Asaia spp. accelerate development of the yellow fever mosquito, Aedes aegypti, via interactions with the vertically transmitted larval microbiome

Background: Aedes aegypti mosquitoes are the primary vectors of yellow fever, dengue, chikungunya and Zika virus. Control programs primarily rely on insecticide application, which encounter challenges related to efficacy and resistance evolution. Alternative strategies, such as the sterile insect technique, highly depend on efficient mass-rearing of healthy insects prior to mass release. Based on effects seen in other mosquito species, we tested the hypothesis that acetic acid bacteria of the Asaia genus are mutualists for developing Ae. aegypti larvae. We tested for beneficial interactions across three Asaia species and whether Asaia inoculation benefited both axenic and conventionally reared larvae. To better understand the underlying mechanisms, we characterized the larval microbiome using culture-based methods and 16S rRNA gene amplicon sequencing. Results: Even though Asaia bacteria were transient members of the gut community in conventionally reared insects, two Asaia species accelerated larval development relative to controls. Despite their transient nature, the two mutualist Asaia species had lasting impacts on the larval microbiome, mostly by altering the relative abundance of the most dominant bacteria genera Klebsiella and Pseudomonas and other minor components. Axenic larvae that were inoculated with Asaia were dominated by this group, but always exhibited slower development than conventionally reared insects. Conclusions: These results reveal Asaia as a poor mutualist for Ae. aegypti, with its positive effect on the host mediated by interactions with other bacteria. A practical application of Asaia for improving mass-rearing efficiency results from the acceleration of development time to pupation by a day.