Development and decrease of insecticide-resistance in Culex pipiens molestus larvae

Abstract

In the present paper, the author describes the feature of development and decrease of insecticide resistance of the larvae of Culex pipiens molestus against p, p'-DDT, dieldrin and diazinon. The test colony, Fukagawa strain, was collected at Tokyo-Sarue lumber yard in 1962. The test larvae were exposed to varying concentrations of insecticides following WHO method. Originally in 1962, the 4th instar larvae, showed a (LC)_<50> value of 17.87 p.p.m. to p, p'-DDT. After being bred free of insecticide for 20 generations, their DDT-resistance lightly decreased. At the 13th generation of continuous DDT-selection the larvae showed only 8-10% mortality to 100p.p.m. DDT. The colony kept under continuous dieldrin-pressure showed a (LC)_<50> value of approximately 10p.p.m. dieldrin. In the test with the 10th generation of the diazinon-exposed colony the larvae showed considerable rise of resistance, the (LC)_<50> being 0.2857p.p.m.