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

Aedes aegypti mosquitoes are the primary vectors of yellow fever, dengue, chikungunya and Zika virus. Control programs primarily rely on insecticide application, encountering challenges related to efficacy and resistance evolution. Alternative strategies 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. Even though Asaia bacteria were transient members of the gut community in conventionally reared insects, two Asaia species accelerated larval development relative to control. Despite their transient nature, the two mutualist Asaia species had lasting impacts on the larval microbiome, chiefly by altering the relative abundance of Sphingobacterium spp.. Axenic larvae were predominantly colonized by Asaia when inoculated with these species. However, exhibited slower development than conventionally reared insects. These results reveal Asaia as a poor mutualist for Ae. aegypti, with its positive effects on the host mediated by interactions with other bacteria. Nevertheless, this study showed Asaia spp. practical applications in improving mass-rearing efficiency: a single inoculation of Asaia into the rearing water of conventional mosquitoes accelerated time to pupation by a day, indicating that the application of carefully screened isolates could provide substantial gains in rearing efficiency.