Insect biology and host range: risk assessment in biological control
J-R BaarsBioControl Research UnitSchool of Biology and Environmental ScienceUniversity College Dublin
Natural Enemies
Species: Pyrrhalta nymphaeaeCommon name: Waterlily leaf beetleOrder: ColeopteraFamily: Chrysomelidae
Life History: Egg batches 6-20 3 Larval instars 10 eggs/dayLarva-Adult 13-24 days Damage High leaf turnover
5-17% net primary production
Plant HostsSpatterdock, Nuphar advena (L.) Sibth. & Sm. (Nymphaeaceae)Waterlilies, Nymphaea spp. (Nymphaeaceae)Smartweed, Polygonum hydropiperoides Michx. (Polygonaceae)Smartweed, Polygonum amphibium L. (Polygonaceae)Bog myrtle, Myrica gale L. (Myricaceae)Water shield, Brasenia schreberi J.F. Gmel. (Cabombaceae)Arrowheads, Sagittaria sp. (Alismataceae)Willows, Salix sp. (Salicaceae)Water chestnut, Trapa natans L. (Trapaceae)
Top down control
Framework for Weed BC
Target weed ecology
Exploration for potential control agents
Evaluation of biological control potential
Host specificity testing
Agent release and redistribution
Agent evaluation
Briese DT 2000 Classical Biological Control. In: Australian Weed Management Systems (ed. B Sindel) pp. 161-192.l
Submerged aquatic weed Vegetative growth Spread by fragmentation & layering Top 75cm of submerged shoots
(50cm x 50cm) = 160m2 Leaf surface area
Complex ecology dependant on location
Lagarosiphon major
Target Weed Ecology
Exploration – Origin
Identifying the native range of the weed
Locate evolutionary centres of origin – locate phytophage diversity
Searching areas best ecoclimatically matched
Characterise agent & weed populations using molecular markers
Exploration – Origin
Lagarosiphon is native to sub-Saharan Africa & Madagascar
9 species are described (Symoens & Triest, 1983)
L. major native to southern Africa
Herbarium specimens held by SANBI
Altitude range: 750 - >2000m a.s.l
Exploration – Origin
Stem-borer
Shoot-tip borer
Leaf-miner
Leaf defoliator
Leaf Pathogen
Agent selection criteria
Host specificity
Effectiveness
• Process and release a large number of candidates to find successful agents
• Prioritise by understanding the ecology of the weed-herbivore system, targeting specific parts of the weed’s life cycle
Two philosophies:
Life cycle: Hydrellia lagarosiphonAdult
Eggs
Larva
Pupa
Widespread
Damaging
Short life cycle
Indications that it is host specific
Other similar ephydrids used as biocontrol agents
Ephydridae in Ireland
~29 species in the genus Hydrellia
~12 recorded in Ireland
Largest genus in the Hydrellinae
Little ecology known about the species
Exception include species of economic importance
e.g. Hydrellia griseola
Hydrellia lagarosiphon on L. major
Ephydrids as pests
Hydrellia griseola, Smaller Rice Leaf Miner Pest on wheat, barley, rice, maize, and
timothy Leaf mines causes reduction of plant
photosynthesis intensity and of crop yield 14-16% damage to leaf surface, rice yields
decrease by 6-9% Populations regulated by parasitic wasps
Ephydrids as BC agents
2 species released in US ~ Hydrellia pakistanae~ H. balciunasi
Target species Hydrilla verticillata
Originate from Asia and Australasia
Released in Southern US after host specificity testing
Balciunas et al 2002 Balciunas et al 2002
Ephydrids as BC agents
Leaf impact Released 1987 In early 2000s high
populations were recorded
Low levels of leaf damage ~20% reduce photosynthesis
Ephydrids as BC agents
Populations in US
Taking ~18 yrs to build up
Deliberately released in 30 sites
Spread to sites 300-400km from release sites
Grodiwitz et al 2004
Ephydrids as BC agents
Fly impact damages Hydrilla infestations in Lake Seminole US
Monocultures replaced by mixture of species
Grodiwitz et al 2004
Before
After
Hydrellia lagarosiphon
1-11 larva in shoot tips in the country of origin
±50 leaves damaged/larva
Leaf damage increases with larval density
Carrying capacity suggests 3-4 larvae can be maintained per shoot tip
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Day s
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Num
ber of leaves damaged
Evaluation of BC potential
Damage stimulates growth
Side shoots increase with herbivory
Shoot tip viability dependant on size and levels of larval damage
Shoot viability decreases with increasing larval density
531
Larv al de nsitie s
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Evaluation of BC potential
Host specificity testing
Aims to predict the damage to nontarget species following release
Colonisation of nontarget species & temporary spill-over
The process has evolved over time as our understanding of host-plant interactions improve
An analytical process is followed to assess the potential risks
Ecology, behaviour and phylogeny
Determine the fundamental and realised host range
Host specificity testing
Fundamental host rangeAbsolute limits of a species host rangeIndependent of ecological setting
Realised host range Variation in host acceptance following releaseSpatial and temporal overlap of species
