The susceptibility of tsetse flies to topical applications of insecticides. III.—The effects of age and pregnancy on the susceptibility of adults of Glossina morsitans Westw

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Abstract
Solutions of dieldrin, γ BHC, p, p′DDT and Baytex were applied topically to pregnant females of Glossina morsitans Westw. and also, in most cases, to fertilised flies over 21 days old and not noticeably pregnant, to virgin flies over 21 days old, and to males over 18 days old. Pregnant flies required about nine times as much dieldrin as young flies for comparable mortalities, and non-pregnant fertilised flies about four times as much. It was not possible to determine proper regression lines for other insecticides and classes of flies but significant increases in tolerance, as compared with that of young flies, were shown by pregnant flies to γ BHC and DDT, by old virgins to dieldrin and DDT but not γ BHC, and by fertilised flies to γ BHC and DDT. Pregnant flies and virgins showed no increased tolerance to Baytex, and old males showed none to dieldrin, γ BHC or DDT.These results are discussed in relation to aerial spraying of tsetse habitats and it is suggested that they explain some unexpected past results.