The Use and Safety of Bacillus pathogens for the Control of Mosquito Larvae

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The Use and Safety of Bacillus pathogens for the
Control of Mosquito Larvae

• Lawrence A. Lacey
• Yakima Agricultural Research Lab
• USDA-ARS
• Wapato, WA

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Problems associated with sole reliance upon
chemical pesticides

• Resistance
• Safety to humans and domestic animals
• Environmental contamination
• Recurrent cost and sustainability

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Integrated Pest Management (IPM) Integrated
Vector Control (IVC)

• Ecologically based and relies on natural
  mortality factors and sound knowledge of the
  ecosystem and its components
• Can include judicious and compatible use of
  chemical insecticides, environmental management,
  personal protection and biological control

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IVC Considerations

• Ecologically based will rely on conservation of
  natural enemies
• Compatible use of chemical insecticides
• Good reconnaissance
• Special considerations for biological control
  agents
• Community participation

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Tolypocladium
FUNGI
Culicinomyces
Lagenidium
Coelomomyces
BACTERIA Bacillus
VIRUS NPV, CPV
MICROSPORIDIA Amblyospora Edhazardia
NEMATODES Romanomermis
Pathogens and parasites of mosquitoes
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Candidate Entomopathogenic Bacteria for Control
of Mosquito Larvae

• Bacillus thuringiensis var. israelensis
• Bacillus sphaericus

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Bacillus thuringiensis history

• Discovery in Japan and Germany of strains with
  activity against Lepidoptera (1901-1911) -
  development of products for microbial control of
  Lepidoptera (1950s-present) subsequent discovery
  of several other strains with Lepidopteran
  activity
• Discovery in Israel (1976) of strains with
  activity against Diptera (Nematocera) and
  subsequent rapid development of products for
  black fly and mosquito control
• Discovery and development of beetle active
  strains in Germany and elsewhere

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Bacillus thuringiensis

• Naturally occurring in soil, phylloplane and
  other habitats
• Serological classification
• 50 serovars described
• Classification according to protein composition
• 7 crystal toxin classes

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Bacillus thuringiensis
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Bacillus thuringiensis var. israelensis
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Mode of action of d-endotoxins

• Toxins responsible for larvicidal effects located
  in proteinaceous parasporal inclusion produced at
  time of sporulation
• Must be ingested
• Dissolved in basic Gut pH (9) and further
  cleaved by proteolytic enzymes
• Binds to specific sites on midgut cells
• Disrupts osmotic balance

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Healthy gastric caecum
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Gastric caecum following ingestion of Bti
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Bacillus thuringiensis target specificity

• B.t. var kurstaki - Lepidoptera
• B.t. var. tenebrionis - Coleoptera
  (Chrysomelidae)
• B.t. var. israelensis Diptera (Nematocera)

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Bacillus thuringiensis var. israelensis target
insects

• Susceptible targets
• Culicidae (mosquitoes)
• Simuliidae (black flies)
• Chironomidae (midges pests and NTOs)
• Sciaridae (fungus gnats)
• Other Nematocera

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Commercial large scale fermentation of Bacillus
thuringiensis
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Formulations of Bti for mosquito control

• Wettable powder
• Granules penetration of foliage
• Briquettes slow release
• Pellets penetration and slow release
• Flowable concentrates aerial application
  (especially ULV), stream treatment

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Aerial application of Bti for control of mosquito
larvae
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Beecomist ULV generator
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Advantages of Bti

• Highly efficacious against black fly and mosquito
  larvae
• Application with conventional equipment
• Specific for nematocerous Diptera
• No resistance development
• Safe to handle

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Some limitations of Bti

• Very short residual activity in organically
  enriched environments necessitating frequent
  reapplication to many habitats
• May rapidly settle out of feeding zone of
  targeted larvae

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Bacillus sphaericus
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Cellular pathology of Bacillus sphaericus in
Culex quinquefasciatus
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Bacillus sphaericus
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Treatment of polluted Culex larval habitat with
Bacillus sphaericus
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Reproduction of B. sphaericus in midgut of Culex
quinquefasciatus
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Subsequent mortality in Culex quinquefasciatus
that survived an LC60 of Bacillus sphaericus
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Survival rate of Culex quinquefasciatus adults
following exposure as larvae to Bacillus
sphaericus
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Advantages of Bacillus sphaericus

• Highly efficacious against many species of
  mosquito larvae
• Application with conventional equipment
• Good residual activity in polluted habitats
• May recycle in certain situations
• Specific for mosquitoes
• Safe to handle

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Some limitations of Bacillus sphaericus

• Narrower range of susceptible mosquito species
• Resistance in some populations of Culex
  quinquefasciatus

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Safety and Ecotoxicology of Entomopathogenic
Bacteria Used for Mosquito Control
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Tests on vertebrate toxicity of Bti and B.
sphaericus

• Fish
• Birds
• Mammals

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Direct effects of Bacillus spp. on invertebrate
NTOs during mosquito control

• Beneficial Nematocera
• Predatory mosquito larvae
• Chironomids
• Chironomus, Tanytarsus, Reotanytarsus

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Toxorhynchites amboinensis with prey
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Gambusia affinis
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Mesocyclops aspericornis predator of Aedes
aegypti
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Indirect effects of Bacillus spp. for mosquito
control

• Prey removal and effect on community structure
• Generalized predators
• Specialized predators

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Safety and ecotoxicology of Bti and B.
sphaericus summary

• No vertebrate toxicity
• Are not active against non-nematocerous insects
• Bti can kill nontarget nematocerous Diptera such
  as certain chironomids, fungus gnats, etc. but
  elevated concentrations usually required

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Suggested reading

• List available by e-mail. Contact me at
  llacey_at_yarl.ars.usda.gov