efficiency of the predator anthocoris nemorum (het.: anthocoridae) against the greenhouse whitefly,...

26 Odette Rohfritsch

References

BECK, S. D., 1965: Resistance of plants to insects. Ann. Rev. Entomol. 10, 207-232. EIDMANN, H. H.; ERIKSSON, M., 1978: Unterschiede im Befall der Fichtengallenlaus Sacchiphantes

abietis L. an Fichten-Kreuzungen. Anz. Schadlingskde., Pflanzenschutz, Umweltschutz 51, 177-183.

GAUMONT, R., 1957: Etudes sur la biologie de quelques Chermesidae. These Sc. Nat. Paris. MEYER, J., 1957: Cecidogenese comparee de quelques galles d’Arthropodes et evolution cytologi-

MILES, P. W., 1969: Interaction of plant phenols and salivary phenolases in the relationship

PLUMB, G. H., 1953: The formation and development of the Norway Spruce Gall caused by

REILHES, R., 1946: Coloration durable par I’iode des celluloses simplement deshydratees, du

ROHFRITSCH, O., 1971: DPveloppement cecidien et rBle du parasite dans quelques galles d’Arth-

- 1976: Traces de succion de deux Chermesidae: Chermes abietis L., Chermes strobilobius Kalt,

- 1977: Ultrastructure of the nutritive tissue of the Chermes abietis L. fundatrix on Picea excelsa

THALENHORST, W., 1972: Zur Frage der Resistenz der Fichte gegen die Gallenlaus Sacchiphantes

TJIA, B.; HOUSTON, D. B., 1975: Phenolic constituents of Norway Spruce resistant or susceptible

que des tissus nourriciers. These, Strasbourg, 321 pp., 290 Figs.

between plants and Hemiptera. Entomol. Exp. Appl. 12, 1-77.

Adelges abietis. The Connecticut Experiment Station Bulletin 566, 1-77.

glycogene et des amidons. Rev. Gen. Bot. 53, 97-120.

ropodes. Marcellia 37, 233-339.

dans les bourgeons de Picea excelsa L. Marcellia 39, 69-84.

L. Marcellia 40, 135-150.

abietis (L.). 2. f . ang. Ent. 71, 225-249.

to the Eastern Spruce Gall Aphid. Forest Science 21, 180-184.

Author’s address: Dr. ODETTE ROHFRITSCH, Laboratory of Cecidology, Institute of Botany, 28 rue Goethe, F-67083 Strasbourg Cedex

Department of Plant and Forest Protection, Swedish University of Agricultural Sciences, Uppsala, Sweden

Efficiency of the predator Anthocoris nemorum (Het.: Anthocoridae) against the greenhouse whitefly, Trialeurodes

vaporariorum (Horn. : Aleyrodidae)

By BARBARA SOHM EKBOM

Abstract

Anthocoris nemorum was raised on three different diets: 1. whitefly (Trialeurodes vaporariorum) larvae only, 2. Myzus persicae only, and 3. a mixed diet with both whiteflies and aphids. A. nemorum nymphs were able to complete development on all three diets. Duration of development was not significantly different for the three treatments. Instars 2 to 5 took about 21 days at 20 “C.

Cage trials of the effectiveness of the predator against the whitefly were done using tomatoes and cucumbers as host plants. Mortality due to predation was low and probably not high enough for whitefly control. A . nemorum was able to use the plants available for reproduction. The use of predators in the greenhouse is discussed.

U.S. Copyright Clearance Center Code Statement: 0044-2240/81/9201-0026 $ 02.50/0 2. ang. Ent. 92 (1981), 26-34 0 1981 Verlag Paul Parey, Hamburg und Berlin ISSN 0044-2240 / ASTM-Coden: ZANEAE

Efficiency of A . nernorum against T , waporariorum 27

1 Introduction

Biological control of the greenhouse whitefly (Tvialeuvodes vapovariorum Westwood) using the parasitoid Encarsia fovmosa Gahan is a well-penetrated subject (VET et al. 1980). The limits of the parasitoid, however, become clearer as experience is gained and the parasitoid probably cannot be considered an ultimate solution to the whitefly problem. In Sweden the parasitoid has been used, with satisfaction, by many growers but use of E. fovrnosa is not expanding, rather declining (Nedstam personal communication). Some prob- lems which may limit the use of the parasitoid are low effectiveness on certain host plants (cucumber), the need for chemical treatments against other insect pests (i. e. thrips and Liriomyza sp.), and the limits of the greenhouse climate (i. e. energy saving measures which lower greenhouse temperatures). Screening of alternative biological control measures has been urged so that the positive reception of biocontrol under glass will not be destroyed (VET et al. 1980). In this paper a general predator (Anthocoris nernorum L.) is investigated as an alternative or complementary biological control agent of the whitefly.

