Nutritional sex-specificity on bacterial metabolites during mosquito development leads to adult sex-ratio distortion

Mosquitoes rely on their microbiota for B vitamin synthesis. We previously found that Aedes aegypti third-instar larvae cleared of their microbiota were impaired in their development, notably due to a lack of folic acid (vitamin B9). In this study, we investigated the effects of other B vitamins on the development of germ-free mosquito larvae. We found that diet supplementation using a cocktail of seven B vitamins did not improve mosquito developmental success, but rather had a significant impact on the sex-ratio of the resulting adults, with an enrichment of female mosquitoes emerging from B vitamin-treated larvae. A transcriptomic analysis of male and female larvae identified some sex-specific regulated genes upon vitamin treatment. When treating germ-free larvae with high doses of individual B vitamins, we detected a specific toxic effect related to biotin (vitamin B7) exposure at high concentrations. We then provided germ-free larvae with varying biotin doses or with varying bacterial counts, and showed that males are sensitive to biotin toxicity at a lower concentration than females, and require less bacteria-derived nutrients than females. These findings shed new light on sex-specific nutritional requirements and toxicity thresholds during the development of insect larvae, which impact the sex ratio of adults.