310 - Survey of Aedes aegypti insecticide resistance mechanisms across the United States Virgin Islands in 2020

A study in 2015 found insecticide resistance to permethrin and malathion on St. Croix, USVI. A broader survey to detect insecticide resistance in Aedes aegypti was conducted in 2020 in the U.S. Virgin Islands. Mosquitoes were collected from St. Croix (n=3 sites), St. Thomas (n=3), and St. John (n=2). Eight chemicals were tested from each site: permethrin, malathion, alpha-cypermethrin, lambda-cyhalothrin, deltamethrin, etofenprox, d-phenothrin, and naled. Mosquitoes across all islands were either susceptible to organophosphates or had low levels (87-97% mortality) of resistance with a weak mechanism behind the resistance per the CDC bottle bioassay. Resistance to pyrethroids (0-97% mortality) and strength of pyrethroid resistance (0-100% mortality after 2 hours of exposure) was variable across the islands. In general, most susceptible populations were on St. John. Further testing was done to determine which resistance mechanism(s) contributed to the observed resistance. Results from enzyme and molecular assays screening for metabolic and altered target site mechanisms will be presented. Overexpression of enzyme classes and frequency of altered target site genes was detected. Field trials with formulated products is indicated to determine what application rates might be effective in each location.