Risk assessment tools
Test plant listsExtensive list of plants selected using ‘Centrifugal phylogenetic method’ (Wapshere 1975)
~ a sequence of plants from those most closely related to the target weed to progressively more distantly related
Experimental tests • No-choice tests• Choice tests• Field tests
Family Species Butomaceae Butomus umbellatus Eupatorium cannabinum Alismataceae Sagittaria sagittifolia Sagittaria latifolia Sagittaria rigida Sagittaria subulata Baldellia ranunculoides Luronium natans Alisma plantago-aquatica Alisma lanceolatum Alisma gramineum Damasonuim alisma Hydrocaritaceae Hydrocharis morsus-ranae Elodea canadensis Hydrilla verticillata Elodea nuttallii Stratiotes aloides Egeria densa Elodea callitrichoides Vallisneria spiralis Najadanceae Najas flexilis Najas marina Najas graminea Scheuchzeriaceae Scheuchzeria palustris Aponogetonaceae Aponogeton distachyos Juncaginaceae Triglodin palustre Triglodin maritimun Potamogetonaceae Potamogeton natans Potamogeton polygonifolius Potamogeton nodosus Potamogeton coloratus Potamogeton lucens Potamogeton gramineus Potamogeton lucens x P. perfoliatus (P. x salicifolius) Potamogeton gramineus x P. lucens (P. x zizii) Potamogeton alpinus Potamogeton gramineus x P. perfoliatus (P. x nitens) Potamogeton praelongus Potamogeton epihydrus Potamogeton perfoliatus Potamogeton friesii Potamogeton pusillus Potamogeton rutilus Potamogeton obtusifolius Potamogeton trichoides Potamogeton berchtoldii Potamogeton compressus Potamogeton crispus Potamogeton acutifolius Potamogeton filiformis Potamogeton pectinatus Groenlandia densa Zannichelliaceae Zannichellia palustris Ruppiaceae Ruppia maritima Ruppia cirrhosa
Test plant list
Tanaka et al 1997. The phylogeny of the family Hydrocharitaceae inferred
Tanaka et al 1997
Les et al 2006. A reappraisal of phylogenetic relationships in the monocotyledon family Hydrocharitaceae (Alismatidae) Aliso 22: 211-230.
Phylogeny
Classification proposed by Les et al 2006
Les et al 2006. A reappraisal of phylogenetic relationships in the monocotyledon family Hydrocharitaceae (Alismatidae) Aliso 22: 211-230.
Proposed Classification
No native species in the subfamily Anacharidoideae
3 genera need consideration~Hydrocharis~Stratiotes~Najas
Other alien species include Hydrilla & Vallisneria
Les et al 2006
3 genera need consideration~Hydrocharis~Stratiotes~Najas
Related plants
Host screening
Host range determined by larval stage
Adult
Eggs
Larva
Pupa
Adult
Eggs
Larva
Pupa
Heard, T.A., 2000. Concepts in insect host-plant selection behaviour and their application to host specificity testing.
Host screening
Behavioural constraints
False +vesFalse -ves
(Heard 2000)
Host screening
Fecundity of adults dependant on temperature
Egg viability reduces through the life time of adult fly
2d 4d 6d 8d 10d 12d 14d 16d 18d 20d 22d
Day s
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% E
gg
viability
20 oC
16 oC
13 oC
10 oC
2d 4d 6d 8d 10d 12d 14d 16d 18d 20d 22d 24d 26d
Day s
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Accum
ulative num
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ggs
20 oC
16 oC
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Risk Assessment
The use of host specificity testing and field host-use studies to make pre-release relativity-based predictions of likelihood that the agents threaten nontarget plants
Test conditions designed for candidate agent evaluated
Host tests can predict the likelihood of nontarget attack
Retrospective assessments in the USA and Australia indicate that host testing procedures can predict field host host
Acknowledgements
Support by the following are kindly acknowledged
Hydrellia lagarosiphon
• First discovered in 2008, IFI funded survey (Baars et al. 2010 - Hydrobiologia)
• New species to science
• Described by John Deeming (Wales Natural History Museum) (Deeming, 2011 –African Entomology)
• Two additional populations maintained from collection trip in SA (May 2010)
• Variation in the male genitalia
• DNA analysis (barcoding)
Life+ project CAISIE
• Collection trip to import known candidates (i.e. Bagous spp.)
• Survey to establish the presence of additional candidates
• Collection trip conducted in April-May 2010
• Over 50 sites were visited, 18 with L. major
Survey Objectives
Shoot tip midge (Chironomidae)
• Shoot-tip mining midge (cf. Polypedilum sp.)
• Similar species found on other Hydrocharitaceae
• Host-specificity in question
• Taxonomy in question
• Not easily reared under laboratory conditions
Leaf feeding moth (Lepidoptera)
• Leaf feeding larvae (Nymphulinae, Paraponyx spp. & Synclita spp.)
• Host specificity in question
• USA call to consider Lepidopteran species to be considered for Hydrilla verticillata
Climate match native vs exotic
• Different species persisting in different climatic areas, better pre-adapted?
• Biotypes of species Thermal tolerance
• One of the main contributory factors to failure in weed biocontrol