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
Natural Enemies
Species:
Common name:
Order:
Family:
Pyrrhalta nymphaeae
Waterlily leaf beetle
Coleoptera
Chrysomelidae
Life History:
Egg batches 6-20
3 Larval instars
10 eggs/day
13-24 days
High leaf turnover
5-17%  net primary production
Larva-Adult
Damage
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)
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
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




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
Shoot-tip borer
Leaf-miner
Leaf defoliator
Leaf Pathogen
Stem-borer
Agent selection criteria
 Host specificity
 Effectiveness
Two philosophies:
•
Process and release a large number of candidates to find
successful agents
•
Prioritise by understanding the ecology of the weedherbivore system, targeting specific parts of the weed’s
life cycle
Life cycle: Hydrellia lagarosiphon
Adult
 Widespread
 Damaging
Eggs
 Short life cycle
 Indications that it is
host specific
 Other similar
ephydrids used as
biocontrol agents
Pupa
Larva
Ephydridae in Ireland
 ~29 species in the genus Hydrellia
 ~12 recorded in Ireland
 Largest genus in the Hydrellinae
Hydrellia lagarosiphon on L. major
 Little ecology known about the species
 Exception include species of economic importance
 e.g. Hydrellia griseola
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
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
Before
 Fly impact damages
Hydrilla infestations in
Lake Seminole US
 Monocultures replaced by
mixture of species
After
Grodiwitz et al 2004
Evaluation of BC potential
300
Hydrellia lagarosiphon
250
 1-11 larva in shoot tips in
the country of origin
 Leaf damage increases with
larval density
150
100
Number of leaves damaged
 ±50 leaves damaged/larva
200
 Carrying capacity suggests
3-4 larvae can be
maintained per shoot tip
50
0
-1
0
1
2
3
4
5
6
No. Pupae
10
9
1
3
5
7
9
8
7
6
5
4
Number of Larvae
3
2
1
0
0
2
4
6
8
10
12
14
16
Days
18
20
22
24
26
28
30
Evaluation of BC potential
 Damage stimulates growth
 Side shoots increase with
herbivory
 Shoot tip viability
dependant on size and
levels of larval damage
5
4
 Shoot viability decreases
with increasing larval
density
3
2
1
Number of side shoots
0
1
3
Larval densities
5
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 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
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
Test plant list
Family
Butomaceae
Species
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
Tanaka et al 1997. The phylogeny of the family Hydrocharitaceae inferred
Tanaka et al 1997
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
Les et al 2006. A reappraisal of phylogenetic relationships in the monocotyledon family Hydrocharitaceae (Alismatidae) Aliso 22: 211-230.
Related plants
 3 genera need
consideration
~Hydrocharis
~Stratiotes
~Najas
Host screening
Adult
 Host range determined by
larval stage
Eggs
Pupa
Larva
Host screening
 Behavioural constraints
False +ves
False -ves
(Heard 2000)
Heard, T.A., 2000. Concepts in insect host-plant selection behaviour and their application to host specificity testing.
Host screening
35
20 oC
30
25
 Fecundity of adults
dependant on temperature
16 oC
20
15
13 oC
10
Accumulative number of eggs
 Egg viability reduces
through the life time of
adult fly
10 oC
5
0
2d
4d
6d
8d
10d
12d
14d
16d
18d
20d
22d
24d
26d
Days
100
20 oC
16 oC
13 oC
10 oC
80
60
40
% Egg viability
20
0
2d
4d
6d
8d
10d
12d
Days
14d
16d
18d
20d
22d
Risk Assessment
The use of host specificity testing and field hostuse 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
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
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