Assessment of Culex quinquefasciatus microbiota and the impact of Lysinibacillus sphaericus larvicide exposure on susceptible and resistant strains.

Bacterial symbionts play crucial roles in mosquito development and other features. Increasing evidence suggests that exposure to insecticides can modulate mosquito-associated microbiota, with potential implications for vector control strategies. The goal of this study was to compare the bacterial communities of Culex quinquefasciatus from a laboratory-susceptible (S) strain and a resistant (R) strain to the microbial larvicide Lysinibacillus sphaericus, and a field-collected sample (F) was included as an external reference. Additionally, we assessed whether larval exposure to L. sphaericus influences microbiota structure in laboratory strains. Our results revealed distinct bacterial composition across developmental stages and mosquito groups. Larvae from the S strain exhibited lower bacterial diversity compared to F samples, with Wolbachia and Thorsellia dominant taxonomic signatures, respectively. S females showed significantly higher bacterial diversity, with a marked reduction in Wolbachia relative abundance. In contrast, R and F females showed no changes. Within laboratory strains L. sphaericus treatment had a minor influence on the community of resistant individuals that kept a stable community dominated by Wolbachia throughout the life stages. In contrast S females surviving from larvicide exposure displayed a significant microbiota remodeling with enhanced diversity. Our findings indicate that L. sphaericus resistance phenotype seems to have a limiting effect of diversity found in both life stages, while susceptible females surviving L. sphaericus exposure showed a marked restructuring. Our results suggest that microbiota may act as a relevant component of the set of mosquito responses to microbial larvicides, suggesting modulation of the bacterial communities with potential effects on mosquito biology.