Studies of house-entering habits of mosquitoes in The Gambia, West Africa: experiments with prefabricated huts with varied wall apertures.

The house-entering behaviour of nocturnal mosquitoes was studied in The Gambia. Mosquitoes were captured as they attacked man in the open and in experimental huts which comprised 1.8 m cube frames with corrugated iron roofs and plywood walls of various heights. Catches of all species were similar in the open and in a roofed, but unwalled, hut frame. The mosquitoes taken in catches in unwalled huts and others with wall heights of 0.6, 1.2 and 1.7 m (giving an 8 cm eaves-level entry slit) fell into two categories. The first group, which included the endophilic species Anopheles gambiae Giles s.l., An. melas Theobald and Mansonia spp. were only slightly affected by increasing wall height, but the second group, including the exophilic mosquitoes Aedes spp., An. pharoensis Theobald, Cx poicilipes (Theobald) and Cx thalassius Theobald showed a very marked progressive exclusion. In comparisons of catches in two huts with 8 cm entry slits at eaves or ground level, large numbers of An. pharoensis found access through the ground level entry but not at eaves level. No consistent difference could be demonstrated for other species. It is concluded that the house-entering behaviour which distinguishes endophagic mosquito species includes at least two distinct responses: flight upwards to eaves level and the passage from outside to indoors. It is also suggested that house entry as a component in host-seeking behaviour and indoor resting are distinct, but not necessarily exclusive, behavioural traits.