The bionomics of salt-water Anopheles gambiae in East Africa.

Following residual spraying of houses in Pemba Island with dieldrin as part of a malaria eradication programme, Anopheles gambiae were found breeding in salt-water pools in many parts of the island. Studies were made on the bionomics of this salt-water form of the mosquito, dealing in particular with its behaviour, feeding preferences, role as a malaria vector, larval reaction to brackish water and adult susceptibility to dieldrin.The first-stage larvae of the freshwater and salt-water forms were found to exhibit a distinct difference in their reaction to 75% sea water, the former dying within 1(1/2) hours and the latter surviving 6 hours or more. It is suggested that this reaction may provide the best way of distinguishing with certainty between the two forms in East Africa.The results of precipitin tests and indoor and outdoor catches showed that, after spraying, the salt-water form was mainly exophilic with a preference for feeding on cattle. Exposure of adult to 0.4% dieldrin by the WHO test method indicated that they were still susceptible to that insecticide after two spraying cycles.