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

Aims: A wide range of vector control programmes rely on the efficient production and release of male mosquito. Asaia bacteria are described as potential symbionts of several mosquito species but their relationship with Aedes aegypti has never been rigorously tested. Here, we aimed to quantify the benefits of three Asaia species on host development in Ae. aegypti, and the ability of these bacteria to form a stable symbiotic association with growing larvae.

Methods and results: In order to disentangle direct and indirect effects of Asaia inoculation on host development, experiments used insects with an intact microbiome and those reared in near-aseptic conditions, while we characterized bacterial communities and Asaia densities with culture dependent and independent methods (16S rRNA amplicon sequencing). Neonate larvae were inoculated with Asaia spp. for 24 h, or left as uninoculated controls, all were reared on sterile food. Aseptic larvae were produced by surface sterilization of eggs. Although all Asaia were transient members of the gut community, two species accelerated larval development relative to controls. The two mutualistic species had lasting impacts on the larval microbiome, largely by altering the relative abundance of dominant bacteria, namely Klebsiella and Pseudomonas. Axenic larvae were dominated by Asaia when inoculated with this species but showed slower development than conventionally reared insects, indicating that Asaia alone could not restore normal development.

Conclusions: Our results reveal Asaia as a poor mutualist for Ae. aegypti, but with a species-specific positive effect on improving host performance mediated by interactions with other bacteria.