Submitted to: Journal of the Mosquito Control Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 31, 2007
Publication Date: September 16, 2008
Citation: Hoffmann, W.C., Fritz, B.K., Farooq, M., Cooperband, M.F. 2008. Effects of wind speed on aerosol spray penetration in adult mosquito bioassay cages. Journal of the American Mosquito Control Association. 24:419-426. Interpretive Summary: The use of ultra low volume (ULV) insecticide droplets for adult mosquito control was developed by the USDA in the 1960s and is broadly used for controlling adult mosquito populations today. Insecticide efficacy and control success is frequently assessed using sentinel or mosquito cages, but few studies have investigated how varying wind speed may affect ULV droplet entry into cages. Studies were conducted to determine the size of droplets that enter two different mosquito cages. These studies showed that both cages reduced the wind speed and amount of spray inside the cages as compared to that outside of the cages. The results from these studies will help researchers and mosquito control personnel to better understand how these differences inside and outside of cages could affect insecticide efficacy measurements.
Technical Abstract: Bioassay cages are commonly used to assess efficacy of insecticides against adult mosquitoes in the field. To properly correlate adult mortality readings to insecticidal efficacy and/or spray application parameters, it is important to know how the cage used in the bioassay interacts with the spray cloud containing the applied insecticide. This study compared the size of droplets, wind speed, and amount of spray material penetrating cages and outside of cages in a wind tunnel at different wind speeds. Two bioassay cages, CMAVE (Center for Medical, Agricultural and Veterinary Entomology) and Circle, were evaluated. The screen materials used on these cages reduced the size of droplets, wind speed, and amount of spray material inside the cages as compared to the spray cloud and wind velocity outside of the cages. When the wind speed in the dispersion tunnel was set at 0.6 m/sec (1.3 mph), the mean wind speed inside of the CMAVE Bioassay Cage and Circle Cage was 0.045 m/sec (0.10 mph) and 0.075 m/sec (0.17 mph), respectively. At air velocities of 2.2 m/sec (4.9 mph) in the dispersion tunnel, the mean wind speed inside of the CMAVE Bioassay Cage and Circle Cage was 0.83 m/sec (1.86 mph) and 0.71 m/sec (1.59 mph),respectively. Consequently, there was a consistent 50-70% reduction of spray material penetrating the cages compared to the spray cloud that approached the cages. These results provide a better understanding of the impact of wind speed, cage design and construction on ultra low volume spray droplets.