Insecticidal effects of triorganotin (IV) compounds on the Anopheles stephensi mosquito larvae

Fourteen triorganotin compounds were tested against the second to the fourt h instar larval stages of Anopheles stephensi (An, stephensi), a vector for human malaria. In general, the tricyclohexyltin compounds were the most ef fective. The LC50 values of the tricyclohexyltin compounds ranged from 0.01 0 mu M for the chloride to 0.258 mu M for the fluoride substituent against the second instar larval stage. Triphenyltin hydroxide and triphenyltin flu oride were the least effective larvicides. This was attributed to their pol ymeric nature. The efficacy of the triorganotins declined from the second i nstar to the fourth instar larval stages due to the formation of a thicker chitin covering. In general, the toxicity of the triorganotin compounds was found to be more dependent on the nature of organic ligand attached to the tin atom and not the anionic substituent.