Ent 222: Ecological Backlash to Pest Management with Insecticides:

What is the goal of pest management?

 reduce pest population and or damage

But this goal is not always achieved, and even if it is successful the effects may be short lived

Why does control of insects fail?

• Inappropriate or incompatible control methods

• Improper application of insecticides: dosage, timing

Even when applied correctly, ecological backlash can occur

What is ecological backlash?

response by pests or other organisms that reduce control effectiveness

T/F Backlash is never delayed?

False

Backlash is often delayed …

Initial results may appear successful

Encourages repeated use of the same tactic

How can control change over time?

It may

• Gradually decline

• Fail suddenly

• Become ineffective

What are the three major types of ecological backlash?

• Resistance: Pest becomes less sensitive to insecticides

• Resurgence: Pest population rebounds after control

• Replacement: New pest species emerge

What is resistance?

The ability of certain individuals to tolerate or avoid factors that are lethal or reduce reproduction in most of the population and pass this ability onto their offspring

→ Genetic // evolutionary phenomenon

How is resistance recognized?

• Repeated failure of a product

• Even when used according to label recommendations

⇒ Most common with pesticide use; can develop in response to any pest management tactic

What is the rate of resistance development based on?

• Genetics of the resistance factor

• Selection pressure (greater burden → faster resistance)

What is the origin of resistance?

• Mutations produce individuals predisposed to resist control measures

• Pre-adapative mutants exist in populations at low frequencies

What is the difference between monogenic resistance and polygenic resistance?

Monogenic resistance: Controlled by a single gene that develops quickly

Polygenic resistance: Controlled by multiple genes that develops slowly

How big of a problem is insecticide resistance?

• One of top four global environmental issues

• First reported case with lime sulfur in 1908

• Experiencing exponential growth; 539 insect species were resistant to >1 insecticide in 2000, while resistance was rare in the 1950s

T/F resistance is limited to arthropods?

→ Not limited to arthropods

Plant pathogens, Weed species, Nematodes and Rodents

How many resistant species are agriculturally important? medicinally // vetinarilly? natural enemies?

56% agricultural importance

37% medical / veterinary importance

5% natural enemies

What are the key insect groups that are resistant to insecticides?

35% Diptera

16% Lepidoptera

14% Acari

14% Coleoptera

11% Hemiptera

What CF Wilkinson quote is related to resistance?

“Insects are forewarned and forearmed to meet the challenges presented to them”

What is biochemical resistance?

• Insecticide attacked by 1 or more enzymes

  • Enzymes detoxify insecticides before they reach site of action

What are the two steps of biochemical resistance?

Stage 1: High concentrations of mixed-function oxidases that produce primary products

Stage 2: Secondary metabolism of primary products into water soluble conjugates

Excretion can occur after stage 1, but most commonly after stage 2

What is physiological resistance?

Stage 1: High concentrations of mixed-function oxidases that produce primary products

Stage 2: Secondary metabolism of primary products into water soluble conjugates

Excretion can occur after stage 1, but most commonly after stage 2

What are the 3 steps to physiological resistance?

1. Alterations at the site of insecticide activity

2. Decrease penetration of insecticide through body wall through modification of cuticle

3. Increased rates of excretion or sequestration of insecticide so insecticide does not reach target site

What is behavioral resistance?

Changes in behaviour by which insects avoid insecticides

What is cross resistance?

Insecticides with resistance to one insecticide able to resist other insecticides

Most cross resistant occurs within classes

It can also occur between classes

Occurs because of similar toxicity modes of chemicals involved

What does resistance to microbial insecticides look like with Bt?

• Lab studies indicate potential in several species

• Diamondback moth is the only previous species with significant resistance in field populations

• While there is a potential to become worse with Bt transgenic crop plants

What is an example of resistance to cultural control?

European cornworm

• Resistant to a 2-year rotation of corn and soybeans in north-central US

• This resistant genotype shows extended diapause

• And some resistant biotypes can survive on soybean

What are some operational factors promoting resistance?

• Prolonged exposure to single insecticide

• Every generation of insect is selected

• Insecticide selection pressure is high

• No refugia

• Large geographical areas are treated

• Selection occurs before mating

• Insecticide closely related to one used earlier

• Low economic threshold recommended for application

What are some examples of the biological factors promoting resistance?

• No migration between populations

• Monophagous

• Short generation time

• Many offspring per generation

• Highly mobile, increasing exposure

How can we slow development of resistance?

Use of combined tactics to achieve pest suppression

• Integration of ecological tactics, natural enemy suppression and resistant plants with chemical insecticides.

• Diverse pressures on pest populations

Employ passive tactics

• Place no burden on pest population 

• Selective pressures are lessened and resistant development is less likely to occur: irrigation and fertilization of crops, injury tolerance levels.

Modify use patterns

• Management by …

What is management by moderation?

reduce selective pressure and conserve susceptible genes in populations. Helps to conserve the environment and natural enemies

→ Impractical with high-value crops

For example: less frequent application, preserve refugia

What is management by saturation?

saturate insect defense mechanisms by doses that can overcome resistance and kill susceptible and heterozygotes. There is a possible adverse impact on the environment.

→Applicable to high value crops

What is management by multiple attack with multiple insecticides?

reduces selection pressure by imposing several independently acting insecticides. But there are environmental risks, destruction of natural enemies and risk potential resistance to several compounds.

What is the ultimte goal of IPM?

We want to practice integrated IPM and use several control tactics that work in different ways

By rotating pesticides with different modes of action or by alternating chemical with nonchemical control tactics, a pest population is exposed to selective pressure that changes from generation to generation