Culex pipiens is the primary vector of WNV. It exists as two bioforms which can hybridize in nature. I characterized the behavioral and genetic variation across eight populations collected from above- and below-ground habitats. Three of the five above-ground populations had hybrid ancestry in our single locus assay, whereas the below-ground populations did not. In choice tests, four above-ground populations were avian-seeking, while the fifth showed no clear preference. All three belowground populations predominately sought the human host. Genetic ancestry was not correlated with host preference. Chemosensation drives host-seeking behaviors in female mosquitoes, which led me to quantify the expression of two chemosensory genes: odorant binding proteins (OBPs) 2 and 12. Both OBPs were more highly expressed in the heads of human-preferring females. While the patterns of OBP2 expression indicate that it may contribute to human host detection, OBP12 expression patterns are more consistent with odor-guided oviposition.