Laboratory and semifield data indicate that vector Culicoides spp. in Florida are susceptible to permethrin.

The genus Culicoides includes numerous species that are biting nuisances and vectors of pathogens affecting humans, livestock, and wildlife. For instance, Culicoides paraensis is the primary vector of Oropouche virus to humans, while other species, such as Culicoides sonorensis, Culicoides insignis, and Culicoides venustus transmit viruses causing hemorrhagic disease in ruminants, particularly bovids and cervids. Current control practices for 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 semifield experiments to evaluate permethrin susceptibility in wild biting midges collected on 5 Florida deer farms, including known and suspected hemorrhagic diseasevector 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). Centers for Disease Control and Prevention bottle bioassays using 10.75 µg permethrin per bottle resulted in 100% mortality within 30 min across all Culicoides spp. Similarly, semifield cage trials with ultra-low volume permethrin-based space sprays applied at maximum label rate caused 100% mortality of all Culicoides spp. and susceptible Ae. aegypti within 1 h 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 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.