Droplet Distribution of Formulated Products on Mosquitoes Exposed Via Wind Tunnel: Method Development for Assessment of Product Efficacy Using Fluorescent Dye

Abstract

Mosquito control programs (MCP) rely on methods such as the Centers for Disease Control and Prevention (CDC) bottle bioassay to monitor insecticide resistance for technical grade active ingredients. However, CDC bottle bioassays are not designed to assess formulated insecticide products (FP). A compact wind tunnel allows for FP testing in a laboratory setting and is more convenient than a field trial for assessing FP. This study develops a method for investigating FP droplet number and spread on mosquitoes in a novel compact wind tunnel and analyzes the extent to which this relates to mosquito mortality. Four mosquito populations (two wild, two lab; Aedes albopictus and Culex pipiens/quinquefasciatus) were reared in incubators at 28°C using established methods. Adult female mosquitoes (4-7 d old) were exposed to four FP (oil-based: ReMoa Tri®, Duet®, Biomist®; water-based: AquaDuet®) mixed with fluorescent dye (1g/L dye:FP ratio) in a wind tunnel to visualize droplet distribution. Mortality was monitored 2, 24, and 48 h post-exposure. No significant differences (P > 0.05) were observed in the number of droplets per mosquito between FP, indicating homogeneous droplet distribution in the wind tunnel. Significant differences (P < 0.05) were observed in droplet distribution between mosquito body parts and this varied by FP. Droplet counts on mosquitoes (subset of cages analyzed) were significantly related to aggregate mosquito mortality for Biomist® and ReMoa Tri®, but not for AquaDuet® or Duet®.