Abstract

After village huts in the Kisumu area of Kenya had been sprayed with a nominal 2 g/m2 of OMS-43 (fenitrothion) as part of an insecticidal evaluation programme 964 adults of the Anopheles gambiae complex collected from huts were identified cytogenetically as either An. gambiae (species A) or An. arabiensis (species B). Similarly, cytogenetic methods were used to identify 349 adults collected from granaries and artificial pit-shelters. In addition, 2203 larvae of the gambiae complex collected from different types of habitats were specifically identified cytogenetically. As in a previous survey made prior to insecticidal spraying, adults of An. arabiensis predominated in outdoor collections while An. gambiae was highly endophilic. However, it appeared that spraying with fenitrothion had resulted in an increase in both the degree of exophily in An. arabiensis and also its relative numbers in respect to An. gambiae, although the overall pooulation of both species was greatly reduced by spraying. Insecticidal spraying may have diverted both species from feeding on man to cattle. Except for one village, where larvae of An. arabiensis were commoner than expected in cattle hoof-prints, there was little difference between the selection of different types of larval habitats by the two sibling species. Chromosomal inversions were more common in adults of An. arabiensis than in An. gambiae.