Phenotypic Variation among Culex pipiens Complex (Diptera: Culicidae) Populations from the Sacramento Valley, California: Horizontal and Vertical Transmission of West Nile Virus, Diapause Potential, Autogeny, and Host Selection

Abstract

The vector competence and bionomics of Culex pipiens form pipiens L. and Cx. pipiens f. molestus Forskäl were evaluated for populations from the Sacramento Valley. Both f. pipiens and f. molestus females became infected, produced disseminated infections, and were able to transmit West Nile virus. Form molestus females also transmitted West Nile virus vertically to egg rafts and F1 progeny, whereas f. pipiens females only transmitted to egg rafts. Culex pipiens complex from urban Sacramento blood-fed on seven different avian species and two mammalian species. Structure analysis of blood-fed mosquitoes identified K = 4 genetic clusters: f. molestus, f. pipiens, a group of genetically similar hybrids (Cluster X), and admixed individuals. When females were exposed as larvae to midwinter conditions in bioenvironmental chambers, 85% (N = 79) of aboveground Cx. pipiens complex females and 100% (N = 34) of underground f. molestus females did not enter reproductive diapause.

Comparison of the Potential for Different Genetic Forms in theCulex pipiensComplex in North America to Transmit Rift Valley Fever Virus1

“…However, the results for one virus may not apply to another virus. For example, populations of form pipiens and form molestus have been shown to have nearly identical susceptibility to WNV (Nelms et al 2013). Similarly, while populations of Cx.…”

“…pipiens and Cx. quinquefasciatus (Say) are similar in their response to WNV (Turell 2012, Nelms et al 2013, there are significant differences in their response to RVFV (Turell et al 2010, Turell 2012). In addition, Cx.…”

“…pipiens (Kilpatrick et al 2010, Nelms et al 2013). Therefore, it is possible that the difference in susceptibility between the 2 populations may just be a difference between 2 populations of Cx.…”

The role of Culex pipiens mosquitoes in transmission of West Nile virus in Europe

“…Vector competence of North American lines of biotype pipiens (Pennsylvania) and of biotype molestus (New Jersey) populations were equal, but lower than vector competence of their hybrid progeny (Ciota et al 2013a). In contrast, significant differences in vector competence were found between biotype pipiens (Woodland) and biotype molestus (Sacramento) populations (Nelms et al 2013). No differences in transmission rates were found between four different autogenous and anautogenous Cx.…”

“…Previous studies showed that proper identification and separation of biotypes is essential, because genetic differences between biotypes and populations influence vector competence (Brustolin et al 2016, Ciota et al 2013a, Nelms et al 2013). Furthermore, our previous studies showed that temperature is an important determinant of vector competence of Cx.…”