The evolution of Insecticide Resistance How it happens How to stop it happening?

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The evolution of Insecticide ResistanceHow it
happensHow to stop it happening?

• John McKenzie
• University of Melbourne

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Adaptation

• A mechanistic understanding of the role
• of natural selection in evolution

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Evolution A (very) simple summary
Differences between individuals (Phenotype)
Variation Heritable component to differences (Genotype)
Selection Individual phenotypes (genotypes) have different survivorship and/or fertility
Change Increase (decrease) of phenotypes (genotypes) in a population
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The Advantage of Insecticide Resistance as a
System to Study Adaptation

• The selective agent is known
• The biochemical/physiological/molecular basis of
  selection is understood
• Relative fitness differences are large
• Can measure differences in the laboratory and
  field Evolution is rapid

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Three Questions for Todays Talk

• What is the genetic basis of insecticide
  resistance?
• How does selection occur?
• Can we use this knowledge to delay the onset of
  resistance

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Answers to these Questions
Genetics Single Gene (, R, RR)
Selection Acts in a concentration-dependent manner
Delay Yes
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Resistance Fitness Sets(Selection)

Insecticide Absent Insecticide Absent Insecticide Present Insecticide Present
gt R gt RR gt R gt RR R RR R RR
Susceptible Resistant Susceptible Resistant
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Dosage Mortality Lines (Idealised)
R RR
100
Mortality (Probit Scale)
0
A B
LOG (Insecticide Concentration) LOG (Insecticide Concentration) LOG (Insecticide Concentration) LOG (Insecticide Concentration)
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History of Field Resistance for Australian Sheep
Blowfly Control
Dieldrin Diazinon Cyromazine
Introduced 1955 1957 1978
Resistance Observed 1957 1965 Not yet
Genetics Rdl (V) Rop-1(IV) ?
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Life Cycle of Australian Sheep Blowfly
Emergence Adults (protein feed) Mate
Metamorphosis Females deposit eggs on sheep
Pupation in soil Females deposit eggs on sheep
Wandering larvae fall from sheep Larvae Develop
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Relative Viability with Time after Treatment
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Can we use this knowledge to delay resistance?
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Is it possible to generate field type
resistance in the laboratory?
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Selecting Single Gene Resistant Mutants

• Expose susceptible flies to a mutagen
• Mate to untreated susceptible flies
• Expose offspring to lethal concentration of
  Insecticide
• Survivors are possible resistant mutants
• (Re test)

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Results of Laboratory Selection
Dieldrin Diazinon
Resistance due to Rdl Rop-1
Molecular Change Susceptible Resistant Point Mutation Serine alanine Susceptible Resistant Point Mutation Glycine Aspartic Acid
Relative to Natural Resistance Same Same
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Levels of Resistance
LC100 R LC100 For Larvae
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Square-Wave Delivery
Experimental
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The Evolution of Insecticide Resistance(A
Cross-Disciplinary Approach)
Applied Outcomes
Chemical Kinetics
Molecular Analysis
Biochemical Analysis
Population Biology/Ecology
Genetic Analysis
Population Genetics and Evolutionary Principles