Culex restuans (Diptera: Culicidae) in the upper Midwest: a review of ecology, biology, control, and contributions to human WNV in the region.

West Nile virus (WNV) is a mosquito-borne flavivirus endemic to the United States. Several regions, including parts of the Midwest, experience sustained WNV transmission with annual local and regional outbreaks. In the upper Midwest, Culex pipiens Linnaeus and Culex restuans Theobold, play key roles in WNV circulation, with Cx. pipiens considered the primary epidemic vector responsible for human cases and Cx. restuans linked to early-season enzootic amplification. These species share ecological niches, have similar host preferences, and are morphologically difficult to distinguish. Both are implicated in WNV transmission, but species-level differentiation is not routinely prioritized for many surveillance and control programs due to logistical challenges and limited evidence to support the effort. This narrative review investigates the role of Cx. restuans in WNV transmission in the upper Midwest, focusing on distribution, morphology, vector competence, population dynamics, and vector control. We synthesize current evidence and identify knowledge gaps that may inform vector surveillance practices and contribute to more targeted WNV control strategies.