Differential fitness effects of gut and reproductive tract bacteria in larval and adult stages of the yellow fever mosquito, Aedes aegypti.

The development of axenic (microbiota-free) and gnotobiotic (fully defined and controlled microbiota) mosquito models has opened an opportunity to resolve current questions regarding mosquito-microbiota interactions, including fitness effects, microbiota acquisition, and tissue tropism. In this work, we introduced each of two focal bacterial strains - Enterobacter sp. and Asaia sp. originally isolated from Aedes aegypti midguts and reproductive tracts, respectively - into axenic Ae. aegypti larvae or adults to evaluate the effects of bacterial source and inoculation route on mosquito fitness. Asaia inoculated into mosquitoes at the first instar larval stage resulted in elevated larval and pupal mortality and surviving adults with reduced body and egg clutch sizes compared to adults from Enterobacter-inoculated larvae and conventional controls. In contrast, although inoculation of Asaia into newly emerged axenic adults resulted in lower survival among gnotobiotic females, no differences were observed in body or egg clutch sizes between Asaia- and Enterobacter-inoculated adults compared to axenic and conventional controls. These results suggest that the influence of bacteria on mosquito fitness is greater during the larval stage than in the adult stage, with bacteria isolated from distinct adult tissues differentially affecting host fitness. Source tissue and inoculation methods should be considered when evaluating the feasibility of bacterial candidates for microbiota-based vector control approaches.