Larval sites of the mosquito Aedes aegypti formosus in forest and domestic habitats in Africa and the potential association with oviposition evolution

Abstract

Adaptations to anthropogenic domestic habitats contribute to the success of the mosquito Aedes aegypti as a major global vector of several arboviral diseases. The species inhabited African forests before expanding into domestic habitats and spreading to other continents. Despite a well-studied evolutionary history, how this species initially moved into human settlements in Africa remains unclear. During this initial habitat transition, African Ae. aegypti switched their larval sites from natural water containers like tree holes to artificial containers like clay pots. Little is known about how these natural versus artificial containers differ in their characteristics.Filling this knowledge gap could provide valuable information for studying the evolution of Ae. aegypti associated with larval habitat changes. As an initial effort, in this study, we characterized the microenvironments of Ae. aegypti larval sites in forest and domestic habitats in two African localities: La Lopé, Gabon, and Rabai, Kenya. Specifically, we measured the physical characteristics, microbial density, bacterial composition, and volatile chemical profiles of multiple larval sites. In both localities, comparisons between natural containers in the forests and artificial containers in the villages revealed significantly different microenvironments. We next examined whether the between-habitat differences in larval site microenvironments lead to differences in oviposition, a key behavior affecting larval distribution. Forest Ae. aegypti readily accepted the artificial containers we placed in the forests. Laboratory choice experiments also did not find distinct oviposition preferences between forest and village Ae. aegypti colonies. These results suggested that African Ae. aegypti are likely generalists in their larval site choices. This flexibility to accept various containers with a wide range of physical, microbial, and chemical conditions might allow Ae. aegypti to use human-stored water as fallback larval sites during dry seasons, which is hypothesized to have initiated the domestic evolution of Ae. aegypti.

Biology and Behaviour of Aedes aegypti in the Human Environment: Opportunities for Vector Control of Arbovirus Transmission

“…There is a site in the Rabai District of Kenya where sympatric populations of Aaa and the ancestral Aaf forms introgress freely in urban areas yet remain genetically distinct in rural/forest settings [ 3 , 197 ]. This fortuitous location has been invaluable for a wide range of studies [ 120 , 204 , 205 ] and hence is quite widely known and sometimes perhaps considered representative of Aedes aegypti in sub-Saharan Africa as a whole. However, the ease with which the forms are separable here is rare and not in any way typical of Africa.…”

Entomological Surveillance of Aedes Mosquitoes: Comparison of Different Collection Methods in an Endemic Area in RIO de Janeiro, Brazil

“…Such preference to use human-stored water as fallback larval sites during dry seasons, is hypothesized to have initiated the domestic evolution of Ae. aegypti [ 101 ], and might be a factor already happening to Ae. albopictus in Rio de Janeiro [ 45 ].…”

Aedes albopictus invasion across Africa: the time is now for cross-country collaboration and control

“…However, this subspecies has been recorded in periurban and urban areas in the past decade and, with larval habitats including artificial containers, suggests adaptation to deforestation and urbanisation in Africa. 9 Furthermore, A a aegypti has now been recorded in coastal areas of Africa, probably being reintroduced and hybridised with A a formosus. 10 The introduction of A a aegpyti to Africa and hybridisation with A a formosus has implications for arbovirus transmission.…”