Biochemical Mode of Action of Bromophos on Bombyx mori L.

The biochemical action of bromophos, an organophosphorus insecticide with relatively low toxicity to the silkworm, was studied on Bombyx mori. Acetylcholinesterase activity in the IV instar larvae shows differential tissue distribution, being highest in the integument followed by the gut and lowest in the haemolymph. In vivo inhibition of acetylcholinesterase by topical application of bromophos to the IV instar larvae was observed. The inhibition recovered rapidly within 12 h. The inhibition was dose-related. In vitro inhibition studies showed that cholinesterase of the gut is more sensitive to bromophos than that of fhe integument enzyme as judged db IC₅₀ values. The parent phosphorothioate compound is by itself a good inhibitor of cholinesterase.