Effect of the organophosphorous insecticide, chlorpyrifos (Dursban), on growth, fecundity and mortality ofBiomphalaria alexandrinaand on the production ofSchistosoma mansonicercariae in the snail

Abstract

ABSTRACTExposure ofBiomphalaria alexandrinato sublethal concentrations (0·125, 0·25 and 0·05 ppm) of the organophosporous insecticide, chlorpyrifos (Dursban), induced a reduction in egg production and egg hatchability. Exposure ofSchistosoma mansonimiracidia to the insecticide (60 min, 0·05 ppm) prior to infection ofB. alexandrinadid not affect the subsequent production of cercariae. However, exposure ofS. mansoni—infected snails to the insecticide until day 55, from day 20 to day 62 and from day 35 to 62 following infection resulted in blockage of cercarial shedding. cercarial shedding commenced in some snails when the treatement stopped. Exposure to the insecticide in concentrations of 0·125 and 0·25 ppm during the first 20 days following infection did not affect the subsequent production of cercariae, but exposure to 0·5 ppm during the first 20 days affected markedly the production of cercariae due to a high snail mortality. The findings indicate that the cercaria is the target stage for the activity of chlorpyrifos on the intramolluscan larval development. It is suggested thatS. mansonicercarial production inB. alexandrinamay he a useful system for monitoring the effect of low concentrations of pesticides on the aquatic environment, and that the ability by chemical means to interrupt the cercarial production might be a useful tool in further analyses of important aspects of the snail/parasite relationship.