A three-year survey of mosquito populations in Brown County, South Dakota, USA, and implications for west nile virus

West Nile virus (WNV), a serious mosquito-borne zoonotic disease, has been reported in all contiguous states. The prevalence of WNV is particularly high in South Dakota, with the highest incidence in Brown County. Prior to 2013, monitoring of mosquito populations in Brown County was restricted to the Aberdeen city limits, the county’s largest city. Here, we report results from 2013-2015 surveillance activities outside of Aberdeen, where control is limited. Data presented includes insecticide resistance analyses from the 2015 season. Eight locations were surveyed using carbon dioxide light traps. Traps were placed at various rural locations throughout Brown County, including Sand Lake National Wildlife Refuge and Richmond Lake State Park and other locations in the James River Valley. Mosquitos were collected 4-5 days/week from June-September. Individuals were identified to species, and Culex tarsalis were tested for WNV; Minimum Infection Rates (MIR) were then calculated. All sites had MIRs >0.6, indicating the need for increased vigilance and testing, with two sites exhibiting an MIR >4.0, suggesting high viral activity and the need for prompt action. This indicates that the rural localities sampled provide ideal habitat for disease-carrying species and that increased efforts are needed to prevent WNV.