. ir. Patrick De Clercq for his

brilliant supervision. He gave me a valuable opportunity to do my PhD at the Laboratory of

Agrozoology, Ghent University. For me, he is not only an excellent advisor but also a

respected colleague. He is always very kind to discuss, encourage and listen to my ideas. I

much appreciate his time spent to read, correct and comment on my manuscripts, especially

during his busy time and even his holiday period to help finish my writing on time. I would

like to thank him again for his support and encouragement.

I sincerely want to thank the members of the examination committee: Prof. dr. ir.

Geert Haesaert, Prof. dr. Gilbert Van Stappen, Prof. dr. ir. Luc Tirry, Prof. dr. ir. Stefaan De

Smet, Prof. dr. Felix Wäckers and Prof. dr. Nguyen Van Dinh for their thorough reading of

my manuscript and their useful comments and suggestions that undoubtedly helped to

improve my thesis further.

I would like to give special thanks to Dominiek Vangansbeke who accompanied me

for the past four years. It is hard for me to find enough words to express my gratitude to him

for so much help and his contributions to this thesis. I feel so lucky to have him as a colleague

in my PhD project and I enjoyed very much our discussion about the research, culture, food

and whatever. I also thank Jochem Bonte for his guidance in statistical analysis. I sincerely

thank Lü Xin and Thomas Spranghers for sharing the ideas about the Chinese oak silkworm

and black soldier fly hemolymph and providing the materials for my experiments. I would

like to acknowledge the students Simon Craeye and Vincent Bouguet for their contributions to

this dissertation. I wish you all success in your research and in your careers.

I enjoyed very much working in the office which I shared with Joachim Moens and

Annelies Scholaert and later with Veerle Van Damme and Xie Jia Qin. I am deeply grateful

for their warm friendship and help. I would like to express my sincere thanks to Leen Dierick,

Bjorn Vandekerkhove, Rik Van Caenegem and Didier Van de Velde for their help with

administrative and other issues. I would like to extend my thanks to other colleagues and

friends in the Laboratory of Agrozoology: Thijs Machtelinckx, Sara Maes, Brecht Ingels,

Veronic De Puysseleyr, Jisheng Liu, Yu Na, and more.

I would like to thank Koppert B.V., Biobest N.V., the Artemia Reference Center

(ARC) of Ghent University and the Guangdong Entomological Institute, China for support

and for providing materials used in this research.

I gratefully acknowledge the funding received towards my PhD from the Ministry of

Education and Training (MOET, project 322). I would like to express my deep appreciation to

all of my colleagues at the Entomology Department, Vietnam National University of

Agriculture for their encouragement and support. Especially, I am very thankful to Prof.

Nguyen Van Dinh for all his help, advice, and encouragement.

I would like to thank all my Vietnamese friends in Ghent, especially to Anh Ngoc,

Minh Phuong, Thu Giang, Thanh Que for their help, support and understanding, especially

during the period of high pressure from work.

I am deeply thankful to my family, specifically, my parents, my mother-in-law, and

my sisters, who have supported and encouraged me throughout my life. This last word of

acknowledgment I have saved for my dear wife Thanh Ngoc, my beloved daughter Ngoc Anh

and son Duc Anh for their love, sacrifice and endless support. Without the encouragements

from them, I don’t think I could have finished my PhD study.

Nguyen Duc Tung, January 2015

i

Table of Contents

List of abbreviations .................................................................................................. iv

Chapter 1 Introduction, objectives and thesis outline ............................................ 1

1.1 General introduction .......................................................................................... 2

1.2 Objectives of the study ........................................................................................ 2

1.3 Thesis outline ...................................................................................................... 3

Chapter 2 Bio-ecology, biological control potential and rearing of Amblyseius

swirskii: a literature review ........................................................................................ 5

2.1 General biology of the Phytoseiidae (Acari) ...................................................... 6

2.2 Amblyseius swirskii ........................................................................................... 8

2.2.1 Classification ............................................................................................... 8

2.2.2 Distribution .................................................................................................. 8

2.2.3 Morphology and identification .................................................................... 9

2.2.3.1 Eggs ...................................................................................................... 9

2.2.3.2 Larvae and nymphs .............................................................................. 9

2.2.3.3 Adult ................................................................................................... 10

2.2.4 Bio-ecology ............................................................................................... 13

2.2.4.1 Development ...................................................................................... 13

2.2.4.2 Reproduction ...................................................................................... 17

2.2.4.3 Prey spectrum and feeding behaviour ................................................ 22

2.2.5 Practical application of phytoseiid mites in biological control ................. 25

2.2.5.1 Target pests and crops ........................................................................ 25

2.2.5.2 Commercial use and release strategies ............................................... 28

2.3 Rearing of natural enemies .............................................................................. 29

2.3.1 Introduction ............................................................................................... 29

2.3.2 Factitious foods ......................................................................................... 30

2.3.3 Artificial diets ............................................................................................ 33

2.3.3.1 Types of artificial diets ....................................................................... 33

2.3.3.2 Function of diet components .............................................................. 34

2.3.3.3 Role of insect components in artificial diets ...................................... 36

2.3.3.4 Artificial diets for phytoseiid mites .................................................... 37

ii

2.3.4 Pollen ......................................................................................................... 38

Chapter 3 Development and reproduction of Amblyseius swirskii on an artificial

diet enriched with pupal hemolymph of Antheraea pernyi ................................... 41

3.1 Introduction ...................................................................................................... 42

3.2 Materials and methods ..................................................................................... 43

3.2.1 Stock colony of Amblyseius swirskii ......................................................... 43

3.2.2 Stock colony of Carpoglyphus lactis ........................................................ 44

3.2.3 Pollen ......................................................................................................... 45

3.2.4 Preparation of artificial diet ....................................................................... 45

3.2.5 Rearing microcosms .................................................................................. 45

3.2.6 Experimental setup .................................................................................... 46

3.2.7 Life table parameters calculation .............................................................. 47

3.2.8 Statistical analysis ..................................................................................... 47

3.3 Results .............................................................................................................. 48

3.4 Discussion ........................................................................................................ 51

Chapter 4 Beneficial effect of supplementing an artificial diet for Amblyseius

swirskii with Hermetia illucens hemolymph ........................................................... 55

4.1 Introduction ...................................................................................................... 56



4.2.2 Black soldier fly rearing and hemolymph collecting ................................ 57

4.2.3 Preparation of artificial diets ..................................................................... 58

4.2.4 Development and reproduction on the different artificial diets ................ 58

4.2.5 Diet switching experiment......................................................................... 58



4.3 Results .............................................................................................................. 59

4.4 Discussion ........................................................................................................ 64

Chapter 5 Different factitious and artificial foods support the continuous

rearing of Amblyseius swirskii .................................................................................. 67

5.1 Introduction ...................................................................................................... 68




iii

5.2.3 Experimental setup .................................................................................... 70

5.2.3.1 Multigeneration experiment ............................................................... 70

5.2.3.2 Predation experiment .......................................................................... 71



5.3 Results .............................................................................................................. 72

5.4 Discussion ........................................................................................................ 79

Chapter 6 Solid artificial diets for Amblyseius swirskii ......................................... 83

6.1 Introduction ...................................................................................................... 84




6.2.3 Development and reproduction on the different artificial diets ................ 86

6.2.4 Pre-establishment greenhouse experiment ................................................ 86



6.3 Results .............................................................................................................. 88

6.4 Discussion ........................................................................................................ 92

Chapter 7 Performance of four species of phytoseiid mites on artificial and

natural diets .............................................................................................................. 97

7.1 Introduction ...................................................................................................... 98

7.2 Materials and methods ................................................................................... 100

7.2.1 Stock colonies of predatory mites ........................................................... 100

7.2.2 Preparation of artificial diet ..................................................................... 100

7.2.3 Experimental setup .................................................................................. 101

7.2.4 Life table parameters calculation ............................................................ 101

7.2.5 Statistical analysis ................................................................................... 101

7.3 Results ............................................................................................................ 102

7.4 Discussion ...................................................................................................... 107

Chapter 8 General discussion, conclusions and future perspectives ................. 111

Summary ................................................................................................................. 123

Samenvatting .......................................................................................................... 127

References ............................................................................................................... 133

Curriculum vitae .................................................................................................... 155

iv

LIST OF ABBREVIATIONS

ANOVA: analysis of variance

ARC: Artemia Reference Center, Ghent University

df: degrees of freedom

L:D: light-dark cycle expressed in hours (e.g. 16:8 indicates 16h photophase and 8h

scotophase)

n: number of sampled individuals

P: significance of a statistical test

R0: net reproductive rate

RH: relative humidity

rm: intrinsic rate of increase

SE: standard error

SPSS: Statistical Product and Service Solution (formerly Statistical Package for the

Social Sciences, distributed by SPSS Inc., Chicago, Illinois, USA)

T: generation time

1

Chapter 1

INTRODUCTION, OBJECTIVES AND THESIS OUTLINE

Chapter 1

2

1.1 General introduction

Predatory mites of the Phytoseiidae family are important biological control agents of

tetranychid mites and small, soft-bodied insects like thrips and whiteflies (Chant, 1985). The

subjects of this study, the phytoseiids Amblyseius swirskii Athias-Henriot, Neoseiulus

californicus (McGregor), Neoseiulus cucumeris (Oudemans), Amblyseius andersoni Chant,

and Amblydromalus limonicus Garman & McGregor (Acarina: Phytoseiidae), are all being

used on a commercial scale as biological control agents of thrips, whiteflies and spider mites

in protected vegetable and ornamental crops.

Biological control is the use of an organism to reduce the population density of

another organism. It is the most environmentally safe pest management method and can also

be economically profitable. The potential of augmentation biological control to suppress

insect pests has been recognized for many years (Doutt and Hagen, 1949; DeBach, 1964;

Parella et al., 1992). In augmentation biological control, large numbers of beneficial

arthropods (predators, parasitoids) are mass reared and released in the field (Stinner, 1977;

Collier and Van Steenwyk, 2004). Hence, a cost-effective method for their mass production is

an essential prerequisite (van Lenteren, 2003). Rearing phytoseiid mites on plant materials

infested with natural prey has several disadvantages, such as large space requirements,

inconsistent yields of predators, harvesting difficulties and variable results with different

species (McMurtry and Scriven, 1965). Rearing procedures based on factitious prey like

storage mites (Zhang, 2003; Bolckmans and van Houten, 2006) also involve space and labor

to maintain large parallel cultures of the factitious prey. Further, there may be health risks for

workers in production facilities or greenhouses caused by allergens associated with the

factitious mite prey (Bolckmans and van Houten, 2006; Fernandez-Caldas et al., 2007). The

availability of adequate artificial or factitious foods could eliminate many of the above-

mentioned problems associated with the mass production of predatory mites (Kennett and

Hamai, 1980). In addition, such foods may be useful as food supplements to support predator

populations after release in the crop (Wade et al., 2008).

1.2 Objectives of the study

The overall objective of this study was to develop alternative food sources for phytoseiid

predatory mites (with focus on the economically important species A. swirskii) in support of

their mass production and use as food supplements to sustain their populations after release in

the crop.

Introduction, objectives and thesis outline

3

The main research questions are:

1. What is the impact of different artificial and factitious diets on the development and

reproduction of A. swirskii?

2. What is the effect of these artificial and factitious diets on the developmental,

reproductive and predation performances of A. swirskii after several generations of

rearing?

3. What is the value of artificial diets for the rearing of other commercially available

phytoseiid mites?

4. What is the most adequate formulation of artificial diets for easy and effective

application in the crop as a food supplement for predatory mites?

1.3 Thesis outline

The purpose of the literature survey in Chapter 2 is to provide an overview of the

information available on phytoseiid predatory mites, with focus on A. swirskii, treating their

morphology, bio-ecology and practical application in biological control. This chapter also

includes an introduction to some aspects of the rearing of natural enemies, with particular

attention to alternative foods. In the next three research chapters, several alternative foods are

evaluated for rearing A. swirskii. Chapter 3 investigates the effects of a meridic artificial diet

supplemented with hemolymph of oak silkworm pupae (Antheraea pernyi Guérin-Méneville

(Lepidoptera: Saturniidae)) on the development and reproduction of the predatory mite. In

Chapter 4 the potential of prepupal hemolymph of black soldier fly, Hermetia illucens (L.)

(Diptera: Stratiomyidae), to improve the basic meridic artificial diet is evaluated. The chapter

focuses on the effect of the hemolymph concentration in the artificial diet on the

developmental and reproductive performance of A. swirskii. Chapter 5 examines the use of

Ephestia kuehniella Zeller eggs (Lepidoptera: Pyralidae) and decapsulated cysts of Artemia

franciscana Kellogg (Anostraca: Artemiidae) as factitious food sources and the impact of

supplementing artificial diets for A. swirskii with these foods. The developmental,

reproductive and predatory performance of the phytoseiid on these various diets after a single

generation is compared with that after 6 generations of continuous rearing. Chapter 6 focuses

on the effect of formulation on the suitability of artificial diets for A. swirskii. Whereas in

above chapters, all diets were offered in liquid form, in this chapter different solid diets are

tested. The developmental and reproductive parameters of A. swirskii are assessed when fed

on cattail pollen (Typha latifolia L.), on lyophilized forms of liquid artificial diets

supplemented with a watery extract of decapsulated cysts of A. franciscana or with pupal

Chapter 1

4

hemolymph of A. pernyi, and on solid artificial diets supplemented with powdered dry A.

franciscana cysts or with lyophilized pupal hemolymph of A. pernyi. In Chapter 7 the

impact of a meridic artificial diet supplemented with a watery extract of A. franciscana on the

biological performance of four species of phytoseiid mites which are commercially available

in Europe (N. californicus, N. cucumeris, A. andersoni, and A. limonicus) is investigated. The

final chapter (Chapter 8) presents a general discussion of the findings in this study and

provides some further research perspectives.

5

Chapter 2

BIO-ECOLOGY, BIOLOGICAL CONTROL POTENTIAL AND REARING OF

AMBLYSEIUS SWIRSKII: A LITERATURE REVIEW

Chapter 2

6

2.1 General biology of the Phytoseiidae (Acari)

The family Phytoseiidae is the most important family of acarine predators of plant pest mites

in agriculture (Huffaker et al., 1969; Helle and Sabelis, 1985; McMurtry and Croft, 1997;

Gerson et al., 2003). Phytoseiid mites are small, free-living and are the only Mesostigmata to

have extensively exploited the foliage habitat of higher plants.

Figure 2.1 Dorsal (left) and ventral (right) aspect of a typical female adult phytoseiid mite,

including setal nomenclature (Helle and Sabelis, 1985).

The adult dorsal shield of phytoseiid species is 200-600 µm in length. The adult female

idiosoma, dorsal shield or caudoventral area have less than or equal to 38, 23 or 10 pairs of

setae, respectively; paravertical setae (z1) are absent; there are one pair of setae in the R-

series or 2 pairs of setae in the r-series and no setae in the UR-series. The palpal claw has 2

tines; corniculae are slender, proximal, parallel blade-like. The tritostemum is well developed,

with 2 lacinae. Chelicera has both digits well developed, dentition variable; anterior margin of

tectum is smooth or minutely denticulate, without processes. The peritremal shield on most

species is fused anteriorly with the dorsal shield, free or fused posteriorly with the exopodal

plate beside coxa IV. The genital setae are always inserted on the genital shield of the females.

The males have sternogenital shield and ventriana shield separate. The female genital shield

truncates posteriorly, with a straight posterior margin. Most adult females have a ventrianal

A literature review

7

shield, a few species with separate ventral and anal shields or with a simple anal shield (Chant

and McMurtry, 2007).

The life cycle of phytoseiid mites typically comprises five developmental stages: egg,

larva, protonymph, deutonymph and adult; the larval stage has only six legs whereas the

nymphal and adult stages have eight legs (Woolley, 1988).

Based on habitat and food spectrum, phytoseiid mites are classified as type I

(specialized predators of Tetranychus species), type II (selective predators of tetranychid

mites), type III (generalist predators) and type IV (specialized pollen feeders/generalist

predators) (McMurtry et al., 2013). Specialist species such as Phytoseiulus persimilis Athias-

Henriot, Neoseiulus fallacis Garman, Neoseiulus longispinosus Evans, Phytoseiulus

macropilis Banks, are known as oligophagous predators of spider mites of the family

Tetranychidae (Gerson et al., 2003; Moraes et al., 2004). Generalist phytoseiids can feed on

mites of different families: eriophyids, tarsonemids, and tydeids, and on small insect species,

such as thrips or whiteflies (Gerson and Weintraub, 2012). As a special feature, generalist

phytoseiids can also feed on plant materials, including exudates (Kreiter et al., 2002;

Nomikou et al., 2003a), pollen (Nomikou et al., 2001; Kutuk and Yigit, 2011; Goleva and

Zebitz, 2013), and nectar (van Rijn and Tanigoshi, 1999a). However, generalist species may

differ in their prey preferences and in their ability to utilize certain prey as a food source,

resulting in their species-specific suitability to control particular target pests (Schausberger

and Walzer 2001).

This study is mainly concerned with the phytoseiid mite Amblyseius swirskii which is

classified by McMurtry et al. (2013) as having a type III life style. This generalist predator is

known to utilise various prey species such as tetranychid and eriophyid mites and different

insect species including whiteflies, mealybugs, and scale crawlers. Like other type III

phytoseiid mites, this species can reproduce on a diet of pollen alone. Other species used in

this study are the commercially distributed phytoseiids Neoseiulus californicus (McGregor), N.

cucumeris (Oudemans), Amblyseius andersoni Chant, and Amblydromalus limonicus Garman

& McGregor. Based on their level of food specialization, A. andersoni, N. cucumeris, and A.

limonicus are classified by McMurtry et al. (2013) as generalist predators (type III), whereas

N. californicus is a more selective predator of tetranychid mites (type II). Although N.

californicus prefers tetranychid mites as food, it can also feed on other mite species, small

insects, such as thrips, and even pollen when the primary prey is unavailable.

Chapter 2

8

2.2 Amblyseius swirskii

2.2.1 Classification

Amblyseius swirskii was described in 1962 from Beit Dagan, Central District, Israel on

Prunus amygdalus by C. Athias-Henriot (Athias-Henriot, 1962).

Synonyms:

Suspected senior synonym: Amblyseius enab El-Badry (Faraji et al., 2011)

Senior synonym: Amblyseius rykei Pritchard & Baker (Zannou et al., 2007; Zannou and

Hanna, 2011)

Other Names: Typhlodromips swirskii (Moraes et al., 1986) and Amblyseius swerski [sic]

(Abo-Taka, 1996)

The taxonomic classification of A. swirskii is as follows:

KINGDOM Animalia

SUBKINGDOM Eumetazoa

PHYLUM Arthropoda

SUBPHYLUM Chelicerata

CLASS Arachnida

SUBCLASS Micrura

INFRACLASS Acari

SUPERORDER Anactinotrichida

ORDER Mesostigmata

SUBORDER Dermanyssina

SUPERFAMILY Ascoidea

FAMILY Phytoseiidae

GENUS Amblyseius Berlese, 1904

SPECIES swirskii Athias-Henriot 1962

2.2.2 Distribution

Amblyseius swirskii is native to the Eastern Mediterranean region. It naturally occurs in Israel,

Italy, Cyprus, Greece and Egypt, and can be found on various crops like apples, apricot, citrus,

vegetables and cotton (EPPO, 2014). In North America it was first released in 1983 for

A literature review

9

control of citrus pests in California. Since 2005, A. swirskii has been released as a biological

control agent in many European countries (Austria, Belarus, Belgium, Denmark, Finland,

France, Germany, Greece, Guernsey, Hungary, Italy, Jersey, Morocco, the Netherlands,

Norway, Poland, Spain, Turkey, UK)(EPPO, 2014), North America (Arthurs et al., 2009),

South America (Argentina, Brazil) (Cédola and Polack, 2011), North Africa (Kade et al.,

2011), Saudi Arabia (Fouly et al., 2011), China (Xia et al., 2011) and Japan (Sato and

Mochizuki, 2011). Zannou et al. (2007) and Zannou and Hanna (2011) synonymized A.

swirskii with Amblyseius rykei (Pritchard & Baker). Amblyseius rykei was reported from the

Democratic Republic of Congo, Benin, Burundi, Ghana, Kenya, Malawi, Nigeria, Tanzania

and Zimbabwe (Moraes et al., 2004; Zannou et al., 2007).

2.2.3 Morphology and identification

2.2.3.1 Eggs

Eggs are oval-shaped, pale-whitish and approximately 0.20 mm in length and 0.15 mm in

width (Figure 2.2). A. swirskii lays eggs on the underside of plant leaves, mainly at the inter-

section of main and lateral ribs. Females prefer to lay eggs on leaf hairs (trichomes) near plant

domatia (small hairy tufts or pockets found on the lower surface of some leaves) which may

be an adaptation to avoid egg predators.

Figure 2.2 Egg (right) and empty egg shell (left) of Amblyseius swirskii. Scale in μm (Photo:

Author).

2.2.3.2 Larvae and nymphs

Larvae are pale white to nearly transparent in color and approximately 0.22 mm in length and

0.16 mm in width. Larva only has three pairs of legs (Figure 2.3).

Chapter 2

10

Figure 2.3 Larva of Amblyseius swirskii with three pairs of legs. Scale in μm (Photo: Author).

The protonymph (2nd

stage) is about 0.26 mm in length and 0.16 mm in width. The

deutonymph (3rd

stage) is approximately 0.28-0.34 mm in length and 0.16-0.19 mm in width

and the difference in sizes of males and females is visible. Both nymph stages have four pairs

of legs and are darker than the larvae (Figure 2.4).

Figure 2.4 Protonymph (left) and deutonymph (right) of Amblyseius swirskii. Scale in μm

(Photo: Author).

2.2.3.3 Adult

Adult females are about 0.5 mm in length and 0.3 mm in width, shiny, pear shaped, and have

an unsegmented body and four pairs of legs. Males are smaller than females with about 0.3

mm long and 0.17 mm wide, and are usually oval (Figure 2.5). They are often more active

than females or nymphs, and can run fast. Males also may be seen guarding quiescent female

deutonymphs and will mate with the females immediately after they molt. The color of mites

may vary from deep red to pale yellow depending on the prey items eaten. Mites feeding on

thrips and whitefly are generally pale yellow to pale tan, while adults fed on eggs of the

A literature review

11

aphidophagous gall midge Aphidoletes aphidimyza (Rond.) (Diptera: Cecidomyiidae) have

been observed to be yellowish-brown to red (Messelink et al., 2011).

Figure 2.5 Female adult (left) and mating adult pair (right) of Amblyseius swirskii. Scales in

μm (Photo: Author).

Like other phytoseiid species, A. swirskii is characterized by its long legs, with the

front pair pointing forward, and by the relatively few hairs (< 20 pairs) on its back. The

predator cannot be readily distinguished from some other phytoseiid mites with the naked eye,

and positive identification requires examination under a microscope. Zannou and Hanna

(2011) and Cédola and Polack (2011) described A. swirskii specimens and provided detailed

morphometrics. The general habitus and details of diagnostic setae and spermatheca are

illustrated in Figure 2.6; the chelicerae are shown in Figure 2.7.

Chapter 2

12

Figure 2.6 Amblyseius swirskii Athias-Henriot: a, dorsal view; b, ventral view; c, detail of

serrate setae Z4 and Z5; d, spermatheca. Scales in μm (Cédola and Polack, 2011).

Figure 2.7 Scanning electron microscope image of chelicera, adaxial profile, of Amblyseius

swirskii female taken at x2,700, white scale bar is 10 μm (Adar et al., 2012).

A literature review

13

2.2.4 Bio-ecology

2.2.4.1 Development

Amblyseius swirskii passes through four immature stages (egg, larva, protonymph and

deutonymph) before reaching the adult stage. The rate of development of A. swirskii is mainly

influenced by the type of food and environmental conditions. Reported immature

developmental times for this species are quite variable, ranging from 4.8 days when the

predator is fed on Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) at 26oC (Fouly et al.,

2011) to 24.1 days on pollen of Zea mays L. at 15oC (Allen, 2010) (Table 2.1). When A.

swirskii is fed on live prey it generally develops faster than when fed on pollen. For example,

the immature developmental time of the mite reared on Aculops lycopersici (Massee) (Acari:

Eriophyidae) or Tetranychus urticae Koch (Acarina: Tetranychidae) was shorter than that on

pollen of Typha latifolia L. or Ricinus communis (L.)(Abou-Awad and Elsawi, 1992; Park et

al., 2011). Temperature is another major factors affecting the development of A. swirskii. No

egg hatching was observed to occur at 13oC and 60% relative humidity (RH) (Lee and

Gillespie, 2011). The developmental times of all stages were reported by Ali and Zaher (2007)

and Xia et al. (2011) to decrease with increasing temperature from 15 to 35oC; however Allen

(2010) and Lee and Gillespie (2011) reported that when the temperature was higher than 30oC

at 70-75% RH or than 32oC at 60% RH the development of the predator slowed down. Zaher

et al. (2007) also noted that the relative humidity influenced the developmental success of A.

swirskii, with 70 and 85% RH being the most suitable for the predator at 25oC.

Chapter 2

14

Table 2.1 Duration of total developmental time and total mortality from egg to adult of

Amblyseius swirskii at different temperatures and on different prey species

Prey species

Temp-

rature

(°C)

RH (%)

Total

develop-

ment

(days)

Total

survi-

val

(%)

Reference

Acari: Eriophyidae

Aculops lycopersici (Massee) 25 70 5.1 100 Park et al. (2011)

Aculops lycopersici (Massee) 28 70 7.0 100 Momen and Abdel-Khalek (2008)

Aculus fockeui (Nalepa and

Trouessart)

28 70 6.6 100 Momen (2009)

Cisaberoptus kenyae Keifer

(mobile stages)

25 70 20.0 - Ali and Zaher (2007)

Acari: Suidasiidae

Suidasia medanensis (Oudemans) 25 70 5.0 90 Midthassel et al. (2013)

Acari: Tarsonemidae

Polyphagotarsonemus latus

(Banks)

25 80 6.2 95 Onzo et al. (2012)

Acari: Tetranychidae

Eutetranychus orientalis (Klein) 15 70 18.5 - Ali and Zaher (2007)







Eutetranychus orientalis (Klein)

(adults)

25 70 11.3 - Ali and Zaher (2007)


(immatures)

25 70 10.8 - Ali and Zaher (2007)

Panonychus ulmi (Koch) (adults) 25 70 13.8 - Ali and Zaher (2007)

Tetranychus truncatus (Ehara)

(eggs & larvae)

15 85-90 20.5 - Xia et al. (2011)


(eggs & larvae)

18 85-90 15.9 - Xia et al. (2011)


(eggs & larvae)

20 85-90 11.3 - Xia et al. (2011)

A literature review

15


Amblyseius swirskii at different temperatures and on different prey species (continued)

Prey species

Temp-

rature

(°C)

RH (%)

Total

develop-

ment

(days)

Total

survi-

val

(%)

Reference



(eggs & larvae)

25 85-90 6.6 - Xia et al. (2011)


(eggs & larvae)

30 85-90 5.1 - Xia et al. (2011)


(eggs & larvae)

35 85-90 4.0 - Xia et al. (2011)

Tetranychus urticae Koch 26 70 5.5 - El-Laithy and Fouly (1992)

Tetranychus urticae Koch 27 70-80 11.6 100 Abou-Awad and Elsawi (1992)

Tetranychus urticae Koch (eggs) 25 70 14.7 - Ali and Zaher (2007)

Tetranychus urticae Koch

(immatures)

25 70 14.2 - Ali and Zaher (2007)

Acari: Tydeidae

Tydeus californicus (Banks)

(mobile stages)

25 70 21.4 - Ali and Zaher (2007)

Acari:Tenuipalpidae

Cenopalpus pulcher (C. & F.)

(adults)

25 70 13.2 - Ali and Zaher (2007)

Hemiptera: Aleyrodidae

Bemisia tabaci (Gennadius) 26 70 4.8 - Fouly et al. (2011)

Bemisia tabaci (Gennadius) 27 - 100 Nomikou et al. (2001)

Bemisia tabaci (Gennadius) 27 - 93 Nomikou et al. (2001)

Bemisia tabaci (Gennadius) (2nd

instar nymphs)

25 70 15.3 - Ali and Zaher (2007)

Bemisia tabaci (Gennadius) (1st

instar nymphs)

25 70 15.8 - Ali and Zaher (2007)

Bemisia tabaci (Gennadius) (eggs) 25 70 16.3 - Ali and Zaher (2007)

Hemiptera: Aphididae

Aphis durantae Theobald (adults) 25 70 19.4 - Ali and Zaher (2007)

Hemiptera: Coccidae

Chrysomphalus ficus Rilly (eggs) 25 70 18.0 - Ali and Zaher (2007)

Chrysomphalus ficus Rilly

(nymphs)

25 70 17.0 - Ali and Zaher (2007)

Chapter 2

16


Amblyseius swirskii at different temperatures and on different prey species (continued)

Prey species

Temp-

rature

(°C)

RH (%)

Total

develop-

ment

(days)

Total

survi-

val

(%)

Reference

Hemiptera: Coccidae

Coccus hesperidium (L.) (eggs) 25 70 19.0 - Ali and Zaher (2007)

Coccus hesperidium (L.) (nymphs) 25 70 18.5 - Ali and Zaher (2007)

Thysanoptera: Thripidae

Frankliniella occidentalis

(Pergande)

25 60 7.8 67 Wimmer et al. (2008)

Thrips tabaci Lind. 25 60 7.8 78 Wimmer et al. (2008)

Pollen

Phoenix dactylifera L. 25 70 12.3 - Ali and Zaher (2007)

Ricinus communis L. 27 70-80 15.0 100 Abou-Awad and Elsawi (1992)

Typha latifolia L. 25 70 6.2 100 Park et al. (2011)

Typha latifolia L. 13 60 - 0 Lee and Gillespie (2011)

Typha latifolia L. 15 60 22.1 94-100 Lee and Gillespie (2011)








Zea mays L. 25 80 7.5 99 Onzo et al. (2012)

Zea mays L. 15 70-75 24.1 - Allen (2010)

Zea mays L. 18 70-75 20.4 - Allen (2010)

Zea mays L. 20 70-75 12.8 - Allen (2010)

Zea mays L. 23 70-75 10.7 - Allen (2010)

Zea mays L. 25 70-75 8.3 - Allen (2010)

Zea mays L. 27 70-75 6.1 - Allen (2010)

Zea mays L. 30 70-75 8.8 - Allen (2010)

Zea mays L. 25-27 60-85 6.9 Zannou and Hanna (2011)

Artificial diet

Pollen artificial diet * 27 70-80 10.9 100 Abou-Awad and Elsawi (1992)

- no data presented; * Pollen artificial diet consisted of 2/3 artificial diet (yeast, milk, cystine,

proline, arginine, sucrose, and glucose) + 1/3 pollen of Ricinus communis (L.)

A literature review

17

2.2.4.2 Reproduction

Like other phytoseiid species, females of A. swirskii need mating to produce eggs

(Helle et al., 1978; Hoy, 1985). Mating frequency affects the fecundity of the females. The

reproduction of A. swirskii females kept in the company of males throughout their lifetime

was highest (47 eggs/female), followed by that of the females paired with males every 5 days

(35 eggs/female), and was lowest for the females that only had a single mating (25

eggs/female) (Zaher et al., 2007). Reported fecundities of A. swirskii in the literature vary

largely, from 1.3 eggs/female (Lee and Gillespie, 2011) to 57.6 eggs/female (Xia et al.,

2011)(Table 2.2). The reproduction of A. swirskii is affected by the food type (prey species or

plant material), food quantity and environmental conditions. The reproduction of A. swirskii

was higher on the natural prey A. lycopersici or T. urticae than on pollen of T. latifolia or R.

communis, respectively (Abou-Awad and Elsawi, 1992; Park et al., 2011). Fouly et al. (2011)

proved that food quantity offered highly affected fecundity and all life table parameters of A.

swirskii: intrinsic rate of increase averaged 0.14, 0.17 or 0.22 females/female/day when the

predatory mites were provided with 4, 8 or 12 eggs of B. tabaci/female/day, respectively.

Different temperatures also affected egg production of the predator (Ali and Zaher, 2007; Lee

and Gillespie, 2011; Xia et al., 2011). The daily oviposition of A. swirskii increased from 0.49

to 2.4 eggs/female/day when the temperature increased from 15 to 35oC (Ali and Zaher, 2007).

Zaher et al. (2007) reported that the relative humidity also influenced the fecundity of the

predator, with females laying more eggs at 70% and 80% RH (13 and 12 eggs/female/10 days,

respectively) than at 55% and 95% RH (10 and 9 eggs/female/10 days, respectively). Zaher et

al. (2007) also reported the effect of host plant leaf surface on A. swirskii oviposition; in the

latter study, the females fed on Eutetranychus orientalis (Klein) (Acari: Tetranychidae)

deposited more eggs on the smooth leathery leaves of grapefruit (15.8 eggs/10 days) than on

the coarse reticulated leaves of guava (10.8 eggs/10 days). Yousef et al. (1982) noted the

effect of photoperiod on the reproduction of A. swirskii, with increasing photoperiods

resulting in lower prey consumption and an associated drop in fecundity.