2 Predators in the greenhouse

The best example of the use of a predator as a biological control agent in the greenhouse is the predatory mite Phytoseiulus persirnilis Athias-Henriot against the spider mite Tetranychus urticae Koch. This biological control method has had great success during the seventies (VAN LENTEREN et a1 1979; GOULD 1980). Predators against aphids have been objects of many experiments. Chrysopa carnea Stephens (TULISALO et al. 1977; SCOPES 1969; BELGLYAROV and USHCHEKOV 1974) and several coccinellid species (GURNEY and HUSSEY 1970; HAMALAINEN 1980) have been tested as aphid predators in the greenhouse. These attempts have not been entirely successful due to difficulties with mass production and failure of the insects to reproduce in the greenhouse. One predator, a gall midge Aphidoletes aphidimyza (Rond.), is able to control aphid populations and is being used on a commercial basis (MARKKULA and TIITTANEN 1980). The two commercially successful predators (P. persirnilis and A. aphidimyza) have several things in common: easy mass production, ability to withstand transport, and they can reproduce and thrive in the greenhouse (MARKKULA and TIITTANEN 1980).

Investigations on the use of predators for controlling thrips in the greenhouse have been carried out in England with the anthocorid Orius niger Wolff (GREATHEAD 1976) and extensive studies are being done in the Netherlands with the predatory mite Amblyseius mackenziei Sch. et Pr. (RAMAKERS 1980).

Several polyphagous predators have been recorded as enemies of the greenhouse whitefly: Deracoccoris serenus Dgl. Sc., Orius majusculus Reuter, 0. niger (ARZONE 1976), Conwentzia sp., Chrysopa sp. and Chrysopa nufilab- rzs Burmeister (VET et al. 1980). None of these have been objects of further studies. Two more predators, which have been studied in Bulgaria can be added to the list: Chrysopa perla L. (BABRIKOVA 1979) and Macrolophus costalis Fiet. (KHRISTOVA et al. 1974). Consumption of whitefly larvae by these

28 Barburu Sohm Ekbom

predators was studied in the investigations. Trials done at the same time as those described in this paper showed that Nabis sp. preys on whitefly larvae but was seldom (8 Yo) able to complete development on a whitefly diet. Given the problem of insect pests other than whiteflies, such as thrips, a predator might be advantageous if it also eats other pests.

3 Anthocoris nemorum as a predator

COLLYER (1967), in her review of the hosts of A. nemorum presents a long list of host species from many different insect orders as well as mites and spiders. Several aphid species; Myzus persicae (Sulzer) (LAUENSTEIN 1977) Dre- panosiphum platanoides (Schrank) (RUSSEL 1970). Phorodon humuli (Schrank) (CAMPBELL 1977), Aphis pomi Degeer (NIEMCZYK 1971); and one diptera Drosophila melanogaster (Meig.) and the gall midge A . aphidimyza (LAUEN- STEIN 1977) can be added to the list of accepted prey. NIEMCZYK (1970) raised A. nemorum on diet of Sitotroga eggs.

A nemorum has been studied as a natural predator on fruit trees (NIEMCZYK 1971), sycamore trees (DIXON and RUSSEL 1972), and on hops (CAMPBELL 1977). The biology of the anthocorid in Scotland (HILL 1957) and England (COLLYER 1967; ANDERSON 1962a) have been investigated and development and fecundity have been studied on several different prey species (ANDERSON 1962b; LAUENSTEIN 1977). Prey in natural situations has also been studied on broom (Sarothamnus separius L.) (DEMPSTER 1963). Searching behavior (LAUENSTEIN 1980a; DIXON and RUSSEL 1972) and efficiency of prey-capture (EVANS 1975; DIXON and RUSSEL 1972) have also been studied. A. nemorum searches randomly, in a straight course, using its antennae and rostrum to recognize prey, but will change behavior when prey is found and search a small area more thoroughly by moving with a high rate of turning (LAUENSTEIN 1980a).

NIEMCZYK et al. (1976) and DIXON and RUSSEL (1972) consider A. nemorum to be important in decreasing pest poplations in field situations, but the presence of alternative prey is important when pest populations are low.

