This project will investigate the environmental and genetic factors that critically influence sporogonic development and mosquito susceptibility to Plasmodium falciparum parasites. This research is based on the general hypotheses that the vector competence of Anopheles gambiae is determined by the genetic conditions of mosquitoes and parasites and mediated by environmental conditions. The long-term goal is to improve our understanding of the impact of environmental and climate-driven factors on mosquito vector competence and to identify molecular markers for refractoriness that can be used to study transmission. There are 3 specific aims: 1) to evaluate the effects of abiotic environmental factors on P. falciparum sporogonic development in African malaria vectors with particular emphasis on ambient temperature, 2) to evaluate the effects of biotic factors on P. falciparum sporogonic development in African malaria vectors, and 3) to determine the genetic mechanisms of vector competence in the An. Gambiae/P. falciparum system. The experimental design will involve using P. falciparum parasites, from both in vitro cultures and from naturally-infected volunteers, and its natural vector An. Gambiae to test two hypotheses: 1) parasite development and vector competence are affected by environmental variables such as temperature, adult feeding history, and larval nutrition status, and 2) the genes that confer mosquito refractoriness to the malaria parasites can be identified, isolated and characterized via determination of linkage association between the refractory phenotype and molecular markers of mosquitoes. In addition, we will examine whether mosquito refractoriness is parasite strain-specific. Information on the mechanisms naturally regulating the successful development of malaria parasites in vector species will facilitate the development of new molecular tools for better studying vector-malaria parasite relationships and the natural transmission of P. falciparum to humans living in malaria endemic areas.