Chapter 2

18

Table 2.2 Reproduction and intrinsic rate of increase of Amblyseius swirskii at different

temperatures and on different prey species

Prey species

Tempe

-rature

(°C)

RH

(%)

Fecundity

(eggs/♀)

Oviposition

rate

(eggs/♀/day)

Intrinsic

rate of

increase

rm

Reference

Acari: Eriophyidae

Aceria ficus (Cotte) 29 70-80 - - 0.155 Abou-Awad et al. (1999)

Aculops lycopersici (Massee) 25 70 38.1 1.90 0.201 Park et al. (2011)

Aculops lycopersici (Massee) 28 70 35.4 1.70 0.235 Momen and Abdel-

Khalek (2008)

Aculus fockeui (Nalepa &

Trouessart)

28 70 43.0 1.90 0.244 Momen (2009)

Cisaberoptus kenyae Keifer

(mobile stages)

25 70 8.8 0.83 0.027 Ali and Zaher (2007)

Rhyncaphytoptus ficifoliae

Keifer

29 70-80 - - 0.122 Abou-Awad et al. (1999)

Acari: Suidasiidae

Suidasia medanensis

(Oudemans)

25 70 22.52 1.71 0.222 Midthassel et al. (2013)

Acari: Tarsonemidae


(Banks)

25 80 - - 0.130 Onzo et al. (2012)


(Banks)

19 - - 1.69 0.139 Abou-Awad et al. (2014)


(Banks)

28 - - 2.36 0.170 Abou-Awad et al. (2014)


Eutetranychus orientalis (Klein) 15 70 18.3 0.49 0.069 Ali and Zaher (2007)







A literature review

19


temperatures and on different prey species (continued)

Prey species

Tempe

-rature

(°C)

RH

(%)

Fecundity

(eggs/♀)

Oviposition

rate

(eggs/♀/day)

Intrinsic

rate of

increase

rm

Reference



(adults)

25 70 34.2 1.12 0.155 Ali and Zaher (2007)


(immatures)

25 70 38.0 1.30 0.161 Ali and Zaher (2007)

Panonychus ulmi (Koch) (adult) 25 70 25.2 0.70 0.098 Ali and Zaher (2007)


(eggs & larvae)

18 85-90 23.8 0.89 0.071 Xia et al. (2011)


(eggs & larvae)

20 85-90 38.3 1.43 0.098 Xia et al. (2011)


(eggs & larvae)

25 85-90 57.6 1.93 0.148 Xia et al. (2011)


(eggs & larvae)

30 85-90 40.6 2.09 0.184 Xia et al. (2011)


(eggs & larvae)

35 85-90 35.3 2.31 0.198 Xia et al. (2011)

Tetranychus urticae Koch 26 70 - 1.24* 0.167 El-Laithy and Fouly

(1992)

Tetranychus urticae Koch 27 70-80 - 1.41 - Abou-Awad and

Elsawi (1992)


(eggs)

25 70 21.0 0.53 0.075 Ali and Zaher (2007)


(immatures)

25 70 22.8 0.61 0.077 Ali and Zaher (2007)

Acari:Tenuipalpidae

Cenopalpus pulcher (C. & F.)

(adults)

25 70 28.2 0.82 0.106 Ali and Zaher (2007)

Chapter 2

20



Prey species

Tempe

-rature

(°C)

RH

(%)

Fecundity

(eggs/♀)

Oviposition

rate

(eggs/♀/day)

Intrinsic

rate of

increase

rm

Reference

Hemiptera: Aleyrodidae

Bemisia tabaci (Gennadius) 26 70 - - 0.220 Fouly et al. (2011)

Bemisia tabaci (Gennadius) 27 - - 1.6** 0.213 Nomikou et al.

(2001)

Bemisia tabaci (Gennadius) 27 - - 1.7** 0.208 Nomikou et al.

(2001)

Bemisia tabaci (Gennadius) (2nd

instar nymphs)

25 70 18.5 0.46 0.063 Ali and Zaher

(2007)

Bemisia tabaci (Gennadius) (1st

instar nymphs)

25 70 18.0 0.43 0.061 Ali and Zaher

(2007)

Bemisia tabaci (Gennadius)

(eggs)

25 70 16.0 0.37 0.056 Ali and Zaher

(2007)

Hemiptera: Aphididae

Aphis durantae Theobald

(adults)

25 70 9.4 0.20 0.027 Ali and Zaher

(2007)

Hemiptera: Coccidae


(eggs)

25 70 12.0 0.26 0.042 Ali and Zaher

(2007)


(nymphs)

25 70 14.0 0.31 0.047 Ali and Zaher

(2007)

Coccus hesperidium (L.) (eggs) 25 70 10.5 0.22 0.034 Ali and Zaher

(2007)

Coccus hesperidium (L.)

(nymphs)

25 70 11.0 0.23 0.036 Ali and Zaher

(2007)

Thysanoptera: Thripidae


(Pergande)

25 60 - 0.92 0.056 Wimmer et al.

(2008)

Thrips tabaci Lind. 25 60 - 0.99 0.024 Wimmer et al.

(2008)

A literature review

21



Prey species

Tempe

-rature

(°C)

RH

(%)

Fecundity

(eggs/♀)

Oviposition

rate

(eggs/♀/day)

Intrinsic

rate of

increase

rm

Reference

Pollen

Phoenix dactylifera L. 25 70 30.5 0.94 0.129 Ali and Zaher

(2007)

Ricinus communis (L.) 27 70-80 - 0.84 - Abou-Awad and

Elsawi (1992)

Typha latifolia L. 25 70 26.8 1.60 0.185 Park et al. (2011)

Typha latifolia L. 15 60 1.3 - -0.002 Lee and Gillespie

(2011)

Typha latifolia L. 18 60 2.6 - 0.016 Lee and Gillespie

(2011)


(2011)


(2011)


(2011)


(2011)


(2011)


(2011)

Zea mays L. 25 80 - - 0.160 Onzo et al. (2012)

Zea mays L. 25-27 60-85 - 1.60 0.200 Zannou and Hanna

(2011)

Artificial diet

Pollen artificial diet *** 27 70-80 - 0.90 - Abou-Awad and

Elsawi (1992)

Artificial diet **** 27 70-80 - 0.30 - Abou-Awad et al.

(1992)

- no data presented; * the value was calculated by the average total egg laying divided by the

average oviposition period; **peak oviposition rates were calculated from the average

oviposition rates of the 2nd

to 5th

day after reaching adulthood; *** pollen artificial diet

consisted of 2/3 artificial diet (yeast, milk, cystine, proline, arginine, sucrose, and glucose) +

1/3 pollen of Ricinus communis (L.); ****artificial diet consisted of yeast, milk, cystine,

proline, arginine, sucrose, and glucose

Chapter 2

22

2.2.4.3 Prey spectrum and feeding behaviour

Like other type III generalist predatory mites, A. swirskii feeds on a broad spectrum of food

sources. The predator is an effective predator of thrips and whiteflies. Further, the predatory

mite also feeds on various phytophagous mites, including tetranychid, tarsonemid and

eriophyid mites, other hemipteran insects and eggs of several lepidopterans (Table 2.3).

Table 2.3 Natural prey of Amblyseius swirskii

Prey Classification Reference

Aceria ficus (Cotte) Acari: Eriophyidae Abou-Awad et al. (1999)

Aculops lycopersici (Nalepa

& Trouessart)

Acari: Eriophyidae Momen and Abdel-Khalek

(2008); Park et al. (2010); Park et

al. (2011)

Aculus fockeui (Massee) Acari: Eriophyidae Momen (2009)

Cisaberoptus kenyae Keifer Acari: Eriophyidae Ali and Zaher (2007)

Phyllocoptruta oleivora

(Ashmead)

Acari: Eriophyidae Maoz et al. (2014)

Rhyncaphytoptus ficifoliae

Keifer

Acari: Eriophyidae Abou-Awad et al. (1999)


(Banks)

Acari: Tarsonemidae van Maanen et al. (2010); Onzo et

al. (2012); Abou-Awad et al.

(2014)

Cenopalpus pulcher (C. &

F.)

Acari: Tenuipalpidae Ali and Zaher (2007)

Eutetranychus orientalis

(Klein)

Acari: Tetranychidae Ali and Zaher (2007)

Panonychus ulmi (Koch) Acari: Tetranychidae Ali and Zaher (2007)

Tetranychus truncatus

(Ehara)

Acari: Tetranychidae Xia et al. (2011)

Tetranychus urticae Koch Acari: Tetranychidae Abou-Awad et al. (2000);

Messelink et al. (2010); Xu and

Enkegaard (2010); Xiao et al.

(2013)

Tydeus californicus (Banks) Acari: Tydeidae Ali and Zaher (2007)

A literature review

23

Table 2.3 Natural prey of Amblyseius swirskii (continued)

Prey Classification Reference

Bemisia tabaci (Gennadius) Hemiptera:

Aleyrodidae

Nomikou et al. (2001); Berndt et

al. (2007); Calvo et al. (2008);

Messelink et al. (2008); Chow et

al. (2010); Fouly et al. (2011);

Park et al. (2011)

Trialeurodes vaporariorum

Westwood

Hemiptera:

Aleyrodidae

Berndt et al. (2007); Messelink et

al. (2008); Medd and Greatrex

(2014)

Aphis durantae Theobald Hemiptera: Aphididae Ali and Zaher (2007)

Chrysomphalus ficus Ashm. Hemiptera: Coccidae Ali and Zaher (2007)

Coccus hesperidum (L.) Hemiptera: Coccidae Ali and Zaher (2007)

Diaphorina citri Kuwayama Hemiptera: Psyllidae Juan-Blasco et al. (2012)

Phthorimaea operculella

(Zeller)

Lepidoptera:

Gelechiidae

El-Sawi and Momen (2005)

Spodoptera littoralis Boisd. Lepidoptera:

Noctuidae

El-Sawi and Momen (2005)


(Pergande)

Thysanoptera:

Thripidae

Messelink et al. (2008); Wimmer

et al. (2008); Chow et al. (2010);

Xu and Enkegaard (2010); Calvo

et al. (2011)

Scirtothrips dorsalis Hood Thysanoptera:

Thripidae

Arthurs et al. (2009)

Thrips tabaci Lindeman Thysanoptera:

Thripidae

Wimmer et al. (2008)

Amblyseius swirskii can also develop and reproduce on non-prey foods like pollen and

honeydew (Momen and El-Saway, 1993). Cattail pollen (T. latifolia) was reported to be an

excellent food source for the laboratory rearing of A. swirskii, with short developmental time,

low mortality under different temperatures, and an acceptable fecundity (Lee and Gillespie,

2011; Park et al., 2011). Goleva and Zebitz (2013) investigated the developmental and

reproductive performance of A. swirskii fed on pollens of 21 plant species. The results showed

Chapter 2

24

that A. swirskii can feed on 19 and develop to adulthood when feeding on 18 out of the 21

tested pollens. The latter authors classified the suitability of the pollens for preimaginal

development into six groups: (1) highly suitable: Schlumbergera hybrid, Crocus vernus Hill >

Echinocereus sp. > Paulownia tomentosa (Thunb.) Steud., Aesculus hippocastanum Haynes,

(2) suitable: Ricinus communis L. > Betula pendula Roth, Zea mays L., Tulipa gesneriana L. >

Abutilon sp. > Calla palustris L., (3) ample suitable: Cucurbita pepo L. > Pinus sylvestris L. >

Narcissus pseudonarcissus L., (4) bad: bee pollen, (5) negligible suitability: Corylus avellana

L. > Helianthus annuus L. > Poaceae mix, and (6) not edible or toxic, resulting in 100 %

mortality: Lilium martagon L., Hippeastrum sp. and Hibiscus syriacus L..

The mass rearing procedures for A. swirskii are based on the use of storage mites, like

Carpoglyphus lactis L. (Acari: Carpoglyphidae) and Thyreophagus entomophagus

(Laboulbene) (Acari: Acaridae), as a food source (Bolckmans and van Houten, 2006; Fidgett

and Stinson, 2008). Baxter et al. (2011) found that using Suidasia medanensis Oudemans

(Acari: Astigmata) in sachets as a delivery system for A. swirskii was better than the use of C.

lactis as a food mite.

The degree of cannibalism and intraguild predation varies among phytoseiids

(Schausberger, 2003; Schausberger, 2004). Avoidance of kin cannibalism is considered as an

important trait for predators to increase their inclusive fitness (Schausberger, 2003; Saito,

2010). Momen and Abdel-Khalek (2009) reported that A. swirskii females did not eat

conspecific eggs or protonymphs, but did eat larvae at very low frequencies. Zhang et al.

(2014) found that the presence of A. swirskii mothers significantly affected offspring survival

in all immature stages compared with the absence of the mothers, indicating possible maternal

cannibalism. However, the difference in immature survivorship between mother-presence and

mother-absence was small, showing that kin cannibalism is relatively low. Like cannibalism,

intraguild predation is a common phenomenon amongst phytoseiid mites when prey are

scarce. Momen and Abdel-Khalek (2009) investigated the intraguild predation and

cannibalism on eggs and immatures by the adult females of Euseius scutalis (Athias-Henriot),

Typhlodromus athiasae Porath and Swirski and A. swirskii (Acari: Phytoseiidae) under

laboratory conditions. The authors found that A. swirskii had higher predation rates on

heterospecific than on conspecific prey. The predatory mite fed more on con- and

heterospecific larvae than on con- and heterospecific protonymphs.

Predation capacity is a crucial criterion to evaluate a biological control agent. El-Laithy

and Fouly (1992) noted that A. swirskii daily consumed 10.9 nymphs of T. urticae on

mulberry leaves under conditions of 26º C and 70% RH. This result was confirmed by Xu and

A literature review

25

Enkegaard (2010) who found that the predatory mite was capable of preying on spider mite

nymphs with a consumption of 4-6 nymphs within a 12 h period at 25º C and 70 % RH.

Momen and El-Saway (1993) observed a higher number of spider mites (15 nymphs/day)

being eaten by the predator at higher temperature (27º C) and a longer starvation period (2

days). Xu and Enkegaard (2010) demonstrated that A. swirskii significantly preferred first

instar larvae of F. occidentalis to both protonymphs and deutonymphs of T. urticae spider

mites. The predator could eat 4.33-4.71 first instar larvae of the thrips per day at 25º C and 70%

RH, a value that is similar to that reported by Bolckmans et al. (2005) (4.9 thrips larvae/day)

at the same temperature. Arthurs et al. (2009) found that A. swirskii was able to eat 2.73

larvae or 1.09 adults of chilli thrips, S. dorsalis, per day in a no choice test and 1.89

larvae+0.24 adults thrips/day in a choice test at 26º C; the predator significantly preferred

larval to adult thrips. With a smaller prey like the broad mite P. latus, a female adult of A.

swirskii can consume 20.2 or 31.6 adult mites/day depending on a prey density of 25 or 50

adults, respectively at 25º C (Onzo et al., 2012). Amblyseius swirskii exhibited a type II

functional response with a maximum daily predation of 15.1 eggs of T. urticae per day at 26º

C (Xiao et al., 2013). Predation rates of female A. swirskii on eggs and 1st instars of B. tabaci

were significantly higher than on the other stages of the whitefly (20 eggs or 15 first instars

being killed by a female predator per day compared to 1.2 second instars, 0.5 third instars or

0.1 fourth instars per day) at 25º C (Nomikou et al., 2004).

2.2.5 Practical application of phytoseiid mites in biological control

2.2.5.1 Target pests and crops

In commercial augmentative biocontrol A. swirskii is mainly used to control whitefly and

thrips outbreaks in greenhouse vegetables (especially cucumber, pepper and eggplant) and

some ornamental crops (chrysanthemum, roses, gerbera) in Europe and North America

(Messelink et al., 2006; Berndt et al., 2007; Buitenhuis et al., 2010b; Chow et al., 2010).

Several studies have been carried out since the initial discovery that A. swirskii has

potential as a biological control agent of agricultural pests. Most of this work has concentrated

on the management of the cotton whitefly, B. tabaci, that causes considerable yield loss and

economic injury in various crops worldwide. Several studies have deemed A. swirskii to be an

effective biological control agent of this pest. Nomikou et al. (2002) reported that A. swirskii

was able to suppress B. tabaci population growth on cucumber plants in a greenhouse. The

numbers of whiteflies on the plants without predators was significantly higher than on plants

Chapter 2

26

with predators in weeks 5 and 7–9 after infestation. This resulted in 21-fold higher

populations in the absence of predators in week 9. On average, the whitefly populations on

plants without the predator showed a 62-fold increase, while the populations in the treatments

increased 4-fold. Hoogerbrugge et al. (2005) also concluded that A. swirskii was a promising

control agent of B. tabaci in protected sweet pepper crops. Calvo et al. (2008) noted that at

release rates of 25 and 100 mites per m2 3 weeks after establishment of B. tabaci, the whitefly

nymphs were virtually eliminated. In further experiments, Calvo et al. (2009) demonstrated

that the joint release of A. swirskii and the parasitic wasp Eretmocerus mundus Mercet

(Hymenoptera: Aphelinidae) caused a significant suppression of the whitefly population when

compared with the introduction of the parasitoid alone. The density of the cotton whitefly in

the control treatment was ca. 60 nymphs/leaf after 8 weeks, which was ca. 50 times higher

than that observed in the treatment with A. swirskii released once at a rate of 50 mites/m2. The

effectiveness of A. swirskii for the control of the greenhouse whitefly T. vaporariorum on

cucumber plants was investigated by Medd and Greatrex (2014). The authors found that the

use of loose-material products of A. swirskii resulted in significantly higher mobile mite

numbers on plants than when using sachets, but this increase in mite populations did not

correspond to a significantly greater reduction in whitefly numbers. Further, in both release

methods, the A. swirskii treatments appeared not to yield significant differences in terms of

whitefly numbers from the controls. In contrast, Berndt et al. (2007) reported that the

predatory mite led to a satisfactory control of T. vaporariorum. After release of A. swirskii six

weeks, no whitefly larvae were visible on the gerbera plants throughout the experiment.

Amblyseius swirskii also shows to be a potential predator of various thrips pests.

Messelink et al. (2006) evaluated ten phytoseiid predators for the control of the western

flower thrips, F. occidentalis, on greenhouse cucumber. The authors found that A. swirskii

reached much higher population levels resulting in a significantly better control of thrips than

the standard species N. cucumeris. Arthurs et al. (2009) conducted experiments to evaluate

two species of phytoseiid mites, N. cucumeris and A. swirskii, as predators of the chilli thrips,

S. dorsalis, on sweet pepper. The authors found that both mite species established and reduced

thrips numbers significantly over 28 days following a single release (30 mites/plant).

However, A. swirskii proved a more effective predator than N. cucumeris, consistently

maintaining thrips below 1 individual per terminal leaf, compared with up to 36 for N.

cucumeris and 70 in the control treatment.

Several studies were conducted to investigate the effectiveness of A. swirskii to control

simultaneously both whiteflies and thrips. Messelink et al. (2008) reported that A. swirskii

A literature review

27

was able to control F. occidentalis in the presence or absence of T. vaporariorum, although

whitefly control was sufficient only when thrips were also present. They concluded that

control of whiteflies was improved by the presence of thrips, but that thrips control was not

affected by the presence of whiteflies. These results contradict somewhat those of Calvo et al.

(2011) who concluded that 75 A. swirskii per m2 could be an adequate rate for controlling

both B. tabaci and F. occidentalis pests either alone or simultaneously in cucumber

greenhouses.

To reduce the expenses related to releases of the predatory bug Orius sp. (Hemiptera:

Anthocoridae), an effective but relatively expensive thrips predator, it was suggested to

reduce its release rate by simultaneously releasing the predatory mite A. swirskii, which is a

less expensive predator. Weintraub et al. (2011) noted that there was no difference in F.

occidentalis control among Orius laevigatus Fieber (Hemiptera: Anthocoridae) alone and O.

laevigatus plus A. swirskii release strategies, suggesting that a reduced release rate of the

anthocorid can maintain effective thrips control. There was also no significant difference in

the quality or quantity of the sweet pepper yield between treatments in which either 2 or 6 O.

laevigatus/m2 or 100 A. swirskii plus 2 or 6 O. laevigatus per m

2 were released. Dogramaci et

al. (2011) demonstrated that A. swirskii and Orius insidiosus (Say) (Hemiptera: Anthocoridae)

were effective predators of the chilli thrips. The thrips populations were always maintained at

equivalent or lower levels under the predator combination treatments compared with the

single predator treatments. The latter study provided evidence that intraguild interactions

between the two predator species were not sufficient to prevent them from being used

simultaneously.

El-Laithy and Fouly (1992) conducted a comparison between A. swirskii and A.

scutalis, both of which in their native environments are found widely distributed and in high

abundances in association with the two spotted spider mite, T. urticae, suggesting some

potential for use as biological control agents. The authors found the oviposition period of A.

swirskii to be almost double that of A. scutalis (22.3 compared to 12.9 days). The longevity of

both mites was similar, but A. swirskii showed a much higher fecundity and prey consumption

than A. scutalis. They concluded that A. swirskii had considerable potential as an agent against

spider mites but is not as active as the specialist phytoseiid P. persimilis, which is a widely

used and very effective predator of spider mites in glasshouse crops.

Chapter 2

28

2.2.5.2 Commercial use and release strategies

Since the start of commercial production in 2005, several biological control companies have

produced A. swirskii. The major producers are Koppert B.V. (Berkel en Rodenrijs, The

Netherlands), Biobest N.V. (Westerlo, Belgium), and Syngenta Bioline Limited (Little

Clacton, UK).

Koppert B.V. commercializes this predator under the product names SWIRSKI-

MITE®, SWIRSKI-MITE LD

® and SWIRSKI-MITE PLUS

®. SWIRSKI-MITE

® contains

50,000 predatory mites (nymphs and adults) mixed with bran in a 500 ml bottle. SWIRSKI-

MITE LD®

is a paper sachet containing 125 predatory mites and storage mites mixed with

bran, with 500 sachets per outer. SWIRSKI-MITE PLUS® is also a paper sachet containing

250 predatory mites and storage mites mixed with bran, with 100 or 500 sachets per outer

(Koppert, 2014). Biobest N.V. distributes A. swirskii under the names Swirskii-System® and

Swirskii-Breeding-System®

. Swirskii-System® consists of 25,000 or 50,000 predatory mites

in a 500 ml plastic pot. A Swirskii-Breeding- System®

breeding sachet contains approximately

250 A. swirskii in a carrier of bran and feeder mites. Each Swirskii-Long-Life-System® sachet

contains approximately 150 A. swirskii in a carrier of bran, 2 feeder mite species and an

alternative food source for these feeder mites (Biobest, 2014). Syngenta Bioline Limited

supplies the predatory mite under the products name Swirskiline®

and Bugline swirskii.

Swirskiline® Loose is a shaker tube of 1 litre containing 25,000 mites. Swirskiline

® Bulk is a

5 litre bag containing 125,000 mites. The Swirskiline®

sachet is a Gemini and hooked sachet,

each sachet containing a breeding colony of 250 predators at the time of packing. Bugline

Swirskii® is a string of sachets that can be laid onto the crop along a plant row (Syngenta,

2014).

Amblyseius swirskii is not susceptible to diapause (Bolckmans et al., 2005) it can be

used throughout much of the season provided daytime temperatures regularly exceed 22°C.

The mites are released directly in the crops in bran or vermiculite carriers sprinkled on the

leaves or substrates, but they can also be released via sachets (see below), or may be

broadcast via air blast or other automated distribution systems (Opit et al., 2005; Buitenhuis et

al., 2010a). The recommended release rates are typically between 25 and 100 mites per m²

depending on pest species, pest density, and crop. Preventive dispersal consists of 20 mites/m²,

when thrips or whiteflies are present 50 mites/m² are recommended. When the plants are

heavily infested by thrips or whiteflies the predatory mites are released at a rate of 100

A literature review

29

mites/m² in infested areas only and always in combination with other beneficials (Koppert,

2014).

Slow-release sachets (breeding systems) that contain a substitute prey (bran mites)

have been developed, and allow gradual release of the predators through a small hole in the

sachet over several weeks (Baxter et al., 2011). These sachets are water resistant and provide

resources for the reproducing mites during the release period. In this way A. swirskii can be

kept in the crop for longer periods, offering more protection, which makes it interesting for no

pollen bearing crops such as cucumber. Sachets containing 150-250 mites can be suspended

on the plants, at a rate of 1 sachet/2 m². Introduction can be repeated every 4 weeks to

maintain a continuous presence of A. swirskii in the crop (Biobest, 2014).

For crops producing little or no pollen like certain ornamental crops, vegetable crops,

and in plant nurseries, a food supplement can be distributed in the crop to enhance

establishment and population growth of A. swirskii or to help the predator population survive

periods of low prey availability. For instance, the pollen product NutrimiteTM

(consisting of

Typha angustifolia L. pollen) has been commercialized by Biobest N.V. for this purpose. The

product can be sprayed over the crop by a Nutrigun at a dosage of 500g/ha every 2 weeks

(Biobest, 2014).

2.3 Rearing of natural enemies

2.3.1 Introduction

In augmentative biological control natural enemies are mass-reared in bio-factories for release

in large numbers to obtain an immediate control of pests (van Lenteren, 2012). However,

augmentation is applied on a commercial scale in relatively few agricultural systems (van

Lenteren, 2012). One of the main reasons of the relatively low adoption of this pest

management strategy (van Lenteren, 2012) is that augmentative releases are frequently more

expensive than chemical pesticides (Collier and Van Steenwyk, 2004). Cost-effective rearing

techniques are therefore needed to make augmentation a more competitive strategy for

managing arthropod pests. One approach to facilitating this is reducing the costs associated

with rearing natural enemies by using factitious or artificial foods instead of their natural prey

or hosts (Riddick, 2009).

Chapter 2

30

2.3.2 Factitious foods

Factitious prey (hosts) are typically live, frozen, lyophilized or irradiated insects, mites and

crustaceans that support the development and reproduction of predators (parasitoids) in lieu of

natural or target prey (hosts). These food sources can not only be used for the mass production

of natural enemies but also used as a preventative strategy to help establish or maintain a

population of certain beneficial arthropods in the crop when pest populations are low, so as to

reduce the frequency of releases (Jonsson et al., 2008). The success of rearing a predator on a

factious food highly depends on its feeding habits, i.e. whether the predator is polyphagous,

oligophagous, or monophagous. Highly polyphagous species have better chances of surviving

and reproducing on factitious prey (Riddick, 2009).

Eggs of certain lepidopterans have been found to be a nutrient-rich food for several

generalist coccinellids (Herrera, 1960; Riddick, 2009). Specty et al. (2003) noted that eggs of

the Mediterranean flour moth Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) contained a

higher percentage of amino acids and lipids than the pea aphid Acyrthosiphum pisum (Harris)

(Hemiptera: Aphididae), and found that E. kuehniella eggs could support the growth and

reproduction of the multicolored Asian lady beetle Harmonia axyridis (Pallas) (Coleoptera:

Coccinellidae) to a similar and better extent as the aphid, respectively. Attia et al. (2011) and

Maes et al. (2014) proved that Cryptolaemus montrouzieri Mulsant (Coleoptera:

Coccinellidae) larvae developed faster on E. kuehniella eggs than on eggs of the mealybug

Planococcus citri (Risso)(Hemiptera: Pseudococcidae), which is the predator's natural prey.

De Clercq et al. (2005b) reported that adults of Adalia bipunctata (L.) (Coleoptera:

Coccinellidae) reared on live pea aphids, A. pisum were only half as fecund as those offered

irradiated or frozen E. kuehniella eggs, but egg hatch was significantly better on live aphids

than on flour moth eggs. Ephestia kuehniella eggs have also shown to be a suitable factitious

food for anthocorid bugs. Alauzet et al. (1992) reared Orius majusculus (Rt.) (Hemiptera:

Anthocoridae) on eggs of E. kuehniella, larvae of Cacopsylla pyri (L.) (Hemiptera: Psyllidae)

and Rhopalosiphum padi (L.) (Hemiptera: Aphididae) at five temperatures (12.5, 15, 20, 25

and 30oC). They found that at all temperatures the nymphs fed on E. kuehniella eggs

developed faster than those given the other food sources. Vacante et al. (1997) noted that a

high percentage nymphs of both Orius albidipennis (Reuter) and O. laevigatus (Hemiptera:

Anthocoridae) successfully developed to adult on diets containing E. kuehniella eggs. Chyzik

et al. (1995) reported that the fecundity and survival Orius albidipennis (Reuter) (Hemiptera:

Anthocoridae) on the onion thrips T. tabaci and on eggs of Ephestia cautella Walker

A literature review

31

(Lepidoptera: Pyralidae) were significantly higher than on the spider mite T. urticae; female

longevity was significantly higher on Ephestia eggs than on thrips and mites. Fauvel et al.

(1987) reported that the daily fecundity of Macrolophus caliginosus Wagner (Hemiptera:

Miridae) females reared on E. kuehniella eggs was approximately 3 or 8 times higher than

that of females reared on Aphis gossypii Glover (Hemiptera: Aphididae) or Tetranychus

turkestani Ugarov & Nycolsky (Acari: Tetranychidae), respectively. Vandekerkhove et al.

(2006) reported that M. caliginosus females fed E. kuehniella eggs had superior ovarian

scores and laid more eggs than those fed an artificial diet based on egg yolk. López-Arroyo et

al. (1999) evaluated developmental performance of the lacewings Ceraeochrysa cincta

(Schneider), Ceraeochrysa cubana (Hagen), and Ceraeochrysa smithi (Navas) (Neuroptera:

Chrysopidae) when larvae were reared on eggs of the moths E. kuehniella or Sitotroga

cerealella (Olivier) (Lepidoptera: Gelechiidae), or on the peach aphid Myzus persicae (Sulzer)

(Hemiptera: Aphididae). In all chrysopid species, the predators fed on moth eggs developed

significantly faster and in some cases had higher adult weights than those reared on aphids.

Pappas et al. (2011) evaluated the effect of E. kuehniella eggs and the nymphs of the aphid A.

pisum on the development and reproduction of Dichochrysa flavifrons (Brauer) and

Dichochrysa zelleri (Schneider) (Neuroptera: Chrysopidae). Preimaginal development of both

species was significantly shorter when their larvae were fed on E. kuehniella eggs than on A.

pisum nymphs. In D. flavifrons, the intrinsic rate of increase (rm ) was higher when larvae

were fed on E. kuehniella eggs than on A. pisum nymphs, while the converse was recorded in

D. zelleri. Few studies have, however, tested lepidopteran eggs for predatory mites. The eggs

of E. kuehniella were reported to support the development of the phytoseiid mite Iphiseius

degenerans (Berlese) (Acari: Phytoseiidae): 80% of the tested larvae reached adulthood, the

developmental time of females fed on this diet was same as that of those fed on sweet pepper

pollen or T. urticae brushed off onto the rearing arena , but longer than that of females reared

on almond, apple, castor bean or plum pollen (Vantornhout et al., 2004).

Cysts of the brine shrimp Artemia sp. (Anostraca: Artemiidae), a routinely used feed

in aquaculture (Van Stappen, 1996), are a non-insect type of factitious food which has been

tested for rearing a number of insect predators. Artemia cysts may have a number of practical

advantages over E. kuehniella eggs when used for rearing predatory arthropods. The market

price of decapsulated Artemia cysts is substantially lower than that of E. kuehniella eggs and

the cysts can be stored in dry form for several years in a cool and dry place without the need

for deep freezing (Arijs and De Clercq, 2001). Arijs and De Clercq (2001) were the first to

test cysts of the brine shrimp A. franciscana as a food for a heteropteran predator. The authors

Chapter 2

32

compared the development and reproduction of the anthocorid O. laevigatus on A.

franciscana cysts versus that on E. kuehniella eggs. The predators fed on hydrated

decapsulated cysts had similar developmental and reproductive rates as those fed frozen

Ephestia eggs. A follow-up study by Bonte and De Clercq (2008) confirmed that brine shrimp

cysts are suitable food for this anthocorid. Riudavets et al. (2006) compared the reproduction

of the mirid M. caliginosus and the anthocorid Orius majusculus (Reuter) (Hemiptera:

Anthocoridae), using dry cysts of Artemia sp. or frozen E. kuehniella eggs as food sources.

Whereas numbers of offspring of M. caliginosus females fed on either diet were similar, the

survival rate and numbers of offspring of O. majusculus fed on E. kuehniella eggs were higher

than on Artemia cysts. Castañé et al. (2006) found that M. caliginosus reared on dry or

hydrated cysts of Artemia sp. had the same nymphal survivorship, nymphal developmental

time, adult weight and fecundity as that obtained with E. kuehniella eggs. However, nauplii of

the brine shrimp yielded a significant reduction in survivorship, a delay in nymphal

development and a lower reproduction. Whereas Artemia cysts are less expensive than E.

kuehniella eggs and can support the development and reproduction of several predatory bugs,

prolonged rearing on the cysts as a sole food has been associated with fitness losses, at least in

Orius bugs (De Clercq et al., 2005a). For solving this problem, currently dry Artemia cysts are

routinely mixed with E. kuehniella eggs as a food for the production of different predatory

heteropterans; this practice may help to reduce inputs of expensive lepidopteran eggs and thus

rationalize the production process of these economically important predators (De Clercq et al.,

2014).

In the mass production of various generalist phytoseiids, storage mites, such as

Carpoglyphus lactis L. (Acari: Carpoglyphidae), Thyreophagus entomophagus (Laboulbene)

(Acari: Acaridae), Lepidoglyphus destructor (Acari: Glyciphagidae) and Suidasia medanensis

(Acari: Suidasiidae) are being used as primary food sources instead of natural prey

(Bolckmans and van Houten, 2006; Fidgett and Stinson, 2008; Midthassel et al., 2013).

Schliesske (1981) first used Tyrophagus casei (Oudemans) (Acari: Acaridae) as alternative

prey for N. cucumeris and Neoseiulus barkeri (Hughes) (Acari: Phytoseiidae). The author

found that both phytoseiid mites successfully developed and reproducted on this prey.

Bolckmans and van Houten (2006) tested reproduction of A. swirskii on juveniles and adults

of C. lactis and found that the daily oviposition and total fecundity of the females fed on

juvenile stages of the prey were similar as that on adult stages of the prey (1.80

eggs/female/day and 29 eggs over 16 days versus 1.84 eggs/female/day and 33 eggs over 18

days, respectively). The authors also noted that A. cucumeris was able to reproduce on C.

A literature review

33

lactis (2.13 eggs/female/day). Fidgett and Stinson (2008) reported that population of A.

cucumeris reared on T. entomophagus increased 10 fold within 14 days. This value is more

than double that routinely achieved for A. cucumeris in the commercial production on a diet

of Tyrophagus putrescentiae Schrank (Acari: Acaridae). The latter authors also indicated that

T. entomophagus and C. lactis were suitable food sources for A. swirskii, although the

population of the predator fed on the first prey was 38% greater than that on the second prey.

