Laboratory tests on mosquito tolerance to insecticides and the development of resistance by Aedes aegypti

Three strains of Aëdes aegypti and a strain of Culex molestus were used in tests to determine the relative susceptibility levels of the larvae to various insecticides and to investigate the development of resistance in the laboratory through selection by larval treatment only. The procedures and test methods used are described and the results discussed and set out in tabular and graphic form.It was found, inter alia, that selection of fourth-stage larvae of a laboratory strain of Aëdes and Culex for 15 generations with DDT at the LC(50) level did not induce any appreciable decrease in susceptibility; that with another Aëdes strain, naturally three times as resistant to DDT as the laboratory strain, selection for eight generations further increased this resistance to seven times its natural level; that selection of the laboratory strain of Aëdes with gamma-BHC for 15 generations induced a twofold increase in resistance to this compound, which also extended to DDT and dieldrin; and that selection of the same strain with dieldrin, over 14 generations at a low mortality level to avoid after-effects of this insecticide, did not induce any appreciable decrease in susceptibility.