Host Preference in Aedes (Stegomyia) Species Mosquitoes With Special Reference to the Anthropophilic and Non Anthropophilic Forms of Aedes (Stegomyia) Simpsoni Theobald (Diptera, Culicidae) in Uganda

Abstract

Host preference in Aedes (Stegomyia) species mosquitoes was investigated with special reference to the anthropophilic and non-anthropophilic forms of Aedes (Stegomyia) simpsoni Theobald in Uganda. Four aspects were studied; namely 1, the natural hosts of A. simpsoni in an area where it is non-anthropophilic: 2, the Genetic and environmental factors controlling host preference: 3, isolation of Bwamba anthropophilic populations: 4, the response and stimuli involved in host preference. Host preferences of anthropophilic and non-anthropophilic strains of both A. simpsoni and Aedes aegypti are stable in culture and are predominantly genetic, not environmental, in origin. The genotype of the male parent is the main determining factor. The character is probably polygenic but at relatively few loci. In the two strains of A. simpsoni there is at least partial genetic isolation as measured by the hatchability of hybrid eggs. Proximately, host selection appears to be based on response by females to specific odours and the site of reception is the antennae. The experimental measured response to odour alone suffices to explain the observed host preference. Rodents are the main hosts of A. simpsoni in the non-anthropophilic population in Bwayise. The actual species used is probably

determined by interplay of innate preferences and host availability, especially in relative synchrony of diurnal activity rhythm of the rodent with that of the mosquito. Further data on this is required. The non-anthropophilic population do occasionally bite man. Non-anthropophily is merely one aspect of non-primatophilyi the Bwayise strain does not normally feed upon wild primates either. This explains the almost total absence of human yellow fever in non-anthropophilic areas in Uganda, even though, in non-anthropophilic areas reservoirs of disease are present in monkeys and some A. simpsoni do bite man. The anthropophilic.Bwamba strain is isolated from the non anthropophilic Uganda strains by the geographical and ecological barriers of the Ruwenzori mountains and the Semliki flats. Recently established areas on the West (Bwamba) side of the mountains were found to contain a population of anthropophilic tendencies. Colonization of those areas may be either by direct importation in Colocasia plants, or by dispersal along the new cultivated tracts through former forest areas. Spread of the anthropophilic form out of Bwamba is rendered less likely by the partial genetic incompatibility between the two strains: but the circumstances and possible hazard are worth serious considerations.