Studies of House Leaving and Outside Resting of Anopheles gambiae Giles and Anopheles funestus Giles in East Africa. I.—The Outside Resting Population

The behaviour of Anopheles gambiae Giles and A. funestus Giles was studied under natural conditions in a lowland area of Tanganyika. Studies on the outside resting population were carried out by direct searching for natural resting sites, and by the use of artificial box shelters partly buried in the ground in shaded localities. Catches in these give a valid sample when set up at some distance from houses. Fed and gravid females comprised 67 per cent. of the outside resting gambiae population, the latter group being between 12 and 4·5 times as numerous as the former. Rather less than half the funestus females caught were unfed, the remainder of the population being mainly composed of gravid females. Precipitin tests on the small numbers of fed females caught outside were nearly all positive for man. The identification of gravid funestus females was confirmed by periodic examination of the eggs. Entry of females into outside shelters did not occur solely in the period around sunrise. An appreciable number of funestus females did not enter before 07.00 hours and this was particularly so in shaded shelters. The building of a hut in the vicinity of a box shelter caused a drastic reduction in the numbers of mosquitos resting in the latter. Outside biting activity in these two species is of negligible importance as a source of females resting outside.