Development of resistance to various insecticides in Culex pipiens fatigans Wiedemann.

Since larvicidal treatment to reduce the numbers of Culex fatigans, the tropical house mosquito, offers a promising means of preventing the spread of filariasis, an assessment was made of the liability of C. fatigans to develop resistance to certain important insecticides. Strains of this mosquito from Burma, Cameroon, Sierra Leone and the USA (California) were submitted to larval selection for periods of seven to 23 generations. It was found that resistance to DDT or deutero-DDT rapidly developed to high levels and that to dieldrin or CP-47412 to moderate levels; dieldrin did not select for DDT-resistance.The organophosphorus compounds chosen developed only a modest tolerance-fivefold to sixfold with malathion or parathion, twofold to fourfold with fenthion or diazinon; the carbamate insecticide Hercules 5727 induced a threefold to fivefold tolerance. There was a general cross-tolerance from the selecting agent to all of the organophosphorus compounds tested and to the carbamate. A Rangoon strain that had already been made DDT-resistant subsequently developed a ninefold resistance to fenthion after 23 generations of selection with this organophosphorus compound, but this is still insufficient to annual the larvicidal effectiveness of fenthion.