27 - Evaluating efficacy of pre-season larvicide treatment on WNV vectors in Cook County, IL

The metropolitan region surrounding Chicago, IL, has historically high incidence of West Nile virus (WNV) disease. Culex restuans and Cx. pipiens are the primary enzootic and epidemic vector species for WNV in this area, respectively. Cx. restuans are more abundant in spring and Cx. pipiens in late summer. We conducted a cluster-randomized trial to assess the efficacy of early (April) and late (June) season larvicide treatments, aiming to reduce Cx restuans and its amplification of WNV. Sumilarv® 0.5G, (Sumitomo Chemical, Tokyo, Japan) was applied to 8 treatment sites (April 4–June 4, 2023) within the operational area of North Shore Mosquito Abatement District. Mosquitoes were collected weekly from 96 CDC gravid traps and 48 CDC miniature light traps for 24 weeks after initial treatments. Adult mosquitoes were identified to species using morphological characters and screened for WNV via RT-qPCR. Ovitraps were deployed once a month to examine ratio of the two species compared with species from the CDC gravid and miniature light traps. We hypothesized early treatment sites would have a decreased abundance of Cx. restuans compared with sites in the late treatment group, and reduced infection rates. This study will help inform vector control applications and elucidate population dynamics of Cx. restuans and Cx. pipiens in the upper Midwest.