2.3.3 Artificial diets

Rearing arthropod parasitoids and predators in vivo requires the simultaneous rearing of

multiple organisms. Artificial diets are intended to eliminate the need to rear host (or prey)

species, thereby reducing the complexity of the system to manageable levels (Morales-Ramos

et al., 2014). Artificial diets allow rapid build-up of arthropod parasitoids or predators without

the time lag required to build up host or prey populations. It also allows to avoid risks of

diseases which may occur in the host, prey or plant culture. King et al. (1985) considered the

development of artificial diets may contribute to increase the success of augmentative

biological control, and Cohen (1992) considered the lack of suitable artificial diets the

greatest barrier to the mass production of entomophagous insects.

2.3.3.1 Types of artificial diets

Several terms are used to describe types of artificial diets. Dougherty (1959) classified

artificial diets according to three categories: holidic, meridic and oligidic, depending on

ingredients used. Holidic diets pertain to media whose intended constituents, other than

purified inert materials, have an exactly known chemical structure before compounding.

Meridic diets pertain to media composed of a holidic base to which is added at least one

substance or preparation of unknown structure (for example, protein, regardless of “purity”)

or of uncertain purity. Oligidic diets pertain to media in which crude organic materials supply

most dietary requirements. However, the distinction between these three classifications has

not always been clear; for this reason Grenier and De Clercq (2003) suggested another

classification system separating artificial diets based on the presence or absence of insect

components (i.e., tissues, hemolymph, cells, protein, amino acids, etc.). Based on formulation,

artificial diets can also be classified as (1) diets as powder or fragments, (2) semiliquid diets

Chapter 2

34

for chewing phytophages, (3) liquid diets for sucking phytophages, or (4) liquid diets for

endoparasitoids (Parra, 2012).

2.3.3.2 Function of diet components

An artificial diet for arthropods normally contains several main ingredients, including a

nitrogen source (e.g. protein, free amino acids), carbohydrates, lipids, vitamins, minerals and

water. Sometimes, other ingredients like stabilizers, preservatives, “fillers” or bulking agents

are added to the diet which helps to preserve its structure. Most successful diets contain

special components called “token stimuli” that do not have a direct nutritional function but

stimulate feeding responses (Cohen, 2004). A diet must provide all essential nutrients to allow

an arthropod to complete its development and reproduction. Whereas most nutritional studies

were performed on insect diets, very few works in this field have been done with mites.

Proteins are the source of amino acids required for the production of tissues and

enzymes in insects. Some amino acids, such as arginine, lysine, leucine, isoleucine,

tryptophan, histidine, phenylalanine, methionine, valine and threonine, are essential for

normal growth of an arthropod. Others are essential for certain species such as glycine for

some dipterous insects, alanine for Blattella cockroaches and proline for Phormia blowflies.

A good balance between different amino acids is of particular importance (Chapman, 1998).

The protein in the diet plays an important part in egg production (Johansson, 1964). Protein is

of primary importance for yolk production and is essential for oogenesis in many insects

(Chapman, 1998). In Calliphora blowflies, for instance, the intake of protein during the early

stages of egg development activates the corpora allata to secrete a factor leading to an

increase in carbohydrate intake during the period of yolk deposition (Strangways-Dixon,

1959).

Lipids including fatty acids, phospholipids and sterols are components of cell walls as

well as having other specific functions. Insects are able to synthesize many fatty acids and

phospholipids, so they are not usually essential dietary constituents, but many insects do

require a dietary source of polyunsaturated fatty acids, and all insects require sterols

(Chapman, 1998). The addition of lipids such as cholesterol has contributed to the success of

artificial diets for various insects (Hobson, 1935; Gupta et al., 2005b; Gupta et al., 2005a).

Carbohydrates are used as fuels by a majority of insects. They may be converted to

fats, and may contribute to the production of amino acids. They are, therefore, important

components of the diets of most insects, but they are not necessarily essential because they

can be synthesized from fats or amino acids (Chapman, 1998). Most insects are able to absorb

A literature review

35

and metabolize fructose and glucose, but some monosaccharides such as arabinose, ribose,

xylose, and galactose, while readily absorbed, are not metabolized (Chippendale, 1978).

Generalist feeders like herbivores and predators are able to digest disaccharides, such as

sucrose and maltose, while some parasitoids and mites are not (Singh, 1977; Cohen, 2004).

However, it is worth noting that the requirement for carbohydrates in the diet is species

dependent. Many insects, including key biocontrol agents, are fully dependent on nectar or

honeydew feeding to obtain the carbohydrates essential for their survival (Wäckers and van

Rijn, 2005).

Vitamins are divided into two groups depending on their solubility in water or lipids.

Insects need vitamins for growth and in general they can not synthesize them (Chapman,

1998). Vitamin B, a water-soluble vitamin, includes seven compounds: thiamine, riboflavin,

nicotinic acid, pyridoxine, pantothenic acid, folic acid and biotin that are required by all

insects (Chapman, 1998). Another water-soluble vitamin, vitamin C is known to play a role in

the molting and detoxification processes. It is more important in herbivorous than in

entomophagous insects (Chapman, 1998; Cohen, 2004). Lipid-soluble vitamins include

retinol, carotenoids (A), tocoferols (E), calciferol (D), and phyloquinone (K). Only vitamins A

and E are known to be required in insects, where they play a role in the synthesis of pigments

and in reproduction, respectively (Chapman, 1998).

Minerals are nearly always present as impurities in any artificial diet so that very little

work on the precise amounts required by insects has been undertaken (McFarlane, 1991).

Sodium, potassium, calcium, magnesium, chloride and phosphate are essential components of

the diet of all insects because they play a role in the functioning of insect cells (Chapman,

1998). Iron, zinc and manganese are also essential elements in insect diets because the first

element joins in cytochromes while the last two elements play a part in hardening the cuticle

in many insects (Chapman, 1998).

Water is the most fundamental nutrient and it plays an important role in all life

processes. Most insects take up sufficient water from their food or from a drinking source;

only a small group of insects can use metabolic activities to create water themselves. The

water content of an insect diet is a crucial factor: if it is too low the diet may not provide

enough water for the insect or cause difficulty in food intake, whereas if it is too high it may

encourage microbial contamination. Cohen (2004) suggested that the normal amount of water

present in the artificial diet should be the same as that in the insect's natural food. However,

sometimes water content is confused with water activity which is a thermodynamic concept

indicating the availability of water present in a given material. Water activity is a measure of

Chapter 2

36

the potential of water to move from one region to another. Different diets with the same water

content can have different water activities, resulting in different water availability for the

insect (Cohen, 2004).

2.3.3.3 Role of insect components in artificial diets

Grenier and De Clercq (2003) noted that adding insect components (i.e. tissues, hemolymph,

cells, protein, amino acids, etc.) to artificial diets enhances their acceptability and improves

their nutritional quality for a number of entomophagous insects. Artificial diets containing

insect components may be useful when predators or parasitoids require certain nutrients,

feeding stimulants, and other chemical cues found in arthropod prey or hosts (De Clercq,

2008). For instance, many artificial media for egg parasitoids of the genus Trichogramma

contain lepidopteran pupal hemolymph and/or pupal holotissues to stimulate egg laying by the

parasitoid females or to provide adequate nutrition for development of the larvae. Strand and

Vinson (1985) obtained complete in vitro culture of Trichogramma pretiosum Riley

(Hymenoptera: Trichogrammatidae) on an artificial medium supplemented with 40%

hemolymph of Manduca sexta (L.) (Lepidoptera: Sphingidae). Trichogramma dendrolimi

(Matsumura) and Trichogramma maidis Pint. et Voeg. (Hymenoptera: Trichogrammatidae)

successfully developed on artificial diets composed of egg yolk and Helicoverpa zea (Boddie)

(Lepidoptera: Noctuidae) hemolymph (Grenier and Bonnot, 1988). Trichogramma dendrolimi

was successfully reared in vitro in a medium containing hemolymph of Antheraea pernyi

Guérin-Méneville (Lepidoptera: Saturniidae) (Guan et al., 1978). The insect components also

play a positive role in the development and reproduction of other parasitoids. Dindo (1995)

reported successful in vitro culture of Brachymeria intermedia (Nees) (Hymenoptera:

Chalcididae) on bovine and chicken based commercial foods supplemented with 10-20%

pupal homogenate of Galleria mellonella L. (Lepidoptera: Pyralidae). Liu et al. (1988) noted

that the parasitoid wasp Anastatus japonicus Ashmead (Hymenoptera: Eupelmidae) could

completely develop on artificial diet containing hemolymph from the pupae of A. pernyi or

Philosamia cynthia ricini Donovan (Lepidoptera: Saturniidae) and longevity and fecundity of

artificially reared females were greater than those of parasitoids reared on host silkworm eggs.

Approximately 60% of the egg parasitoid Tetrastichus schoenobii Ferriere (Hymenoptera:

Tetrastichidae) reared on artificial diet supplemented with hemolymph from A. pernyi

completed development to the adult stage (Ding et al., 1980). Fanti and Bratti (1991) found

that a diet supplemented with G. mellonella pupal hemolymph and 20-hydroxyecdysone could

A literature review

37

support the development of the parasitoid fly Pseudogonia rufifrons (Wiedemann) (Diptera:

Tachinidae).

In comparison with insect parasitoids, the use of insect components in artificial diets

for insect predators is less studied. Ferkovich and Shapiro (2004) found that the fecundity of

the predatory anthocorid O. insidiosus was significantly increased when the bugs were fed on

an artificial diet supplemented with a cell line derived from eggs of the Indian meal moth

Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae). Matsuka and Okada (1975) reported

that the addition of pulverized drone honeybee powder to diets (consisting of yeast, chicken

liver, banana, royal jelly, pollen, and dried milk) slightly enhanced diet efficacy on

development of the ladybird H. axyridis. Bonte et al. (2010) fed the two-spot ladybird A.

bipunctata with an artificial diet based on a beef and chicken protein supplemented with

pollen and Artemia cysts. They found that developmental time increased, and body size and

fecundity of the coccinellid decreased in comparison to a diet of pea aphids. However, larval

survival rate and adult longevity were unaffected by the artificial diet as compared with the

natural aphid prey. Matsuka et al. (1982) found that adult females of Rodolia cardinalis

Mulsant (Coleoptera: Coccinellidae) lived longer but produced significantly fewer eggs when

fed an artificial diet of powdered honeybee brood with sucrose rather than live prey, Icerya

purchasi Maskell (Hemiptera: Margarodidae). Ogura and Hosoda (1995) tried to rear

Trogossita japonica Reitter (Coleoptera: Trogossitidae) on artificial diets consisting of

silkworm pupal powder, dry yeast, sucrose, peptone, squid liver oil, agar, and distilled water.

The authors found that the diet supported the development of the larvae, but diet-reared larvae

yielded smaller adults, which mated and oviposited at normal levels when provided with

natural prey.

2.3.3.4 Artificial diets for phytoseiid mites

Whereas a good body of literature exists on artificial diets for insect predators, far fewer

attempts have been made at rearing predatory mites on artificial diets (Singh, 1977).

McMurtry and Scriven (1966) reported longer developmental times and lower oviposition

rates when four phytoseiids (Amblydromalus limonicus Garman and McGregor, Amblyseius

hibisci (Chant), Typhlodromus occidentalis Nesbitt and Typhlodromus rickeri Chant) (Acari:

Phytoseiidae) were fed on various artificial diets (sucrose, molasses, yeast + sucrose or yeast

+ molasses) compared with mite prey and pollen as food sources. Shehata and Weismann

(1972) tested three artificial diets for the specialist spider mite predator P. persimilis. Their

results indicated that the larvae could develop to adults but the females failed to produce

Chapter 2

38

viable eggs. Kennett and Hamai (1980) investigated oviposition rate and developmental

capacity of 9 predaceous mites (A. hibisci, A. limonicus, Amblyseius largoensis (Muma),

Metaseiulus pomoides Schuster & Pritchard, T. occidentalis, Typhloseiopsis arboreus (Chant),

Typhloseiopsis pyri Scheuten, P. persimilis, and I. degenerans) fed on artificial and natural

diets. The authors reported that complete development and oviposition occurred for seven out

of nine species when fed on an artificial diet consisting of bee honey, sugar, yeast flakes,

yeast hydrolysate, enzymatic casein hydrolysate and fresh egg yolk. Oviposition rates of all

species fed on the artificial diet were lower than those on a natural diet. Ochieng et al. (1987)

reported that Amblyseius teke Pritchard and Baker could complete more than 25 generations

when reared on a liquid diet composed of bee honey, milk powder, egg yolk and Wesson's salt.

Abou-Awad et al. (1992) noted that the predacious mites Amblyseius gossipi El-Badry and A.

swirskii developed and reproduced successfully on artificial diets composed of yeast, milk,

cysteine, proline, arginine, sucrose, glucose, streptomycin sulphate and sorbic acid. However,

fecundity of both species fed on the artificial diet was lower than on natural prey, although the

eggs showed no abnormalities. Shih et al. (1993) conducted experiments to investigate the

responses of Euseius ovalis (Evans) to natural food resources and two artificial diets (diet A

consisted honey 15 g, ascorbic acid 100 mg, vitamin B complex 300 mg, Bovril (a

commercial beef extract) 500 mg, choline chloride 0.1 g, and distilled water 120 mL; and diet

B consisted D (-) fructose 10 g, fresh egg yolk 20 g, yeast powder 10 g, honey 10 g, choline

chloride 0.1 g, distilled water 180 ml). Immature development was successful in the first

generation but offspring was not able to complete its life cycle when maintained on the

artificial diets. The females of E. ovalis fed on artificial diets showed a shorter oviposition

period, lower daily and total reproductive rates, and shorter longevity than those fed on

natural diets. Ogawa and Osakabe (2008) investigated the development and survival of

Neoseiulus californicus (McGregor) on an artificial diet (composed of honey, sucrose,

tryptone, yeast extract, fresh egg yolk, and distilled water). The phytoseiid successfully

developed on the artificial diet, but only few eggs were deposited. The above studies suggest

that, although phytoseiid mites can develop on different artificial diets, fecundity in most

cases was inferior to that on natural or factitious prey.

2.3.4 Pollen

Pollen is an extremely rich source of many of the nutrients essential to the development and

reproduction of entomophagous arthropods. Pollen provides important food elements:

proteins, free amino acids, carbohydrates, lipids, vitamins, flavonoids, and minerals are all

A literature review

39

common in pollen grains. In fact, the protein and oil contents of pollens are both qualitatively

and quantitatively superior to those of most vegetative tissues and even many prey items.

Given its nutritional status, it is not surprising that many insects that ordinarily do not

consume plant tissues eat pollen, and that some can even complete development upon it in the

absence of prey (Lundgren, 2009b).

Predatory mites in several families (e.g. Phytoseiidae, Erythraeidae, Cheyletidae,

Stigmaeidae) feed on pollen to varying degrees. As stated above, McMurtry et al. (2013)

classify the feeding behavior of phytoseiid predatory mites into four groups, in which only

type I specialized predators of Tetranychus species not feed on pollen, whereas type II, III and

IV predatory mites are found to be more or less feeding on pollen. In the type II group, pollen

promotes reproduction of certain species, but at a much lower rate than mite prey. Most

species feeding on pollen belong to Neoseiulus genus including N. californicus (Swirski et al.,

1970), Neoseiulus fallacis (Garman) (Afifi et al., 1988), Neoseiulus idaeus Denmark & Muma

(Tanigoshi et al., 1993), Neoseiulus longispinosus (Evans) (Mori, 1977) (Acari: Phytoseiidae)

and one from Typhlodromus genus (T. rickeri) (Overmeer, 1985). In comparison to type II,

more species in the type III group have been reported feeding on pollen. These mites can

reproduce on pollen and in some species the reproduction rate is at least as high as on animal

prey (McMurtry and Rodriguez, 1987; Marisa and Sauro, 1990; Duso and Camporese, 1991).

The group of type IV specialized pollen feeders comprises only the genus Euseius; members

of this group (e.g. Euseius tularensis (Congdon) (Acari: Phytoseiidae)) can subsist on pollen

in the absence of prey with minimal reductions in fitness (Grafton-Cardwell et al., 1999).

Population increase of these species often can be correlated with pollen fallout onto the

foliage rather than the presence of any prey species (McMurtry, 1992).

In the practice of biological control, several species of predatory mites can be

provided with pollen as a supplementary or alternative food source in order to avoid

cannibalism when prey gets scarce (van Rijn and Tanigoshi, 1999b; Nichols and Altieri,

2004). Pollen can be supplied as an additional food source either by using banker plants

(Ramakers and Voet, 1996; Huang et al., 2011), by artificial pollen sources (e.g., plastic cups

with pollen placed between the crop plants) (Nomikou et al., 2010), by dusting or spraying

pollen from such various plants as cattail, castor bean, and maize (van Rijn et al., 2002;

Skirvin et al., 2006).

Chapter 2

40

41

Chapter 3

DEVELOPMENT AND REPRODUCTION OF AMBLYSEIUS SWIRSKII ON AN

ARTIFICIAL DIET ENRICHED WITH PUPAL HEMOLYMPH OF ANTHERAEA

PERNYI

This chapter is based on:

Nguyen, D. T., Vangansbeke, D., Lü, X., & De Clercq, P. 2013. Development and reproduction of

the predatory mite Amblyseius swirskii on artificial diets. BioControl, 58: 369-377.

Chapter 3

42

3.1 Introduction

Amblyseius swirskii (Athias-Henriot) (Acari: Phytoseiidae) is being used on a commercial

scale as a biological control agent of whiteflies and thrips in several greenhouse crops

(Nomikou et al., 2001; Messelink et al., 2006; Calvo et al., 2011). Amblyseius swirskii can

feed on various types of food including arthropod prey but also plant materials like pollen and

honeydew (Momen and El-Saway, 1993). Previous studies showed that A. swirskii can

successfully develop and reproduce on a wide range of food sources such as whiteflies

(Nomikou et al., 2001; Calvo et al., 2008; Messelink et al., 2008), thrips (Arthurs et al., 2009;

Chow et al., 2010), eriophyid mites (El-Laithy, 1998; Park et al., 2010), broad mites (van

Maanen et al., 2010; Onzo et al., 2012), spider mites (Xu and Enkegaard, 2010) and plant

pollen (Kutuk and Yigit, 2011; Park et al., 2011).

Depending on the species, phytoseiid mites are reared on phytophagous mite prey,

other natural foods such as pollen, or factitious prey like storage mites. In the commercial

production of A. swirskii, storage mites, including the dried fruit mite, Carpoglyphus lactis L.

(Acari: Carpoglyphidae), and Thyreophagus entomophagus (Laboulbene) (Acari: Acaridae),

are used as the primary food source (Bolckmans and van Houten, 2006; Fidgett and Stinson,

2008). The rearing procedures based on natural or factitious foods are often time-consuming

and/or expensive. The availability of an effective artificial diet for phytoseiids could eliminate

many of the problems associated with their mass rearing (Kennett and Hamai, 1980).

Whereas a good body of literature exists on artificial diets for insect predators

(Thompson, 1999; Riddick, 2009), relatively few studies have focused on the development of

artificial diets for phytoseiid mites. McMurtry and Scriven (1966) tested several artificial diets

for four phytoseiid species: Amblyseius limonicus Garman & McGregor, Amblyseius hibisci

(Chant), Typhlodromus occidentalis Nesbitt, and Typhlodromus rickeri Chant. Their results

showed that immature development was poor and oviposition rates were low compared to

natural prey or pollen. Shehata and Weismann (1972) reported that females of Phytoseiulus

persimilis (Athias-Henriot), deposited eggs when fed on three artificial diets, and larvae

developed to adulthood; however, the female offspring failed to produce eggs, and had a

smaller size and shorter longevity than conspecifics preying on T. urticae. Kennett and Hamai

(1980) found that seven out of nine species of phytoseiid mites could develop and reproduce

when fed an artificial diet composed of honey, sugar, yeast flakes, yeast hydrolysate,

enzymatic casein hydrolysate, and fresh egg yolk. However, the oviposition rate of all species

fed on artificial diet was only about one third of that achieved on natural diets. Abou-Awad et

A. swirskii artificial diet enriched A. pernyi pupal hemolymph

43

al. (1992) showed that Amblyseius gossipi El-Badry and A. swirskii developed, survived and

reproduced on several artificial diets consisting of yeast, milk, cystine, proline, arginine,

sucrose, glucose, streptomycin sulphate, and sorbic acid. However, females fed on the best

performing artificial diet had lower oviposition rates than those on natural diet. Ogawa and

Osakabe (2008) reported that an artificial diet composed of yeast components, saccharides,

and egg yolk supported development and survival of Neoseiulus californicus (McGregor), but

again fecundity on the artificial diet was low.

The above studies suggest that, although phytoseiid mites can develop on different

artificial diets, fecundity in most cases was negatively affected. Hence, for making a diet

suitable for commercial mass rearing of phytoseiids, the factor to be improved is reproduction.

Several studies have demonstrated that the use of insect materials in artificial diets can

enhance survival and oviposition of entomophagous insects (Grenier and De Clercq, 2003).

For instance, many artificial media for egg parasitoids of the genus Trichogramma contain

lepidopteran pupal hemolymph and/or pupal holotissues to stimulate egg laying by the

parasitoid females or to provide adequate nutrition for development of the larvae (e.g., Liu et

al. (1979); Strand and Vinson (1985); Nettles (1990); Lü et al. (2013)). Also, the fecundity of

the predatory anthocorid Orius insidiosus (Say) was significantly increased when the bugs

were fed on an artificial diet supplemented with a cell line derived from eggs of the Indian

meal moth Plodia interpunctella (Hübner) (Ferkovich and Shapiro, 2004). Conceivably,

insect materials like hemolymph could also be useful to supply nutritional factors for growth

and reproduction of predatory mites such as A. swirskii.

In the present study, we determined the life table parameters of A. swirskii when fed

on cattail pollen (Typha latifolia L.), dried fruit mite (C. lactis), or a meridic artificial diet

modified from Ogawa and Osakabe (2008), and a similar diet supplemented with hemolymph

of oak silkworm pupae (Antheraea pernyi Guérin-Méneville) (Lepidoptera: Saturniidae).

3.2 Materials and methods

3.2.1 Stock colony of Amblyseius swirskii

The stock colony of A. swirskii was initiated from specimens supplied by Biobest N.V.

(Westerlo, Belgium) and was cultured in a climatic cabinet set at 25 ± 1°C, 70 ± 5% RH and a

16:8 h (L:D) photoperiod. Mites were reared on green plastic arenas (10 x 10 x 0.3 cm)

(Multicel, SEDPA, France) on top of a thick foam pad placed in water in a plastic tray (20 x

13 x 5 cm). The edges of the arenas were covered with tissue paper immersed in the water to

Chapter 3

44

provide moisture and deter the mites from escaping (Figure 3.1). A small piece of sewing

thread was placed on the arenas to serve as an oviposition substrate. Every two days the eggs

were collected and transferred to new arenas. Cattail pollen (T. latifolia) was dusted every two

days as a food source for the mites.

Figure 3.1 Amblyseius swirskii colony rearing arena

3.2.2 Stock colony of Carpoglyphus lactis

A colony of C. lactis was initiated from mites supplied by Biobest N.V. and was kept in a

climatic cabinet at 25°C. Mites were reared in insect breeding dishes (10 x 4 cm) (SPL Life

Sciences Co. Ltd., Korea) with a mesh hole (4 cm in diameter) in the lid (Figure 3.2); the

dishes were placed in a foam box (30 x 20 x 20 cm) with 2 cm of water. The diet of C. lactis

was modified from Zdarkova et al. (1999), and consisted of 1/2 wheat germ (Dr. Grandel,

Augsburg, Germany), 1/3 yeast torula (MP Biomedicals LLC, Illkirch, France), and 1/6 Pond

Food Balance Sticks (Vitakraft, Bremen, Gemany); the diet was mixed with vermiculite to

provide food and shelter for the mites.

Figure 3.2 Carpoglyphus lactis colony rearing box


45

3.2.3 Pollen

Fresh cattail pollen (T. latifolia) was also supplied by Biobest N.V. and stored at -18°C. For

the experiments, the pollen was thawed and kept in a refrigerator at 5°C for max. 1 week.

3.2.4 Preparation of artificial diet

The artificial diet was composed of honey (Meli N.V., Veurne, Belgium), sucrose (MP

Biomedicals LLC, Illkirch, France), tryptone (Fluka Analytical, Sigma-Aldrich Co., St. Louis,

USA), yeast extract (Duchefa, Haarlem, The Netherlands), fresh hen's egg yolk, and distilled

water, and was prepared according to Ogawa and Osakabe (2008), with some modifications as

laid out below. Two artificial diets (AD) were prepared.

The first diet (AD1) consisted of 5% honey, 5% sucrose, 5% tryptone, 5% yeast

extract, 10% egg yolk, and 70% distilled water (w/w). Honey, sucrose, and tryptone were

dissolved into the distilled water, after which the yeast extract and egg yolk were added.

Unlike Ogawa and Osakabe (2008), we did not filter sterilize any of the ingredients. All

ingredients were then blended using a Virtis mixer (SP Industries Inc., Gardiner, New York,

USA).

The second diet (AD2) consisted of 80% AD1 supplemented with 20% (w/w)

hemolymph of oak silkworm pupae (A. pernyi) originating from a culture at the Guangdong

Entomological Institute, China. The pupal hemolymph was collected from live A. pernyi

pupae which were immersed in a water bath at 60°C for 10 minutes to avoid melanization of

the hemolymph. After surface sterilization of the pupae with 75% ethanol, the hemolymph

was collected by pressing the pupae under sterile conditions. The hemolymph was then

lyophilized and stored in a deep freezer at -18°C. The lyophilized hemolymph was

redissolved using distilled water before being added to the diet.

For both AD1 and AD2, fresh diet was prepared every week and kept in a refrigerator

at 5°C.

3.2.5 Rearing microcosms

To examine the development and reproduction of individual A. swirskii, modified Munger

cells were used as rearing microcosms (Ogawa and Osakabe, 2008). Each cell consisted of a

transparent acrylic board (top board; 40 x 40 mm, 2 mm thick) with a 19 mm diameter hole in

the center, a black acrylic board (middle board; 40 x 40 mm, 5 mm thick) with a 18 mm

Chapter 3

46

diameter hole in the center, and another black acrylic board (bottom board; 40 x 40 mm, 2

mm thick) with a 1 mm diameter hole in the center. Clear transparency film (3M™ Dual-

Purpose Transparency Film) was placed between the top and middle boards and was pierced 4

times with a fine needle allowing ventilation but precluding escape of the mites. The hole in

the bottom board was plugged with a rolled piece of tissue paper saturated with tap water to

serve as a water source for the mites (Figure 3.3). A paper clip was used to hold the boards

together. The microcosms were placed on a plastic support containing tap water.

Figure 3.3 Rearing microcosm

3.2.6 Experimental setup

Eight hours before the start of the experiments, new black threads were placed in the stock

colony of A. swirskii. Eggs deposited on the threads were transferred individually to the

rearing microcosms; 48, 54, 55, and 53 eggs were used for the treatments with T. latifolia

pollen, C. lactis, AD1, and AD2, respectively. All diets were offered from the larval stage of

the predator on and refreshed every 2 days. In the treatment with C. lactis, predators were

supplied with a mixture of life stages of the storage mite. Artificial diets were absorbed on a

small piece of filter paper (2 x 2 mm) which was placed on the bottom board of the cells. To

obtain data on the duration of each developmental stage of A. swirskii and on mortality and

escape rates, observations were made every 24 hours until all individuals had reached

adulthood. The developmental stage of each individual was determined based on the presence

of exuviae in the cells. After completing immature development, each female was paired with

a male that was reared on the same diet as the female. Males that died during the experiment

were replaced. Adults were observed daily to determine the preoviposition and oviposition

period, longevity and fecundity. Progeny from females of the same age were transferred to

new cells and fed on the same diet as their parents in order to determine the sex ratio of the


47

offspring for each treatment. The experiments were done in a growth chamber at 23 ± 1°C, 65

± 5% RH and a 16:8 h (L:D) photoperiod.

3.2.7 Life table parameters calculation

The intrinsic rate of increase (rm) was calculated according to the formula of Lotka (1907) and

Birch (1948):

∑𝑙𝑥𝑚𝑥𝑒−𝑟𝑚∗𝑥 = 1

where x equals the female age (days), lx is the age specific survival of the females at age x and

mx is the number of daughters produced per female at age x. The latter parameter is obtained

by multiplying the mean number of eggs laid per female by the proportion of female offspring

produced at age x. The Jackknife procedure was used according to Meyer et al. (1986) and

Hulting et al. (1990) to calculate the standard error of rm. Other parameters calculated (Maia

et al., 2000) were the generation time T, i.e. mean time span between the birth of individuals

of a generation and that of the next generation (days),

T =∑xlxmx

∑ lxmx

and the net reproductive rate, R0, i.e. the mean number of female offspring produced per

female (females/female)

R0 =∑lxmx

3.2.8 Statistical analysis

Data were subjected to statistical analysis (IBM SPSS Statistics, Ver. 20) to analyze the effect

of diet on the duration of the immature stages, preoviposition and oviposition period, daily

and total oviposition, and adult longevity of A. swirskii. When a Kolmogorov–Smirnov test

indicated that means were normally distributed, the parameter was analyzed using a one-way

analysis of variance (ANOVA). If a Levene test indicated heteroscedasticity, a Tamhane test

was used instead of Tukey's test. When means were not normally distributed, a nonparametric

Kruskal-Wallis ANOVA was used and means were separated using a Mann-Whitney U test.

Immature survival and sex ratios of the progeny were compared by means of a logistic

Chapter 3

48

regression. This regression is a generalized linear model using a probit (log odds) link and a

binomial error function. Each test consists of a regression coefficient that is calculated and

tested for being significantly different from zero, for which P-values are presented

(McCullagh and Nelder, 1989). P-values smaller than or equal to 0.05 are considered

significant. Fertility life table parameters, including the net reproductive rate (Ro), generation

time (T), and intrinsic rate of increase (rm) were estimated using the Jackknife procedure as

described by Maia et al. (2000).

3.3 Results

The developmental times of all male immature stages and egg, larval, and protonymphal

stages of females did not differ among diets (Table 3.1). However, the developmental time of

female deutonymphs was significantly affected by diet. Female deutonymphs reared on C.

lactis or AD2 took significantly less time to develop to adulthood than those fed on the other

diets. The total developmental time of females fed on C. lactis or AD2 was significantly

shorter than that of females fed on AD1. Nearly all individuals reached adulthood on the

different diets, with immature survival rates of 100, 100, 96.36, and 98.11% when the

predators were fed on T. latifolia pollen, C. lactis, AD1, and AD2, respectively. Survival rate

was not affected by diet (χ2 = 4.52; df = 3; P = 0.210).


49

Table 3.1 Developmental time (days) of the immature stages of Amblyseius swirskii fed on

four diets at 23°C

Diet n

Developmental stage

Egg Larval Protonymph Deutonymph

Total

immature

Females

T. latifolia pollen 32 2.84 ± 0.07 a 0.73 ± 0.04 a 1.86 ± 0.08 a 2.00 ± 0.13 c 7.44 ± 0.13 bc

C. lactis 36 2.89 ± 0.05 a 0.76 ± 0.04 a 2.10 ± 0.06 a 1.25 ± 0.08 a 7.00 ± 0.07 a

AD1 44 2.73 ± 0.08 a 0.76 ± 0.06 a 2.08 ± 0.07 a 2.00 ± 0.09 c 7.57 ± 0.11 c

AD2 35 2.83 ± 0.08 a 0.76 ± 0.04 a 2.04 ± 0.10 a 1.63 ± 0.10 b 7.26 ± 0.11 ab

χ2 3.12 0.55 7.26 31.67 16.15

df 3 3 3 3 3

P 0.373 0.908 0.064 <0.001 <0.001

Males

T. latifolia pollen 16 2.75 ± 0.11 a 0.94 ± 0.04 a 2.00 ± 0.15 a 1.13 ± 0.09 a 6.81 ± 0.14 a

C. lactis 18 2.94 ± 0.06 a 0.78 ± 0.06 a 1.83 ± 0.11 a 1.11 ± 0.08 a 6.67 ± 0.14 a

AD1 9 2.67 ± 0.17 a 0.94 ± 0.15 a 1.61 ± 0.14 a 1.44 ± 0.24 a 6.67 ± 0.24 a

AD2 17 2.88 ± 0.08 a 0.94 ± 0.04 a 2.00 ± 0.10 a 1.29 ± 0.11 a 7.12 ± 0.15 a

χ2 4.42 5.89 5.17 5.09 5.45

df 3 3 3 3 3

P 0.220 0.117 0.160 0.165 0.141

n: number of individuals reaching the adult stage.

Means ± SE within a column and sex followed by the same letter are not significantly

different (Mann-Whitney U test; P > 0.05). χ2-, df- and P-values refer to Kruskal-Wallis

ANOVAs.

Whereas all females reproduced on pollen, C. lactis, and AD2, ca. 60% of the females

maintained on AD1 died without producing eggs. Diet significantly influenced the duration of

the preoviposition period (F = 20.09; df = 3, 99; P<0.001). Females fed on AD2 had

significantly shorter preoviposition periods than those fed on T. latifolia pollen and AD1

(Table 3.2). However, oviposition period and female longevity were longer on AD2, C. lactis,

and T. latifolia pollen than on AD1 (oviposition period: F = 6.79; df = 3, 99; P<0.001 and

female longevity: F = 7.81; df = 3, 99; P<0.001). Diet had no influence on the sex ratio of

Chapter 3

50

offspring with the proportion of females ranging from 0.68 to 0.72 (χ2 = 2.52; df = 3, P =

0.472). The daily oviposition rate of A. swirskii reared on AD2 was significantly higher than

that of females reared on the other diets (F = 29.17; df = 3, 99; P<0.001).

