More rain and growth means more work for South Walton Mosquito Control

Jim Thompson
Northwest Florida Daily News

SANTA ROSA BEACH — Ride across the southern end of Walton County and the signs of growth are obvious: crowded roads, new houses and apartment complexes, and land being cleared for commercial projects.

But Darrin Dunwald is keeping his eye out for another indicator of growth between Choctawhatchee Bay and the Gulf of Mexico.

He's on the lookout for watery places, from storm drain pipes to low places in residential and commercial developments, to trash cans, old tires and other sites where water can accumulate.

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Those and other places can provide a perfect breeding ground for mosquitoes, which can in turn transmit diseases like West Nile virus, the dengue virus and the Zika virus to humans.

Darrin Dunwald, director of the South Walton County Mosquito Control District, shows off one of the hens the department has placed around the southern end of the county as part of its sentinel program. While the birds can't get sick from mosquito-borne illnesses, regular blood samples taken from the hens can alert mosquito control staff to the existence of viruses that are potentially fatal to humans.

As director of the South Walton Mosquito Control District, a special tax district covering the south end of the county, it is Dunwald's job, along with his staff of 19 people, to keep the mosquito population under control as much as possible, all within a budget of about $5 million.

Mosquitoes will never be eliminated entirely, Dunwald said, but the SWMCD uses a number of techniques — larvicide to keep mosquitoes from hatching, night spraying in areas where mosquitoes have been detected, maintenance of the district's 42 miles of mosquito control ditches that drain stormwater, and even the introduction of Gambusi affinis (the tiny mosquitofish, which feeds on mosquitoes) — in areas where mosquitos have become a problem.

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In addition to all that, crews respond to calls for service from people in the district who have spotted mosquitoes on their property. It doesn't take very much standing water to provide a breeding ground for them, according to Dunwald.

A mosquito larva lies in a sample cup at a wetlands area in Santa Rosa Beach.

"I've seen hundreds of larvae in a magnolia leaf," he said.  

Delving deeper into mosquito control efforts, Dunwald said that last year, the SWMCD conducted 83 nighttime spray missions. This year, he said the district has conducted 213 nighttime spray missions, a reflection of the amount of rain that has fallen this year.   

And the mosquitofish isn't the only creature that helps the SWMCD's control efforts. Across its 70 square miles of service area, the SWMCD maintains 16 chicken coops, each with six chickens and a mosquito trap.

Each Monday, employees collect blood samples from the chickens and bring them back to the district's laboratory for analysis to determine whether any of them have been bitten by a mosquito carrying a disease that could pose a threat to humans, like West Nile virus.

People who come across the coops need not worry that the chickens are being harmed in any way, Dunwald said.

Lindsey Ashman, an entomologist assistant with the South Walton County Mosquito Control District, uses a microscope to catalog and count the types of mosquitos caught in one of the traps set up around the south end of the county. That allows the staff to pinpoint and treat mosquito "hot spots."

"They're a dead-end host," he said, meaning that a mosquito bite "won't kill the bird or harm the bird." The chickens also have plenty of room in their coops, along with water and high-quality feed, Dunwald said.  

Mosquitoes collected in the traps at the chicken coops are also examined in the lab, to determine which species — some of which might pose a danger to humans as disease vectors — are present.

"It's a lot of science," Dunwald said, to determine "what species are going to hatch out, when they're going to be hatching and where they're going to be hatching."

The science of mosquito control also includes something called "integrated pest management," Dunwald said, explaining that the various control chemicals have to be switched around so they don't develop an immunity to one particular chemical.

That has meant some occasional experimenting, like the time the SWMCD tried garlic oil, which is advertised, and available widely, as a mosquito repellent, he said. It didn't work, though, on the large scale contemplated by the SWMCD.

A pile of mosquitos awaits sorting and cataloging by entomologist assistant Lindsey Ashman at the South Walton County Mosquito Control District. The staff uses the data to locate and treat mosquito "hot spots."

"In fact, we had more mosquitoes," Dunwald smiled.      

A 21-year veteran of the SWMCD, he was named director earlier this year in the wake of lawsuits and personnel departures and an election that saw two longtime board members replaced.

In a Tuesday interview, Dunwald worked to make it clear that he has been moving to improve the district's operations in the months since he was named to lead it. He's hired a new office manager, an administrative assistant and two field technicians, and has created and staffed a new position — an environmental operations director — whose duties include monitoring development in the county to determine how it might impact mosquito control efforts.

Dunwald also has involved himself in that work. He regularly attends meetings of the Walton County Technical Review Committee, one of the boards that reviews development proposals, to provide comments and recommendations in instances where a proposed development could adversely affect a mosquito control ditch or provide breeding grounds.

Joseph Wallace, a mosquito control technician with the South Walton County Mosquito Control District, uses a sample cup to check for mosquito larvae in a wetlands area in Santa Rosa Beach.

"We're trying to stop them (developers) from impacting our ditches," Dunwald said. 

One of the ways in which that could happen, and which also could provide new breeding grounds for mosquitoes, is the practice of raising the level of a proposed residential or commercial development, using soil to raise it above surrounding property to avoid flooding.

Dunwald pointed out that raising a piece of land can often result in water running off of a site in unpredictable ways, potentially creating a new wet breeding ground for mosquitoes or altering the capacity of a mosquito control ditch to shed water from a given area.

Gambusia fish are grown in a pond at the South Walton County Mosquito Control District headquarters in Santa Rosa Beach. The fish, which are placed in ponds to eat mosquito larvae, is one of the tools technicians use to control the population of mosquitos.

And there are other ways developers and their subcontractors create opportunities for mosquitoes to hatch, Dunwald said. Just sitting a construction waste Dumpster at an angle where water can't drain out of it can create a perfect breeding ground, he noted.

A similar problem can develop in connection with people visiting South Walton to enjoy a vacation along its beaches. Visitors aren't likely to pay attention to standing water accumulating in trashcans or other containers at their vacation accommodations, Dunwald said.

Those also visitors can sometimes bring standing water with them, maybe in the bottom of a kayak that may already harbor mosquito larvae. That could be particularly problematic if a new mosquito species is brought into the area, he said.

On Tuesday, though, Dunwald had a more immediate concern. Flooding rains from the previous couple days had left large puddles of standing water along the roadsides and elsewhere, and mosquito control ditches were filled with running water.

"As much rain as we've got, we're going to have a lot of mosquitoes," he said.