Wolbachia modulates prevalence and viral load of Culex pipiens densoviruses in natural populations.

The inadequacy of standard mosquito control strategies calls for ecologically safe novel approaches, for example the use of biological agents such as the endosymbiotic alpha-proteobacteriaWolbachiaor insect-specific viruses (ISVs). Understanding the ecological interactions between these "biocontrol endosymbionts" is thus a fundamental step.Wolbachiaare transmitted vertically from mother to offspring and modify their hosts' phenotypes, including reproduction (e.g., cytoplasmic incompatibility) and survival (e.g., viral interference). In nature,Culex pipiens(sensu lato) mosquitoes are always found infected with genetically diverseWolbachiacalledwPip that belong to five phylogenetic groups. In recent years, ISVs have also been discovered in these mosquito species, although their interactions withWolbachiain nature are unknown. Here, we studied the interactions between a widely prevalent ISV, the Culex pipiens densovirus (CpDV,Densovirinae), andWolbachiain northern TunisianC. pipienspopulations. We showed an influence of differentWolbachiagroups on CpDV prevalence and a general positive correlation betweenWolbachiaand CpDV loads. By investigating the putative relationship between CpDV diversification andwPip groups in the different sites, we detected a signal linked towPip groups in CpDV phylogeny in sites where all larvae were infected by the samewPip group. However, no such signal was detected where thewPip groups coexisted, suggesting CpDV horizontal transfer between hosts. Overall, our results provide good evidence for an ecological influence ofWolbachiaon an ISV, CpDV, in natural populations and highlight the importance of integratingWolbachiain our understanding of ISV ecology in nature.