In‐vivo and in‐vitro studies on DDT uptake and metabolism in susceptible and resistant strains of the mosquito Aedes aegypti L.

Abstract

AbstractTwelve strains of Aedes aegypti have been compared for resistance to pp′‐DDT, uptake of pp′‐DDT, and dehydrochlorination of pp′‐DDT to pp′‐DDE in vivo and in vitro both at the larval and adult stages. Resistant larvae were shown to contain significantly more pp′‐DDE than susceptible larvae after a standard exposure to pp′‐DDT but also substantially more pp′‐DDT in an unmetabolised state. There was a small increase in the percentage dehydrochlorinated in vivo in the resistant strains compared with the susceptible strains, but this was not correlated with the level of resistance nor with dehydrochlorination in vitro. However, dehydrochlorination in vitro was correlated with resistance. Adult resistance was correlated positively with dehydrochlorination, both in vivo and in vitro, but the resistant adults did not contain increased levels of unmetabolised DDT. By comparing resistance levels at the two stages, it was found that there were two kinds of resistant strain: four strains of Asian origin and one from West Africa were highly resistant as larvae but showed almost no resistance as adults; five strains from Central and South America were highly resistant at both stages. The different mechanisms of resistance in adults and larvae are discussed in relation to genetic studies.