Effects of larval treatment with the insect development inhibitor PH60:40 on the vectorial capacity of Aedes aegypti (L.) for Brugia pahangi (Buckley and Edeson).

The effects of PH60:40, an insect development inhibitor, on fourth instar larvae of Aedes aegypti were investigated. Apart from delayed lethal action, possible effects on the vectorial capacity of Brugia pahangi were investigated. Two strains of A. aegypti were used, one DDT-susceptible and a good filarial vector and the other DDT-resistant and a refractory vector. A baseline exposure was found which caused only low mortalities in both strains. The treatments did not have any appreciable effect on the vectorial capacity of the good vector strain, but modified the refractory nature of the poor vector strain. It was considered possible that this could be due to a generalized harmful stress of the treatment rather than to a specific action of the chemical. Larvae were therefore subjected to heat treatments, as an example of stress, and these produced similar mortalities as with PH60:40. They did not. however, alter the vectorial capacity of survivors of either strain, so that the effects described do not seem to be due to simple stress.