Genetics of house-entering behaviour in East African populations of Aedes aegypti (L.) (Diptera: Culicidae) and its relevance to speciation

Abstract

Samples of larvae of Aedes aegypti (L.) were collected in three principal habitats, domestic, peridomestic and feral, in the Rabai area in eastern Kenya. The samples from the domestic habitat represent the population of the domestic form, A. a. aegypti, and the feral samples from tree holes from Bejumwa Forest represent the feral subspecies, A. a. formosus (Wlk.). The peridomestic samples from steps cut into trunks of coconut palms most probably represent hybrids between the domestic and the feral forms. These samples were brought to the laboratory where they reproduced in high numbers, and crosses were made between the three populations. Adults of the parental populations and those resulting from the crosses were marked with different colours of fluorescent pigments, released in the peridomestic habitat in the Rabai area and subsequently recaptured in biting catches on man in the domestic and peridomestic habitats. The results indicate that domesticity, particularly house-entering behaviour, in A. aegypti is genetically controlled and is a product of the action of several genes. The gene action in terms of house-entering behaviour is additive as can be clearly seen from the recapture data for the various crosses. The percentage entering houses was highest among mosquitoes of the form from inside houses (the domestic A. a. aegypti population (D)) and the percentages decreased progressively through the peridomestic (P) and hybrid forms to the feral population of A. a. formosus (F) in the following manner: D (45·)DP (15 ·5), PD (13·9), P (9·8), DF (5·7), FD (73·), PF (1·5), FP. (0·6) and F (0·6).The recaptures outdoors were in the reverse order, the highest percentage being for F (187·) and the lowest for D (8·5), DP (8·0) and PD (7·7). The data suggest that the larvae from the peridomestic habitat may represent hybrids between the domestic and feral formsA model for the inheritance of behavioural characters in mosquitoes is presented. On the basis of isolating mechanisms and partial hybridisation, it is concluded that A. a. aegypti and A. a. formosus have developed as geographically isolated allopatric populations. This supports the existing polytypic concept of speciation in A. aegypti. Spatial distribution, non-random mating and the existing series of isolating mechanisms indicate that the domestic type form has been introduced into East Africa, most probably on ships.