A. nemorum when attempting to capture aphids will meet escape reactions which will lower their capability to capture and kill aphids (EVANS 1976). Smaller prey are easier for the anthocorids to catch (DIXON and RUSSEL 1972; EVAN 1976). Small soft bodied prey such as mites are easier for anthocorids to catch and penetrate with their rostrum.

A. nemorum has been introduced to New Zealand (GREATHEAD 1976) and Canada (CARL and ZWOLFER 1965) as a probable biological control agent, but has not shown any particular success in these attempts.

4 Material and methods

4.1 The predator

Individuals of A . nemorum were collected from locations in Uppsala, Sweden, in the autumn of 1978. Insects were found in both wooded and meadow areas. The insects were placed in small containers with felt-lined bottoms to maintain moisture and as net-covered top to allow for

Efficiency of A . nemorum uguinst T. wuporuriorum 29

ventilation. The containers were kept in a cold room (4 "C) until January 1979 when the insects were introduced to plants (mugwort, Artemisia wulguris L. and yarrow, Achilleu mzllefolium L.) in the greenhouse. The main foods available were thrips and Myzus persicue. In February 1979 first instar nymphs were observed and transferred to the laboratory for feeding trials. In cage experiments offspring from these original A. Nemorum were used as well as insects collected in approximately the same locations as 1978.

4.2 Consumption of prey during development

First and second instar nymphs were placed individually in petri dishes (9 cm). Moist filter paper placed in the bottom served as a source of water. Three different combinations of prey were offered to the anthocorids: 1. larvae of T. wuporariorum, 2. nymphs of M. persicue, 3. a combination of T. wuporariorum and M. persicue. 21 individuals were followed in each treatment. Prey was supplied in sufficiently abundant quantities so that food was always available. Number of prey eaten were counted and observations of molting were made at least every other day. Petri dishes were kept in the laboratory at room temperature (20 "C f 2 "C).

Whitefly larvae vary in size and, as it was not possible to offer only one instar, a conversion factor was used to express consumption of whitefly larvae in terms of fourth instar larvae. The four instars were weighed o n a Cahn scale and a mean for 10 replicates was used to compare the relative size of the instars. Aphid nymphs of an intermediate (instars 2-3) size were used and where other sizes were used the results were also converted.

4.3 Cage trials

From May 1979 to September 1979 cage trials were done to test the effectiveness of A. nemorum as a whitefly predator. Seven trials, each two weeks long, were done. Each trial consisted of three treatments with three replicates for each of the two crops - tomatoes (variety: Stella) and cucumbers (variety: Landora). The treatments were: 1. control, 2. release of adult A. nemorum 3. release of A. nemorum nymphs. Numbers of released insects varied from 5 to 10 per cage.

All plants were exposed to a whitefly infestation for at least two weeks before the trial was begun. The plants were measured to approximate the leaf area and whitefly larvae in 15 (tomato) and 20 (cucumber) 1 cm2 areas were counted. The leaves were marked so that new leaves would not be included in the final counts.

Two plants were placed in each cage (40 cm X 40 cm X 80 cm) in an open air insectary. In each cage round yellow sticky traps were placed to catch emerging adults (EKBOM 1981). After two weeks plants were removed and 15 (tomatoes) or 20 (cucumber) 1 cm2 discs were removed randomly from the leaves, pasted on cards, and examined under the microscope. The number of whitefly larvae present, those eaten, and those emerged were counted. The number of predators found and their life stages were noted when disc-samples were taken.

5 Results

5.1 Prey consumption

There is no significant difference between the duration of development within the prey combinations used, except for the fifth instar which is significantly shorter with M. persicae as prey than with whiteflies (table 1). The length of the first instar was difficult to determine as nymphs were brought into the laboratory in that stage. Development times are approximately the same as those found for 20 "C by ASGARI (1966) (Aphidula (=Aphis) pomi as prey) and slightly longer than those found for 20 "C by CAMPBELL (1977) (Phorodon humuli as prey).

