To determine the effectiveness of the Wide Area Larvicide Spraying (WALS) method, the number of mosquitoes in three treatment zones were compared with an untreated control zone. Mosquito traps were placed weekly to monitor the number of adult mosquitoes before, during and after the treatments. Over the course of 24 weeks, 6,870 Ae. aegypti were collected. We found that there was an overall reduction of Ae. aegypti mosquitoes during and immediately following the WALS treatments compared to the control. The number of mosquitoes then gradually increased in weeks / months following the end of the treatments. We found that the treatment successfully reached the cryptic habitats that Ae. aegypti breed in, preventing them from utilizing these breeding sites and reducing the overall mosquito population.
These results are broadly similar to those found in other areas and show that this is an effective method for controlling this invasive, day biting mosquito. Due to some limitations of this method, such as the cost of material and the amount of labor required for applications, WALS treatments appear to be particularly suitable for relatively small, isolated problem areas and would likely be considered as part of a response to a potential outbreak of an Aedes transmitted virus, such as Dengue or Zika.
This was the first year of a multiyear project to better understand the benefits and limitations of the WALS treatment method for controlling invasive Ae. aegypti. The district will continue the project during the summer of 2023 to further determine the effectiveness of this method. Future information regarding WALS treatments in summer 2023 will be added to the website.