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

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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er of L

arvae 1 3 5 7 9

-1 0 1 2 3 4 5 6

No. Pupae

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150

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250

300

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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ots after exp

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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

0

20

40

60

80

100

% 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

0

5

10

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20

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30

35

Accum

ulative num

ber of e

ggs

20 oC

16 oC

10 oC

13 oC

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