An update on the ecology of the La Crosse virus vector, Aedes triseriatus in western Wisconsin, USA

Abstract

La Crosse encephalitis is a vector-borne disease in humans caused by La Crosse virus (LACV). Since the 1980s, the number of LACV cases have declined in the Midwest. Potential causes for this shift include a change in the vector population of Aedes triseriatus mosquitoes in response to mosquito control efforts in Wisconsin, or competition with Aedes japonicus, an introduced mosquito species. In 2020, 2021 and 2023, I conducted mosquito surveillance to assess abundance of Ae. triseriatus and other mosquitoes in La Crosse and Trempealeau counties, Wisconsin. Mosquitoes collected in 2020 and 2021 were tested for LACV virus. Aedes triseriatus, Ae. japonicus, and five other mosquito species were observed. Aedes triseriatus was the most abundant mosquito overall in every year of the study and was more likely to be in forested as compared to urban areas in 2023. These data show that Ae. triseriatus continues to thrive, despite potential competition with Ae. japonicus. La Crosse virus was not detected in mosquitoes collected in 2020 and 2021 (mosquitoes were not tested in 2023). The abundance of Ae. triseriatus underscores the continued risk of LACV transmission in this area.