Effects of forced egg retention on the temporal progression of West Nile virus infection in culex pipiens quinquefasciatus (Diptera: Culicidae)

Environmental factors that impact the biology of mosquito vectors can have epidemiological implications. Lack of oviposition sites facilitated by environmental factors such as temperature and drought can often force Culex spp. mosquitoes to retain their eggs. Culex pipiens quinquefasciatus Say were fed blood meals containing West Nile virus (WNV; family Flaviviridae, genus Flavivirus) and either allowed to oviposit or forced to retain their eggs through different time points postinfection (9, 13, 20, 27 d) at 28°C. Oviposition status did not significantly affect rates of WNV infection (% with virus-positive bodies), dissemination (% with virus-positive legs), or transmission (% with virus-positive saliva) for any of the tested time points. As expected, WNV titers in bodies and legs were significantly (P < 0.05) higher at late time points compared with early time points. No significant differences were observed in WNV titers in saliva between time points. There were no significant effects of oviposition status on virus titers of bodies, legs, or saliva. However, we found that egg retention may increase vector competence at early and late time points after infection and that a single oviposition event may decrease vector competence, possibly by activating an immune response against the virus. Environmental changes that influence mosquito biology are important determinants of virus transmission, and further studies are needed to assess the effects of drought on virus transmission risk and how these interactions affect our interpretation of field data.