The evolution of Insecticide Resistance

How it happens

How to stop it happening?

John McKenzieUniversity 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 B

LOG (Insecticide Concentration)

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) ?

Life Cycle of Australian Sheep Blowfly

Emergence Adults

(protein feed)

& Mate

Metamorphosis

Females deposit eggs

on sheepPupation in soil

Wandering larvae fall from sheep

Larvae Develop

Relative Viability with Time after Treatment

Dieldrin

0

0.2

0.4

0.6

0.8

1

1.2

5 10 15 20

Relative Viability

RR

R+

++

Diazinon

0

0.2

0.4

0.6

0.8

1

1.2

5 10 15 20

Relative Viability

RR

R+

++

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

Serine alanine

Susceptible Resistant Point Mutation

Glycine Aspartic Acid

Relative to Natural Resistance

Same Same

Levels of Resistance

0

2

4

6

8

10

12

Dieldrin DiazinonInsecticide

Cyromazine

LC100 R+

LC100 ++

For Larvae

End of Capsule Life (24 days)

0

10

20

30

40

1 2 3 4

ControlEgg to Adult Survival

(Percentage)

0

0.1

0.2

0.3

0.4

0.5

0.6

1 2 3 4

Weeks after Capsule Administration

Cyromazine Concentration

In Serum (_g/ml)

Experimental

Square-Wave Delivery

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