Studies in House Leaving and Outside Resting of Anopheles gambiae Giles and Anopheles funestus Giles in East Africa. II.—The Exodus from Houses and the House Resting Population

Observations on the behaviour of Anopheles gambiae Giles and A. funestus Giles in experimental huts and ordinary African houses were carried out in a low-lying area of Tanganyika. Special attention was paid to the exodus of females at different stages of the gonotrophic cycle and to the composition in terms of ovarian development of the house resting population. About 5 per cent. of the biting population of gambiae and the same number of funestus were shown by the use of window traps to be leaving experimental huts after feeding. Forty three per cent. of half-gravid gambiae left an experimental hut at dusk, 12–24 hours after entering for a blood meal, whereas only 3 per cent. of funestus left under the same conditions. Daytime spray catches of gravid gambiae and funestus made in ordinary African houses during the hot season were about 50 per cent. and 30 per cent. lower, respectively, than the corresponding numbers of recently fed specimens. A. funestus therefore makes rather less use of outside shelters than gambiae during the hot months. In the cool season about 50 per cent. of half-gravid and gravid funestus were absent from house catches. No mortality could be detected amongst funestus females resting under natural conditions for 24 hours in an experimental hut. Re-entry of gravid funestus into unoccupied and open types of inhabited houses occurs at dawn.