Table 3.2 Reproduction and life table parameters of Amblyseius swirskii fed on four diets at

23°C

Parameter

T. latifolia

pollen

(n = 29)

C. lactis

(n = 31)

AD1

(n = 16)

AD2

(n = 27)

Preoviposition period

(days)b

3.14 ± 0.21 b 2.77 ± 0.13 ab 4.81 ± 0.44 c 2.41 ± 0.10 a

Oviposition period (days)a 25.48 ± 1.78 a 24.68 ± 1.65 a 12.81 ± 3.02 b 25.67 ± 2.05 a

Female longevity (days)a 34.45 ± 2.38 a 35.90 ± 2.05 a 22.56 ± 3.52 b 42.07 ± 2.63 a

Female proportion of the

progenyc

0.68 ± 0.007 a 0.72 ± 0.004 a 0.70 ± 0.029 a 0.71 ± 0.011 a

Oviposition rate

(eggs/female/day)b

1.18 ± 0.04 b 1.21 ± 0.03 b 0.92 ± 0.08 c 1.52 ± 0.03 a

Total number of eggs

(eggs/female)a

29.00 ± 1.72 b 29.03 ± 1.72 b 9.94 ± 2.26 d 38.26 ± 2.89 a

Net reproductive rate Ro

(females /female)b

19.71 ± 0.042 c 20.58 ± 0.04 b 6.46 ± 0.098 d 27.21 ± 0.069 a

Generation time T (days)b 19.00 ± 0.29 ab 17.33 ± 0.18 b 22.08 ± 2.50 a 18.30 ± 0.23 b

Intrinsic rate of increase rm

(females /female/day)b

0.158 ± 0.002 b 0.175 ± 0.002 a 0.104 ± 0.013 c 0.181 ± 0.002 a

n = number of reproducing females observed

Means ± SE within a row followed by the same letter are not significantly different (P>0.05;

aTukey or

bTamhane test;

cProbit (Wald Chi-square) test)

Peak oviposition was reached after 3 days on AD2, after 7 days on C. lactis and after 8

days on T. latifolia and AD1 (Figure 3.4). Also, the total number of eggs was significantly

higher for females offered AD2 versus the other diets (F = 21.78; df = 3, 99; P<0.001) (Table

3.2).


51

Figure 3.4 Daily oviposition rate of Amblyseius swirskii fed on four diets at 23°C

Differences in developmental and reproductive characteristics were reflected in life

table statistics. Net reproductive rate (Ro) (F = 16813.98; df = 3, 99; P<0.001) of A. swirskii

fed on AD2 was significantly higher than that of predators fed on C. lactis, T. latifolia pollen,

or AD1. Mean generation time (F = 5.01; df = 3, 99; P<0.001) of predators reared on AD1

was significantly longer than that of conspecifics reared on AD2 and C. lactis. Finally, the

intrinsic rates of increase (rm) of the predators fed on AD2 and C. lactis were greater than on

the other diets (F = 45.72; df = 3, 99; P<0.001) (Table 3.2).

3.4 Discussion

The main objective of our study was to develop a suitable artificial diet for mass rearing of the

economically important phytoseiid predator A. swirskii. The artificial diets that we tested were

modified from that formulated by Ogawa and Osakabe (2008) for N. californicus and

compared with cattail pollen, a standard food in several predatory mite studies (Lee and

Gillespie, 2011; Park et al., 2011), and the dried fruit mite, C. lactis, which is routinely used

in the commercial production of A. swirskii (Bolckmans and van Houten, 2006). Our findings

indicate that A. swirskii can develop and reproduce with similar or even better success on an

artificial diet as compared to pollen or storage mites. Our results with cattail pollen and C.

Chapter 3

52

lactis are consistent with previous reports (Nomikou et al., 2003b; Bolckmans and van Houten,

2006; Fidgett and Stinson, 2008; Lee and Gillespie, 2011).

A more favorable diet will result in higher population growth of an arthropod, as

indicated by superior life table parameters (Grenier and De Clercq, 2003). The highest

intrinsic rates of increase in our study were observed when A. swirskii was fed with AD2 or C.

lactis (0.182 and 0.175 females/female/day, respectively). These figures were higher than

those reported for A. swirskii when fed on the twospotted spider mite Tetranychus urticae

Koch at 26°C (0.167) (El-Laithy and Fouly, 1992), the western flower thrips Frankliniella

occidentalis (Pergande) and onion thrips Thrips tabaci Lindeman at 25°C (0.056 and 0.024,

respectively) (Wimmer et al., 2008), and the eriophyoid fig mites Aceria ficus (Cotte) and

Rhyncaphytoptus ficifoliae Keifer at 29°C (0.155 and 0.122, respectively) (Abou-Awad et al.,

1999). On the other hand, the rm values of A. swirskii on AD2 or C. lactis calculated here were

slightly lower than the value of 0.201 reported by Park et al. (2011) when the predator was

offered the tomato russet mite Aculops lycopersici (Massee) as prey at 25°C, and when fed on

the cotton whitefly Bemisia tabaci Gennadius at 27°C (0.213) (Nomikou et al., 2001). Thus,

on both the factitious prey C. lactis and on the enriched artificial diet AD2, A. swirskii

performed well and in some cases even better than on several of its natural prey. However, it

should be noted that comparison of life table statistics among studies is complicated by

differences in experimental methods, climatic conditions and calculation of estimates, which

may explain some of the contrasting results in the literature.

The artificial diet developed by Ogawa and Osakabe (2008) supported immature

development and survival of the predatory mite N. californicus but its oviposition rate on this

diet was negligible compared with a diet of T. urticae. However, a slightly modified version

of this artificial diet used in our study (AD1, without insect hemolymph) proved suitable to

support development of A. swirskii and also allowed some reproduction. The oviposition rate

of A. swirskii on AD1 (0.92 eggs/female/day) was higher than that on an artificial diet

designed by Abou-Awad et al. (1992) (0.30 eggs/female/day); moreover, it was similar to that

of mites reared on the natural prey F. occidentalis (Wimmer et al., 2008) (0.92

eggs/female/day) and superior to that of females fed on the carmine spider mite Tetranychus

cinnabarinus (Boisduval) and brown soft scale Coccus hesperidum (L.) (0.31 and 0.02

eggs/female/day, respectively) (Ragusa and Swirski, 1977). The relatively good performance

of A. swirskii on artificial diet AD1 may be due to the generalist feeding habits of this

phytoseiid mite (Momen and El-Saway, 1993). However, this diet has still limitations in terms


53

of fecundity, with 60% of the females failing to lay eggs and dying shortly after molting to the

adult stage.

Nettles (1990) and Grenier and De Clercq (2003) noted that adding insect components

such as hemolymph to artificial diets enhanced their acceptability and improved their

nutritional quality for a number of entomophagous insects. Hemolymph of lepidopteran larvae

or pupae has been used in artificial media for parasitoid wasps, especially for Trichogramma

species. For instance, Trichogramma pretiosum Westwood successfully completed

development in artificial medium when it was supplemented with hemolymph of Manduca

sexta (L.) (Strand and Vinson, 1985; Xie et al., 1986). Cônsoli and Parra (1997) reported that

Trichogramma galloi Zucchi and T. pretiosum could be reared in a medium consisting of 70%

Helicoverpa zea (Boddie) larval hemolymph. Pupal hemolymph of A. pernyi or Philosamia

cynthia ricini Drury was used in an artificial medium for Trichogramma dendrolimi

(Matsumura) (Liu et al., 1979) and Anastatus sp. egg parasitoids (Liu et al., 1988). Lü et al.

(2013) also indicated that insect hemolymph is a key component of artificial media for

Trichogramma spp. Our study indicates, however, that supplementing artificial diets with

insect hemolymph may also be useful to improve their nutritional value for predatory

arthropods. When 20% pupal hemolymph of A. pernyi was added to diet AD1 to create AD2

in the present study, oviposition rate and intrinsic rate of increase of A. swirskii were

substantially increased. These results suggest that the hemolymph played a positive role both

in fecundity and survival of the predator. Further research is needed to identify the

components of the pupal hemolymph which are responsible for the increased performance.

In conclusion, the artificial diet AD2 supported development and reproduction of A.

swirskii to the same extent as a factitious prey which is routinely used in the mass rearing of

the phytoseiid, indicating the potential of artificial diets to rationalize the mass production of

this economically important biological control agent. However, nutritional imbalances within

the diet is possibly expressed only in the subsequent generations (De Clercq et al., 2005a).

Therefore, developmental and reproductive performance of A. swirskii fed on AD2 will need

to be assessed over subsequent generations. Furthermore, whereas A. pernyi is currently

widely used in silk production in China, pupal hemolymph of this insect may become less

available in the future, which may result in a higher price for this diet component and thus in a

higher production cost of the artificial diet (Lü et al., 2013). Thus, future work is warranted to

reduce the percentage of pupal hemolymph in the diet or to replace it by a more easily

available nutrient.

Chapter 3

54

55

Chapter 4

BENEFICIAL EFFECT OF SUPPLEMENTING AN ARTIFICIAL DIET FOR

AMBLYSEIUS SWIRSKII WITH HERMETIA ILLUCENS HEMOLYMPH


Nguyen, D. T., Bouguet, V., Spranghers, T., Vangansbeke, D., & De Clercq, P. 2014. Beneficial

effect of supplementing an artificial diet for Amblyseius swirskii with Hermetia illucens hemolymph.

Journal of Applied Entomology, DOI: 10.1111/jen.12188.

Chapter 4

56

4.1 Introduction

Amblyseius swirskii (Athias-Henriot) (Acari: Phytoseiidae) is a generalist predatory mite that

has been commercialized since 2005 and is presently being used on a worldwide scale as an

augmentative biological control agent against thrips and whiteflies in a range of greenhouse

crops (Nomikou et al., 2002; Messelink et al., 2006; Messelink et al., 2008). The predator can

develop and reproduce on variety of other food sources including spider mites (El-Laithy and

Fouly, 1992), eriophyid mites (Abou-Awad et al., 1999; Park et al., 2011), broad mites

(Swirski et al., 1967; van Maanen et al., 2010) and pollen (Swirski et al., 1967; Ragusa and

Swirski, 1977; Park et al., 2011).

In an augmentative biocontrol strategy, large quantities of beneficial insects and mites

are produced and released in the crop. A conservative method for mass-rearing these natural

enemies is via a so-called natural, tri-trophic system, comprising the predator (parasitoid), the

herbivorous prey (host), and the prey's host plant (De Clercq et al., 2014). In order to

rationalize the production line the number of trophic levels can be reduced, allowing to lower

costs for labour and production facilities, like greenhouses (Grenier, 2009). One way to do

this can be by using of factitious foods. In the mass production of various generalist

phytoseiids, like A. swirskii, storage mites, such as Carpoglyphus lactis L. (Acari:

Carpoglyphidae) and Thyreophagus entomophagus (Laboulbene) (Acari: Acaridae), are being

used as primary food sources instead of natural prey (Bolckmans and van Houten, 2006).

However, the rearing procedures of phytoseiid mites based on these factitious foods are often

time-consuming and allergy problems can be generated by using storage mites (Fernandez-

Caldas et al., 2007). The availability of an effective artificial diet may tackle these problems,

shorten the production line and consequently represent a step towards a more cost-effective

mass rearing (Riddick, 2009).

In Chapter 3, we found that an artificial diet enriched with pupal hemolymph of the

Chinese oak silkworm, Antheraea pernyi (Guérin-Méneville) (Lepidoptera: Saturniidae)

supported development and reproduction of A. swirskii to the same extent as the routinely

used storage mite Carpoglyphus lactis (L.). However, the silkworm hemolymph is not easily

available resulting in a higher cost and lower reliability for the continuous production of the

artificial diet (Xie et al., 1997; Heslin et al., 2005; Lü et al., 2013; Lü et al., 2014). Therefore,

if the silkworm hemolymph extract could be replaced by a more easily available and cheaper

nutrient, the cost of diet production may be further reduced.

Effect of H. illucens hemolymph in artificial diet of A. swirskii

57

The black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae) can feed on a

wide variety of decomposing vegetal and animal matter (James, 1935). This species is

particularly interesting because the larvae can use a wide array of waste materials, converting

them into proteins and fats that are suitable for consumption by various animals, including

poultry (Hale, 1973), swine (Newton et al., 1977), and fish (Bondari and Sheppard, 1987).

Furthermore, in organic waste management soldier fly larvae can assist in suppressing

populations of houseflies, Musca domestica L. (Diptera: Muscidae) (Furman et al., 1959), and

help to reduce infectious bacterial populations in chicken and cow manure (Erickson et al.,

2004; Liu et al., 2008). The larvae can also convert organic waste into biodiesel fuel (Li et al.,

2011a). Prepupal black soldier flies contain on average 44% dry matter, which is composed of

42% protein and 35% fat, including essential amino and fatty acids (Hale, 1973).

The hypothesis tested in this study was that the high amount of proteins and other

nutrients extracted from black soldier fly prepupae could improve the nutritional quality of an

artificial diet for the development and reproduction of the predatory mite A. swirskii. Life

table parameters of A. swirskii were determined when the predator was fed on a basic meridic

artificial diet (section 3.2.4 ) supplemented with different concentrations (0, 5, 10 and 20%) of

prepupal hemolymph of H. illucens.



A stock colony of A. swirskii was reared as described in section 3.2.1

4.2.2 Black soldier fly rearing and hemolymph collecting

A colony of black soldier flies, H. illucens, was initiated with specimens supplied by

Millibeter BVBA (Antwerp, Belgium). The colony was maintained in a greenhouse at the

faculty of Bioscience Engineering, Ghent University, at 25 ± 5 °C and 40 – 80 % RH. Newly

hatched larvae were placed into stainless steel containers (34 x 25 x 20 cm) with vented lids.

Larvae were reared on solid organic waste springing from a fruit and vegetable fermentation

installation. Fresh substrate was added weekly until the larvae reached the prepupal stage and

migrated out of the substrate.

Hemolymph was collected from H. illucens prepupae (ca. 5 days old), which had been

washed with tap water. Prepupae were immersed in a water bath at 60 oC for 10 min to avoid

Chapter 4

58

melanisation of the hemolymph. After surface sterilization of the prepupae with 75 % ethanol,

the hemolymph was collected by cutting the end of the prepupal abdomen and pressing the

prepupae under sterile conditions. In order to obtain 1 mL of hemolymph, about 20-25

prepupae were processed. The hemolymph was then stored in a deep freeze at -18 oC.

4.2.3 Preparation of artificial diets

The basic diet (AD0) was prepared as described in section 3.2.4 . The enriched diets AD5,

AD10 and AD20 consisted of 95%, 90% or 80% of AD0 supplemented with 5, 10 or 20%

(w/w) prepupal hemolymph of the black soldier fly, respectively. The ingredients were

blended using a Virtis mixer (SP Industries Inc., Gardiner, New York, USA). The diets were

stored in a deep freeze at -18°C and thawed before use. Thawed diets were kept in a

refrigerator at 5 °C for max. 1 week.

4.2.4 Development and reproduction on the different artificial diets

Sixty eggs (< 8 h old) of A. swirskii per treatment were transferred individually from the stock

colony to rearing microcosms that were modified from Munger cells as described in section

3.2.5 . The foods were offered ad libitum from the larval stage of the predator on, and

refreshed every 2 days. Artificial diets were absorbed on a small piece of filter paper (2 x 2

mm) which was placed on the bottom board of the cells. The mites were observed and

different parameters were recorded same as that described in section 3.2.6 . Mites that escaped

or died as a result of manipulation were excluded from data analysis; these escape and death

rates did not differ among treatments and varied between 3 and 18 % (χ2

= 5.353, df = 3, P =

0.148; Probit (Wald Chi-square) test). The experiments were done in a growth chamber at 23

± 1 °C, 65 ± 5 % RH and a 16:8 h (L:D) photoperiod.

4.2.5 Diet switching experiment

In the first experiment, most females fed on the basic diet (AD0) were not able to produce

viable eggs; therefore, a diet switching experiment was conducted to investigate the role of

prepupal hemolymph of the black soldier fly in stimulating egg laying by A. swirskii when its


59

immature stages were reared on the basic diet.Eggs (<8h old) were collected from the colony

and transferred to green plastic arenas (5 x 5 x 0.3 cm) (Multicel, SEDPA, France), placed on

a wet sponge in a vented insect breeding dish (10 x 4 cm) (SPL Life Sciences Co. Ltd., Korea)

containing water. The edges of the arenas were covered with tissue paper immersed in the

water to provide moisture and deter the mites from escaping. Every two days the juvenile

mites were offered fresh basic artificial diet AD0. When the mites reached adulthood, males

and females were paired and each pair was transferred to an individual Munger cell. Four

cohorts were presented with one of the different artificial diets (AD0, AD5, AD10 or AD20),

as described above. Adults were observed daily until the females stopped laying eggs in order

to determine the oviposition period and fecundity.


Life table parameters were calculated as explained in section 3.2.7


Data were subjected to statistical analysis (IBM SPSS Statistics, Ver. 21) to evaluate the

effect of diet on the developmental time, preoviposition and oviposition period, daily and total

oviposition, and adult longevity of A. swirskii. When a Kolmogorov–Smirnov test indicated

that data were normally distributed, they were analysed using a one-way analysis of variance

(ANOVA). If a Levene test indicated heteroscedasticity, a Tamhane post-hoc test was used

instead of a Tukey test. When means were not normally distributed, a nonparametric Kruskal-

Wallis ANOVA was used and means were separated using Mann-Whitney U tests. Immature

survival rates and sex ratios were compared by means of a logistic regression. This regression

is a generalized linear model using a probit (log odds) link and a binomial error function.

Each test consists of a regression coefficient that is calculated and tested for being

significantly different from zero, for which P-values are presented (McCullagh and Nelder,

1989). In all tests, P-values smaller than or equal to 0.05 were considered significant.

4.3 Results

Immature survival rates were not significantly different among diets enriched with

hemolymph of H. illucens prepupae, but these values were significantly higher than those of

predatory mites fed on the basic diet AD0 (χ2 = 12.882, df=3, P=0.005; Probit (Wald Chi-

Chapter 4

60

square) test). The survival rates were 82%, 100%, 98% and 98% when the predators were fed

on AD0, AD5, AD10 and AD20, respectively.

Table 4.1 Developmental times of immature stages of Amblyseius swirskii fed on artificial

diets enriched or not with Hermetia illucens prepupal hemolymph at 23°C

Diet n

Developmental time (days)

Larval Protonymph Deutonymph

Total immature

(Larva-adult)

Females

AD0 38 0.80 ± 0.04 a 2.14 ± 0.07 c 1.95 ± 0.07 b 4.89 ± 0.10 c

AD5 42 0.71 ± 0.04 a 1.98 ± 0.08 c 1.43 ± 0.09 a 4.12 ± 0.05 b

AD10 40 0.78 ± 0.04 a 1.68 ± 0.07 b 1.65 ± 0.08 a 4.10 ± 0.09 ab

AD20 41 0.72 ± 0.04 a 1.33 ± 0.04 a 1.85 ± 0.06 b 3.90 ± 0.05 a

χ2 3.523 57.585 22.334 69.217

df 3 3 3 3

P 0.318 <0.001 <0.001 <0.001

Males

AD0 11 0.95 ± 0.05 ab 1.95 ± 0.11 c 1.18 ± 0.18 a 4.09 ± 0.16 b

AD5 16 0.81 ± 0.06 a 1.88 ± 0.12 bc 1.00 ± 0.13 a 3.69 ± 0.12 ab

AD10 19 1.00 ± 0.00 b 1.53 ± 0.14 ab 1.32 ± 0.15 a 3.84 ± 0.16 ab

AD20 17 0.94 ± 0.04 ab 1.29 ± 0.11 a 1.24 ± 0.14 a 3.47 ± 0.12 a

χ2 10.372 15.244 2.866 8.405

df 3 3 3 3

P 0.016 0.002 0.413 0.038

n: number of individuals reaching the adult stage; AD0, AD5, AD10 and AD20: basic

artificial diet enriched with 0%, 5%, 10% and 20% of H. illucens prepupae hemolymph,

respectively. Means ± SE within a column and sex followed by the same letter are not

significantly different (Mann-Whitney U test; P > 0.05). χ2-, df- and P-values refer to Kruskal-

Wallis ANOVAs.

The developmental time of the female larvae did not differ among diets (Table 4.1).

However, diet had a significant effect on the developmental rate of the nymphal stages of the

females. Female protonymphs fed on AD20 demonstrated the fastest development, followed

by females fed on AD10 and females developed slowest in this stage on AD5 and AD0.


61

Female deutonymphs reared on AD5 or AD10 needed significantly less time to develop to

adulthood than those fed on the other diets. The total developmental time was significantly

shorter for females offered any of the enriched artificial diets versus the basic diet.

Deutonymphal times of males were not affected by diet. Whereas male larvae developed

slower on AD10 than on AD5, male protonymphs fed on AD20 and AD10 had shorter

developmental times than those fed on AD0. Male total developmental time was significantly

shorter on AD20 than on AD0.

Table 4.2 Reproduction and life table parameters of Amblyseius swirskii fed on artificial diets

enriched or not with Hermetia illucens prepupal hemolymph at 23°C

Parameter AD0

(n = 37)

AD5

(n = 36)

AD10

(n = 33)

AD20

(n = 38)

Preoviposition period (days)a 6.76 ± 0.24 c 2.44 ± 0.10 b 2.33 ± 0.11 ab 2.18 ± 0.06 a

Oviposition period (days)a 0.24 ± 0.17 b 22.33 ± 1.74 a 20.30 ± 1.30 a 22.08 ± 1.46 a

Female longevity (days)a 7.95 ± 0.90 b 33.08 ± 2.94 a 35.24 ± 3.24 a 31.03 ± 2.39 a


progenyc

- 0.68 ± 0.03 a 0.66 ± 0.03 a 0.71 ± 0.02 a

Oviposition rate

(eggs/female/day)b

0.10 ± 0.05 b 1.18 ± 0.03 a 1.19 ± 0.04 a 1.32 ± 0.05 a

Total fecundity (eggs/female)a 0.19 ± 0.12 c 25.47 ± 1.89 ab 23.70 ± 1.47 b 27.34 ± 1.52 a

Net reproductive rate R0

(females/female)b

- 14.94 ± 0.78 b 14.58 ± 0.62 b 17.60 ± 0.73 a

Generation time T (days)b - 14.84 ± 0.19 b 14.17 ± 0.20 a 13.65 ± 0.15 a

Intrinsic rate of increase rm

(females/female/day)a

- 0.182 ± 0.002 c 0.189 ± 0.002 b 0.210 ± 0.002 a

n = number of reproducing females observed

AD0, AD5, AD10 and AD20: basic artificial diet enriched with 0%, 5%, 10% and 20% of H.

illucens prepupal hemolymph, respectively.

Means ± SE within a row followed by the same letter are not significantly different (P>0.05;

aMann-Whitney U test,

bTukey test;

cProbit (Wald Chi-square) test)

The preoviposition period, oviposition period and longevity of females fed on the diets

enriched with hemolymph were significantly shortened as compared with females fed on AD0

Chapter 4

62

(Table 4.2) (preoviposition period: χ2

= 91.542; df = 3; P < 0.001; oviposition period: χ2

=

83.409; df = 3; P < 0.001 and female longevity: χ2

= 75.612; df = 3; P < 0.001). Similarly, the

oviposition rate and total number of eggs of females reared on AD0 were far lower than those

of females presented with AD5, AD10 or AD20 (oviposition rate: F = 176.613; df = 3, 140; P

< 0.001 and total number of eggs: χ2

= 75.612; df = 3; P < 0.001). Females maintained on

AD0 laid on average only 0.19 eggs during their lifetime as compared with 23.7-27.3 eggs for

those fed enriched diets; none of the eggs in the AD0 group produced viable offspring.

Consequently, life table parameters could not be calculated for the AD0 cohort. Females fed

on AD20 had significantly shorter preoviposition periods than those fed on AD5. However,

the percentage of hemolymph supplemented in the artificial diet had no influence on

oviposition period, oviposition rate and longevity of the females and on the female proportion

of their offspring (χ2 = 2.868; df = 2, P = 0.238).

Figure 4.1 Daily oviposition rate of Amblyseius swirskii fed on artificial diets enriched or not

with Hermetia illucens prepupal hemolymph at 23°C. AD0, AD5, AD10 and AD20: basic

artificial diet enriched with 0%, 5%, 10% and 20% of H. illucens prepupal hemolymph,

respectively.

Peak oviposition was reached on the 4th

day of adulthood on AD0 and AD20, on the

5th

day on AD5 and on the 8th

day on AD10. Whereas egg laying by females on AD0 was


63

almost completely terminated after 10 days of adulthood, females fed on AD5, AD10 and

AD20 continued to lay eggs until about 46 days of adulthood (Figure 4.1). The total egg

production of A. swirskii was significantly higher on AD20 than on AD10.

Life table parameters of female A. swirskii on artificial diets enriched with different

percentages of hemolymph are shown in Table 4.2. The net reproductive rate (R0) was highest

on AD20 (F = 5.339; df = 2, 104; P = 0.006), while generation times (T) were similar on

AD10 and AD20 but higher than on AD5 (F = 11.081; df = 2, 104; P < 0.001). The intrinsic

rate of increase rm was highest on AD20, followed by AD10 and lowest on AD5 (χ2

= 61.310;

df = 2; P < 0.001).

Table 4.3 Reproduction of Amblyseius swirskii fed on basic diet during the juvenile and adult

stages or switched from adulthood to artificial diets enriched with different concentrations of

Hermetia illucens prepupal hemolymph at 23°C

Diet n Oviposition

period (days)a

Oviposition rate

(eggs/female/day)b

Total fecundity

(eggs/female)b

AD0 12 5.58 ± 1.95 b 0.84 ± 0.07 b 3.50 ± 0.61 b

AD5 12 10.75 ± 1.74 a 1.21 ± 0.04 a 13.08 ± 2.14 a

AD10 9 10.89 ± 2.58 ab 1.19 ± 0.11 a 11.44 ± 2.07 a

AD20 12 11.17 ± 1.83 a 1.13 ± 0.06 a 12.00 ± 1.69 a

χ2/F 8.280 6.467 7.022

df 3 3, 41 3, 41

P 0.041 0.001 0.001

n = number of reproducing females observed. AD0, AD5, AD10 and AD20: basic artificial

diet enriched with 0%, 5%, 10% and 20% of H. illucens prepupal hemolymph, respectively.

Means ± SE within a column followed by the same letter are not significantly different

(P>0.05; aMann-Whitney U test,

bTukey test)

Diet switching influenced the reproduction of A. swirskii females (Table 4.3). Adult

females fed with AD5 and AD20 had significantly longer oviposition periods than females

maintained on AD0. Mites switched to the enriched artificial diets had significantly higher

oviposition rates and total fecundities as compared with those that were maintained on AD0,

but there was no effect of hemolymph concentration. The daily oviposition rates of females

switched to AD5, AD10 or AD20 rapidly increased in comparison to those kept on AD0 from

Chapter 4

64

the first day of the oviposition period (Figure 4.2). This trend was maintained until the

females stopped laying eggs.

Figure 4.2 Effect of diet switching from basic diet during the juvenile stages to artificial diets

enriched with different concentrations of Hermetia illucens prepupal hemolymph during the

adult stage on daily oviposition rate of Amblyseius swirskii at 23°C. AD0, AD5, AD10 and

AD20: basic artificial diet enriched with 0%, 5%, 10% and 20% of H. illucens prepupal

hemolymph, respectively.

4.4 Discussion

The development and reproduction of an arthropod natural enemy fed on an unnatural or

artificial diet are the two most important parameters to evaluate the value of the diet for

rearing purposes (Grenier and De Clercq, 2003). A more favourable diet will result in a higher

population growth, which is reflected in higher intrinsic rates of increase. In this study, A.

swirskii fed on the artificial diets enriched with prepupal hemolymph of black soldier fly, H.

illucens, had a faster development and better fecundity than when offered a basic diet without

this component. The highest intrinsic rate of increase in the current study was recorded for


65

females fed on an artificial diet supplemented with 20% of the prepupal hemolymph (AD20,

0.210 females/female/day). This growth rate is higher than the values observed on artificial

diets enriched with hemolymph of oak silkworm pupae (A. pernyi) (0.181 females/female/day

at 23 oC) (Chapter 3). The growth rate on AD20 was also superior to that reported for A.

swirskii reared on a number of natural prey species including tomato russet mite Aculops

lycopersici (Massee) (0.201 females/female/day) (Park et al., 2011), spider mite Tetranychus

urticae Koch (0.167 females/female/day) (El-Laithy and Fouly, 1992), eriophyoid fig mites

Aceria ficus (Cotte) or Rhyncaphytoptus ficifoliae Keifer (0.155 or 0.122 females/female/day,

respectively) (Abou-Awad et al., 1999) and thrips Frankliniella occidentalis (Pergande) or

Thrips tabaci Lind. (0.056 or 0.024 females/female/day, respectively) (Wimmer et al., 2008).

The highest rm-value in our study is only slightly lower than that reported by Nomikou et al.

(2001) when the predatory mite was fed on the tobacco whitefly, Bemisia tabaci (Gennadius)

(0.218 females/female/day).

Our study indicates that supplementing a nutritionally suboptimal artificial diet with

black soldier fly hemolymph significantly improved its value for supporting development and

reproduction of A. swirskii. Even at the lowest concentration of hemolymph added (5%)

juvenile survival improved, the production of viable eggs was stimulated and as a

consequence the intrinsic rate of increase substantially increased. Furthermore, in the diet

switching experiment, females reared on the basic diet in their juvenile stages and presented

with artificial diet enriched with the prepupal hemolymph in the adult stage only, showed

improved reproductive rates as compared with females maintained on the basic diet. This

confirms our earlier findings when the same basic artificial diet was enriched with 20%

hemolymph of oak silkworm pupae (A. pernyi), significantly increasing immature survival,

shortening development time and raising fecundity of A. swirskii (Chapter 3). Grenier and De

Clercq (2003) noted that adding insect components (i.e. tissues, hemolymph, cells, protein,

amino acids, etc.) to artificial diets enhances their acceptability and improves their nutritional

quality for a number of entomophagous insects. Artificial diets containing insect components

may be useful when predators or parasitoids require certain nutrients, feeding stimulants, and

other chemical cues found in arthropod prey or hosts (De Clercq, 2008). The positive role of

insect hemolymph in artificial diets is particularly well known in parasitoid wasps of the

genus Trichogramma. Strand and Vinson (1985) obtained complete in vitro culture of

Trichogramma pretiosum Riley on an artificial medium supplemented with 40% hemolymph

of Manduca sexta (L.). Trichogramma dendrolimi and T. maidis successfully developed on

artificial diets composed of egg yolk and Helicoverpa zea (Boddie) hemolymph (Grenier and

Chapter 4

66

Bonnot, 1988). Trichogramma dendrolimi was successfully reared in vitro in a medium

containing hemolymph of Antheraea pernyi (Guan et al., 1978).

The black soldier fly is considered to be a good candidate for industrial-scale

production, which is defined as a minimum reach of 1 tonne per day of fresh-weight insects

(FAO, 2012). This is related to a number of beneficial traits, including a short development

cycle, high survival of immatures and oviposition rate, good potential of biomass increase per

day (i.e. weight gain per day), high conversion rate (kg biomass gain per kg feedstock), ability

to live in high densities (kg biomass per m2); and low vulnerability to disease (Van Huis et al.,

2013). Additionally, the fly can successfully develop on a wide range of food sources

including chicken feed (Tomberlin et al., 2002; Diener et al., 2009), chicken manure

(Sheppard et al., 1994; Yu et al., 2011; Zhou et al., 2013), pig manure (Newton et al., 2005;

Zhou et al., 2013), cattle manure (Myers et al., 2008; Li et al., 2011b; Zhou et al., 2013),

human feces (Lalander et al., 2013; Banks et al., 2014), pig liver (Nguyen et al., 2013),

kitchen waste (Diener et al., 2011; Nguyen et al., 2013), fruits and vegetables (Nguyen et al.,

2013), fish offal (St-Hilaire et al., 2007; Nguyen et al., 2013), palm kernel meal (Hem et al.,

2008) and coffee pulp (Larde, 1990). These characteristics enable cost-effective production of

large amounts of insect biomass, including hemolymph. The intrinsic rate of increase of A.

swirskii fed on the basic artificial diet enriched with black soldier fly prepupal hemolymph in

this study was equally high as that of females reared on the basic diet supplemented with

hemolymph of oak silkworm pupae A. pernyi (Chapter 3). This indicates that H. illucens

prepupal hemolymph has a similar positive role in artificial diets for A. swirkii as the above-

mentioned, more expensive and/or less available arthropod materials (Lü et al., 2013; De

Clercq et al., 2014).

To our knowledge our study is the first that shows the potential of H. illucens as a

nutrient source for the rearing of beneficial arthropods. Arguably, more research is warranted

to understand the role of H. illucens hemolymph for the nutritional physiology of A. swirskii

and to explore the potential of this material to enhance the value of artificial diets for other

entomophagous mites and insects.

67

Chapter 5

DIFFERENT FACTITIOUS AND ARTIFICIAL FOODS SUPPORT THE

CONTINUOUS REARING OF AMBLYSEIUS SWIRSKII


Nguyen, D. T., Vangansbeke, D., & De Clercq, P. (2014). Artificial and factitious foods support the

development and reproduction of the predatory mite Amblyseius swirskii. Experimental and Applied

Acarology, 62: 181-194.

Chapter 5

68

5.1 Introduction

The predatory mite Amblyseius swirskii Athias-Henriot is an economically important

biological control agent of several key pests in greenhouses, such as whiteflies, thrips,

eriophyid mites and broad mites (Nomikou et al., 2001; Messelink et al., 2008; Arthurs et al.,

2009; Park et al., 2010; van Maanen et al., 2010). Amblyseius swirskii is a type III generalist

predator, implying that it can feed on various types of food including arthropod prey, pollen,

and honeydew (McMurtry and Croft, 1997).

The potential of augmentation biological control to suppress insect pests has been

recognized for many years (Doutt and Hagen, 1949; DeBach, 1964; Parella et al., 1992).

However, augmentation is applied on a commercial scale in relatively few agricultural

systems (van Lenteren, 2012). One of the main reasons is that augmentative releases are

frequently more expensive than pesticides (Collier and Van Steenwyk, 2004). Cost-effective

rearing techniques are needed to make augmentation a more competitive strategy for

managing arthropod pests. One approach to facilitating this is reducing the costs associated

with rearing natural enemies by using factitious (i.e., unnatural) foods (Riddick, 2009).

