COMPARISON OF DIFFERENT INSECTICIDE EXPOSURE METHODS TO ASSESS INSECTICIDE RESISTANCE IN MOSQUITOES

Abstract

Mosquito issues related to pathogen transmission and nuisance are handled by mosquito control programs throughout North Carolina and elsewhere. Field trials are a common method for evaluating the efficacy of insecticide-formulated products (FP); however, this method is cumbersome, expensive, and labor-intensive. A novel compact wind tunnel used in a laboratory setting was developed as an alternative method for evaluating FP efficacy and mosquito mortality was compared between the field trial and wind tunnel methods of exposure. Two different FP (Biomist® 3+15 and Duet®) were applied to wild and laboratory populations of Aedes albopictus and Culex pipiens/quinquefasciatus. The field trial included FP application via truck-mounted ultra-low volume (ULV) equipment to caged mosquitoes set up in a 9 x 3 grid with 100 ft distances between rows of stations. Mosquitoes were transferred to clean cages immediately post-exposure, incubated at 28°C, and mortality monitored for 36 h. Wind tunnel experiments consisted of exposing each replicate mosquito cage to aerosolized FP for 10 s, following the same post-exposure methods as in the field trial. Mosquito knockdown was recorded 2 h post-exposure, and mortality was recorded at 36 h. Mosquito mortality in the group exposed to FP at 100 ft (closest location to ULV treatment) during the field trial was similar (p>0.05) to mosquitoes exposed in the wind tunnel for Biomist® and Duet®. Mosquito mortality in the group exposed to FP 200 ft and 300 ft from the field trial spray line was similar to the wind tunnel for Duet®, but significantly lower than wind tunnel results for Biomist® (200 ft: p=0.019, 300 ft: p=0.049). There was nearly 100% mortality in the lab Ae. albopictus, wild Ae. albopictus, and lab Cx. pipiens/quinquefasciatus for Biomist® and Duet® in the wind tunnel, but field trial results varied depending on distance from the spray line and mosquito population. Wild Cx. pipiens/quinquefasciatus showed insecticide resistance in both the field trial and wind tunnel experiments for all tested FP. Based on these results, the wind tunnel could be used as a screening step for FP or a potential alternative testing method when field trials are not possible.