Transcript The evolution of Insecticide Resistance How it happens How

The evolution of Insecticide Resistance
How it happens
How to stop it happening?
John McKenzie
University of Melbourne
Adaptation
A mechanistic understanding of the role
of natural selection in evolution
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
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
Three Questions for Today’s Talk
• What is the genetic basis of insecticide resistance?
• How does selection occur?
• Can we use this knowledge to delay the onset of
resistance
Answers to these Questions
Genetics
Single Gene (++, R+, RR)
Selection
Acts in a concentration-dependent manner
Delay
Yes
Resistance Fitness Sets
(Selection)
Insecticide Absent
Insecticide Present
++ > R+ > RR
++ ≤ R+ ≤ RR
Susceptible
Resistant
Susceptible
Resistant
Dosage Mortality Lines (Idealised)
++
R+
RR
100
Mortality
(Probit Scale)
0
A
LOG (Insecticide Concentration)
B
History of Field Resistance for
Australian Sheep Blowfly Control
Dieldrin
Diazinon
Cyromazine
Introduced
1955
1957
1978
Resistance
Observed
1957
1965
Not yet
Rdl (V)
Rop-1(IV)
?
Genetics
Life Cycle of Australian Sheep Blowfly
Emergence
Adults
(protein feed)
& Mate
Metamorphosis
Females
deposit eggs
on sheep
Pupation in soil
Wandering
larvae fall from
sheep
Larvae Develop
Relative Viability with Time after Treatment
1.2
Relative Viability
1
0.8
0.6
RR
R+
0.4
++
0.2
0
5
10
Dieldrin
15
20
1.2
Relative Viability
1
0.8
RR
0.6
R+
++
0.4
0.2
0
5
10
Diazinon
15
20
Can we use this knowledge
to delay resistance?
Is it possible to generate
field type resistance in the laboratory?
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)
Results of Laboratory Selection
Dieldrin
Diazinon
Resistance due to
Rdl
Rop-1
Molecular Change
Susceptible
Resistant
Point Mutation
Susceptible
Resistant
Point Mutation
Serine
Glycine
Relative to Natural
Resistance
Same
alanine
Same
Aspartic Acid
Levels of Resistance
12
10
LC100 R+
LC100 ++
For Larvae
8
6
4
2
0
Dieldrin
Diazinon
Insecticide
Cyromazine
Square-Wave Delivery
End of Capsule Life
(24 days)
40
30
Egg to Adult
Survival 20
(Percentage)
10
Control
Experimental
0
1
2
1
2
3
4
0.6
0.5
Cyromazine 0.4
Concentration
0.3
In Serum
0.2
(μg/ml)
0.1
0
3
Weeks after Capsule Administration
4
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