BACTERIAL POPULATION-DYNAMICS IN 3 ANOPHELINE SPECIES - THE IMPACT ONPLASMODIUM SPOROGONIC DEVELOPMENT

The functional role of bacteria in the midgut of adult mosquitoes is u nknown. In this study, we examined the population dynamics of midgut b acteria of laboratory reared Anopheles stephensi, An. gambiae, and An. albimanus. Mosquito midguts were dissected under sterile conditions a nd examined for the presence of bacteria using standard microbiologic techniques. Ninety percent and 73% (n = 30) of newly emerged An. gambi ae and An. stephensi, respectively, harbored bacteria. In contrast, on ly 17% (n = 23) of An. albimanus harbored any bacteria. The bacterial population increased 11-40-fold in the presence of a blood meal, but t hen decreased to pre-blood meal levels in 3-5 days. Pseudomonas cepaci a, Enterobacter agglomerans, and Flavobacterium spp. were found in all three anopheline species. Midgut bacteria were acquired both transtad ially and through the sugar meal. Transtadial transmission was demonst rated by successfully passaging Escherichia coli HS5 from the larval t o the adult stage. However, midgut bacteria were acquired more efficie ntly through the sugar meal than through transtadial passage. An incre ase in midgut bacterial counts after mosquitoes were exposed to a bact eria/sugar suspension significantly reduced oocyst infection rates and densities in Plasmodium falciparum-infected mosquito cohorts. Since b acteria occur naturally in wild mosquitoes, it may be possible to modi fy anopheline vector competence using introduced or indigenous bacteri a.