The Coachella Valley Mosquito and Vector Control District is responsible for providing vector control services for 2,400 square miles of desert valley in Southern California. Laboratory Manager, Jennifer Henke, says 2016 was the year the operation changed—when Aedes aegypti was added to its list of detected species capable of transmitting viruses to people, alongside Culex quinquefasciatus and Culex tarsalis.

Fortunately, the District has not yet been affected by the diseases that Aedes aegypti transmit, yet they are diligent in taking precautionary measures to prevent the spread of any illness. This prompted the decision to implement WALS™, a biorational application strategy to control container mosquitoes in cryptic habitats, using VectoBac® WDG. “We find Aedes aegypti everywhere,” Jennifer says. “So, trying to treat them in the same way as Culex doesn’t work. We need to treat lots of properties at the same time.”

Coachella Valley had never before performed a WALS application directly over residents’ homes, and anticipated residents might have concerns about the new technique. The District strategized along with city officials on ways to educate residents, and ultimately designated a timeframe to address questions and concerns prior to implementing a WALS approach. They distributed door hangers, developed a FAQ document and educated employees on how to answer basic questions from the public. Jennifer says the overall response from the community was positive, supported by a media event where television stations came out to cover this first-of-its-kind spray operation in California.

The cup test

So, what were the results? To test the effectiveness of WALS, the District placed cups in the yards of residences where it conducted aerial applications. To ensure VectoBac WDG would reach hidden places where mosquito larvae might live, the cups were placed in areas that were 25%, 50% and 100% obstructed from the sky. The team collected cups at least one hour after the application ended; they added water to the cups; then larvae; and they waited four days. The results: In cups that were 100% obstructed from the WALS application, Coachella Valley achieved 90% larval mortality! Cups that were less obstructed had even higher larval mortality!

Coachella Valley conducted a similar experiment for ground applications using truck-mounted sprayers, including both the A1 Super Duty sprayer and ADAPCO’s Guardian L 190 sprayer. The District wanted to be sure street-front sprays would reach backyards, so they placed cups in both the front and backyards. Some cups were at least 50% obstructed from WALS applications. The experiment resulted in 100% larval mortality!

In addition to effectively treating Aedes mosquitoes, Jennifer’s team is encouraged that the treatment will be effective for Culex mosquito control, as well. Surveillance of WALS applications have been set up to watch trap numbers and preliminary trap counts have shown WALS to be effective against Culex. The District will continue to conduct air and ground evaluations of WALS applications using VectoBac WDG against both species.

Overall, Jennifer says of WALS, “It’s taken a lot of work by a lot of people, but it’s a great tool to use if you need to get mosquito numbers down. It works really well, and you see quick results.”

Learn More

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