Factitious food sources can also be used as a preventative strategy to help establish or

maintain a population of certain arthropod predators in the crop when pest populations are

low, so as to reduce the frequency of releases (Jonsson et al., 2008).

Eggs of the Mediterranean flour moth Ephestia kuehniella Zeller (Lepidoptera:

Pyralidae) have shown to be a suitable factitious food for various insect predators, including

lady beetles (De Clercq et al., 2005b), anthocorid bugs (Alauzet et al., 1992; Vacante et al.,

1997; Arijs and De Clercq, 2001), mirid bugs (Fauvel et al., 1987; Castañé et al., 2006) and

lacewings (Cohen and Smith, 1998). Cysts of the brine shrimp Artemia sp. (Anostraca:

Artemiidae) are another type of factitious food used for rearing a number of insect predators,

including Orius spp. (Hemiptera: Anthocoridae) (Arijs and De Clercq, 2001) and

Macrolophus spp. (Hemiptera: Miridae) (Castañé et al., 2006). Different species of storage

mites are routinely used as factitious prey in the mass production of phytoseiid mites

(Bolckmans and van Houten, 2006; Fidgett and Stinson, 2008).

The utilization of an artificial diet may be the next step towards a more cost-effective

rearing of predators (Riddick, 2009). Whereas several artificial diets have been developed for

predatory insects, far fewer attempts have been made at rearing predatory mites on artificial

diets. Chapter 3 reported that an artificial diet enriched with pupal hemolymph of the

Chinese oak silkworm, Antheraea pernyi (Guérin-Méneville) (Lepidoptera: Saturniidae),

Factitious and artificial foods support the continuous rearing of A. swirskii

69

allowed development and reproduction of A. swirskii to the same extent as the currently used

storage mite Carpoglyphus lactis (L.) (Acari: Carpoglyphidae). However, this hemolymph is

not easily available resulting in a higher cost and lower reliability for the diet (Xie et al., 1997;

Heslin et al., 2005). Therefore, if pupal hemolymph could be replaced by a more easily

available and cheaper nutrient, the cost of production may be reduced.

Grenier and De Clercq (2003) pointed out that, whereas measures of development and

reproduction of an arthropod natural enemy on an unnatural or artificial diet are indicative for

the value of the diet for rearing purposes, the ultimate quality parameter of an artificially

reared natural enemy is its predation or parasitization efficacy. In the present study, we

investigated the developmental, reproductive and predatory performance of A. swirskii when

fed on frozen E. kuehniella eggs, dry decapsulated cysts of A. franciscana, and on meridic

artificial diets supplemented with A. pernyi pupal hemolymph (AD1), E. kuehniella eggs

(AD2) or A. franciscana cysts (AD3). Performance of the phytoseiid after a single generation

on the various diets was compared with that after 6 generations of continuous rearing.



The stock colony of A. swirskii was reared as described in section 3.2.1


Artificial diets AD1, AD2, and AD3 were prepared by supplementing a basic artificial diet

prepared according to section 3.2.4 with hemolymph from A. pernyi pupae, E. kuehniella

eggs, and decapsulated cysts of Artemia franciscana (Kellogg), respectively. Pupal

hemolymph of A. pernyi was provided in lyophilized form by the Guangdong Entomological

Institute, Guangzhou, China. Frozen eggs of E. kuehniella were supplied by Koppert B. V.

(Berkel en Rodenrijs, The Netherlands). Decapsulated A. franciscana cysts were provided by

the Artemia Reference Center (ARC) of Ghent University (Ghent, Belgium) and originated

from the Great Salt Lake (Utah, USA).

Chapter 5

70

AD1 consisted of 80% basic artificial diet supplemented with 20% (w/w) pupal

hemolymph of A. pernyi; lyophilized hemolymph was redissolved using distilled water before

being added to the diet (section 3.2.4 ). The supplements for AD2 and AD3 were prepared by

finely grinding 10 g of eggs of E. kuehniella or dry decapsulated cysts of A. franciscana,

respectively, to dust in a ceramic mortar. Next, 40 g of the basic artificial diet was added in

the mortar and the components were further ground and mixed using a pestle. The resulting

mixture was centrifuged at 12,000 rpm at 5°C for 15 min in an Eppendorf Centrifuge 5430R

(Eppendorf AG, Barkhausenweg, Hamburg, Germany), then the aqueous supernatant was

transferred to 2 ml Eppendorf tubes and subsequently stored in a freezer at -18°C.


Eight hours before start of the experiments, new black threads were placed in the stock

colony of A. swirskii. Eggs deposited on the threads were transferred individually to the

rearing microcosms that were modified from Munger cells as described in section 3.2.5 .

Frozen eggs of E. kuehniella, dry decapsulated cysts of A. franciscana, AD1, AD2 or AD3

were supplied ad libitum. For the artificial diets, approximately 2 µl of diet was absorbed on

a small piece of filter paper (2 x 2 mm) placed on the bottom board of the rearing microcosms.

All diets were offered from the larval stage of the predator on and refreshed every 2 days. To

obtain data on the duration of each developmental stage of A. swirskii and on mortality and

escape rates, observations were made every 24 hours until all individuals had reached

adulthood. The mites were observed and the same parameters were recorded as that described

in section 3.2.6 . Mites that escaped or died due to unnatural causes were excluded from data

analysis; escape rates varied between 0 and 33%. The experiments were done in a growth

chamber at 23 ± 1°C, 65 ± 5% RH and a 16:8 h (L:D) photoperiod.

5.2.3.1 Multigeneration experiment

The offspring from first generation (G1) adults obtained in the above experiment was

maintained on the same diet up to the fifth generation. The mites were reared on green plastic

arenas (3 x 3 x 0.3 cm) (Multicel, SEDPA, France), placed on a wet sponge in a polystyrene


71

insect breeding dish (10 x 4 cm) (SPL Life Sciences Co. Ltd., Korea) with a mesh hole (ø 4

cm) in the lid. The dishes were kept in a growth chamber set at 23 ± 1°C, 70 ± 5% RH and a

16:8 h (L:D) photoperiod. Eggs from fifth generation females were collected to be used in an

experiment set up as described above, in order to assess the developmental and reproductive

performance in the sixth generation (G6) of rearing on each diet. However, the mites fed on

AD1 did not succeed in reaching the third generation, and could thus not be included in this

experiment.

5.2.3.2 Predation experiment

Predation capacity of female adults of A. swirskii on first instars of the Western flower thrips,

Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) was assessed in the first (G1)

and sixth (G6) generation of rearing on each of the diets, except for AD1 which was tested in

G1 only. Thrips were cultured in plastic boxes containing vermiculite and green bean pods

(Phaseolus vulgaris L.) at 23 ± 1°C, 70 ± 5% RH and a 16:8 h (L:D) photoperiod and first-

instar larvae (<24h old) were collected from the rearing containers for testing. Twenty-five

gravid females (ca. two days old) were starved for 24 h in individual glass tubes (4.5 cm in

length, 0.7 cm in diameter), stoppered with a cotton ball; starved females were not supplied

with water. Then, each female was transferred to a square bean (Phaseolus vulgaris L.) leaf

disc (25 x 25 mm) that was placed upside down on a water-saturated polyurethane sponge (10

x 50 x 50 mm) in a polystyrene insect breeding dish (100 x 40 mm) with a mesh hole (ø 40

mm) in the lid (SPL Life Sciences Co. Ltd., Korea). The four edges of the leaf disc were

covered with moist tissue paper to provide free water and preclude escaping. Fifteen first

instars of F. occidentalis) were placed on each leaf disc as prey for the mites. After 24 h, the

number of thrips corpses was recorded. Females which escaped or were found dead on the

moist tissue paper were excluded from analysis; escape rates varied between 0 and 20%.



Chapter 5

72


Two-way analysis of variance (ANOVA) (IBM, SPSS Statistics 20) was conducted to

evaluate the effects of diet and generation on the duration of the immature stages,

preoviposition and oviposition period, daily and total oviposition, adult longevity and life

table parameters of A. swirskii. When an interaction was detected between the main factors,

means were compared among diets and a pairwise multiple comparison procedure was used

(Kutner et al., 2005). When a Kolmogorov–Smirnov test indicated that means were normally

distributed, the parameter was analyzed using a one-way analysis of variance (ANOVA). If a

Levene test indicated heteroscedasticity, a Tamhane test was used instead of a Tukey test.

When means were not normally distributed, a nonparametric Kruskal-Wallis ANOVA was

used and means were separated using a Mann-Whitney U test. Immature survival rates and

sex ratios were compared by means of a logistic regression. This regression is a generalized

linear model using a probit (log odds) link and a binomial error function. Each test consists of

a regression coefficient that is calculated and tested for being significantly different from zero,

for which P-values are presented (McCullagh and Nelder, 1989). In all tests, P-values smaller

than or equal to 0.05 were considered significant.

5.3 Results

Whereas in G1 the immature mortality of A. swirskii did not differ among diets, mortality in

G6 was significantly higher than in G1, except on a diet of A. franciscana cysts (χ2=127.71,

df=8, P<0.001). In G6, mites fed on AD2 or AD3 suffered from greater mortality (65.6 and

37.1%, respectively) than those reared on E. kuehniella or A. franciscana (13.6 and 1.9%,

respectively) (Figure 5.1). Mortality of mites in G6 continuously reared on the artificial diets

occurred mainly in the egg and larval stages.


73

Figure 5.1 Mortality (%) of the different immature stages of Amblyseius swirskii fed in the

first (G1) and sixth (G6) generation on different factitious and artificial foods. Numbers

within or above the different sections in each bar refer to mortality percentages in the egg,

larval, protonymphal and/or deutonymphal stages.

Bars with the same letter are not significantly different (P>0.05; Probit (Wald Chi-square)

test). AD1, artificial diet 1 (with pupal hemolymph of A. pernyi); AD2, artificial diet 2 (with

E. kuehniella eggs); AD3, artificial diet 3 (with A. franciscana cysts).

Chapter 5

74

Table 5.1 Two-way ANOVA indicating the effect of diet and generation on developmental, reproductive and predation parameters of

Amblyseius swirskii

Source Duration of

immature stage

Pre-

oviposition

period

Oviposition

period

Female

longevity

Total

number

of eggs

Oviposition

rate

Net

reproductive

rate

Generation

time

Intrinsic

rate of

increase

Predation

rate Females Males

Diet F 9.948 5.79 5.658 15.271 2.075 5.341 22.730 33.975 18.674 138.47 6.405

df 3 3 3 3 3 3 3 3 3 3 3

P <0.001 0.001 0.001 <0.001 0.104 0.001 <0.001 <0.001 <0.001 <0.001 <0.001

Generation F 0.784 0.862 2.874 0.014 0.209 4.668 14.877 96.117 4.738 313.677 30.986

df 1 1 1 1 1 1 1 1 1 1 1

P 0.377 0.355 0.091 0.906 0.648 0.032 <0.001 <0.001 0.031 <0.001 <0.001

Diet x

Generation

F 4.01 0.26 2.708 2.458 0.997 0.837 2.203 11.221 7.379 81.935 0.354

df 3 3 3 3 3 3 3 3 3 3 3

P 0.008 0.854 0.046 0.064 0.395 0.475 0.089 <0.001 <0.001 <0.001 0.786

Error df 257 111 229 229 229 229 229 229 229 229 176


75

Two-way ANOVA (Table 5.1) showed significant interactions between diet and

generation for the developmental time of females, whereas no interaction occurred for male

developmental time. The developmental time of males was significantly affected by diet but

did not differ between generations. In G1, the males fed on E. kuehniella eggs had the longest

developmental time, but in G6 male developmental time did not differ among diets.

Developmental times of females offered E. kuehniella eggs did not differ between

generations, whereas they were shorter in G6 on A. franciscana and AD2, and longer on AD3

as compared to those in G1 (Table 5.2).

Table 5.2 Development time (days) of Amblyseius swirskii fed in the first (G1) and sixth (G6)

generation on different factitious and artificial foods

Diet/Generation n

a Developmental duration (days)

b

Females n Males n

E. kuehniella/G1 63 8.21 ± 0.25 ab 48 8.23 ± 0.46 a 13

E. kuehniella/G6 59 8.00 ± 0.25 ab 32 8.26 ± 0.57 a 19

A. franciscana/G1 55 7.67 ± 0.14 a 33 7.09 ± 0.09 bc 22

A. franciscana/G6 52 7.42 ± 0.12 bcd 33 7.33 ± 0.16 ab 18

AD1/G1 57 7.65 ± 0.18 abcd 31 6.96 ± 0.11 c 24

AD2/G1 56 7.36 ± 0.14 cd 33 7.00 ± 0.07 c 22

AD2/G6 64 6.67 ± 0.24 e 18 7.00 ± 0.41 ac 4

AD3/G1 50 7.31 ± 0.10 d 39 6.91 ± 0.09 c 11

AD3/G6 62 7.97 ± 0.14 a 29 7.50 ± 0.22 ab 10

χ2 36.75 30.99

df 8 8

P <0.001 <0.001

aInitial number of tested individuals;

bMeans ± SE; means within a column followed by the

same letter are not significantly different (P>0.05), according to a Mann-Whitney U test

(duration); χ2-, df- and P-values refer to Kruskal-Wallis ANOVAs. AD1, artificial diet 1

(with pupal hemolymph of A. pernyi); AD2, artificial diet 2 (with E. kuehniella eggs); AD3,

artificial diet 3 (with A. franciscana cysts).

Chapter 5

76

Table 5.3 Reproduction and longevity of Amblyseius swirskii in the first (G1) and sixth (G6) generation on different factitious and artificial foods

Diet/Generation n Preoviposition period (days)

a

Oviposition period (days)

a

Female longevity (days)

a

Oviposition rate (eggs/female/day)

a

Total number of eggs

(eggs/female)a


progenya

E. kuehniella/G1 42 2.41 ± 0.10 bc 21.83 ± 1.09 b 44.12 ± 3.28 a 1.48 ± 0.04 ab 31.64 ± 1.51 ab 0.71 ± 0.01 ab E. kuehniella/G6 32 3.91 ± 0.79 a 19.47 ± 1.15 b 41.06 ± 2.85 a 1.48 ± 0.05 abc 28.34 ± 1.70 b 0.66 ± 0.02 c

A. franciscana/G1 28 2.39 ± 0.13 bc 25.64 ± 1.93 ab 37.79 ± 3.04 a 1.50 ± 0.04 ab 37.71 ± 2.75 ab 0.75 ± 0.02 a A. franciscana/G6 33 2.27 ± 0.08 c 28.94 ± 1.38 a 41.79 ± 2.54 a 1.27 ± 0.04 cde 35.48 ± 1.27 a 0.71 ± 0.02 abc

AD1/G1 28 2.71 ± 0.18 ab 21.82 ± 1.31 b 40.32 ± 3.54 a 1.60 ± 0.05 a 34.50 ± 2.18 ab 0.74 ± 0.02 ab

AD2/G1 29 3.24 ± 0.29 a 33.55 ± 2.40 a 49.14 ± 2.92 a 1.13 ± 0.07 de 34.10 ± 2.07 ab 0.70 ± 0.02 bc AD2/G6 12 3.42 ± 0.42 a 28.58 ± 3.96 ab 46.00 ± 5.22 a 0.91 ± 0.09 e 26.25 ± 4.58 ab 0.72 ± 0.03 abc

AD3/G1 32 2.06 ± 0.04 d 22.50 ± 0.91 b 41.50 ± 2.42 a 1.38 ± 0.04 bcd 30.72 ± 1.22 ab 0.76 ± 0.02 a AD3/G6 29 2.21 ± 0.09 cd 25.34 ± 1.87 ab 46.76 ± 3.30 a 1.21 ± 0.04 de 29.90 ± 2.18 ab 0.75 ± 0.02 ab

χ2/F 44.19 7.54 1.22 13.43 2.82 17.90

df 8 8, 256 8, 256 8, 256 8, 256 8 P <0.001 <0.001 0.287 <0.001 0.005 0.022

aMeans ± SE; means within a column followed by the same letter are not significantly different (P > 0.05) according to a Mann-Whitney U test

(preoviposition period), Tamhane test (oviposition period, oviposition rate, total number of eggs), Tukey test (female longevity), or Probit (Wald

Chi-square) test (female proportion of progeny); χ2-, df- and P-values refer to Kruskal-Wallis ANOVAs; F-, df- and P-values refer to one-way

ANOVAs. AD1, artificial diet 1 (with pupal hemolymph of A. pernyi); AD2, artificial diet 2 (with E. kuehniella eggs); AD3, artificial diet 3

(with A. franciscana cysts).


77

Two-way ANOVA showed significant interactions between diet and generation for

preoviposition period but there was no interaction for the parameters oviposition period,

female longevity, oviposition rate and total number of eggs (Table 5.1). The preoviposition

periods did not differ between G1 and G6 on all diets, except E. kuehniella eggs (Table 5.3).

The shortest preoviposition period was recorded on AD3 in G1 (2.06 days). Oviposition

periods were similar in both generations and ranged from 19.5 days to 33.6 days for females

fed on E. kuehniella in G6 and AD2 in G1, respectively. Female longevity was not affected by

diet or generation. The proportion of female progeny did not differ between generations,

except on E. kuehniella. Daily oviposition rates were influenced by both diet and generation

and ranged from 0.91 to 1.60 eggs/female/day. In G1, the females reared on E. kuehniella, A.

franciscana or AD1 showed similar oviposition rates, which were in turn significantly higher

than those on AD2. Oviposition rates did not differ between generations when the mites were

fed on E. kuehniella, AD2 or AD3. No differences were observed between generations in the

total number of eggs produced when females were reared on the different diets. Total

fecundity was similar among females reared on the different diets except in G6 where the

females supplied with A. franciscana cysts produced more eggs than those given E. kuehniella

eggs.

Significant interactions between diet and generation were found for the life table

parameters net reproductive rate, generation time and intrinsic rate of increase (Table 5.1).

The net reproductive rates in G1 were significantly higher than those in G6, except on A.

franciscana (Table 5.4). In G1, different diets did not result in different net reproductive rates.

Females in G6 had longer generation times than those in G1 on all diets, except on A.

franciscana cysts, which yielded a shorter generation time in G6 than in G1. Likewise, the

intrinsic rates of increase in G1 were significantly higher than in G6, but not on a diet of A.

franciscana cysts for which similar growth rates were observed in both generations.

Chapter 5

78

Table 5.4 Life table parameters of Amblyseius swirskii in the first (G1) and sixth (G6)

generation on different factitious and artificial foods

Diet/Generation n

Net reproductive

rate (Ro, females

per female)a

Generation time

(T, days)a

Intrinsic rate of

increase (rm,

females/female/day)a

E. kuehniella/G1 42 21.78 ± 1.09 a 18.22 ± 0.24 ab 0.169 ± 0.001 c

E. kuehniella/G6 32 16.01 ± 0.90 b 18.39 ± 0.33 ab 0.151 ± 0.004 d

A. franciscana/G1 28 28.33 ± 2.03 a 19.03 ± 0.28 a 0.176 ± 0.002 bc

A. franciscana/G6 33 25.63 ± 0.85 a 17.87 ± 0.15 b 0.182 ± 0.001 ab

AD1/G1 28 24.71 ± 1.65 a 18.49 ± 0.31 ab 0.174 ± 0.002 bc

AD2/G1 29 23.23 ± 1.39 a 19.65 ± 0.43 a 0.160 ± 0.004 cd

AD2/G6 12 4.67 ± 0.80 c 21.22 ± 0.96 ab 0.073 ± 0.007 e

AD3/G1 32 22.76 ± 0.91a 16.84 ± 0.17 c 0.186 ± 0.001 a

AD3/G6 29 14.14 ± 0.98 b 18.40 ± 0.40 ab 0.144 ± 0.002 d

F 21.91 9.63 92.88

df 8, 256 8, 256 8, 256

P <0.001 <0.001 <0.001

aMeans ± SE; means within a column followed by the same letter are not significantly

different (P>0.05) according to Tamhane’s test; F-, df- and P-values refer to one-way

ANOVAs. AD1, artificial diet 1 (with pupal hemolymph of A. pernyi); AD2, artificial diet 2

(with E. kuehniella eggs); AD3, artificial diet 3 (with A. franciscana cysts).

Two-way ANOVA indicated that there was no significant interaction between diet and

generation for predation capacity of A. swirskii females on F. occidentalis larvae (Table 5.1).

Diet had a significant influence on predation capacity, but there was no effect of generation,

except on E. kuehniella eggs where G1-females killed more prey than G6-females (F= 5.94,

df= 8, 200, P<0.001) (Figure 5.2). Predators reared for multiple generations on artificial diets

AD2 and AD3 had similar predation rates as those maintained on A. franciscana cysts.


79

Figure 5.2 Mean (±SE) number of first instar Frankliniella occidentalis killed during a 24-h

period by Amblyseius swirskii females in the first (G1) and sixth (G6) generation on different

factitious and artificial foods

Bars with the same letter are not significantly different (P>0.05; Tukey test). Number of

replicates is indicated by the number in each bar. AD1, artificial diet 1 (with pupal

hemolymph of A. pernyi); AD2, artificial diet 2 (with E. kuehniella eggs); AD3, artificial diet

3 (with A. franciscana cysts).

5.4 Discussion

The main goals of this study were to (1) investigate the potential of two factitious food

sources (A. franciscana and E. kuehniella) that are routinely used for the production of a

number of insect predators, for rearing the phytoseiid predator A. swirskii, (2) evaluate the

potential of arthropod components that can improve the artificial diet developed in Chapter 3

for this predatory mite, (3) assess the effects of long-term rearing on these factitious foods and

artificial diets on the predator’s fitness.

Our results indicate that all factitious and artificial foods tested were accepted by the

different life stages of A. swirskii and sustained the development and reproduction of the

predator for at least a single generation. The highest intrinsic rates of increase in our study

were recorded in the first generation when A. swirskii was fed on decapsulated cysts of A.

franciscana and AD3, containing 20% of finely ground cysts (0.182 and 0.186

females/female/day, respectively). These values are higher than those reported on various

Chapter 5

80

natural prey, including Tetranychus urticae Koch (Acari: Tetranychidae) (0.167 at 26oC) (El-

Laithy and Fouly, 1992), F. occidentalis (0.056 at 25oC) and Thrips tabaci (Lindeman)

(Thysanoptera: Thripidae) (0.024 at 25oC) (Wimmer et al., 2008), and only slightly lower than

those reported by Park et al. (2011) on the tomato russet mite, Aculops lycopersici (Massee)

(Acari: Eriophyidae) (0.201 at 25oC) and Nomikou et al. (2001) on the cotton whitefly

Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) (0.213 at 27oC). In the first generation,

growth rates on all tested diets were also similar to or greater than those found on T. latifolia

pollen (0.158 at 23oC) and Carpoglyphus lactis (L.) (Acari: Carpoglyphidae) (0.175 at 23

oC)

(Chapter 3), which is another widely used food in the laboratory rearing and commercial

mass rearing of this phytoseiid. However, it deserves emphasis that comparison of life table

statistics among studies is complicated by differences in experimental methods, climatic

conditions and the calculation of estimates.

In a previous study, we found that enriching a basic artificial diet with pupal

hemolymph of the Chinese oak silkworm, A. pernyi, substantially improved fecundity in A.

swirskii (Chapter 3). In recent years, however, production of this silkworm in China has

decreased. As a result, pupal hemolymph is becoming less easily available and more costly

(Lü et al., 2013), rendering its use as a dietary supplement less attractive. In contrast, eggs of

E. kuehniella and cysts of A. franciscana are widely available. In the present study, growth

rates of A. swirskii on artificial diets enriched with finely ground E. kuehniella eggs (AD2) or

A. franciscana cysts (AD3) were similar to or higher than those on the diet supplemented with

pupal hemolymph of A. pernyi (AD1). Our findings suggest that certain components of E.

kuehniella eggs and A. franciscana cysts can play a critical role in stimulating development

and reproduction of A. swirskii. The positive effect of E. kuehniella on reproduction in the

present study is consistent with the result reported by Ferkovich et al. (2007) who offered the

anthocorid bug Orius insidiosus (Say) an artificial diet supplemented with protein from E.

kuehniella eggs, resulting in a higher oviposition rate compared to an unmodified artificial

diet. Further research is warranted to identify the components of the E. kuehniella eggs and A.

franciscana cysts which are responsible for the increased performance. However, A.

franciscana cysts have a number of practical advantages over E. kuehniella eggs when used

for rearing predatory arthropods. The market price of decapsulated Artemia cysts is

substantially lower than that of E. kuehniella eggs: whereas frozen E. kuehniella eggs

currently cost around 400-500 EUR/kg (F. Wäckers, 2014, pers. comm.), the market price of

decapsulated Artemia cysts is less than 10% of that (G. Van Stappen, 2013, pers. comm.).


81

Unlike E. kuehniella eggs, Artemia cysts can be stored in dry form for several years in a cool

and dry place without the need for deep freezing (Arijs and De Clercq, 2001).

An effective factitious or artificial food should satisfy the nutritional requirements of a

predator and ensure the continuous production of progeny of high quality (Cohen, 2004). As

nutrient imbalances in a diet may be expressed only after several generations of rearing (De

Clercq et al., 2005a), it was the objective to culture the predator for five consecutive

generations on each diet and assess its fitness in the subsequent generation. In G6, the

immature survival of predators reared on E. kuehniella, AD2 and AD3 was significantly lower

than that on the corresponding diet in G1, with stronger declines on the artificial diets than on

lepidopteran eggs. These declines were reflected in the intrinsic rates of increase on the diets.

In contrast, the predator’s performance remained at similar levels across generations on dry

decapsulated cysts of A. franciscana and allowed the production of 15 successive generations

up to present. In addition, artificial diet AD3, supplemented with A. franciscana cysts, proved

superior to the other artificial diets as it allowed to sustain A. swirskii for over 15 consecutive

generations despite lower immature survival rates, whereas the colonies on AD1 and AD3

could not be maintained beyond 3 and 9 generations, respectively.

Whereas Orius bugs can only effectively feed on fully hydrated Artemia cysts (Arijs

and De Clercq, 2001), in the present study the decapsulated cysts did not need to be hydrated

to enable the A. swirskii mites to feed upon them. Dry (i.e., containing 4% of water)

decapsulated A. franciscana cysts supplied in the microcosms, where relative humidity

exceeded 80%, appeared to take up sufficient water from the environment to allow effective

extraction of nutrients by the predatory mites. Vandekerkhove et al. (2009) reported that also

Macrolophus pygmaeus (Rambur) (Hemiptera: Miridae) was able to feed on dry cysts

presented on leaf disks, as contact with the leaf surface allowed partial hydration (up to 20%)

of the cysts. As a practical advantage, dry cysts lead to less problems with moulds in the

rearing containers than fully hydrated cysts (Vandekerkhove et al., 2009). Likewise, all

artificial diets used in the present study were liquid, complicating their use in large-scale

cultures of the mites. Further research (Chapter 6) will focus on dry artificial diets, which are

easier to apply in the cultures and less prone to spoilage.

It is imperative that a predator retains its potential to find and kill the target prey after

long-term rearing on an unnatural prey or artificial diet (Grenier and De Clercq, 2003). Our

study indicates that A. swirskii females did not lose their ability to capture and kill live prey

after six generations of rearing on the tested diets. Only predation rates of predators

maintained on E. kuehniella eggs were slightly lower in G6 than in G1. All predation rates of

Chapter 5

82

A. swirskii females on first instars of F. occidentalis observed in the present study (5.3-8.5

thrips/day) were somewhat higher than those reported by Messelink et al. (2008).

In conclusion, the different factitious prey and artificial diets tested in the present

study supported development and reproduction of A. swirskii for a single generation, but

losses in fitness of the phytoseiid were observed after several generations of rearing on E.

kuehniella eggs and all of the artificial diets. Dry decapsulated A. franciscana cysts proved to

be the most suitable diet for the production of this economically important biological control

agent. More research will be needed to evaluate the suitability of Artemia cysts as a food in

large-scale cultures of A. swirskii or to support existing populations of the mite in the crop.

The potential of this factitious food for other predatory mites also deserves to be investigated.

83

Chapter 6

SOLID ARTIFICIAL DIETS FOR AMBLYSEIUS SWIRSKII


Nguyen, D. T., Vangansbeke, D., & De Clercq, P. 2014. Solid artificial diets for the phytoseiid

predator Amblyseius swirskii. BioControl, 59: 719-727

Chapter 6

84

6.1 Introduction

In augmentative biological control programs, mass produced arthropod natural enemies are

often released in high numbers to obtain pest suppression (Stinner, 1977; Collier and Van

Steenwyk, 2004). Optimizing mass production methods, for instance by developing cost

effective factitious or artificial foods, may reduce the market price of biological control agents

and improve their adoption by growers (De Clercq et al., 2014). The effectiveness of

augmentative releases can also be enhanced by supplementing foods that increase survival

and reproduction of the natural enemies after release, and arrest their emigration from the

targeted area (Wade et al., 2008; Lundgren, 2009a).

The generalist predatory mite Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae)

has been shown to be an effective biological control agent of whiteflies (Nomikou et al., 2002;

Messelink et al., 2008), thrips (Messelink et al., 2006; Messelink et al., 2008) and broad mites

(van Maanen et al., 2010) in several greenhouse crops. The predatory mite also feeds on non-

prey foods like pollen and honeydew (Momen and El-Saway, 1993). The mass rearing

procedures for A. swirskii are based on the use of storage mites, like Carpoglyphus lactis L.

(Acari: Carpoglyphidae) and Thyreophagus entomophagus (Laboulbene) (Acari: Acaridae), as

a food source (Bolckmans and van Houten, 2006; Fidgett and Stinson, 2008).

In chapter 3 and 5, we found that A. swirskii performed well on liquid artificial diets

enriched with a watery extract of Artemia franciscana (Kellogg) (Anostraca: Artemiidae)

cysts or with pupal hemolymph of the Chinese oak silkworm Antheraea pernyi (Guérin-

Méneville) (Lepidoptera: Saturniidae), indicating the potential of these diets to sustain

populations of the predator in the laboratory rearing as well as in the crop after release.

However, liquid diets have certain disadvantages compared to solid diets in stickiness and in

many cases a need for encapsulation (Morales-Ramos et al., 2014).

Solid artificial diets have mostly been developed for arthropods with chewing

mouthparts (Morales-Ramos et al., 2014). However, Cohen (1998) noted that arthropods with

extra-oral digestion, which include phytoseiid mites, can also feed on solid diets. The

objectives of the present study were to determine developmental and reproductive parameters

of A. swirskii fed on cattail pollen (Typha latifolia L.), on lyophilized forms of liquid artificial

diets supplemented with a watery extract of decapsulated cysts of A. franciscana (ArF) or

with pupal hemolymph of A. pernyi (AnF), and on solid artificial diets supplemented with

powdered dry A. franciscana cysts (ArP) or with lyophilized pupal hemolymph of A. pernyi

Solid artificial diets for A. swirskii

85

(AnP). The objective of this study was to design a solid artificial diet that can be used for the

mass production of A. swirskii as well as to support its populations in the crop.



A stock colony of A. swirskii was reared as described in section 3.2.1


Artificial diets ArF and AnF were prepared according section 5.2.2 . The diets were prepared

based on 80 % w/w basic liquid artificial diet (section 3.2.4 supplemented with 20 % w/w

watery extracts of decapsulated cysts of A. franciscana (ArF) or pupal hemolymph from the

Chinese oak silkworm A. pernyi (AnF), respectively. Pupal hemolymph of A. pernyi was

provided in lyophilized form by the Guangdong Entomological Institute, Guangzhou, China.

Decapsulated A. franciscana cysts were provided by the Artemia Reference Center of Ghent

University (Ghent, Belgium) and originated from the Great Salt Lake (Utah, USA).

Diets ArF and AnF were frozen at -18 °C and lyophilized at −57.2 °C and 0.034 mbar

for 6 days (VaCo 5-D freeze-dryer, Zirbus Technology Benelux B.V., Germany). Then the

lyophilized diets were finely ground (particle diameter smaller than 0.3 mm) using a Bosch

coffee grinder (Robert Bosch Hausgeräte GmbH, Munich, Germany), dispensed into 2 ml

Eppendorf tubes and stored at −18 °C.

Artificial diets ArP and AnP were powdered diets composed of 16.6 % sucrose, 16.6 %

tryptone, 16.6 % yeast extract, 6.7 % D-(+)-glucose anhydrous (MP Biomedicals LLC,

Illkirch, France), 6.7 % fructose (Sigma Aldrich Chemie GmbH, Steinheim, Germany), 16.6 %

egg yolk powder (Bouwhuis Enthoven BV, Raalte, The Netherlands), 0.13 % vitamin mix

based on the composition of bovine liver (weight percentages: 25.4 % nicotinic acid, 4.9 %

riboflavin, 0.5 % thiamine, 1.5 % vitamin B6, 12.4 % Ca-pantothenate, 1 % folic acid, 0.1 %

biotin and 54.2 % vitamin C) (Vandekerkhove et al., 2006) and 20 % w/w powdered dry

decapsulated A. franciscana cysts (ArP) or lyophilized pupal hemolymph of A. pernyi (AnP).

The ingredients of both diets were finely ground using a Bosch coffee grinder. Diet particle

diameter was measured using a Leica M80 microscope (Leica Microsystems Belgium BVBA,

Chapter 6

86

Diegem, Belgium) and AxioVision Ver. 4.8.2.0 software (Carl Zeiss MicroImaging GmbH,

Jena, Germany), indicating that the particle diameter was smaller than 0.3 mm. Next, the diets

were dispensed into 2 ml Eppendorf tubes and stored at −18 °C.

6.2.3 Development and reproduction on the different artificial diets

Eggs (less than 8 hours old) were transferred individually from the A. swirskii colony to

rearing microcosms that were modified from Munger cells as described in section 3.2.5 and

offered T. latifolia pollen or one of the artificial diets. All foods were supplied ad libitum. The

foods were offered from the larval stage of the predator on and refreshed every 2 days. After

they had been taken out of the freezer, the diets were kept in a refrigerator at 5 °C for max. 1

week. The mites were observed and different parameters were recorded same as that

described in section 3.2.6 Mites that escaped or died as a result of manipulation were

excluded from data analysis; these escape and death rates did not differ among treatments and

varied between 11 and 18 % (χ2

= 0.730, df = 4; P = 0.948; Probit (Wald Chi-square) test).

