The susceptibility of Culex pipiens fatigans to residual insecticides with particular reference to the Taveta-Pare area of East Africa.

Observations have been made on Culex pipiens fatigans in the Taveta-Pare area in East Africa from 1954 to 1961, during which time dieldrin was applied to local houses over a 3(1/2)-year period as part of an experiment in malaria control. At the end of the period of residual spraying the numbers of C. p. fatigans had been reduced by two-thirds in the Taveta area, but in the South Pare area, only some 160 km away, this mosquito was twice as numerous as before spraying. The results of susceptibility tests carried out in untreated and dieldrin-treated areas showed that the susceptibility of C. p. fatigans in East Africa to chlorinated hydrocarbon insecticides was low compared with that of Anopheles gambiae, and varied by at least 20 times in some areas relatively short distances apart. C. p. fatigans from all areas sampled were, however, susceptible to fenthion and malathion.