Previous observations in an East African village had revealed that Anopheles gambiae and A. funestus were almost completely anthropophilic, and that only 5 per cent of the biting population was known to rest outside after feeding. Spray-catching in all the houses in the village was therefore used to ascertain the total size of the biting population. From this figure the total numbers at all stages of ovarian development were estimated.
Spray catches in 119 houses yielded over 27,000 mosquitoes. The total number of A. gambiae and A. funestus was estimated at about 15,000 females of each species. As the area of the investigation totalled 380 acres, the spatial density was calculated to be of the order of 40 females per acre of each species. The outside resting population was estimated at 14–15 females per acre of each species. The annual range of fluctuation in density was estimated from observations on the biting population in an experimental hut, in which catches were made throughout the year. The density of A. gambiae at different seasons was estimated to vary between 2 and 48 females per acre and of A. funestus between 0.5 and 78 females per acre.
These results indicate that the very high rate of malaria transmission in the area is maintained by relatively small numbers of anopheles, and that factors influencing the association of the mosquito with man, and the longevity of the mosquitoes, are of primary epidemiological importance.