Studies on insecticide resistance in anopheline mosquitos.

Abstract

This paper describes observations made both on laboratory colonies in London and on wild-caught material in the field of insecticide-susceptible and -resistant strains of A. gambiae, A. sundaicus and A. stephensi. The techniques used in assessing the susceptibilities of both larvae and adults are described and the effects of species, rearing, age, sex, feeding and ovarian development on susceptibility are discussed. The effect of continued selection by DDT in the laboratory of a presumably homogeneous susceptible strain of A. stephensi is then outlined and the phenomenon of “vigour tolerance” demonstrated. Specific, monofactorially-inherited resistance is then described as witnessed with A. gambiae and A. sundaicus. A. gambiae shows a high degree of resistance to dieldrin and cross-resistance to the related cyclodiene compounds and gamma-BHC, but remains susceptible to DDT. Resistance is due to a single gene, partially dominant, the hybrid showing a moderate degree of resistance. A. sundaicus shows a moderate degree of resistance to DDT and cross-resistance to DDT analogues, but remains susceptible to dieldrin and gamma-BHC. Resistance is again due to a single gene but here it is virtually recessive and the hybrid is to all intents and purposes susceptible. The discriminating dosage technique for distinguishing the phenotypes in these species is described. Resistance in other anophelines and in houseflies is discussed and suggestions made as to methods of detecting anopheline resistance in the field.