Effects of Asaia spp. on the development, size and associated microbiomes of two mosquito species of medical importance.

Vector control is essential for mitigating arbovirus outbreaks that are fuelled by the global spread of medically important mosquito species. Control based on synthetic insecticides can be ineffective due to the increasing evolution of resistance. In response, alternative strategies to insecticides, such as the sterile insect technique, have been developed. These rely on mass production and release of sterile or genetically-modified males to target vector populations. The efficient production of 'high-quality' males is crucial for sustaining these control programmes. Probiotic symbionts, inoculated into larval rearing water, present a potentially valuable tool for insect rearing. Here, we tested the hypothesis that inoculation with Asaia spp. can increase both development rate and adult size of the Yellow Fever mosquito Aedes aegypti and the common house mosquito, Culex pipiens molestus. Based on previous work, we hypothesized that Asaia inoculation would affect insect development via effects on other components of the insect microbiome. To test this, we conducted 16S rRNA amplicon sequencing on larval and pupal stages. Exposure to Asaia spp. shortened larval development time and increased adult size in Ae. aegypti and Cx. p. molestus and increased the proportion of insects completing pupation in Ae. aegypti. Effects on adult size were sex-specific but qualitatively consistent across insect species: Asaia bogorensis increased the size of males and females, while A. krungthepensis affected males only. The microbiome analysis was consistent with Asaia affecting insect development via changes in community structure, although inoculation primarily affected the less frequent bacterial taxa. The positive effects of Asaia inoculation on development rate were qualitatively consistent with previous work conducted in a separate insectary, highlighting the reproducibility of Asaia inoculation as a probiotic technique. Overall, our findings suggest that incorporating Asaia as a probiotic symbiont into mass-rearing systems could enhance productivity and yield larger males for release in vector control programs.