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Managing Floodwater Mosquitoes in Saint Lucie County, Florida

Florida’s Saint Lucie County lies on the Atlantic coast between Daytona Beach and West Palm Beach. With more than 4,000 acres of wetlands, saltmarsh mosquitoes (Aedes taeniorhynchus) are a constant threat for residents and tourists looking to enjoy the county’s many outdoor recreation opportunities. Larval source management has played a key role in the district’s integrated mosquito management efforts for many years, not only as a way of controlling insect populations, but also to preserve and enhance the ecosystem.

For the past 30 years, it’s been Jim David’s job as Director of Mosquito Control and Coastal Management Services to manage this vast expanse of habitat and protect the public from the nuisance and risk of disease transmission posed by vector insects in Saint Lucie County.

“From May 1 to August 1 each year, we implement a mosquito impoundment program that includes controlled flooding of large sections of the marsh floor through a series of pumps and culverts. In addition to creating a physical barrier to egg-laying, which prevents saltmarsh mosquitoes and sand flies from breeding in these areas, the flooding provides habitats for wading birds, native fish, and mangrove plants,” said Jim. Through this program, the district has transformed what once was a threat to public health into an opportunity to foster public culture through ecological tourism and sharing knowledge of wetland habitats.

However, in the few hundred acres of coastal areas that fell outside the mosquito impoundment program, the conditions were more difficult to control. And that small percentage of habitat had the potential to create big problems when it came to public perception of the district’s efforts.

“When you’re dealing with a mosquito that reproduces so rapidly, a couple acres of viable habitat can produce enormous populations of mosquitoes—so quickly—that adulticiding becomes necessary,” Jim explained.

The challenge in managing those areas came from the tidal flows. The district needed a solution that could provide an initial release of larvicide when applied, but still deliver residual control through multiple flooding cycles. Fortunately, Valent BioSciences Corporation had been working with districts like Jim’s on that very challenge, and they had a solution.

“Before we started using MetaLarv® S-PT, we weren’t being as effective as we would have liked in meeting quality-of-life goals,” said Jim. “In areas where the tidal flow was restricted, traditional larviciding methods provided acceptable control. But the areas  with unrestricted tidal flow made effective larviciding difficult.”

The district’s working hypothesis was that the tide was either washing out or diluting the products it was using, or the products weren’t available quickly enough in the system due to organic absorption. “We monitor larvae populations as closely as we can, but it was difficult to match larvae availability with contact time and duration with the products we had,” Jim noted.