Factors affecting the vectorial competence of Anopheles gambiae: a question of scale

Malaria transmission in Africa is without doubt governed by the existence of a group of highly efficient vectors, of which Anopheles gambiae Giles sensu stricto is predominant. The endophilic and anthropophagic behaviours of this mosquito create an intimate association between the human reservoir and insect vectors of malaria. In this paper several mosquito-related and environmental factors that modulate the transmission intensity of malaria in Africa are discussed, in order to illustrate the plasticity of the vectors’ responses to malaria interventions. The An. gambiae group of species serves as an example of the highly complex interactions between humans, malaria parasites and mosquitoes. Larval and adult characteristics are described that affect the geographic distribution, phenology and longevity of the mosquito vectors. It is shown that spatial and temporal variations in the environment have considerably more effect on these characteristics than is commonly assumed. It is suggested that epidemiological studies pay greater attention to such variations, in particular when estimating the entomological inoculation rate and vectorial competence. When considering the use of transgenic mosquitoes for malaria control, these effects should be studied in order to understand how local variations in vector ecology might affect the outcome of a transgenic release.