Bacterial proteins used as larvicides are characterized by what feature?

• A. Larvicide that must be consumed by larvae as an early instar
• B. Contact killer that instantly kills adults
• C. Insect growth regulator that disrupts reproduction
• D. Bird bait for natural predators

Answer: (A)

Bacterial larvicides work as ingestion-activated toxins. The crystal proteins produced by bacteria like Bacillus thuringiensis israelensis are harmless until a mosquito larva ingests them in the water. Inside the larval gut, the alkaline environment and gut enzymes activate the toxins, which then damage the gut lining and kill the larva. This means the products must be eaten by the larvae, with early instars being most susceptible due to higher feeding activity. They are not contact killers for adults, not growth regulators, and not bird bait. So the defining feature is that they must be consumed by larvae, especially in early instars.