The experiments were done in a growth chamber at 23 ± 1 °C, 65 ± 5 % RH and a 16:8 h (L:D)

photoperiod.

6.2.4 Pre-establishment greenhouse experiment

The potential of powdered diets to sustain the pre-establishment of A. swirskii was tested on

chrysanthemum plants in a greenhouse at the Research Center for Ornamental Crops (PCS,

Destelbergen, Belgium). The experiments were conducted between May and August, 2014.

Four young plants (10-12 cm high with 10–20 leaves) were planted in a pot and 4 pots were

placed in a mesh cage (40 x 90 x 80 cm); 8 cages were placed on a bench for each treatment.

A single cage with 4 chrysanthemum pots was seen as one replicate. To prevent predatory

mites from migrating, each pot was placed on capillary matting saturated with water and the

plants did not touch the sides of the cages. Five adult female predatory mites, collected from

the laboratory culture with a fine brush, were released on each plant. Thereafter, three diets,

i.e. the basic (non-supplemented) powdered diet, powdered diet ArP and Nutrimite, a

commercial pollen (Biobest N.V., Westerlo, Belgium) consisting of pollen of narrow-leaved


87

cattail, Typha angustifolia L., were sprayed over the caged plants by way of a Nutrigun,

provided by Biobest N.V. In addition to the three diet supplement treatments, a control

treatment without food was included. All diets were re-applied every two weeks, according to

recommendations given by the producer (Biobest N.V.) for Nutrimite. The numbers of

predatory mites were assessed every 2 weeks in situ by counting the mobile mites on 5

random leaves per pot, resulting in a total of 20 leaves being checked in each cage.




Data were subjected to statistical analysis (IBM SPSS Statistics, Ver. 21) to evaluate the

effect of diet on the developmental time, preoviposition and oviposition period, daily and total

oviposition, and adult longevity of A. swirskii. When a Kolmogorov–Smirnov test indicated

that means were normally distributed, the parameter was analysed using a one-way analysis of

variance (ANOVA). If a Levene test indicated heteroscedasticity, a Tamhane test was used

instead of a Tukey test. When means were not normally distributed, a nonparametric Kruskal-

Wallis ANOVA was used and means were separated using Mann-Whitney U tests. Immature

survival rates and sex ratios were compared by means of a logistic regression. This regression

is a generalized linear model using a probit (log odds) link and a binomial error function.

Each test consists of a regression coefficient that is calculated and tested for being

significantly different from zero, for which P-values are presented (McCullagh and Nelder,

1989).

To test whether there was a consistent difference between densities of the predatory

mite supplemented in the greenhouse with three diets over a period of 16 weeks, the data of

nine independent monitoring times were analyzed by repeated measures ANOVA (between

subject factor: diet; within subject factor: time of sampling). If treatment differences at a

sampling date were significant, one-way analysis of variance (ANOVA) or Kruskal-Wallis

ANOVA was used to compare treatment means.

In all tests, P-values smaller than or equal to 0.05 were considered significant.

Chapter 6

88

6.3 Results

Immature survival of A. swirskii did not differ among diets ranging from 98.2 to 100 % (χ2 =

0.00, df=4, p>0.999; Probit (Wald Chi square) test). Development times of both A. swirskii

females and males were significantly affected by diet (Table 6.1). Females fed on T. latifolia

pollen developed significantly faster to adulthood than those fed on the other diets.

Development times of males offered T. latifolia pollen or both lyophilized diets (ArF and AnF)

were shorter than of those given the powdered diets (ArP and AnP).

Table 6.1 Development time (days) of Amblyseius swirskii fed on T. latifolia pollen or

different solid artificial foods

Diet Developmental duration (days)*

Females n Males n

T. latifolia 6.14 ± 0.11 a 35 5.90 ± 0.18 a 20

ArF 6.97 ± 0.16 b 35 6.25 ± 0.17 a 16

AnF 6.59 ± 0.15 b 37 6.11 ± 0.17 a 19

ArP 8.09 ± 0.08 c 34 7.92 ± 0.08 b 13

AnP 7.97 ± 0.11 c 32 7.71 ± 0.09 b 28

χ2 94.321 64.775

df 4 4

P <0.001 <0.001

n: Number of tested individuals

*Means ± SE; means within a column followed by the same letter are not significantly

different (P>0.05), according to Mann-Whitney U test; χ2-, df- and P-values refer to Kruskal-

Wallis ANOVAs. ArF or AnF: freeze-dried liquid artificial diet supplemented with A.

franciscana cysts or with pupal hemolymph of A. pernyi, respectively; ArP or AnP: basic

powdered diet supplemented with powdered A. franciscana cysts or lyophilized pupal

hemolymph of A. pernyi, respectively.


89

Table 6.2 Reproduction and longevity of Amblyseius swirskii fed on T. latifolia pollen or different solid artificial foods

Diet n Preoviposition

period (days)a

Oviposition

period (days)a

Female

longevity (days)a

Oviposition rate

(eggs/female/day)a

Total number of

eggs (eggs/female)a

Female proportion

of the progeny a

T. latifolia 31 2.35 ± 0.09 a 22.39 ± 1.21 a 36.35 ± 2.36 b 1.57 ± 0.04 a 34.29 ± 1.40 ab 0.78 ± 0.01 a

ArF 30 2.97 ± 0.16 b 24.73 ± 1.15 a 44.73 ± 2.16 ab 1.49 ± 0.03 a 36.37 ± 1.53 a 0.80 ± 0.02 a

AnF 31 2.55 ± 0.14 a 24.06 ± 1.60 a 45.90 ± 2.42 a 1.59 ± 0.05 a 36.97 ± 1.87 a 0.79 ± 0.02 a

ArP 28 3.71 ± 0.09 c 25.43 ± 1.18 a 41.07 ± 1.99 ab 1.25 ± 0.04 b 30.75 ± 0.83 b 0.76 ± 0.03 a

AnP 28 3.71 ± 0.09 c 25.89 ± 1.34 a 39.14 ± 1.82 ab 1.19 ± 0.05 b 30.79 ± 1.94 ab 0.72 ± 0.04 a

χ2/F

71.183 1.100 3.354 20.185 3.503 4.626

df

4 4, 143 4, 143 4, 143 4, 143 4

P

<0.001 0.359 0.012 <0.001 0.009 0.328

n: Number of tested females

aMeans ± SE; means within a column followed by the same letter are not significantly different (P > 0.05) according to Mann-Whitney U test

(preoviposition period), Tukey test (oviposition period, female longevity, oviposition rate), Tamhane test (total number of eggs) or Probit (Wald

Chi-square) test (female proportion of progeny); χ2-, df- and P-values refer to Kruskal-Wallis ANOVAs, and F-, df- and P-values refer to one-

way ANOVAs. ArF or AnF: freeze-dried liquid artificial diets supplemented with A. franciscana cysts or with pupal hemolymph of A. pernyi,

respectively; ArP or AnP: basic powdered diet supplemented with powdered A. franciscana cysts or lyophilized pupal hemolymph of A. pernyi,

respectively.

Chapter 6

90

Diet significantly influenced the duration of the preoviposition period (Table 6.2).

Females fed on T. latifolia pollen or AnF had significantly shorter preoviposition periods than

those fed on ArF, ArP or AnP. Oviposition period of females did not differ among diets and

ranged between 22.4 to 25.9 days. Amblyseius swirskii females reared on AnF lived

significantly longer than those reared on T. latifolia pollen. Oviposition rates of A. swirskii on

T. latifolia pollen, and both lyophilized diets were significantly higher than those of their

counterparts on the powdered diets. However, total number of eggs laid during the females’

lifetime did not differ among T. latifolia pollen and the powdered diets. Diet had no influence

on the sex ratio of offspring with a proportion of females ranging from 0.72 to 0.80.

Table 6.3 Life table parameters of Amblyseius swirskii fed on T. latifolia pollen or different

solid artificial foods

Diets n Net reproductive rate

(Ro, females per

female)a

Generation time

(T, days)a

Intrinsic rate of

increase (rm,


T. latifolia 31 25.93 ± 1.04 a 15.49 ± 0.15 a 0.210 ± 0.001 a

ArF 30 28.77 ± 1.25 a 18.23 ± 0.24 b 0.184 ± 0.002 c

AnF 31 28.97 ± 1.41a 17.23 ± 0.26 c 0.195 ± 0.001 b

ArP 28 22.00 ± 0.54 b 19.46 ± 0.18 d 0.159 ± 0.001 d

AnP 28 21.00 ± 1.02 b 19.34 ± 0.22 d 0.158 ± 0.002 d

F

11.012 60.705 232.645

df

4, 143 4, 143 4, 143

P

<0.001 <0.001 <0.001

n: Number of tested females; aMeans ± SE; means within a column followed by the same

letter are not significantly different (P > 0.05) according to Tamhane test (net reproductive

rate) or Tukey test (generation time, intrinsic rate of increase); F-, df- and P-values refer to

one-way ANOVAs. ArF or AnF: freeze-dried artificial diet supplemented with A. franciscana

cysts or with pupal hemolymph of A. pernyi, respectively; ArP or AnP: basic powdered diet

supplemented with powdered A. franciscana cysts or lyophilized pupal hemolymph of A.

pernyi, respectively.

Differences in developmental and reproductive characteristics were reflected in life

table statistics. Net reproductive rates (Ro) of A. swirskii fed on T. latifolia pollen, or on the


91

lyophilized diets were significantly higher than those of predators fed on both powdered diets

(Table 6.3). Generation time (T) was significantly shorter for females offered T. latifolia

pollen versus the other diets. Finally, the intrinsic rate of increase (rm) of the predator was

highest on T. latifolia pollen, followed by the lyophilized diets, and lowest on the powdered

diets.

Figure 6.1 Influence of supplemental foods on the density of Amblyseius swirskii on caged

chrysanthemum plants in a greenhouse.

Data shown are means ± SE. Means at the same monitoring date followed by the same letter

are not significantly different (P > 0.05).

The diets, sampling times, as well as their interaction significantly affected the numbers of A.

swirskii per leaf (F(3,28) = 47.557, P<0.001; F(8,21) = 75.101, P<0.001; F(24,61.508) = 7.715,

P<0.001, respectively). The population densities of the predator on all diets were significantly

higher than those in the control at all sampling times (Figure 6.1). Mite populations increased

rapidly in all diet treatments. At week 2 and 4 after release, densities of mites did not differ

among diets but were higher than those in the control (χ2=19.029, df=3, P<0.001 and

F=11.366, df=3, 28, P<0.001, for week 2 and 4, respectively). The highest densities of A.

swirskii were recorded on ArP and the basic diet 12 weeks after release (1.9 and 1.3 mites/leaf,

respectively), whereas the highest number of mites on Nutrimite (1.2 mite/leaf) was observed

eight weeks after release.

Chapter 6

92

6.4 Discussion

Artificial diets for carnivorous arthropods can have a consistency ranging from liquid to solid,

depending mostly on two factors: water content and molecular cohesion (Morales-Ramos et

al., 2014). Artificial diets have been developed for a number of phytoseiid mites, with varying

success (McMurtry and Scriven, 1966; Kennett and Hamai, 1980; Ochieng et al., 1987; Abou-

Awad et al., 1992; Ogawa and Osakabe, 2008). All of these artificial diets were liquid in form.

Liquid diets are expected to be easily accessible to predatory mites and have the practical

advantage that they can be easily sprayed over the crop when used as a supplemental food. On

the other hand, solid artificial diets have a number of advantages over liquid and semiliquid

diets, both in the laboratory rearing and when applied as supplemental foods in the crop.

These include non-stickiness and the possibility of direct presentation without the need for

encapsulation (Morales-Ramos et al., 2014). Lower water content of solid diets limits

microbial contamination and allows easier long term storage. When applied as a supplemental

food in the field, solid artificial diets are easier to distribute in the crop (e.g. by blowers

designed to distribute pollen or eggs of Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae))

and are expected to result in lower soiling of the plant surface and thus to interfere less with

plant physiology and crop quality.

Previous studies demonstrated the potential of liquid artificial diets supplemented with

pupal hemolymph of A. pernyi or with a watery extract of A. franciscana cysts to support the

development and reproduction of A. swirskii (Chapter 3 and Chapter 5). The objective of the

present study was to develop an adequate solid diet as a food for the mass rearing or for

application in the field. Our results indicate that A. swirskii performed well, both in terms of

its development and reproduction, when exclusively fed on various powdered solid artificial

diets, although its performance did not match that on T. latifolia pollen.

Among the four artificial diets tested, the highest intrinsic rate of increase of A.

swirskii (0.195 females/female/day at 23 °C) was recorded on freeze-dried artificial diet AnF,

a meridic diet enriched with pupal hemolymph of A. pernyi. Although lower than on T.

latifolia pollen in the present study, this growth rate exceeds the values reported for A.

swirskii feeding on several natural prey, including the two spotted spider mite Tetranychus

urticae Koch (Acari: Tetranychidae) (0.167 at 26 oC) (El-Laithy and Fouly, 1992), the

western flower thrips Frankliniella occidentalis (Pergande) (0.056 at 25 oC) and onion thrips

Thrips tabaci (Lindeman) (Thysanoptera: Thripidae) (0.024 at 25 oC) (Wimmer et al., 2008),


93

and the eriophyoid fig mites Aceria ficus (Cotte) (0.155 at 29 oC) and Rhyncaphytoptus

ficifoliae Keifer (0.122 at 29 oC)(Abou-Awad et al., 1999); interestingly, the growth rate on

AnF is also superior to that on the dried fruit mite C. lactis, a factitious prey which is

routinely used in the mass production of A. swirskii (0.175 at 23 oC) (Chapter 3). Arguably,

caution is warranted when comparing absolute values of intrinsic growth rates among studies

as they may be influenced by differences in climatic conditions, experimental methods, and

calculation of estimates. Interestingly, intrinsic growth rates of A. swirskii in our study are

closely correlated with oviposition rates, with about 90% of the variation in growth rates

being explained by oviposition rates. This confirms the observations by Janssen and Sabelis

(1992), who suggested that an assessment of peak oviposition may be sufficient to estimate

the reproductive performance of predatory mites, precluding the necessity to perform full life

table studies.

The fecundity of females fed on the freeze-dried liquid artificial diets ArF and AnF

was similar to that on T. latifolia pollen and higher than that on the powdered diets ArP and

AnP, which were both composed of solid basic ingredients. Parameters of development and

reproduction of females fed on lyophilized diets were similar to those on the original liquid

versions of the diets as reported in Chapter 5, indicating that the freeze-drying process did

not influence the nutritional quality of the diets and that the predator handled the solid forms

as effectively as the liquid forms. This confirms previous findings with diets for predators and

plant bugs, which have also indicated that the nutritive qualities and palatability are retained

after freeze-drying and rehydration of certain insect diets (Cohen, 2004). Freeze-dried diets

have several practical advantages over liquid diets related to storage, shipment and handling.

For instance, a freeze-dried medium may be stored at room temperature for months with no

loss of nutritional quality (Cohen, 1999). The freeze dried diets used in our study proved to be

highly hygroscopic and quickly reverted to a semi-liquid form. This liquefaction process may

have been accelerated by the high relative humidity in the Munger cells, which was always in

excess of 85 %, and may thus be slower under practical conditions. On the one hand, the

partial liquefaction of these freeze dried diets may be beneficial as it may facilitate feeding by

the mites. On the other, however, it may limit their practical applicability: for instance, when

not replaced on a regular basis like in the present study, such diets may be more prone to

microbial degradation and may thus require the addition of antimicrobial agents. Further, the

freeze-drying process also increases the cost of the artificial diets.

The availability of an adequate artificial diet would preclude the necessity to maintain

parallel cultures of prey mites in the mass production system, resulting in less labour costs

Chapter 6

94

and lower health risks for workers in the production environment (i.e. potential allergy

problems related to the use of storage mites). Even when such artificial diets appear

suboptimal as compared to storage mites in terms of predator population growth rates, they

could be used in part of the production cycle of the phytoseiids. Most ingredients of the

presented diets are relatively inexpensive and easily accessible on the market. Based on

economies of scale, prices may further be reduced if these diets are produced at a larger scale.

In order to enhance cost effectiveness as compared to the liquid diets previously designed in

Chapter 5 and their lyophilized forms tested here, the powdered diets ArP and AnP were

created by replacing the liquid ingredients of the original formulations in Chapter 5 by

powdered solid ingredients. The honey was replaced with sucrose, glucose and fructose, fresh

egg yolk was replaced with spray-dried egg yolk, and a vitamin mix was added. However, A.

swirskii fed on the powdered diets had significantly longer developmental times and lower

oviposition rates and intrinsic rates of increase than those reared on the freeze dried diets.

These differences in performance of the mite can be explained in part by differences in the

nutritional profiles of the corresponding diets. For instance, honey contains other compounds

than sugars, like vitamins, minerals and amino acids, which may have a positive impact on the

development and reproduction of A. swirskii. Guardiola et al. (1995) found that fatty acids

undergo considerable oxidation during spray-drying of egg; therefore, the nutritive value of

egg yolk powder may be lower than that of fresh egg yolk. Further, Debolt (1982) reported

differences in nutritional and sensory qualities of spray-dried egg yolk as compared to fresh

egg yolk for the mirid Lygus hesperus Knight (Hemiptera: Miridae). Nonetheless,

reproductive rates of A. swirskii on the powdered diets in the present study were comparable

to the values found in Chapter 3 on the dried fruit mite C. lactis and higher than the values

reported earlier on some of the predator’s natural prey (Ragusa and Swirski, 1977; Wimmer et

al., 2008). Additionally, the powdered diets proved to be more structurally stable than the

freeze dried diets, which may enhance their practical value in rearing systems and as

supplemental foods in the crop.

In ornamental plant production, there is often a zero tolerance towards pest presence

for aesthetic reasons (Schumacher et al., 2006). In addition, the tolerance for thrips in

chrysanthemums is very low. The availability of effective supplemental food sources should

enable to maintain a population of predatory mites in the crop at sufficiently high levels to

keep the population of thrips at a minimum level (Hoogerbrugge et al., 2008). In our pre-

establishment greenhouse experiment, the value of the powdered basic artificial diet without

or with A. franciscana cyst powder (ArP) was examined on chrysanthemum plants. The


95

results indicated that both powdered diets could support a population of A. swirskii over a

period of several weeks. The population growth of the predator on the artificial diets was

similar to that on Nutrimite, which is commercially used as a supplemental food source for

phytoseiid mites in greenhouse crops. The diets did not only succeed in maintaining the

populations of A. swirskii on the plants but they also yielded positive population growth of the

mite. Although the numbers of mites per leaf only appear to increase gradually over time, in

reality their populations exploded as the plants sprouted many more leaves over the

successive weeks. Hoogerbrugge et al. (2008) also conducted a pre-establishment experiment

with A. swirskii in chrysanthemums using seven different food sources: cysts of the brine

shrimp Artemia sp., honey bee pollen, C. lactis, C. lactis + artificial diet A (not described),

artificial diet B (not described), artificial diet B + honey bee pollen, and eggs of Ephestia

kuehniella Zeller (Lepidoptera: Pyralidae) + fresh corn pollen. The initial number of the

predatory mites introduced in their experiment was 10 females/plant, which is approximately

30 times higher than that in the present study. The authors reported the highest number of

predators to be around 8.2 mites/leaf in the treatment with C. lactis + diet A after 28 days.

This means that, although comparison of both greenhouse studies is complicated by the

different experimental conditions, the populations of A. swirskii in our study in fact increased

faster on Nutrimite and ArP than on the best diet in the study by Hoogerbrugge et al. (2008),

given the much higher initial densities in the latter study. In addition, no damage to the

chrysanthemum leaves was observed after twelve weeks in all diet treatments of our study.

However, some fungal contamination was recorded on the leaves sprayed with the powdered

artificial diets, especially where the diet grains clumped.

In conclusion, A. swirskii was capable of handling and feeding on (powdered) solid

artificial diets, allowing the mite to develop and reproduce successfully for at least a single

generation. Freeze-drying of liquid diets did not influence their acceptability and nutritional

quality for the mite. Artificial diets entirely composed of powdered/dry ingredients were

somewhat inferior to lyophilized liquid diets in terms of their nutritional value, but did

support development and reproduction of the phytoseiid and were physically more stable in

the rearing environment than the lyophilized diets. A greenhouse experiment showed that

powdered artificial diets could indeed support populations of A. swirskii in a chrysanthemum

crop. These findings indicate the potential of dry artificial diets for use in part of the

production cycle of A. swirskii or as supplemental foods to sustain its populations in the crop

after release. Arguably, more studies are needed to assess the practical applicability of

artificial diets in support of biological control programmes using phytoseiid mites. First, it is

Chapter 6

96

warranted to assess the value of the presented artificial diets for supporting the population

growth of other generalist predatory mites. The effects of long-term rearing of the mites on

artificial diets on their quality as biological control agents also need to be explored. Further,

more field research is needed to evaluate the suitability of the tested diets in the crop

environment, with regard to their practical value to support populations of A. swirskii or of

other predatory mites, and possible undesired effects of their application on populations of

arthropod pests (like omnivorous thrips who may also be able to use the diets) and on the

physiology and quality of the crop plants.

97

Chapter 7

PERFORMANCE OF FOUR SPECIES OF PHYTOSEIID MITES ON ARTIFICIAL

AND NATURAL DIETS


Nguyen, D. T., Vangansbeke, D., & De Clercq, P. 2014. Performance of four species of phytoseiid

mites on artificial and natural diets. Biological Control, 80: 56–62, DOI:

10.1016/j.biocontrol.2014.09.016

Chapter 7

98

7.1 Introduction

Phytoseiid predatory mites are important biocontrol agents of tetranychid mites and

small, soft-bodied insects like thrips and whiteflies (Chant, 1985). In augmentation biological

control, large numbers of predaceous mites are released in the field (Stinner, 1977; Collier

and Van Steenwyk, 2004). Hence, a cost-effective method for their mass-rearing is an

essential prerequisite (van Lenteren, 2003). Rearing phytoseiid mites on plant materials

infested with natural prey has several disadvantages, such as large space requirements,

inconsistent yields of predators, harvesting difficulties and variable results with different

species (McMurtry and Scriven, 1965). Rearing procedures based on factitious prey like

storage mites (Zhang, 2003; Bolckmans and van Houten, 2006) also involve space and labor

to maintain large parallel cultures of the factitious prey. Further, there may be health risks for

workers in production facilities or releases in the crop caused by allergens associated with the

factitious mite prey (Bolckmans and van Houten, 2006; Fernandez-Caldas et al., 2007). The

availability of an adequate artificial diet could eliminate many of the above-mentioned

problems associated with the mass production of predatory mites (Kennett and Hamai, 1980).

In addition, these artificial diets may be useful as food supplements to support predator

populations after release in the crop (Wade et al., 2008).

Several artificial diets have been developed for phytoseiid mites, but the results were

mostly inferior to those on natural or factitious prey. McMurtry and Scriven (1966) reported

longer developmental times and lower oviposition rates when four phytoseiids

(Amblydromalus limonicus Garman and McGregor, Amblyseius hibisci (Chant),

Typhlodromus occidentalis Nesbitt and Typhlodromus rickeri Chant) (Acari: Phytoseiidae)

were fed on various artificial diets compared with mite prey and pollen as food sources.

Shehata and Weismann (1972) tested three artificial diets for the specialist spider mite

predator Phytoseiulus persimilis Athias-Henriot. Their results indicated that the larvae could

develop to adults but the females failed to produce viable eggs. Kennett and Hamai (1980)

investigated oviposition rate and developmental capacity of 9 predaceous mites (A. hibisci, A.

limonicus, Amblyseius largoensis (Muma), Metaseiulus pomoides Schuster & Pritchard, T.

occidentalis, Typhloseiopsis arboreus (Chant), Typhloseiopsis pyri Scheuten, P. persimilis,

and Iphiseius degenerans (Berlese)) fed on artificial and natural diets. The authors reported

that complete development and oviposition occurred for seven out of nine species when fed

on an artificial diet consisting of bee honey, sugar, yeast flakes, yeast hydrolysate, enzymatic

Performance of four phytoseiid mites on artificial diets

99

casein hydrolysate and fresh egg yolk. Oviposition rates of all species fed on the artificial diet

were lower than those on a natural diet. Ochieng et al. (1987) reported that Amblyseius teke

Pritchard and Baker could complete more than 25 generations when reared on a liquid diet

composed of bee honey, milk powder, egg yolk and Wesson's salt. Abou-Awad et al. (1992)

noted that the predacious mites Amblyseius gossipi El-Badry and Amblyseius swirskii Athias-

Henriot developed and reproduced successfully on artificial diets composed of yeast, milk,

cysteine, proline, arginine, sucrose, glucose, streptomycin sulphate and sorbic acid. However,

fecundity of both species fed on the artificial diet was lower than on natural prey, although the

eggs showed no abnormalities. Shih et al. (1993) conducted experiments to investigate the

responses of Euseius ovalis (Evans) to natural food resources and two artificial diets.

Immature development was successful in the first generation but offspring was not able to

complete its life cycle when maintained on the artificial diets. The females of E. ovalis fed on

artificial diets showed a shorter oviposition period, lower daily and total reproductive rates,

and shorter longevity than those fed on natural diets. Ogawa and Osakabe (2008) investigated

the development and survival of Neoseiulus californicus (McGregor) on an artificial diet. The

phytoseiid successfully developed on the artificial diet, but only few eggs were deposited.

In our previous studies we found that artificial diets enriched with watery extract of

dry decapsulated cysts of the brine shrimp Artemia franciscana Kellogg (Anostraca:

Artemiidae) or pupal hemolymph of the Chinese oak silkworm (Antheraea pernyi (Guérin-

Méneville)) supported development and reproduction of the generalist predatory mite A.

swirskii. The females fed on these two artificial diets displayed higher intrinsic rates of

increase than those fed on several natural prey and performed as well as those reared on the

factitious prey Carpoglyphus lactis L. (Acari: Carpoglyphidae), which is routinely used in the

mass rearing of this phytoseiid (Chapter 3 and Chapter 5). The objectives of the present

study were to assess the suitability of the artificial diet enriched with A. franciscana as an

alternative food for several other economically important predatory mites by performing full

life table studies under controlled laboratory conditions. The phytoseiids selected for testing

belong to different types based on their level of food specialization (McMurtry et al., 2013): N.

californicus is a selective predator of tetranychid mites (type II), whereas A. andersoni Chant,

N. cucumeris (Oudemans), and A. limonicus are more generalist predators (type III).

Chapter 7

100


7.2.1 Stock colonies of predatory mites

Laboratory cultures of N. cucumeris and A. limonicus were initiated with specimens

supplied by Koppert B.V. (Berkel en Rodenrijs, The Netherlands) and A. andersoni was

supplied by Biobest N.V. (Westerlo, Belgium). The mites were reared on green plastic arenas

(10 x 10 x 0.3 cm) (Multicel, SEDPA, France), placed on a wet sponge in a plastic tray

containing water. The edges of the arenas were covered with tissue paper immersed in the

water to provide moisture and deter the mites from escaping. Every two days the mites were

fed with fresh cattail pollen (Typha latifolia L.), which was also supplied by Koppert B.V. and

stored at -18°C. For the experiments, pollen was thawed and kept in a refrigerator at 5°C for

max. 1 week. A small piece of sewing thread was placed on the arenas to serve as an

oviposition substrate. Every two days the eggs were collected and transferred to new arenas.

A culture of N. californicus was initiated with mites acquired from Koppert B.V. and

was reared on kidney bean leaves heavily infested with two-spotted spider mites (Tetranychus

urticae Koch). The leaves were placed upside down on a layer of water-saturated cotton in a

glass petri dish ( 133 mm), with an extra cotton layer on the leaf edges to provide free water

and prevent the mites from escaping.

Predatory mites were cultured in a growth chamber set at 25 ± 1°C, 70 ± 5% RH and a

16:8 h (L: D) photoperiod.


Artificial diets were prepared according to section 5.2.2 : 80% basic artificial diet

supplemented with 20% (w/w) watery extract of dry decapsulated A. franciscana cysts, which

were provided by the Artemia Reference Center of Ghent University (Ghent, Belgium) and

originated from the Great Salt Lake (Utah, USA). The basic artificial diet was prepared

according to section 3.2.4 . The diet was dispensed into 2ml Eppendorf tubes and stored at

−18°C.


101


Eight hours before start of the experiments, new pieces of sewing thread were placed

in the stock colony of N. cucumeris, A. limonicus and A. andersoni or fifty females of N.

californicus were transferred to new bean leaves infested with mixed life stages of T. urticae.

Deposited eggs (less than 8 hours old) were transferred individually to the rearing microcosms

that were modified from Munger cells as described in section 3.2.5 . Development and

reproduction of the tested phytoseiids on the artificial diet was compared with that on a

natural food source (spider mites for N. californicus or cattail pollen for N. cucumeris, A.

andersoni and A. limonicus). All food sources were offered ad libitum from the larval stage of

the predator on and were refreshed every 2 days. For the artificial diet, approximately 2 µl of

diet was absorbed on a small piece of filter paper (2 x 2 mm) placed on the bottom board of

the rearing microcosms. The mites were observed and different parameters were recorded

same as that described in section 3.2.6 . Mites that escaped or died due to unnatural causes

were excluded from data analysis. Females that died before laying eggs were excluded from

calculation of reproductive parameters. The experiments were done in a growth chamber at 23

± 1°C, 65 ± 5% RH and a 16:8 h (L: D) photoperiod.




Two-way analysis of variance (ANOVA) (IBM, SPSS Statistics 20) was conducted to

evaluate the effects of diet and species on the duration of the immature stages, preoviposition

and oviposition period, daily and total oviposition, adult longevity and life table parameters.

When an interaction was detected between the main factors, means were compared among

species and a pairwise multiple comparison procedure was used (Kutner et al., 2005). When a

Kolmogorov–Smirnov test indicated that data were normally distributed, the pairwise

comparisons among diets in each species were analyzed using Student t-tests. When data were

not normally distributed, a nonparametric Mann-Whitney U test was used. Generalized linear

model with a probit (log odds) link function and a binomial error distribution was used to

Chapter 7

102

compare immature survival rates and progeny sex ratios. Each test consisted of a regression

coefficient that was calculated and tested for being significantly different from zero, for which

P-values are presented (McCullagh and Nelder, 1989). In all tests, P-values smaller than or

equal to 0.05 were considered significant.

7.3 Results

Table 7.1 Results of a logistic regression and a two-way ANOVA indicating the effect of diet

(artificial diet versus Typha latifolia or Tetranychus urticae) and phytoseiid species

(Neoseiulus californicus, Neoseiulus cucumeris, Amblyseius andersoni, Amblydromalus

limonicus) on immature survival and developmental time, reproduction parameters, sex ratio

and life table parameters

Parameter

Diet Species Diet x species Error

term

df F df P F df P F df P

Immature survivala 0.11 1 0.739 3.09 3 0.378 1.25 3 0.74 -

Female development

timeb 248.85 1 <0.001 86.19 3 <0.001 41.34 3 <0.001 227

Male development

timeb 123.29 1 <0.001 42.48 3 <0.001 4.85 3 0.003 193

Preoviposition

periodb 66.80 1 <0.001 25.66 3 <0.001 23.93 3 <0.001 204

Oviposition periodb 24.13 1 <0.001 113.41 3 <0.001 22.49 3 <0.001 204

Female longevityb 7.66 1 0.006 96.34 3 <0.001 7.81 3 <0.001 204

Oviposition rateb 502.47 1 <0.001 164.92 3 <0.001 34.45 3 <0.001 204

Total number of

eggsb 116.51 1 <0.001 15.32 3 <0.001 14.59 3 <0.001 204

Female proportion of

the progeny a 0.44 1 0.505 17.47 3 <0.001 9.76 2 0.008 -

R0b 47.80 1 <0.001 19.16 3 <0.001 11.38 2 <0.001 195

Tb 410.70 1 <0.001 405.66 3 <0.001 153.48 2 <0.001 195

rmb 860.90 1 <0.001 444.86 3 <0.001 56.88 2 <0.001 195

a Probit;

b Two-way ANOVA; Life table parameters (rm, R0 and T) and female proportion of

the progeny were not calculated for N. californicus fed on artificial diet


103

Two-way ANOVA indicated no interaction between diet and species for immature

survival (Table 7.1), whereas interactions were found to be significant for all other parameters.

Diet had no influence on the immature survival rate of all tested species (Table 7.2). Female

developmental times were significantly shorter on natural diets (T. urticae or T. latifolia) than

on the artificial diet, except for A. limonicus. In all species, males developed faster on natural

diets than on the artificial diet.

Table 7.2 Immature survival and developmental time of different phytoseiid mites fed on

artificial diet versus natural food sources

Species Diet Proportion

surviving

Developmental duration (days)*

n Females N Males

N. californicus T. urticae 0.92 ± 0.04 a 32 5.09 ± 0.05 a 24 5.38 ± 0.18 a

Artificial 0.96 ± 0.03 a 20 7.90 ± 0.31 b 28 6.46 ± 0.15 b

χ2/ U 0.818 4.500 81.500

df/Z 1 -6.546 -4.979

P 0.366 <0.001 <0.001

N. cucumeris T. latifolia 0.98 ± 0.02 a 33 6.67 ± 0.09 a 22 6.45 ± 0.11 a

Artificial 0.98 ± 0.02 a 29 9.00 ± 0.21 b 24 8.25 ± 0.11 b

χ2/ U 0.001 0.000 5.000

df/Z 1 -6.988 -5.927

P 0.979 <0.001 <0.001

A. andersoni T. latifolia 0.96 ± 0.03 a 27 5.74 ± 0.10 a 26 5.81 ± 0.12 a

Artificial 0.98 ± 0.02 a 34 6.79 ± 0.12 b 20 6.55 ± 0.14 b

χ2/ U 0.338 118.000 113.500

df/Z 1 -5.387 -3.523

P 0.561 <0.001 <0.001

A. limonicus T. latifolia 0.98 ± 0.02 a 30 5.77 ± 0.11 a 30 5.50 ± 0.17 a

Artificial 0.97 ± 0.02 a 30 5.77 ± 0.09 a 27 6.41 ± 0.12 b

χ2/ U 0.371 443.000 150.500

df/Z 1 -0.127 -4.304

P 0.542 0.899 <0.001

n and N: Number of tested female and male individuals, respectively

*Means ± SE; means within a column and a species followed by the same letter are not

significantly different (P>0.05), according to Probit (Wald Chi-square) test (Immature

survival), or Mann-Whitney U test (Female and male developmental time). χ2-, df- and P-

values refer to Probit (Wald Chi-square) test, U-, Z-, and P- values refer to Mann-Whitney U

test.