Fewer whitefly larvae were consumed during development than aphids (table 2). The aphids are larger (mean aphid (2-3 instar) weight = 0.4 mg,

30 Barbara S o h Ekbom

mean whitefly (4th instar) weight = 0.05 mg) so it would seem that less aphids would be needed. In counting dead aphids, however, it was difficult to assess how much body fluid had actually been sucked out by the predators. Aphids will die after a rostra1 insertion by A. nemorum even if the aphid escapes

Table I. Duration of instars of Anthocorir nemorum with different diets. All values are mean number of days for insects which completed development. Standard deviation is in parenthesis

~ ~~~~

A. nemorum Prey: T r i a l e u r o d e s Prey: T. vaporariorum Prey: E l . p e r s f c a e instar vaporariorum Myzus p e r s i c a e

I1 2 . S(0.19) 3.6(0.48) 5.25(1.71) 111 5.18(0.67) 3.73(0.45) 4.33(0.42)

5.31( 0 . 4 6 ) 10.07(0.60)8’

III+IV+V 19.13( 1.57) II+III+IV+V 21.63( 1.69)

percent nymphs 67 Yo (14121) which completed development

4.79(0.44) 8.71(0.42)AB* 17.27(0.8) 20.4(0.76)

6.00l0.55) 7.33(0.34)A* 17.7N0.93) 21.75(2.87)

I I *means with different letters are significantly different (p>O.Ol - t-test).

initially and is not eaten. (ANDERSON 1961 cited in EVANS 1976). Comparisons with other studies are difficult as the size of the prey is not always given. The numbers of prey consumed for M . persicue are, however, on the same order of magnitude as those for A. pomi (ASGANI 1966) and P. humuli (CAMPBELL 1977). In mixed prey the number of T. vupovariorum eaten per day for each instar remains relatively constant while the number of M. persicue eaten per day increases with older predator instars.

5.2 Cage trials

Mortality of whitefly lawe is expressed in two different ways (table 3), percent mortality using all larvae sampled and percent mortality using only those samples where larvae were eaten or ‘found’ larvae. The second measure of mortality (‘found’ larvae) is used as an estimate of effectiveness once a prey group is found and there is a change in searching behavior.

There are no significant differences between trials, however, some tenden- cies may be noted. Predators were slightly more effective on cucumber plants than on tomatoes. Percent mortality was higher with lower whitefly densities than with high densities.

A. nemorum laid eggs on both cucumbers and tomatoes. At the end of the first trial 120 nymphs were found on the six cucumber plants where adult predators had been introduced. The highest frequency of nymphs occurred in late spring. For dates 28 May to 3 September 110 adults and nymphs were recovered from tomato plants while 395 were taken from cucumber plants. During the last week 3 September to 17 September, when only cucumbers were used, 30 new nymphs were found on plants where only adults were released.

Efficiency of A. nemorum against T. vaporariorum 31

6 Discussion

A . nemorum were able to eat and complete development on a whitefly diet. Development was slightly fas- ter on a mixed diet, whiteflies and M . persicae. As the nymphs grew they ate proportionally more aphids in the mixed diet. Aphids have escape mechanisms (EVANS 1976; RUSSEL 1972) which make them difficult for the smallest A. nemorum nymphs to catch. Whitefly larvae, in all but the first instar, are stationary and have no simple escape be- haviors.

Mortality in the cage trials was not very high. There was a propor- tional decrease in the number of individuals attacked and eaten in the population when densities are high. A higher percent mortality for the groups of prey actually found by the predators is an indication of in- tensified searching behavior once prey is discovered (LAUENSTEIN 1980a).

A. nemorum feeds on plants and while plant sap is not sufficient for development to adults it could help keep predators alive at low prey densities (LAUENSTEIN 1980b). To- mato plants, however, seemed to be less attractive for A. nemorum than cucumber plants. The number of insects recovered after two weeks on tomatoes was much less than for cucumbers. Extract from tomatoes is a deterrent to oviposition for cabbage butterflies (LUNDGREN 1975) and tomato plants may also be un- desirable for A. nemorum.

A. nemorum meets one of the requirements for a greenhouse predator, it can reproduce on the plants available. Easy mass production, however, has not been developed. Only one generation per year of A. nemorum occurs in Scotland (HILL 1957) and in Finland (LISTO et al.

32 Barbara Sohm Ekbom

Table 3 . Cage trials. Treatment gives number and stage of introduced Anthocorts nemorum. Controls are without predators. Density of whitefly (Trialeurodes vuporuriorum) larvae is a mean

for all plants for 1 cm2. Standard deviation in parenthesis. Percent mortality is calculated for all available larvae and for groups of 'found' larvae

Da te Treatment Tomatoes Cucumbers

Whitefly density

Martality Whitefly density

Mortality

all larvae 'found' larvae all larvae 'found' larvae

28.V-7.VI

ll.VI-25.VI

25.VI-9.VII

lO.VII-23.Vll

23.VII-6.VIII

6.VIII-21.VIII

Z1.VIII-3-IX

3.IX-17.IX

control 5 adults 6 nymphs








6.07(>.95) 4.45( 2 .48 )

4.49(1.70) 4.68(1.94)

10. M(7.19) 12.01 ( 2 -96)

16.7(7.07) 13.24( 5.47)

6.59(4.13) 3.24(0.05)

28.04(9.41) 31.38( 5.45)

3.56(4.37) 2.99 ( 3.3)

several plants died during the trial.

