Which insect life stages are most effectively controlled by fumigants?

• A. Egg
• B. Larva and Adult
• C. Pupa
• D. Nymph

Answer: (B)

Fumigants are gases that must reach and diffuse into insects through breathing openings and body tissues. How well they kill depends on how accessible the insect is to the gas and how its tissues take up the chemical. Larvae and adults are usually most affected because they actively respire and have exposed tracheal systems, so the gas quickly penetrates and disrupts vital processes. Eggs are protected by shells and may be tucked into protected cracks, which slows gas entry, while pupae are often enclosed in protective coverings that limit gas diffusion. Nymphs can be less susceptible than active larvae and adults because of their developmental stage and coverings. In short, the mobile, actively respiring larvae and adults tend to be the life stages most effectively controlled by fumigants.