| Culex tarsalis and members of the Culex pipiens complex are the primary vectors of West Nile virus (WNV) in California. Since both Culex species feed on a variety of avian hosts, with varying WNV competence, as well as disease-susceptible mammals, such as horses and humans, determining the bloodfeeding patterns of these mosquitoes may be critical in understanding the transmission dynamics of WNV throughout the state. A novel bloodmeal identification assay was developed based on the LuminexRTM microsphere platform. The assay utilized the barcoding region of the mitochondrial gene cytochrome c oxidase I (COI) and species-specific capture probes to identify 15 common vertebrate hosts. In combination with DNA sequencing, the assay identified the avian, mammalian and reptilian hosts of over 2500 Culex mosquitoes. Sampling bias was explored among collection methods. There was no difference in the hosts of Culex collected in gravid traps and resting locations, whereas partial fed females collected from CO2 traps differed significantly from both gravid trap and resting collections and may be biased toward more defensive hosts. Seasonal changes in bloodfeeding were investigated at a rural farmstead and heronry. When present during nesting, herons and egrets were the most frequent hosts, but Cx. tarsalis demonstrated a shift to more mammalian bloodfeeding during late summer and fall. This shift also corresponded to feeding on a greater diversity of avian hosts and was associated with changes in host availability and increased mosquito abundance. Spatial differences in Culex bloodfeeding were explored throughout California, and nearly 100 different vertebrate host species were identified. Variation in bloodfeeding patterns primarily resulted from differences in host availability and abundance. Several species, including House Sparrow, House Finch, Mourning Dove, and Domestic Dog, were frequent hosts throughout the state, and highly competent corvids, Western Scrub-Jay, Yellow-billed Magpie, and American Crow, were fed upon more frequently than in previous studies. WNV-competent avian hosts were fed upon in each study area and throughout the seasons. By feeding on competent hosts and humans, Cx. tarsalis and the Cx. pipiens complex could serve as both enzootic and epidemic vectors of WNV in California. |
