Ent 222: Genetically based pest management

What is genetically based pest management?

The Use of genetics to control pests through mating of modified pest with their wildtype counterparts”

What are the three main genetic approaches to pest management?

1. Sterile insect technique

• Irradiation: sterilizes males before release

• Inherited sterility: partial sterility passed onto the next generation

2. Transgenic approaches

• Self limiting gene: offspring die before adulthood

• Cytoplasmic incompatibility: incompatible mating → eggs fail to develop

3. RNA interference

• Species-specific gene silencing

• SIGs: dsRNA applied as a spray or irrigation

• HIGs: transgenic crops produce RNA targeting pests

What are the steps to sterile insect release?

Mass rearing of insects: large numbers of insects produced in lab – must be robust and cost effective

Sterilization of insects: gamma-ray or x-ray irradiation , inherited sterility.

• Low dose irradiation = sterile offspring but male remain competitive.

• Transgenic sterilization

Release of sterile males: compete with wild males for mating; over flooding ratio = many more sterile males than wild males.

Where does SIT work best?

Confined geographic areas

Area wide pest management programs

What are the program goals of SIT?

• Population suppression

• Prevent introduction or reintroduction

• Eradication of non-native species

What global organizations are involved in SIT?

• IAEA: International Atomic Energy Agency

• FAO: Food and Agriculture Organization of the United Nations

What groups must cooperate for SIT?

• All levels of government

• Producers and farmers

• Public cooperation

• Area-wide pest management programs

What was the first SIT program?

New World Screwworm Eradication

• A parasite of warm-blooded animals; a major livestock pest

• Females only mate once; this is ideal for SIT

• Scientists: Edward Knipling and Raymond Bushland

• Program started in USA, expanded to Mexico, Central America and Jamaica

Timeline

• 1957-1959 = South Eastern USA

• 1962-1966 = South Western USA

There was a mass rearing facility in Texas with around 150 million flies/week and around 300 workers.

Sterilization: Pupal stage via radioactive cobalt

Release: Adult flies dropped from an aircraft

What is the Okanagan-Kootenay Sterile Insect Release Program for?

Pesticide-free control of codling moth

Area-wide pest management approach

How are the moths raised and released in the Okanagan-Kootenay Sterile Insect Release Program?

Raised: Mass-rearing facility in Osoyoos British Columbia

• Produces around 2 million sterile males per day

• Sterile moths are distinguishable from wild moths

• Adults are collected, packaged and irradiated using gamma radiation

Release method:

• Sterile moths are released from cooled petri-plates on ATVs

• Released every week of the growing season

40 sterile males : 1 wild male

This ensures most females mate with sterile males

How are the Okanagan-Kootenay SIR moths monitored?

Pheromone-baited traps across orchards

Weekly trap checks

Data reported publicly

Sterile : wild ratio is recorded

What were the results of the Okanagan-Kootenay SIR program?

Population declined more slowly in zones 2 and 3 ; in large urban centres backyard trees acted as refuges for codling moth

2011-2014: pheromone mediated mating disruption was used instead of SIR

An increased service area = higher operational demands

Less grower buy in, in zones 2 and 3

But overall there was a 94% population decrease since program initiation

What is the economic threshold for codling moth? was this met by the Okanogan SIR?

Trap captures <2 moths per trap

Goal of reduced insecticide use was met with a 96% reduction in insecticide applications targeting codling moth

What is RNAi?

RNA Interference (RNAi) in pest management

dsDNA binds to target mRNA; silences specific genes in pests

What are the two approaches to RNAi?

Approaches:

1. Host Induced Gene Silencing (HIGs): plant produces dsDNA targeting pest genes; SmartStax Pro Corn produces dsDNA targeting corn rootworm belowground and Bt toxins targeting above ground lepidoptera.

2. Spray Induced Gene Silencing (SIGs): dsDNA applied directly as a spray; Calantha targets Colorado Potato Beetle, stops feeding in 2-3 days

formulations protect dsDNA from degradation in the environment

How is RNAi produced and used?

→ dsRNA production in a variety of organisms; E. coli, symbiotic bacteria, yeast, bacteriophage, and cell-free production platform

→ exogenous application of dsRNA; foliar spraying, root injection and root irrigation

→ dsRNA fate; absorbed by plants and ingested by insects. Internalized dsRNA diced into siRNA to trigger RNAi machinery

→ dsRNA in the environment; not stable under UV irradiation or in the soil

What are the main forms of RNAi application?

• Baits, traps

• Nanoparticles

• Foliar application

• Trunk injection

• Root soaking

• Soil drench, granulates

• Seed dressing

• Recombinant symbiont or virus

• Transgenic crop

• Insect injection

What are the pros and cons of RNAi?

Advantages

• Reduces pesticide use while maintaining yield

• Highly specific with known mode of action

• Natural and generally low toxicity

• Broad agricultural applications

Drawbacks

• GMO concerns may limit acceptance

• Not effective for all insects

• RNA degrades quickly

• Variable or incomplete effects

• Design process can be trial-and-error

Risks

• Off-target gene effects

• Limited understanding of parental RNAi

• Possible immune or toxic effects

• Unknown environmental persistence

• Risk of resistance development