The effect of hybridization of Culex pipiens complex mosquitoes on transmission of West Nile virus

Background: Culex pipiens L. complex mosquitoes have a global distribution and are primary vectors of pathogens of public health significance. In the U. S., Cx. pipiens bioformes, Cx. pipiens form pipiens and Cx. pipiens form molestus, as well as Cx. quinquefasciatus, are primary vectors of West Nile virus (WNV; Flaviviridae, Flavivirus). These mosquitoes reside in distinct but overlapping ecological niches and readily hybridize in areas where they coexist. Although species and population-specific differences in vector competence of Culex mosquitoes for WNV have been identified, the extent to which hybridization within this complex alters WNV transmission potential has not been well characterized. Findings: WNV vector competence of laboratory colonies of Cx. p. f. pipiens, Cx. p. f. molestus, and Cx. quinquefasciatus was assessed and compared to hybrid populations created from reciprocal mating of these lines. The results demonstrate that hybridization has a significant effect on WNV infection, dissemination, and, particularly, transmission in Culex pipiens L. complex mosquitoes. Specifically, enhanced transmission of WNV was measured in all hybrid populations relative to one or both parental stains. Conclusion: These findings demonstrate that environmental or anthropogenic changes resulting in fluctuations in the distribution and extent of hybrid populations of Culex mosquitoes could have a significant impact on transmission patterns of WNV in nature.