Chapter 7

104

Preoviposition periods of A. limonicus females fed on T. latifolia and the artificial diet

were similar, whereas females of the other species fed on their respective natural diets had

significantly shorter preoviposition periods than those fed on the artificial diet (Table 7.3).

Oviposition period of N. californicus did not differ among diets, whereas in A. limonicus

females reared on artificial diet had a shorter oviposition period than those reared on cattail

pollen. In contrast, N. cucumeris and A. andersoni fed on the artificial diet had longer

oviposition periods than those reared on cattail pollen. Whereas no difference in female

longevity was observed among diets for N. californicus, females reared on artificial diet lived

shorter in A. limonicus and A. andersoni and longer in N. cucumeris, than their counterparts

fed on pollen. The total number of eggs deposited by N. californicus, N. cucumeris and A.

limonicus females reared on natural diets was significantly higher than that of females

maintained on the artificial diet but fecundity of A. andersoni was not affected by diet.

Whereas the proportions of female offspring in A. andersoni and A. limonicus were similar on

artificial and natural diets, in N. cucumeris a lower percentage of female offspring was

observed on the artificial diet than on cattail pollen. Because the offspring of N. californicus

fed on the artificial diet did not develop successfully to adulthood, the female proportion of

the progeny and life table parameters were not calculated for this treatment.

105

Table 7.3 Reproductive parameters of several phytoseiid mites fed on artificial diet versus natural food sources

Species Diets n Preoviposition

period (days)a

Oviposition

period (days)a

Female

longevity

(days)a

Oviposition rate

(eggs/female/day)a

Total number

of eggs

(eggs/female)a

Female

proportion of

the progeny a

N. californicus T. urticae 32 2.22 ± 0.10 a 19.44 ± 0.70 a 34.25 ± 2.40 a 2.76 ± 0.07 a 53.34 ± 2.05 a 0.63 ± 0.02

Artificial 10 14.30 ± 4.84 b 15.50 ± 3.40 a 38.00 ± 6.10 a 0.85 ± 0.09 b 12.90 ± 3.41 b -

U/ t/ χ2 1.000 1.135 -0.688 15.035 9.763

Z/df -5.482 9.772 40 40 40

P <0.001 0.283 0.495 <0.001 <0.001

N. cucumeris T. latifolia 33 2.52 ± 0.11 a 30.97 ± 1.43 a 52.64 ± 3.37 a 1.51 ± 0.06 a 45.45 ± 2.26 a 0.73 ± 0.02 a

Artificial 27 4.00 ± 0.16 b 50.52 ± 3.27 b 71.56 ± 4.22 b 0.52 ± 0.02 b 25.78 ± 1.68 b 0.65 ± 0.02 b

U/ t/ χ2 88.500 -5.475 -3.550 14.989 7.003 9.226

Z/df -5.531 35.747 58 38.894 56.053 1

P <0.001 <0.001 0.001 <0.001 <0.001 0.002

A. andersoni T. latifolia 27 2.26 ± 0.11 a 33.07 ± 2.15 a 55.70 ± 3.30 a 1.49 ± 0.07 a 48.56 ± 3.44 a 0.70 ± 0.01 a

Artificial 32 4.34 ± 0.18 b 50.91 ± 2.02 b 68.16 ± 2.62 b 0.92 ± 0.03 b 45.97 ± 2.10 a 0.71 ± 0.01 a

U/ t/ χ2 37.000 -6.034 -2.993 7.736 0.642 0.308

Z/df -6.189 57 57 40.001 43.942 1

P <0.001 <0.001 0.004 <0.001 0.524 0.579

A. limonicus T. latifolia 30 1.73 ± 0.08 a 16.40 ± 0.99 a 22.37 ± 1.83 a 2.57 ± 0.06 a 42.20 ± 2.81 a 0.65 ± 0.02 a

Artificial 21 1.90 ± 0.07 a 11.38 ± 0.84 b 13.10 ± 0.86 b 1.90 ± 0.08 b 22.05 ± 2.40 b 0.69 ± 0.03 a

U/ t/ χ2 261.000 3.853 4.583 6.458 5.447 0.971

Z/df -1.503 48.985 40.254 49 48.964 1

P 0.133 <0.001 <0.001 <0.001 <0.001 0.324

n: Number of tested females; aMeans ± SE; means within a column and a species followed by the same letter are not significantly different (P > 0.05)

according to Mann-Whitney U test (preoviposition period), Student’s t-test (oviposition period, female longevity, oviposition rate, total number of eggs) or

Probit (Wald Chi-square) test (female proportion of progeny). U-, Z-, and P- values refer to Mann-Whitney U test; t-, df- and P-values refer to Student’s t- test;

χ2-, df- and P-values refer to Probit (Wald Chi-square) test.

Chapter 7

106

Net reproductive rate (R0) of N. cucumeris and A. limonicus females offered pollen

was significantly higher than that of females given the artificial diet, whereas in A. andersoni

this parameter did not differ among diets. Females reared on pollen had a shorter generation

time than those on artificial diet for N. cucumeris and A. andersoni, whereas there were no

differences for A. limonicus. For all species, a higher intrinsic rate of increase (rm) was

calculated when the mites were maintained on their respective natural foods as compared to

the artificial diet.

Table 7.4 Life table parameters of different phytoseiid mites fed on artificial diet versus

natural food sources

Species Diets n

Net reproductive

rate (R0, females

per female)a

Generation

time (T,

days)a

Intrinsic rate of

increase (rm,


N. californicus T. urticae 32 29.45 ± 1.18 14.21 ± 0.17 0.238 ± 0.002

Artificial - - - -

N. cucumeris T. latifolia 33 32.97 ± 1.74 a 18.95 ± 0.27 a 0.185 ± 0.003 a

Artificial 27 17.16 ± 1.04 b 31.74 ± 0.71 b 0.090 ± 0.002 b

t 7.804 -16.850 24.357

df 51.076 33.386 58

P <0.001 <0.001 <0.001

A. andersoni T. latifolia 27 33.74 ± 2.62 a 18.03 ± 0.34 a 0.195 ± 0.002 a

Artificial 32 33.16 ± 1.82 a 24.29 ± 0.37 b 0.144 ± 0.003 b

t 0.185 -12.429 13.653

df 47.776 57 57

P 0.854 <0.001 <0.001

A. limonicus T. latifolia 30 26.96 ± 1.67 a 12.79 ± 0.19 a 0.258 ± 0.002 a

Artificial 21 13.83 ± 1.21 b 12.39 ± 0.27 a 0.212 ± 0.003 b

t 6.385 1.248 12.533

df 48.169 49 49

P <0.001 0.218 <0.001

n: Number of tested females

aMeans ± SE; means within a column and a species followed by the same letter are not

significantly different (P > 0.05) according to Student’s t- test


107

7.4 Discussion

The developmental and reproductive performances of the four predatory mites studied

were differentially affected by diet. Where differences were observed, the mites developed

faster and produced more eggs on their natural diets (spider mites for N. californicus or cattail

pollen for N. cucumeris, A. andersoni and A. limonicus) than on the artificial diet. Overall, the

percentage decrease in developmental rate, oviposition rate and intrinsic rate of increase of

the predatory mites fed on artificial diet as compared with natural diet was greatest in N.

californicus, intermediate in N. cucumeris and smallest in A. andersoni and A. limonicus. This

order reflects the level of polyphagy of the different species. N. californicus is classified as a

selective predator of tetranychid mites (McMurtry and Croft, 1997), which may explain its

relatively poor performance on the artificial diet. The more polyphagous species A. andersoni

and A. limonicus, which readily feed and reproduce also on pollens (Duso and Camporese,

1991; van Houten et al., 1995), were also able to develop and reproduce well on the artificial

diet. Our findings are consistent with those reported by McMurtry and Scriven (1966) who

tested several artificial diets for four phytoseiid mites. In the latter study, the studied type II

phytoseiids of the genus Typhlodromus (T. occidentalis and T. rickeri) did not perform well

on the tested artificial diets, whereas better results were obtained for two Amblyseius species

(A. limonicus and A. hibisci) characterized by a more generalist feeding habit.

The artificial diet in the present study supported development of N. californicus well,

with 96% of the mites reaching adulthood. Immature development of females fed on the

artificial diet was longer than that on T. urticae but was similar to that reported by Rencken

and Pringle (1998) and Kim et al. (2009) when the predatory mite was reared at 25°C with

mixed stages of T. urticae. N. californicus fed on the artificial diet at 23°C in our study had

similar developmental rates to those of the predator reared at 25°C on an artificial diet

formulated by Ogawa and Osakabe (2008). However, whereas only few eggs were produced

on the diet used by Ogawa and Osakabe (2008), N. californicus females in the present study

produced 0.85 eggs/day on a similar diet supplemented with A. franciscana. Nonetheless, egg

production on the artificial diet was substantially lower than on the natural prey, T. urticae,

and offspring could not develop successfully to adulthood.

To our knowledge, this is the first time that an artificial diet was tested for N.

cucumeris. The predatory mite developed successfully on the artificial diet, with an immature

survival of 98% and produced viable eggs, the offspring of which succeeded in reaching

adulthood (> 75% survival). A positive intrinsic rate of increase of 0.09 females/female/day-1

Chapter 7

108

was calculated on the artificial diet, showing that N. cucumeris is still able to maintain its

population when exclusively fed on the artificial diet. Thus, whereas the diet is not suitable

for the mass production of this phytoseiid, it still may have some potential to be used as a

food supplement to sustain populations of N. cucumeris in the crop (Chapter 6). Our results

also show the suitability of T. latifolia pollen as a supplemental food for N. cucumeris. The

intrinsic rate of increase of N. cucumeris fed on T. latifolia pollen (0.185 females/female/day)

is higher than the values reported for the phytoseiid when fed on pollen of apple, birch,

Christmas cactus, horse-chestnut, maize, or tulip (0.149, 0.127, 0.155, 0.180, 0.101 or 0.167

females/female/day, respectively) at 25°C (Ranabhat et al., 2014), or on castor pollen and T.

urticae (0.179 and 0.147 females/female/day, respectively) at 25 °C (van Rijn and Tanigoshi,

1999b). The rm value of N. cucumeris on T. latifolia pollen calculated in our study was

slightly lower than the value of 0.208 reported by van Rijn and Tanigoshi (1999b) when the

predator was offered pollen of broad bean (Vicia faba L.), but this difference may in part be

attributed to the higher experimental temperature (25°C) in the latter study.

Amblyseius andersoni females reared on the artificial diet produced less eggs per day

than those given T. latifolia pollen. However, the artificial diet prolonged the oviposition

period, so that an equal amount of eggs was produced on both diets. The life time fecundity of

A. andersoni females reared on T. latifolia and the artificial diet (48.56 and 45.97 eggs/female,

respectively) in this study is substantially higher than the total fecundities reported by

Lorenzon et al. (2012) for females of the species fed on T. latifolia pollen, Eotetranychus

carpini (Oudemans), Panonychus ulmi (Koch), Colomerus vitis (Pagenstecher), or the

mycelium of grape downy mildew Plasmopara viticola (Berk. & Curt.) Berl. (25.7, 24.2, 22.2,

25.6, and 9.3 eggs/female, respectively).

The artificial diet fully supported the development and reproduction of A.limonicus.

Developmental duration of females was similar on T. latifolia pollen and the artificial diet

(5.8 days). Development was shorter than that observed on dry decapsulated cysts of A.

franciscana and E. kuehniella eggs at the same temperature (6.58 and 6.85 days, respectively)

(Vangansbeke et al., 2014). The oviposition rate of A. limonicus on the present artificial diet

(1.90 eggs/female/day) was higher than that on the artificial diet designed by Kennett and

Hamai (1980) (1.22 eggs/female/day) and on the diets (sucrose, molasses, yeast + sucrose and

yeast + molasses) used by McMurtry and Scriven (1966) (0.11, 0.25, 1.13 and 1.18

egg/female/day, respectively).

The use of food supplements, consisting of alternative or artificial foods, can increase

the abundance and impact of arthropod natural enemies in crops where target prey or plant


109

foods like pollen and nectar are absent or only present at low densities (Wade et al., 2008).

While various supplemental foods appear to have potential for enhancing establishment of

insect natural enemies, only few have been reported to support beneficial Acarina (Wade et al.,

2008). For generalist predatory mites, pollen has been reported to be an adequate

supplemental food source to enhance the biological control of thrips and whiteflies on

cucumber (van Rijn et al., 2002; Nomikou et al., 2010). Typha angustifolia L. pollen

(NutrimiteTM

, Biobest NV) is commercially available to support pollen-feeding phytoseiids in

the crop. Drawbacks associated with the application of pollen are the relatively high costs

(Messelink et al., 2014) and the potential beneficial effects on pollen-feeding pests, such as

Frankliniella occidentalis Pergande (Ramakers, 1995). Certain animal foods also have

potential to support populations of phytoseiid mites, such as sterilized eggs of Ephestia

kuehniella Zeller and decapsulated cysts of A. franciscana (Vangansbeke et al., 2014).

Finding inexpensive alternative food sources is one of the major opportunities for enhancing

biological control in protected crops (Messelink et al., 2014). Several artificial diets have been

developed with the aim to reduce the production cost of phytoseiid mites or provide

supplemental foods for supporting their populations after release in the crop. For example, a

simple mixture of yeast, sugar and protein applied on chrysanthemum increased population

levels of A. swirskii (Messelink et al., 2009). In Chapter 3 and Chapter 5, artificial diets

enriched with A. franciscana or A. pernyi were found to support the development and

production of this economically important species. The findings of the present study suggest

that the same diet may also be useful to support populations of other commercially available

phytoseiids, either in the laboratory or in the field. Future studies should focus on the

optimization of artificial diets for phytoseiids in terms of their nutritional value and

formulation. In addition, when evaluating an artificial diet for field support, researchers may

not only limit their focus on promoting the predator, but also diminishing potential beneficial

effects for omnivorous pests. More work is also needed to optimize the application of

artificial diets as food sprays in the crop. Possible limitations of the use of artificial diets as

food sprays include desiccation, and chemical or microbial degradation of the foods, and crop

pollution or damage.

Chapter 7

110

111

Chapter 8

GENERAL DISCUSSION, CONCLUSIONS AND FUTURE PERSPECTIVES

Chapter 8

112

The potential for using augmentative biological control to suppress arthropod pests has been

recognized for many years (Doutt and Hagen, 1949; DeBach, 1964; Parella et al., 1992). This

method has a number of important benefits when compared with chemical control including

lower risks for the environment, lack of phytotoxic effects on the crop, and safety to

producers and consumers, allowing harvesting immediately after release of natural enemies,

unlike most chemical pesticides (van Lenteren, 2003). To date, however, augmentation

biological control is applied on a commercial scale in relatively few agricultural systems (van

Lenteren, 2012). One of the main reasons of the relatively low adoption of this pest

management strategy (van Lenteren, 2012) is that augmentative releases are usually more

expensive to growers than chemical pesticides (Collier and Van Steenwyk, 2004). One

approach to make augmentation a more competitive strategy is reducing the costs associated

with the mass production of natural enemies by using factitious or artificial foods instead of

their natural prey or hosts (Riddick, 2009).

The predatory mite Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) is an

economically important biological control agent of several key pests in greenhouses, such as

whiteflies, thrips and broad mites (Nomikou et al., 2002; Messelink et al., 2006; van Maanen

et al., 2010). The predator was first used in 2005 and is one of the 25 species that make up

more than 90% of the total market value of commercial biological control; it is currently used

in over 20 countries (Cock et al., 2010). Amblyseius swirskii is a type III generalist predator,

implying that it can feed on various types of food including various arthropod prey, pollen,

and honeydew (McMurtry et al., 2013). In the commercial mass production, A. swirskii is

being reared on storage mites, including the dried fruit mite, Carpoglyphus lactis L. (Acari:

Carpoglyphidae), and Thyreophagus entomophagus (Laboulbene) (Acari: Acaridae)

(Bolckmans and van Houten, 2006; Fidgett and Stinson, 2008).

Amblyseius swirskii can develop and reproduce well on pollens, a food source that is

rich in proteins, free amino acids, carbohydrates, lipids, vitamins, flavonoids, and minerals

(Goleva and Zebitz, 2013). The intrinsic rates of increase of the predator reared on pollens

like Typha latifolia L. or Zea mays L., as reported in Chapter 3 and by Zannou and Hanna

(2011), respectively, are higher than those observed on several of its natural prey, including

Frankliniella occidentalis (Pergande), Thrips tabaci Lind.(Wimmer et al., 2008), Bemisia

tabaci (Gennadius) (Nomikou et al., 2001), and Polyphagotarsonemus latus (Banks) (Onzo et

al., 2012). Cattail (T. latifolia) pollen has become a standard food in many laboratory studies

on phytoseiids (Nomikou et al., 2002; Park et al., 2011). However, in our study we noted that

the biological parameters of A. swirskii on T. latifolia pollen were variable depending on the

General discussion, conclusions and future perspectives

113

quality of the pollen batch used. We observed a substantial difference in rm-values (0.158 and

0.210, respectively)(Table 8.1) between the experiments in Chapter 3 and Chapter 6, using

the same environmental conditions and the same population of A. swirskii but different

batches of T. latifolia pollen. The quality of a pollen batch is influenced by harvesting time

(immature pollen grains may have a lower nutrient content), by weather conditions at the time

of pollen harvest (Coates et al., 2006), and by the duration and conditions of storage and

shipment (Bogdanov, 2004). Sufficient quantities of pollen needed for mass rearing predatory

mites may require large greenhouse areas for the production of plants, such as castor bean

(Ricinus communis L.). Alternatively, pollen can be collected in the field, like in the case of

cattail (Typha spp.). Collecting plant pollen outdoors is very labour intensive, and thus

expensive, and often only limited quantities can be collected (Bolckmans and Van Houten,

2011). Variability in quality (e.g., in terms of nutritional value or the presence of pesticide

residues or pathogenic micro-organisms), high costs and problems with continuity may

complicate the use of field collected pollens in the commercial rearing of A. swirskii or other

phytoseiids.

In the mass production of generalist phytoseiids, astigmatid mites are being used as a

primary food source (Zhang, 2003; Bolckmans and van Houten, 2006; Fidgett and Stinson,

2008; Midthassel et al., 2013). Amblyseius swirskii can be mass reared on the astigmatid mites

Suidasia medanensis (Oudemans) (Acari: Suidasidae) (Midthassel et al., 2013), Carpoglyphus

lactis L. (Acari: Carpoglyphidae) (Bolckmans and van Houten, 2006) and Thyreophagus

entomophagus (Laboulbene) (Acari: Acaridae) (Fidgett and Stinson, 2008). In Chapter 3, we

found that A. swirskii reared on C. lactis developed faster than on T. latifolia pollen whereas

the reproduction of the females fed on either food sources was not different (Table 8.1).

Midthassel et al. (2013) reported that the intrinsic rate of increase of A. swirskii fed on S.

medanensis was similar to or higher than on several of its natural arthropod prey. These

findings confirm the potential of these storage mites as a basic food for the mass production

of A. swirskii. Furthermore, the use of astigmatid mites can increase the economic efficacy of

commercial production systems as it allows the predator to be reared at high densities

(Ramakers et al., 1989; Mégevand et al., 1993). On the negative side, however, the use of

astigmatid prey mites may lead to health problems for workers in mass production facilities

caused by allergens originating from these mites (Fernandez-Caldas et al., 2007).

Chapter 8

114

Table 8.1 Intrinsic rate of increase (rm; means ± SE) of Amblyseius swirskii fed on different

artificial and factitious foods tested in the present study

Chapter Treatment Food tested Intrinsic rate

of increase

3 T. latifolia Typha latifolia L. pollen 0.158 ± 0.002

3 C. lactis Carpoglyphus lactis L. mix stages 0.175 ± 0.002

3 AD1 Liquid basic diet 0.104 ± 0.013

3 AD2 Liquid basic diet + 20% of A. pernyi pupal

hemolymph

0.181 ± 0.002

4 AD5 Liquid basic diet + 5% of H. illucens prepupal

hemolymph

0.182 ± 0.002


hemolymph

0.189 ± 0.002


hemolymph

0.210 ± 0.002

5 E. kuehniella/G1 Ephestia kuehniella eggs 0.169 ± 0.001

5 E. kuehniella/G6 Ephestia kuehniella eggs 0.151 ± 0.004

5 A. franciscana/G1 Decapsulated Artemia franciscana cysts 0.176 ± 0.002

5 A. franciscana/G6 Decapsulated Artemia franciscana cysts 0.182 ± 0.001

5 AD1/G1 Liquid basic diet + 20% of A. pernyi pupal hemolymph 0.174 ± 0.002

5 AD2/G1 Liquid basic diet + 20% of E. kuehniella eggs 0.160 ± 0.004

5 AD2/G6 Liquid basic diet + 20% of E. kuehniella eggs 0.073 ± 0.007

5 AD3/G1 Liquid basic diet + 20% of A. franciscana cysts 0.186 ± 0.001

5 AD3/G6 Liquid basic diet + 20% of A. franciscana cysts 0.144 ± 0.002

6 T. latifolia Typha latifolia L. pollen 0.210 ± 0.001

6 ArF Freeze-dried basic diet + 20% of A. franciscana cysts 0.184 ± 0.002

6 AnF Freeze-dried basic diet + 20% of A. pernyi pupal

hemolymph 0.195 ± 0.001

6 ArP Basic powdered diet + 20% of powdered A.

franciscana cysts 0.159 ± 0.001

6 AnP Freeze-dried basic diet + 20% of lyophilized A.

pernyi pupal hemolymph 0.158 ± 0.002

G1, G2: The first and sixth generation of rearing


115

The present study indicated that eggs of Ephestia kuehniella Zeller (Lepidoptera:

Pyralidae), a factitious food used in the mass production of various insect predators and egg

parasitoids, are also a suitable food source for A. swirskii (Chapter 5). This is consistent with

previous results of Romeih et al. (2004), who noted that A. swirskii showed a better response

to flour moth eggs than Neoseiulus californicus (McGregor), Euseius scutalis (Athias-Henriot)

(Acari: Phytoseiidae), and Agistemus exsertus Gonzalez (Acari: Stigmaeidae). The eggs also

proved to be an adequate food source for many other phytoseiid predators including

Amblydromalus limonicus Garman & McGregor (Vangansbeke et al., 2014), Iphiseius

degenerans (Berlese) (Vantornhout et al., 2004), Neoseiulus barkeri (Hughes) and Amblyseius

zaheri Yousef & El-Borolossy (Momen and El-Laithy, 2007), Euseius scutalis (Athias-

Henriot) and Agistemus exsertus Gonz. (Romeih et al., 2004)(Acari: Phytoseiidae). In most of

these studies the E. kuehniella eggs even surpassed the predators’ natural prey in terms of

developmental rate or survival. The good success obtained in several predatory mites with

these lepidopteran eggs could be related to their well-balanced nutritional composition and

easy handling by the mites. The disadvantage of E. kuehniella eggs is that they are very

expensive (with current market prices around 400-500 EUR/kg), mainly due to necessary

investments in climatisation of production facilities and health care of workers (De Clercq et

al., 2014). Furthermore, market prices for these lepidopteran eggs remain high because of a

continuously high demand for these eggs for the mass rearing of other natural enemies like

mirids, anthocorids, chrysopids, coccinellids, and trichogrammatid egg parasitoids in

commercial and research insectaries worldwide.

The value of another factitious food source, dry decapsulated Artemia franciscana

Kellogg (Anostraca: Artemiidae) cysts, was investigated in Chapter 5. The price of non-

decapsulated cysts may vary in the range 50-200 EUR/kg, depending on quality criteria such

as hatching rate, nutritional value, cyst diameter, and further according to annual fluctuations

of offer and demand. Also decapsulated cysts are offered on the market; for this purpose,

generally lower quality non-decapsulated cysts used, which have limited hatchability and thus

a lower market value for use in aquaculture (G. Van Stappen, ARC, Ghent University,

personal communication). Our experiments indicated that the high quality cysts we obtained

from the ARC of Ghent University were a highly suitable diet for the production of A. swirskii.

The mites fed on this diet developed faster than on E. kuehniella eggs and it was the only of

five tested diets not resulting in a decrease of growth rates of A. swirskii after 6 generations of

continuous rearing. Likewise, Vantornhout et al. (2004) and Vangansbeke et al. (2014) found

that dry decapsulated Artemia cysts were an acceptable food source for two other phytoseiids,

Chapter 8

116

I. degenerans and A. limonicus. In contrast, however, Hoogerbrugge et al. (2008) found only a

slightly higher population growth of A. swirskii when decapsulated Artemia sp. cysts were

supplemented in a chrysanthemum crop compared to a control treatment with no food

supplementation. The poor results with brine shrimp cysts in the latter study may be due to

lower nutritional quality of the Artemia batch used, or to an inappropriate level of hydration

or an incomplete decapsulation of the Artemia cysts. Decapsulation of brine shrimp cysts is

done by exposing the encapsulated cysts to a hypochlorite solution (Van Stappen, 1996).

Vandekerkhove et al. (2009) noted that a longer decapsulation time of A. franciscana cysts

had a positive influence on the development of the predatory bug Macrolophus pygmaeus

Rambur (Hemiptera: Miridae). Besides complete removal of the cyst shell, longer

decapsulation times may also cause damage to the hatching membrane, and as such make the

embryo more easily available for feeding predators. Given the short chelicerae of phytoseiid

mites, the decapsulation process is probably of primary importance. Vantornhout et al. (2004)

found that I. degenerans fed on encapsulated Artemia cysts failed to develop beyond the

protonymphal stage. The lack of development may be explained by the fact that I. degenerans

was not able to pierce the alveolar layer of the Artemia cysts. Further, it deserves pointing out

that hypochlorite residues from the decapsulation process may interfere with the acceptability

of decapsulated cysts for arthropod predators. The level of hydration of the cysts has also

been found to affect the immature survival and development of the predators. Vandekerkhove

et al. (2009) indicated that hydration of Artemia cysts had a significant impact on nymphal

survival of M. pygmaeus when cysts were non-decapsulated or poorly decapsulated. Arijs and

De Clercq (2001) showed that Orius laevigatus (Fieber) (Heteroptera: Anthocoridae) cannot

efficiently use dry cysts (i.e., containing less than 10% water) as food; the bugs can only

successfully develop on fully hydrated cysts. In our study, the humidity levels in the Munger

cells exceeded 80 % allowing the dry cysts to absorb some moisture; this may have facilitated

efficient extraction of the nutrients by the mites. This may have relevance not only for the use

of decapsulated Artemia cysts in a mass rearing environment, but also when used as

supplemental foods to sustain populations of predatory mites (or insects, like Macrolophus

bugs) in a greenhouse crop. The relative humidity inside greenhouses is often lower than that

observed in our Munger cells and usually fluctuates (low during the daytime and high during

nighttime). As a result, when the cysts are applied in a greenhouse crop they may experience

cycles of alternating hydration and dehydration, which may affect the feeding efficacy of

predatory mites mites on the cysts. More research is needed to optimize presentation (e.g.


117

level of decapsulation or hydration) of Artemia cysts when used in large-scale mite cultures or

as a supplemental food source for supporting their populations in the crop after release.

The availability of an effective artificial diet may allow rapid build-up of arthropod

parasitoids or predators populations, shorten the production line and consequently represent a

step towards a more cost-effective mass rearing (Riddick, 2009). Several artificial diets for

phytoseiid mites have been described by McMurtry and Scriven (1966), Shehata and

Weismann (1972), Kennett and Hamai (1980), Abou-Awad et al. (1992), and Ogawa and

Osakabe (2008). These studies suggest that, although phytoseiid mites can develop on

different artificial diets, fecundity in most cases was inferior to that on natural or factitious

prey. In Chapter 3, we noted that a slightly modified version of the artificial diet developed

by Ogawa and Osakabe (2008) was suitable to support development of A. swirskii and also

allowed some reproduction. The oviposition rate of A. swirskii on this artificial diet was

higher than that on an artificial diet designed by Abou-Awad et al. (1992). However, this diet

still has limitations in terms of fecundity, with 60% of the females failing to lay eggs and

dying shortly after molting to the adult stage. To enhance acceptability and improve

nutritional quality of artificial diets for entomophagous insects, the inclusion of arthropod

components such as hemolymph proved to be an important element (Nettles, 1990; Grenier

and De Clercq, 2003). The inclusion of insect components in artificial diets may be useful

when predators require certain nutrients, growth factors or phagostimulants found in their

natural prey (De Clercq, 2008). Our study in Chapter 3 showed that the pupal hemolymph of

the Chinese oak silkworm Antheraea pernyi Guérin-Méneville (Lepidoptera: Saturniidae)

played a positive role both in fecundity and survival of the predator. The oviposition rate and

intrinsic rate of increase of A. swirskii fed on basic diet enriched with 20% pupal hemolymph

of A. pernyi were significantly increased in comparison with the basic meridic diet. The

growth rate of A. swirskii reared on artificial diet enriched with the pupal hemolymph was

even higher than the values reported for A. swirskii when fed on natural prey like the two

spotted spider mite, western flower thrips, onion thrips, and eriophyoid fig mites (El-Laithy

and Fouly, 1992; Abou-Awad et al., 1999; Wimmer et al., 2008). Our study also showed that

the artificial diet with pupal hemolymph of A. pernyi supported development and reproduction

of A. swirskii to the same extent as the factitious prey mite C. lactis, which is routinely used in

the mass rearing of the phytoseiid, indicating the potential of an artificial diet to rationalize

the mass production of A. swirskii.

Lü et al. (2013) pointed out that the production of the oak silkworm in China has

diminished in recent years. Pupal hemolymph of this silkworm is therefore becoming less

Chapter 8

118

easily available and more costly, making its use as a dietary supplement for arthropod

parasitoids (e.g. Trichogramma spp.) and predators less attractive. In contrast, eggs of E.

kuehniella and cysts of A. franciscana are widely available. In Chapter 5, growth rates of A.

swirskii on artificial diets enriched with finely ground E. kuehniella eggs or A. franciscana

cysts were similar to or higher than those on the diet supplemented with pupal hemolymph of

A. pernyi. Our findings suggest that certain components of E. kuehniella eggs and A.

franciscana cysts can play a critical role in stimulating development and reproduction of A.

swirskii. Further research is needed to elucidate which factors are responsible for this positive

effect. Dependence on lepidopteran eggs or high quality brine shrimps cysts may, however,

complicate a reliable and cost effective artificial production of the phytoseiid. To further

reduce the cost of the artificial diet, different easily available and cheap arthropod

components were screened in the course of our study. In a preliminary experiment, we found

that the basic artificial diet supplemented with prepupal hemolymph of the black soldier fly

Hermetia illucens (L.) (Diptera: Stratiomyidae) or extract of larvae of the yellow mealworm

Tenebrio molitor L. (Coleoptera: Tenebrionidae) resulted in successful development and

reproduction of A. swirskii. However, the black soldier fly has a shorter development cycle,

higher oviposition rate and better potential of biomass increase per day as compared to the

yellow mealworm. Additionally, the fly can be cost effectively produced at a large scale on

organic waste materials. The results in Chapter 4 indicate that supplementing artificial diet

with black soldier fly hemolymph significantly improved its value for supporting

development and reproduction of A. swirskii. Even at the lowest concentration of hemolymph

added (5%), juvenile survival improved, the production of viable eggs was stimulated and as a

consequence the intrinsic rate of increase substantially increased. The intrinsic rate of increase

of A. swirskii fed on the basic artificial diet enriched with black soldier fly prepupal

hemolymph was equally high as that of females reared on the basic diet supplemented with

pupal hemolymph of A. pernyi. These results demonstrate the potential of H. illucens as a

cheap nutrient source for the rearing of A. swirskii and perhaps other beneficial arthropods.

After several consecutive generations of A. swirskii reared on the artificial diets,

nutrient imbalances became apparent to a more or less extent. In the sixth generation, the

immature survival of the predators reared on artificial diets enriched with E. kuehniella eggs

or A. franciscana cysts was significantly lower than that on the corresponding diet in the first

generation (Chapter 5). However, artificial diet supplemented with A. franciscana cysts

proved superior to the other artificial diets as it allowed to sustain A. swirskii for over 15

consecutive generations despite the lower immature survival rates, whereas the colonies kept


119

on a diet enriched with A. pernyi hemolymph or E. kuehniella egg extract could not be

maintained beyond 3 and 9 generations, respectively. In addition, A. swirskii females did not

lose their capacity to capture and kill live prey after six consecutive generations of rearing on

the tested artificial diets. Although the diet supplemented with A. franciscana cysts showed to

be the most promising diet for the production of A. swirskii, loss of quality in terms of

reduced survival after several generations of continuous rearing remains a concern. In this

context, we found that a switching to T. latifolia pollen after 6 generations of rearing on the

artificial diet could significantly increase the immature survival of the predator to more than

90%. This indicates the importance of providing different types of food (of both plant and

animal origin) to maintain the colony health of these omnivorous predators.

In Chapter 7, the diet supplemented with A. franciscana cysts was found to allow full

development and reproduction of four other phytoseiid mites species. These findings suggest

that the same diet may also be useful to support populations of other commercially available

phytoseiids, either in the laboratory or in the field. This may be of particular significance

when using the artificial diet as a supplemental food in the crop. Finding inexpensive

alternative food sources is one of the major opportunities for enhancing biological control in

protected crops (Messelink et al., 2014). Our results are indeed promising given that only few

existing supplemental foods have been reported to support beneficial Acarina (Wade et al.,

2008), and commercially available supplemental foods like Typha angustifolia L. pollen

(NutrimiteTM

, Biobest N.V.), eggs of E. kuehniella and decapsulated cysts of A. franciscana

are relatively costly.

