| Understanding the primary factors driving the transmission dynamics of West Nile virus (WNV) is essential to predicting and controlling disease risk to wildlife and to humans. In Chapter 1, I found that seasonal drought conditions, associated with specific thresholds of temperature and precipitation, correspond to epizootic levels of transmission. As a follow up, in Chapter 2, I examined the effects of drought-induced egg retention on the reproductive potential of female Culex pipiens. I found that, consistent with an "all-or-none" ovipositing strategy, female Cx. pipiens are able to maintain a high degree of reproductive potential during prolonged drought events. In Chapter 3, since identification limitations have long confounded the roles of native and exotic Culex species in WNV transmission, I used a cost-effective DNA-based assay to identify field-collected specimens. Contrary to expectations, I found the native species, Cx. restuans, to be more abundant and more frequently infected than Cx. pipiens, an exotic species, in both natural and urban habitats. Importantly, I found that Cx. restuans and Cx. pipiens appear to be acting synergistically resulting in high WNV transmission. Lastly, in Chapter 4, in order to rectify the lack of insecticide resistance (IR) studies in local Culex, I examined the occurrence of IR alleles in New Jersey Cx. pipiens . I found two widespread organophosphate resistant alleles, EsterB1 and Ester2, and the classical knockdown resistance (kdr) mutation (L1014F) conferring resistance to pyrethroids. Importantly, I detected double mutants at the kdr and Ester loci, a condition that may accelerate IR. Taken together, my studies reveal that disease risk for WNV is exacerbated by high temperature/low humidity conditions. I elucidated this paradoxical result by showing that female Cx. pipiens can retain their eggs until they find remnant water filled containers, which during drought become concentrated near humans. Further, I elucidated the important role of the native Cx. restuans in the transmission of WNV and the ways that native and exotic species may act synergistically to maximize transmission. Similarly, my baseline analysis of IR in Cx. pipiens indicates the presence of multiple resistance alleles in single individuals that may drive the spread of resistance. |