0 % 6 % 4 0%

0 % 7.5 9.

7 'Yo

0 Yo 1 90 7 %

0 * ! 2 % 3 %

0 I 1 96 0 %

0 Ye 0.2 Yo 0.1 s'c

0 % 1.5 % 7 %

29 Yo 27 *!

29 % 22 Yo

10 % 14 ?'e

8 % 13 %

10 %

4 % 3 %

29 '44 42 %

8.66(7.37) 7.82( 7.2) 6.51(6.45)

4.4(4.45) 4.05(4.49)

2.31(3.41) 2.28( 2.65)

4.24(2.34 ) 3.7( 5 -99)

6.72( 3.61) 2.58(0.88)

17.951 18.13(5.52)

20.71(6.17) 20.08( 11.01)

9.35( 2.38) 11.24(7.07 )

4 Yo 13 '70 2 5 % 5 % 14 %

0 % 12 % 43 % 12 96 26 70

0 % 4 % 79 % 6 57 %

0 % 4 0:a 20 46 3 % 30 %

0 % 7 Yo 19 % 4 U! 11 %

0 4'0 1 % - 6 % 21 %

0 Yo 2 Yo 15 Yo 3 Yo 18 %

0 "! 3 Yo 1 3 % 6 % 29 %

1939) and this would seem to be the case for central Sweden also. Oviposition by the first generation is not a problem, but a continuous culture has not been developed. A nemorum does not seem to be very effective as a whitefly predator considering the mortality rates obtained in the cage trials and while percent predation of 'found' larvae was higher it is doubtful that it is enough to control a whitefly outbreak. If a whitefly mortality of about 10 % could be expected with 5-10 nymphs per 1 m2 (there are about 2 plants per m2 in the greenhouse) over 25 000 A. nemorum would be needed in a 1000 m2 greenhouse to obtain 50 % mortality. C. perla ate 801 whitefly larvae (BABRIKOVA 1979) during its larval period which is 16 times the average for A . nemorum.

A predator may be more effective if it is somewhat specialized on its target prey. Searching may then be aided by some sort of attraction or behavioral reaction between predator and prey. Both P. persimilis and A. aphidimyza show some specialization for their respective target prey. The attraction of a polyphagous predator for greenhouse biological control is however, the possibility of using the same agent for several pests. If biological control in the

Efficiency of A . nemorum against T. vaporariorum 33

greenhouse continues to develop in the direction of methods where each pest has Its own specific naural enemy the use of so many different insects could make biocontrol more difficult for the individual grower.

Acknowledgements

Thc author thanks Inger Ahman for technical assistance. The research was supported by a grant fr<)in the Swedish Council for Forestry and Agricultural Research.

Zusammenfassung

Zum Nutzwert der Raubwanze Anthocoris nemorum bei der Bekampfung der Weij7en Fliege (Trialeurodes vaporariorum)

Anthocoris nemorum wurde auf 3 verschiedenen Kulturen geziichtet: 1. ausschliei3lich Larven der Weii3en Fliege, 2. ausschliei3lich Myzus persicae und 3. gemischte Kultur mit WeiRen Fliegen und Blattlausen. Die Larven der A. nemorum konnten sich auf allen 3 Kulturen fertigentwickeln. Die Entwicklungsdauer unterschied sich nur unbedeutend in den 3 Verfahren. Stadien 2 bis 5 dauerten ca. 21 Tage bei 20 "C.

Zur Bestimmung der Effektivitat des Raubinsekts bei der Bekampfung der Weigen Fliege wurden Versuche auf Tomaten und Gurken als Wirtpflanzen durchgefiihrt. Die Sterblichkeit der Weii3en Fliege auf Grund des Verzehrs durch Anrhocoris war niedrig und vermutlich nicht hoch genug zur Bekampfung des Schidlings. A. nemorum konnte sich auf den genannten Pflanzen vermehren. Der Nutzen von Raubinsekten im Gewachshaus wird diskutiert.

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Author’s address: BARBARA SOHM EKBOM, University of Agric. Sciences, Dept. of Plant and Forest Protection, P. 0. Box 7044, S-750 07 Uppsala, Sweden

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