Insecticide resistance across the Northeast and Mid-Atlantic United States: results from 6 years of monitoring (2019–2024)

In 2019, the Northeast Regional Center for Excellence in Vector-Borne Diseases (NEVBD) initiated a unique region-wide insecticide resistance monitoring program covering the Northeast and Mid-Atlantic United States regions. NEVBD evaluated 2 key mosquito vectors, Aedes albopictus Skuse [Diptera: Culicidae] and Culex pipiens L. [Diptera: Culicidae], for resistance to insecticides deployed against larval and adult mosquitoes. Additionally, Culex restuans Theobald [Diptera: Culicidae] mortality was assessed. Insecticide use surveys provided insights into the region's resistance monitoring capacity and insecticide usage. In response to these surveys, NEVBD developed susceptibility curves, diagnostic doses, and larval bioassays for regionally important larvicides. Adulticide resistance was assessed using CDC bottle bioassays. A total of 42 agencies submitted mosquitoes for testing, including Cx. pipiens (79%), Ae. albopictus (10%) and Cx. restuans (10%). Culex pipiens populations with moderate to high pyrethroid resistance were identified in several locations, along with emerging resistance to organophosphates in Virginia. Additionally, Cx. pipiens resistance to the larvicide methoprene was widespread, while no resistance to Bacillus thuringiensis israelensis (Bti) Berliner or Lysinibacillus sphaericus Meyer and Neide was detected. All Ae. albopictus submitted for larvicide testing were susceptible to Bti; but displayed low-level methoprene resistance. To empower regional partners to make informed vector control decisions, NEVBD's resistance data were made publicly available. In addition, organized training sessions and consultations were provided on resistance monitoring practices. Our results confirm the presence of multi-year region-wide insecticide resistance data for medically relevant mosquitoes across the Northeast and Mid-Atlantic states, highlighting the need for coordinated resistance monitoring and training to successfully protect public health.