A further objective of this study was to find the most adequate formulation of artificial

diets for easy and effective application in a laboratory culture and as a food supplement for

predatory mites in the crop. The artificial diets used in Chapters 3-5 were all liquid diets.

Solid artificial diets have a number of advantages over liquid diets including non-stickiness,

limiting microbial contamination, easy long term storage and the possibility of direct

presentation without the need for encapsulation (Morales-Ramos et al., 2014). More in

particular, solid artificial diets are easier to distribute in the crop by existing blowers designed

to distribute pollen or eggs of E. kuehniella. Solid artificial diets can also be supplied in other

ways used for pollen, like in plastic cups placed between the crop plants (Nomikou et al.,

2010) or by coating twine attached to the plants thus providing the predatory mites at the

same time with shelter and alternative food (Adar et al., 2014). The liquid artificial diets

developed in our study were solidified by freeze-drying or by replacing the liquid ingredients

of the original diet by powdered solid ingredients. In Chapter 6, we found that the fecundity

Chapter 8

120

of females fed on the freeze-dried liquid artificial diets was similar to that on T. latifolia

pollen or liquid versions of the diets and higher than that on the powdered diets. The results

indicated that the freeze-drying process did not influence the nutritional quality of the diets

and that the predator performed on the solid forms as effectively as on the liquid forms.

Freeze-dried diets have a number of practical advantages over liquid diets, related to storage,

shipment and handling. However, the freeze-dried diets used in our study proved to be highly

hygroscopic and quickly reverted to a semi-liquid form; this phenomenon may limit the

practical applicability of such diets as they may be more prone to microbial degradation.

Artificial diets entirely composed of powdered/dry ingredients were somewhat inferior to

lyophilized liquid diets in terms of their nutritional value, but did support the development

and reproduction of the phytoseiid and were physically more stable than the lyophilized diets.

In a pre-establishment experiment with A. swirskii on caged chrysanthemum plants in a

greenhouse, the powdered artificial diet with or without the addition of powdered dry A.

franciscana cysts significantly encouraged population growth of the predatory mite. Predator

densities in the treatment with powdered artificial diet were similar to those of mites supplied

with T. angustifolia pollen. Furthermore, most ingredients of the dry artificial diets tested here

are relatively inexpensive and easily accessible on the market. We estimate that the price of

our powdered artificial diet with or without A. franciscana would be approximately 170 or

100 EUR/kg. Based on economies of scale, prices may further be reduced if these diets are

produced in larger quantities. These findings indicate the potential of dry artificial diets for

use in part of the production cycle of A. swirskii or as supplemental foods to sustain its

populations in the crop after release.

In conclusion, various factitious and artificial diets tested in the present study

supported the development and reproduction of A. swirskii. The phytoseiid performed best on

decapsulated Artemia cysts and a meridic artificial diet enriched with these cysts, indicating

the potential of these foods for use in (parts of) the production cycle of the predator. The

powdered artificial diet supplemented with A. franciscana cysts also has potential for use as a

supplemental food in a conservation biological control strategy to sustain released populations

of the predatory mite in greenhouse crops. Our findings also indicate the potential of using H.

illucens as a cheap source of hemolymph in artificial diets for predatory mites and potentially

other predatory arthropods, as the fly can be cost effectively produced at a large scale on

organic waste materials. However, the effects of long-term rearing of the mites using these

artificial diets on their quality as biological control agents need to be explored. Further, field

research is needed to evaluate the suitability of the artificial diets developed in this study in


121

the crop environment, with regard to their practical value to support populations of A. swirskii

or of other predatory mites, giving attention to possible undesired effects of their application

on populations of arthropod pests (like omnivorous thrips who may also be able to use the

diets) and on the physiology and quality of the crop plants (e.g. fungal contamination).

Chapter 8

122

123

SUMMARY

The predatory mite Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) is an

economically important biological control agent of several key pests in greenhouses, such as

whiteflies, thrips, eriophyid mites and broad mites. In augmentation biological control, large

numbers of predaceous mites are released in the field. Hence, a cost-effective method for their

mass-rearing is an essential prerequisite. Rearing phytoseiid mites on plant materials infested

with natural prey has several disadvantages, such as large space requirements, inconsistent

yields of predators, harvesting difficulties and variable results with different species. Rearing

procedures based on factitious prey like storage mites also involve space and labor to

maintain large parallel cultures of the factitious prey. Further, there may be health risks for

workers in production facilities or in the crop caused by allergens associated with the

factitious mite prey. The availability of adequate artificial or factitious diets could eliminate

many of the above-mentioned problems associated with the mass production of predatory

mites. In addition, these diets may be useful as food supplements to support predator

populations after release in the crop. The overall objective of this study was to develop

alternative food sources for phytoseiid predatory mites (with focus on the economically

important species A. swirskii) in support of their mass production and use as food supplements

to sustain their populations after release in the crop.

In Chapter 3, the development, survival and reproduction of A. swirskii were assessed

when the predator was fed on cattail pollen (Typha latifolia L.), dried fruit mite

(Carpoglyphus lactis L.) (Acari: Carpoglyphidae) or on two artificial diets: a basic artificial

diet composed of honey, sucrose, tryptone, yeast extract, and egg yolk; and the basic diet

enriched with pupal hemolymph of Chinese oak silkworm (Antheraea pernyi (Guérin-

Méneville) (Lepidoptera: Saturniidae)). Mites fed on C. lactis and A. pernyi hemolymph diet

had shorter immature and preoviposition periods than those fed on the other diets. The total

number of deposited eggs was significantly higher for females fed on A. pernyi hemolymph

diet (38.25 eggs/female) than for those maintained on the other diets. The intrinsic rate of

increase (rm) of A. swirskii was highest on A. pernyi hemolymph diet (0.181) and C. lactis

(0.175), followed by T. latifolia pollen (0.158), and basic diet (0.104). The artificial diet

enriched with A. pernyi pupal hemolymph supported development and reproduction of A.

swirskii to the same extent as a factitious prey which is routinely used in the mass rearing of

the phytoseiid. These results indicate the potential of artificial diets for the mass production of

this economically important predatory mite.

Summary

124

For reducing the cost of the artificial diet, the silkworm hemolymph was replaced by

prepupal hemolymph of the black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae),

an easily available and cheap nutrient. In Chapter 4, the survival, development, and

reproduction of the predatory mite A. swirskii were assessed when fed on basic artificial diet

supplemented with 5, 10, or 20% of H. illucens prepupal hemolymph. Developmental time

from larva to adult was shorter for males and females offered artificial diets supplemented

with 20% hemolymph versus the basic diet. The oviposition rate and total fecundity of

females reared on the basic diet were substantially lower than those of females supplied with

the enriched diets. The intrinsic rate of increase was highest on the diet containing 20%

hemolymph, followed by those containing 10 and 5% hemolymph. In a subsequent diet

switching experiment, mites fed on the basic diet in their juvenile stages were switched upon

adulthood to diet enriched with different concentrations of H. illucens hemolymph. The

females that were fed with the enriched diets from the adult stage on had higher oviposition

rates and fecundities than those maintained on the basic diet, but their reproductive

parameters were not significantly affected by the concentration of the hemolymph in the

artificial diet. The results proved that supplementing artificial diets with black soldier fly

hemolymph significantly improved their nutritional value for A. swirskii. Findings of these

experiments indicate the potential of using H. illucens as a cheap source for hemolymph in

artificial diets, as the fly can be cost effectively produced at a large scale on organic waste

materials.

In Chapter 5, A. swirskii was reared on Ephestia kuehniella Zeller eggs (Lepidoptera:

Pyralidae), decapsulated dry cysts of the brine shrimp Artemia franciscana Kellogg

(Anostraca: Artemiidae), and on basic artificial diets supplemented with pupal hemolymph of

the Chinese oak silkworm A. pernyi (AD1), with E. kuehniella eggs (AD2) or with A.

franciscana cysts (AD3). Development, reproduction and predation capacity of the predatory

mites were assessed in the first (G1) and sixth generation (G6) of rearing on the different diets.

Immature survival rates in G1 were similar on all diets (96.8-100%). After 6 generations,

however, survival of A. swirskii was significantly reduced on all diets except on A.

franciscana cysts. Oviposition rates did not differ between generations when females were fed

on E. kuehniella, AD2 or AD3. The total number of deposited eggs was similar among diets

except in G6 where the females fed on A. franciscana cysts produced more eggs than those

maintained on E. kuehniella eggs. On most diets the intrinsic rates of increase in G1 were

superior to those in G6, except for predators supplied with A. franciscana cysts where no

differences were observed among generations. Female mites did not lose their capacity to kill

first instar Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) after six

generations on the different diets, but predation rates in G6 on E. kuehniella were lower than

Summary

125

in G1. In summary, the different factitious and artificial diets tested in this study supported the

development and reproduction of A. swirskii for a single generation but fitness losses occurred

to a varying degree after several generations on E. kuehniella eggs or the artificial diets.

Artificial diet enriched with A. franciscana cysts yielded better results than the other artificial

diets. Amblyseius swirskii performed best on decapsulated Artemia cysts indicating their

potential for use in the mass production of the predator or to sustain its populations in the crop

after release.

Solid artificial diets have a number of advantages over liquid and semiliquid diets,

both in the laboratory rearing and when applied as supplemental foods in the crop. These

include non-stickiness and the possibility of direct presentation without the need for

encapsulation. Lower water content of solid diets limits microbial contamination and allows

easier long term storage. When applied as a supplemental food in the field, solid artificial

diets are easier to distribute in the crop by existing blowers designed to distribute pollen or

eggs of E. kuehniella and are expected to result in lower soiling of the plant surface and thus

to interfere less with plant physiology and crop quality. In Chapter 6, we investigated the

survival, development and reproduction of A. swirskii fed on several dry artificial diets: the

tested diets were freeze-dried forms of previously developed liquid meridic artificial diets

supplemented with a watery extract of decapsulated cysts of A. franciscana or with pupal

hemolymph of Chinese oak silkworm A. pernyi, and newly composed powdered meridic

artificial diets (composed of sucrose, tryptone, yeast extract, glucose, fructose, egg yolk

powder, vitamin mix) supplemented with ground dry A. franciscana cysts or lyophilized

pupal hemolymph of A. pernyi. Performance of the mite on the artificial diets was compared

with that on cattail pollen (T. latifolia). Developmental time of A. swirskii females offered

lyophilized diets was significantly shorter than on powdered diets. Total fecundity was

significantly higher for females fed on the lyophilized diets than for those maintained on the

powdered diet with A. franciscana. Daily oviposition rates were similar on T. latifolia pollen

and both lyophilized diets but lower on both powdered diets. The highest intrinsic rate of

increase was observed when A. swirskii was fed on T. latifolia pollen (0.210

females/female/day), followed by the freeze dried diets enriched with A. pernyi and A.

franciscana (0.195 and 0.184 females/female/day, respectively), and the lowest growth rates

were observed on the powdered diets supplemented with A. franciscana and A. pernyi (0.159

and 0.158 females/female/day, respectively). In a greenhouse experiment, the application of

powdered artificial diets on chrysanthemum plants supported the population growth of A.

swirskii over several weeks. These results proved that the phytoseiid was able to effectively

feed on solid, powdered artificial diets. Freeze-drying of liquid diets did not influence their

value to support the development and reproduction of A. swirskii.

Summary

126

In Chapter 7 the impact of the liquid basic artificial diet supplemented with A.

franciscana watery extract on the biological performance of four species of other phytoseiid

mites which are commercially available in Europe (Neoseiulus californicus (McGregor), N.

cucumeris (Oudemans), Amblyseius andersoni Chant, and Amblydromalus limonicus Garman

& McGregor (Acari: Phytoseiidae)) is investigated. The life table parameters of these

predatory mites fed on A. franciscana artificial diet were compared to that feeding on two-

spotted spider mites Tetranychus urticae Koch (Acarina: Tetranychidae) (N. californicus) or T.

latifolia pollen (N. cucumeris, A. andersoni and A. limonicus). Diet had no influence on the

immature survival rate, ranging from 92 to 98% for all species. Female developmental times

were significantly shorter for predators offered spider mites or pollen than for those fed the

artificial diet, except in A. limonicus. The fecundity of N. californicus, N. cucumeris and A.

limonicus females given spider mites or pollen was significantly higher than that of females

presented with the artificial diet, whereas no differences among diets were observed in A.

andersoni. When N. californicus females were fed on the artificial diet, none of their offspring

succeeded in reaching adulthood. Our findings indicate the potential of this artificial diet for

use in production facilities or in the crop, especially for the more generalist predatory mites A.

andersoni and A. limonicus.

In Chapter 8, a general discussion of the findings is presented and future prospects

are discussed. It is concluded that the different factitious and artificial diets tested in the

present study supported the development and reproduction of A. swirskii. The predatory mite

performed best on decapsulated Artemia cysts and the artificial diet enriched with these cysts,

indicating the potential for use of these foods in (parts of) the production cycle of the predator.

The powdered artificial diet supplemented with A. franciscana cysts also has potential for use

as a supplemental food to sustain released populations of the predatory mite in greenhouse

crops. Our findings also indicate the potential of using H. illucens as a cheap source of

hemolymph in artificial diets for predatory mites and potentially other predatory arthropods.

However, the effects of long-term rearing of the mites on these artificial diets on their quality

as biological control agents need to be explored. Further field research is also needed to

optimize the value of these artificial diets to support the predatory mites in the crop

environment and to assess their effects on the physiology and quality of the crop plants.

127

SAMENVATTING

De roofmijt Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) is een

economisch belangrijke biologische bestrijder van verschillende plagen in kasteelten, zoals

wittevlieg, trips en verschillende soorten plaagmijten. In biologische bestrijding door middel

van vermeerdering worden grote hoeveelheden roofmijten in het veld geïntroduceerd. Een

rendabele methode om deze predators in massa te kweken is bijgevolg een belangrijke

vereiste. Het kweken van deze bladroofmijten op plantenmateriaal geïnfesteerd met hun

natuurlijke prooien heeft verschillende nadelen, zoals de noodzaak voor grote ruimtes voor de

opkweek, variabele opbrengst van de predators, moeilijkheden bij het oogsten en

verschillende resultaten bij de verschillende soorten. Ook kweekmethodes die gebaseerd zijn

op alternatieve prooien, zoals voermijten, brengen veel plaats en arbeid met zich mee. Verder

kunnen gezondheidsrisico’s optreden voor de werknemers in de productie-omgeving en in het

gewas als gevolg van allergenen geassocieerd met de voermijten. De beschikbaarheid van

geschikte kunstmatige voedselbronnen zou veel van de hierboven beschreven beperkingen bij

de massakweek van roofmijten kunnen elimineren. Bovendien kunnen deze diëten nuttig

blijken als voedingssupplementen voor populaties van de roofmijten na introductie in het

gewas. De algemene doelstelling van deze studie omvatte het ontwikkelen van alternatieve

voedselbronnen voor roofmijten van de familie Phytoseiidae (met de focus op de economisch

belangrijke soort, A. swirskii) ter ondersteuning van hun massakweek en voor gebruik als

voedingssupplementen na introductie in het gewas.

In Hoofdstuk 3 werd de ontwikkeling, overleving en reproductie van A. swirskii

nagegaan wanneer de predator werd gevoed met stuifmeel van de grote lisdodde (Typha

latifolia L.), voermijten (Carpoglyphus lactis L.) (Acari: Carpoglyphidae) of twee artificiële

diëten: een basisdieet samengesteld uit honing, sucrose, trypton, gist extract en eigeel; en het

basisdieet verrijkt met hemolymfe van poppen van de Chinese eikenzijderups (Antheraea

pernyi (Guérin-Méneville) (Lepidoptera: Saturniidae)). Roofmijten gevoed met C. lactis en

het dieet verrijkt met A. pernyi hemolymfe vertoonden een kortere ontwikkelingsduur en

preovipositieperiode dan deze gevoed op de andere diëten. Het totaal aantal afgelegde eitjes

was significant hoger voor wijfjes gevoed met het dieet verrijkt met hemolymfe van A. pernyi

(38,25 eitjes/wijfje) dan deze gevoed op de andere diëten. De intrinsieke groeisnelheid (rm)

Samenvatting

128

van A. swirskii was hoogst op het dieet verrijkt met A. pernyi hemolymfe (0,181

wijfjes/wijfje/dag) en C. lactis (0,175), gevolgd door stuifmeel van T. latifolia (0,158), en het

basisdieet (0,104). Het artificieel dieet verrijkt met hemolymfe van A. pernyi poppen

ondersteunde de ontwikkeling en reproductie van A. swirskii in dezelfde mate als de

voermijten die routinematig gebruikt wordt bij de massakweek van deze roofmijt.

Om de kost van het artificieel dieet te verminderen, werd de hemolymfe van de

zijderups vervangen door hemolymfe van prepoppen van de zwarte wapenvlieg, Hermetia

illucens (L.) (Diptera: Stratiomyidae), wat een makkelijk beschikbaar en goedkoop nutriënt is.

In Hoofdstuk 4, werd de overleving, ontwikkeling en reproductie van de roofmijt A. swirskii

nagegaan wanneer deze gevoed werd op het basisdieet verrijkt met 5, 10 of 20% hemolymfe

van prepoppen van H. illucens. De ontwikkelingsduur van larf tot adult was korter voor

mannetjes en wijfjes die artificiële diëten aangeboden kregen verrijkt met 20% hemolymfe

vergeleken met het basisdieet. De ovipositiegraad en totale fecunditeit van wijfjes gekweekt

op het basisdieet waren aanzienlijk lager dan bij deze gekweekt op de verrijkte diëten. De

intrinsieke groeisnelheid was hoogst op het dieet bestaande uit 20% hemolymfe, gevolgd door

de diëten met 10 en 5% hemolymfe. In een daaropvolgende proef werden mijten tijdens hun

onvolwassen stadia gevoed op het basisdieet, om vervolgens, na het bereiken van het adulte

stadium, het voedingsregime te wisselen naar diëten met verschillende concentraties van H.

illucens hemolymfe. Wijfjes die vanaf het adulte stadium gevoed werden op de verrijkte

diëten hadden een hogere dagelijkse en totale ei-afleg dan deze die doorgekweekt werden op

het basisdieet. Hun reproductieve parameters werden echter niet beduidend beïnvloed door de

concentratie aan hemolymfe in het artificieel dieet. De resultaten toonden aan dat het

verrijken van artificiële diëten met hemolymfe van de zwarte wapenvlieg de nutritionele

waarde voor A. swirskii significant verhoogde. De bevindingen van deze experimenten tonen

het potentieel aan van H. illucens als een goedkope bron van haemolymfe in artificiële diëten,

daar deze vlieg goedkoop en op grote schaal op organische afvalstromen kan geproduceerd

worden.

In Hoofdstuk 5 werd A. swirskii gekweekt op Ephestia kuehniella Zeller eitjes

(Lepidoptera: Pyralidae), droge gedecapsuleerde cysten van het pekelkreeftje Artemia

franciscana Kellogg (Anostraca: Artemiidae), en op een artificieel basisdieet verrijkt met

ofwel hemolymfe van poppen van de Chinese eikenzijderups A. pernyi (AD1), E. kuehniella

eggs (AD2), of A. franciscana cysten (AD3). De ontwikkeling, reproductie en

predatiecapaciteit van de roofmijten werd nagegaan in de eerste (G1) en de zesde (G6)

generatie opgekweekt op de diëten. De overlevingspercentages van de juveniele stadia in G1

Samenvatting

129

waren gelijkaardig voor alle diëten (96,8-100%). Echter, na 6 generaties verlaagde de

overleving significant op alle diëten behalve op A. franciscana cysten. De ovipositiegraden

verschilden niet tussen de generaties wanneer de wijfjes gevoed werden op E. kuehniella,

AD2 of AD3. Het totaal aantal afgelegde eitjes was gelijk voor alle diëten, behalve in G6

waar wijfjes die gevoed werden op A. franciscana cysten meer eitjes produceerden dan deze

gekweekt op E. kuehniella eitjes. Bij de meeste diëten was de intrinsieke groeisnelheid in G1

hoger dan deze in G6, behalve voor predators die A. franciscana cysten kregen aangeboden

waar geen verschillen tussen de generaties werden waargenomen. Wijfjes van de roofmijt

verloren hun capaciteit niet om eerstestadiumlarven van Frankliniella occidentalis (Pergande)

(Thysanoptera: Thripidae) te prederen na 6 generaties op de verschillende diëten, maar het

predatievermogen van de G6-roofmijten gevoed op E. kuehniella was lager dan in G1. De

verschillende alternatieve voedselbronnen en artificiële diëten in getest deze studie

ondersteunden de ontwikkeling en reproductie van A. swirskii gedurende de eerste generatie,

maar na enkele generaties werd een verlies aan fitness vastgesteld voor mijten gevoed op E.

kuehniella eitjes en de artificiële diëten. Het artificieel dieet verrijkt met A. franciscana cysten

leverde betere resultaten op dan de andere diëten. Amblyseius swirskii presteerde het best op

gedecapsuleerde Artemia cysten, wat hun potentieel aantoont voor gebruik in de

massaproductie van de predator of om populaties in het veld te ondersteunen.

Vaste diëten hebben verschillende voordelen in vergelijking met vloeibare en

halfvloeibare diëten, zowel in laboratoriumkweken of wanneer gebruikt als ondersteunende

voedingssupplementen in het gewas, zoals hun lagere kleverigheid en de mogelijkheid om ze

aan te bieden zonder de noodzaak ze eerst te encapsuleren. De lagere waterinhoud van vaste

diëten beperkt microbiële contaminatie en verhoogt de bewaartijd. Wanneer diëten als

voedingssupplement in het veld worden toegediend, zijn vaste diëten makkelijker om te

verspreiden in het gewas door gebruik te maken van blazers die ontwikkeld zijn voor

stuifmeel of E. kuehniella eitjes; bovendien zouden ze de planten minder moeten vervuilen en

op deze manier minder met de plantfysiologie en gewaskwaliteit interfereren. In Hoofdstuk 6

werd de overleving, ontwikkeling en reproductie van A. swirskii onderzocht wanneer deze

gevoed werd op verschillende droge artificiële diëten: de geteste diëten waren ofwel

gevriesdroogde formuleringen van de voorheen ontwikkelde vloeibare artificiële diëten

verrijkt met extracten van gedecapsuleerde cysten van A. franciscana of met hemolymfe van

de Chinese eikenzijderups A. pernyi, ofwel nieuw samengestelde artificiële poederdiëten

(bestaande uit sucrose, trypton, gistextract, glucose, fructose, eigeelpoeder en een

vitaminemix) verrijkt met vermaalde droge A. franciscana cysten of gelyofiliseerde

Samenvatting

130

hemolymfe van A. pernyi poppen. De prestaties van de roofmijt werden vergeleken met deze

op een dieet bestaande uit stuifmeel van de grote lisdodde (T. latifolia). De ontwikkelingsduur

van A. swirskii wijfjes die gelyofiliseerde diëten kregen aangeboden was significant korter

dan van de roofmijten gevoed op poederdiëten. De totale ei-afleg was beduidend hoger voor

wijfjes gevoed met de gelyofiliseerde diëten dan voor deze gekweekt op het poederdieet

verrijkt met A. franciscana. De dagelijkse ei-afleg was gelijkaardig op T. latifolia stuifmeel en

beide gelyofiliseerde diëten, maar was lager voor beide poederdiëten. De hoogste intrinsieke

groeisnelheid werd waargenomen wanneer A. swirskii gevoed werd op T. latifolia stuifmeel

(0,210 wijfjes/wijfje/dag), gevolgd door de gevriesdroogde diëten verrijkt met A. pernyi en A.

franciscana (0,195 en 0,184 wijfjes/wijfje/dag, respectievelijk). De laagste groeisnelheid werd

geobserveerd bij de poederdiëten verrijkt met A. franciscana en A. pernyi (0,159 en 0,158

wijfjes/wijfje/dag, respectievelijk). In een serreproef werd aangetoond dat de toediening van

de poederdiëten op chrysanten de populatiegroei van A. swirskii ondersteunde gedurende

verschillende weken. Het vriesdrogen van vloeibare diëten had geen invloed op hun

ondersteunende waarde voor de ontwikkeling en reproductie van A. swirskii.

In Hoofdstuk 7 werd de impact getest van het vloeibare basisdieet verrijkt met een

waterig extract van A. franciscana op de biologische prestaties van 4 soorten roofmijten van

de familie Phytoseiidae die commercieel beschikbaar zijn in Europa (Neoseiulus californicus

(McGregor), N. cucumeris (Oudemans), Amblyseius andersoni Chant, en Amblydromalus

limonicus Garman & McGregor (Acari: Phytoseiidae)). De levenstabelparameters van deze

roofmijten gevoed op het met A. franciscana verrijkte basisdieet werden vergeleken met deze

van roofmijten gevoed met de bonenspintmijt Tetranychus urticae Koch (Acarina:

Tetranychidae) (voor N. californicus) of T. latifolia pollen (voor N. cucumeris, A. andersoni

en A. limonicus). Het dieet had geen invloed op de overleving van de juveniele stadia, die

varieerde tussen 92 en 98% voor alle soorten. De ontwikkelingsduur van de wijfjes was

significant korter voor predators die spintmijten of pollen kregen aangeboden vergeleken met

deze gevoed op het artificieel dieet, behalve voor A. limonicus. De fecunditeit van wijfjes van

N. californicus, N. cucumeris en A. limonicus voorzien met spintmijten of pollen was

significant hoger dan deze van wijfjes die gevoed werden op het artificieel dieet; er werd

echter geen verschil tussen de diëten waargenomen voor A. andersoni. Wanneer N.

californicus wijfjes gevoed werden op het artificieel dieet, waren de nakomelingen niet in

staat het volwassen stadium te bereiken. Onze resultaten tonen het potentieel aan van dit

artificieel dieet voor verschillende Phytoseiidae roofmijten wanneer gebruikt in de

Samenvatting

131

massakweek of in het gewas, in het bijzonder voor de meer polyfage roofmijten A. andersoni

en A. limonicus.

In Hoofdstuk 8 wordt een algemene discussie van de resultaten gepresenteerd en toekomstige

perspectieven worden aangegeven. Als algemene conclusie kan worden gesteld dat de

verschillende alternatieve prooien en artificiële diëten getest in deze studie de ontwikkeling en

de reproductie van A. swirskii ondersteunden. De roofmijt presteerde het best op

gedecapsuleerde Artemia cysten en het artificieel dieet verrijkt met deze cysten, wat het

potentieel van deze voedingsbronnen aantoont in (delen van) de productiecyclus van de

predator. De poedervorm van het artificieel dieet verrijkt met A. franciscana cysten heeft ook

potentieel om gebruikt te worden als voedingssupplement om geïntroduceerde populaties van

deze roofmijt te ondersteunen in kasteelten. Onze bevindingen tonen ook de bruikbaarheid

aanvan H. illucens als een goedkope bron van hemolymfe in artificiële diëten voor roofmijten

en mogelijk ook andere predators. De effecten van het langdurig kweken van roofmijten op

deze artificiële diëten op hun kwaliteit als biologische bestrijders dient verder onderzocht te

worden. Verder praktisch onderzoek is ook aangewezen om de waarde van deze artificiële

diëten als ondersteunende voedingsbron in het gewas in te schatten en om hun effecten op de

fysiologie en kwaliteit van de gewasplanten na te gaan.

Samenvatting

132

133

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155

CURRICULUM VITAE

Personalia

Name: Nguyen Duc Tung

Date of birth: 8th

March 1979

Place of birth: Hanoi

Nationality: Vietnamese

E-mail: [email protected]

Education

2011-2014: PhD student at the Laboratory of Agrozoology, Department of Crop Protection,

Faculty of Bioscience Engineering, Ghent University, Belgium

Thesis: Artificial and factitious foods for the production and population

enhancement of phytoseiid predatory mites

Promoter: Prof. dr. ir. P. De Clercq

2007-2009: M.Sc. in Entomology

Crop Protection Cluster, College of Agriculture, University of the Philippines Los

Baños, Philippines

Thesis: Efficacy of the predatory mite Neoseiulus longispinosus (Evans) (Acari:

Phytoseiidae) to control the two-spotted spider mite Tetranychus urticae Koch

(Acari: Tetranychidae) in green bean and acceptability of the technology to

farmers in Hanoi, Vietnam.

Promoter: Dr. Celia DR. Medina

Curriculum vitae

156

1999-2003: B.Sc. in Plant Protection

College of Natural Resources and Environment, South China Agricultural

University, China

Thesis: Study on parasitic and reproductive characteristics of Chrysonotomyia

formosa (Westwood) (Hymenoptera: Eulophidae) parasitoid of vegetable leaf-

miner Liriomyza sativae Blanchard (Diptera: Agromyzidae).

Promoter: Prof. Dr. Xu Zai Fu

Professional career

2004-present: Lecturer at the Entomology Department, Faculty of Agronomy, Vietnam

National University of Agriculture, Hanoi, Vietnam.

Publications

Duc Tung Nguyen, Dominiek Vangansbeke, Xin Lu & Patrick De Clercq. 2013.

Development and reproduction of the predatory mite Amblyseius swirskii on artificial

diets. BioControl 58: 369-377.

Dominiek Vangansbeke, Lien De Schrijver, Thomas Spranghers, Joachim Audenaert, Ruth

Verhoeven, Duc Tung Nguyen, Bruno Gobin, Luc Tirry & Patrick De Clercq. 2013.

Alternating temperatures affect life table parameters of Phytoseiulus persimilis,

Neoseiulus californicus (Acari: Phytoseiidae) and their prey Tetranychus urticae (Acari:

Tetranychidae). Experimental and Applied Acarology 61: 285-298.

Dominiek Vangansbeke, Duc Tung Nguyen, Joachim Audenaert, Ruth Verhoeven, Bruno

Gobin, Luc Tirry & Patrick De Clercq. 2014. Performance of the predatory mite

Amblydromalus limonicus on factitious foods. BioControl 59: 67-77.

Duc Tung Nguyen, Dominiek Vangansbeke & Patrick De Clercq. 2014. Artificial and

factitious foods support the development and reproduction of the predatory mite

Amblyseius swirskii. Experimental and Applied Acarology 62: 181-194.

Curriculum vitae

157

Dominiek Vangansbeke, Duc Tung Nguyen, Joachim Audenaert, Ruth Verhoeven, Koen

Deforce, Bruno Gobin, Luc Tirry & Patrick De Clercq. 2014. Diet-dependent cannibalism

in the omnivorous phytoseiid mite Amblydromalus limonicus. Biological Control 74: 30-

35.

Dominiek Vangansbeke, Duc Tung Nguyen, Joachim Audenaert, Ruth Verhoeven, Bruno

Gobin, Luc Tirry & Patrick De Clercq. 2014. Food supplementation affects interactions

between a phytoseiid predator and its omnivorous prey. Biological Control 76: 95-100.

Duc Tung Nguyen, Dominiek Vangansbeke & Patrick De Clercq. 2014. Solid artificial diets

for the phytoseiid predator Amblyseius swirskii. BioControl, 59: 719-727.

Duc Tung Nguyen, Dominiek Vangansbeke & Patrick De Clercq. 2015. Performance of four

species of phytoseiid mites on artificial and natural diets. Biological Control, 80: 56-62.

Duc Tung Nguyen, Vincent Bouguet, Thomas Spranghers, Dominiek Vangansbeke & Patrick

De Clercq. 2014. Beneficial effect of supplementing an artificial diet for Amblyseius

swirskii with Hermetia illucens hemolymph. Journal of Applied Entomology, DOI:

10.1111/jen.12188.

Duc Tung Nguyen, Dominiek Vangansbeke and Patrick De Clercq. 2014. Artificial diets

support the development and reproduction of the predatory mite Amblyseius swirskii.

IOBC-WPRS Bulletin 102: 215-218.

Oral presentations

Duc Tung Nguyen, Dominiek Vangansbeke & Patrick De Clercq. 2013. Performance of

Amblyseius swirskii Athias-Henriot and Amblydromalus limonicus Garman

(Mesostigmata: Phytoseiidae) on factitious foods and pollen. 4th

International Symposium

on Biological Control of Arthropods, March 4-8, 2013, Pucon, Chile.

Duc Tung Nguyen, Dominiek Vangansbeke & Patrick De Clercq. 2013. Artificial diets for

rearing the predatory mite Amblyseius swirskii (Acari: Phytoseiidae). 65th

International

Symposium on Crop Protection, May 21, 2013, Ghent, Belgium.

Duc Tung Nguyen, Dominiek Vangansbeke & Patrick De Clercq. 2014. Liquid and solid

artificial diets support the development and reproduction of the predatory mite

Curriculum vitae

158

Amblyseius swirskii. 14th

International Congress of Acarology, July 14-18, 2014, Kyoto,

Japan.

Duc Tung Nguyen, Dominiek Vangansbeke & Patrick De Clercq. 2014. Artificial diets

support the development and reproduction of the predatory mite Amblyseius swirskii.

IOBC Working Group on "Integrated Control in Protected Crops: Temperate Climate",

September 14-18, 2014, Gent, Belgium.

Poster presentations

Duc Tung Nguyen, Dominiek Vangansbeke & Patrick De Clercq. 2013. Artificial and

factitious foods support the development and Reproduction of the predatory mite

Amblyseius swirskii. 4th

Meeting of the IOBC Working Group: “Integrated control of

plant-feeding mites”. September 9-12, 2013, Paphos, Cyprus.

Duc Tung Nguyen, Dominiek Vangansbeke & Patrick De Clercq. 2013. Development and

reproduction of the predatory mite Amblyseius swirskii (Athias-Henriot) (Acari:

Phytoseiidae) on artificial diets. 13th

Workshop of the IOBC Global Working Group on

Mass Rearing and Quality Assurance: “Emerging Opportunities for the Mass Production

& Quality Assurance of Invertebrates”. November 6-8, 2013, Bangalore, India.

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