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Insect biology and host range: risk assessment in biological control

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Presentation on theme: "Insect biology and host range: risk assessment in biological control"— Presentation transcript:

1 Insect biology and host range: risk assessment in biological control
J-R Baars BioControl Research Unit School of Biology and Environmental Science University College Dublin


3 Natural Enemies Species: Pyrrhalta nymphaeae
Common name: Waterlily leaf beetle Order: Coleoptera Family: Chrysomelidae Life History: Egg batches 6-20 3 Larval instars 10 eggs/day Larva-Adult days Damage High leaf turnover 5-17%  net primary production Plant Hosts Spatterdock, 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)

4 Top down control

5 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 l

6 Target Weed Ecology Lagarosiphon major 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

7 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

8 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: >2000m a.s.l



11 Exploration – Origin Shoot-tip borer Leaf-miner Leaf defoliator
Leaf Pathogen Stem-borer

12 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:

13 Life cycle: Hydrellia lagarosiphon
Adult Eggs Larva Pupa Widespread Damaging Short life cycle Indications that it is host specific Other similar ephydrids used as biocontrol agents

14 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

15 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

16 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

17 Ephydrids as BC agents Leaf impact Released 1987
In early 2000s high populations were recorded Low levels of leaf damage ~20% reduce photosynthesis

18 Ephydrids as BC agents Populations in US Taking ~18 yrs to build up
Deliberately released in 30 sites Spread to sites km from release sites Grodiwitz et al 2004

19 Ephydrids as BC agents Before
Fly impact damages Hydrilla infestations in Lake Seminole US Monocultures replaced by mixture of species After Grodiwitz et al 2004

20 Evaluation of BC potential
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

21 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

22 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

23 Host specificity testing
Fundamental host range Absolute limits of a species host range Independent of ecological setting Realised host range Variation in host acceptance following release Spatial and temporal overlap of species

24 Risk assessment tools Test plant lists
Extensive 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

25 Test plant list Tanaka et al 1997
Tanaka et al The phylogeny of the family Hydrocharitaceae inferred

26 Phylogeny Classification proposed by Les et al 2006
Les et al A reappraisal of phylogenetic relationships in the monocotyledon family Hydrocharitaceae (Alismatidae) Aliso 22:

27 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 Les et al A reappraisal of phylogenetic relationships in the monocotyledon family Hydrocharitaceae (Alismatidae) Aliso 22:

28 Related plants 3 genera need consideration ~Hydrocharis ~Stratiotes

29 Host screening Host range determined by larval stage

30 Host screening Behavioural constraints False +ves False -ves
(Heard 2000) Heard, T.A., Concepts in insect host-plant selection behaviour and their application to host specificity testing.

31 Host screening Fecundity of adults dependant on temperature
Egg viability reduces through the life time of adult fly

32 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

33 Acknowledgements Support by the following are kindly acknowledged


35 Hydrellia lagarosiphon
First discovered in 2008, IFI funded survey (Baars et al 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)

36 Life+ project CAISIE Survey Objectives 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

37 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

38 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

39 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

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