Permethrin susceptibility in Culicoides biting midges from Florida

The re-emergence of Oropouche virus in the Americas highlights the need to assess insecticide susceptibility in Culicoides biting midges (no-see-ums). Current control practices against biting midges rely heavily on chemical insecticides, yet their efficacy and potential for insecticide resistance in biting midges remain poorly documented. We conducted laboratory and semi-field experiments to evaluate permethrin susceptibility in wild biting midges collected on five Florida deer farms, including known and suspected HD vector species, using lab-reared mosquitoes (Aedes aegypti) as a susceptible reference. The Culicoides species tested included: C. insignis (n= 944), C. stellifer (n= 269), C. debilipalpis (n= 68), C. venustus (n= 16), C. edeni (n= 5), C. furens (n= 5). Laboratory CDC bottle bioassays using 10.75 µg permethrin per bottle resulted in 100% mortality within 30 minutes across all Culicoides spp. Similarly, field cage trials with ultra-low volume permethrin-based space sprays applied at various doses caused 100% mortality of all Culicoides spp. and susceptible Ae. aegypti within one hour after exposure. Our findings confirm the effectiveness of permethrin for controlling biting midges and suggest that significant resistance to permethrin has not developed in the wild Culicoides populations tested. This study provides a foundation for optimizing vector control strategies against biting midges by demonstrating their susceptibility to permethrin and emphasizing the need for informed, evidence-based practices.