How scientists manage the Great Salt Lake’s wetlands, one of the most prolific mosquito habitats in the West

It was another unusually warm day in Salt Lake City’s ongoing war with mosquitoes.

The high temperature for April 10 was 80 degrees — just a tick below a 2012 record of 81 degrees — as Jason Hardman sloshed through a muddy, stinky swell in the wetlands of the private Harrison Duck Club, southeast of the Great Salt Lake.

Hardman, the Salt Lake City Mosquito Abatement District’s rural field supervisor checked on mosquito larvae — aka, juveniles —he’d found a couple days prior in small puddles between patches of saltgrass.

“I’m amazed at how fast they’re growing,” Hardman said. “This time of year, it should take 10 days for them to get out of the water, and it’s happening a lot faster.”

That’s all due to unseasonably warm air and water temperatures creating perfect hatching conditions for the larvae.

While Hardman “dipped” for the larvae, in mosquito control parlance, seasonal employee Austin Harp readied one of the district’s all-terrain vehicles.

He then drove the ATV, outfitted with a modified farming hopper in concentric loops around the roughly 2-acre swell, spreading corn cobs infused with a naturally occurring bacteria that thwarts the larvae.

Finding mosquitoes when they’re still in their water-born infancy is a key focus for the district, because employees can use more targeted interventions — which are safer for humans and other wildlife — to keep them from maturing and pestering people.

The district is responsible for vast wetlands south and east of the Great Salt Lake that spawn millions of mosquitoes each year, including some that carry dangerous pathogens such as West Nile virus.

“I have no doubts,” district Executive Director Ary Faraji said, “that this is one of the most prolific habitats west of the Mississippi.”

Faraji added that the “huge abundance” of mosquitoes is primarily just a couple of species.

“So our job, historically,” he explained, “has been to prevent the dispersal of these mosquitoes from the wetland habitat surrounding the airport, from going into the city, where all of our people are.”

The abatement district recently raised its property tax rate on city residents and businesses as it grapples with tight budgets in the face of a growing mosquito season that now stretches from April to October and as it looks to add new technology to its bug-battling repertoire.

Out in the Great Salt Lake’s wetlands

District employees keep their eyes on about 40,000 acres of wetlands and farmlands fed by mountain snowmelt via the Jordan River. The land is a patchwork of protected bird habitats, private duck clubs and farms.

The rural area is a vast expanse between the Salt Lake City International Airport and the open but dwindling waters of the Great Salt Lake, dotted with ponds, ephemeral pools and squishy swells like the one Harp and Hardman treated.

Their work includes testing thousands of constantly changing bodies of water that could host mosquito larvae. The juveniles grow in aquatic habitats of various sizes, but in larger lakes, they’ll stay away from open water, instead hugging grassy shorelines.

Last year, the district trapped about 2 million mosquitoes in the field, simply for surveillance purposes — a tiny fraction of the region’s total population. Back at its headquarters, roughly 1.8 million of those dead bugs fill a large blue cooler that might otherwise be used for a backyard barbecue.

Staffers know they can’t kill every mosquito out here — so control is the key.

New industrial development encroaching on the wetlands is complicating how the district treats them. The Utah Inland Port Authority is driving that growth.

“They’ve had to actually make another two-person team to control all this industrial stuff,” Hardman said, while driving past large warehouses north of Interstate 80. “The other thing, too, is it’s more time consuming.”

Hardman said district staffers often have to get permission and follow special security protocols to carry out mosquito control work on industrial properties, slowing down their Sisyphean efforts to address an area that produces millions of mosquitoes each season.

Leading the mosquito abatement army into battle

While there are varieties of mosquito species buzzing around the Wasatch Front, three species make up the vast majority of the bugs that the district traps.

The summer salt marsh mosquito — Aedes dorsalis — bites humans often but is not a carrier of dangerous disease.

The Western encephalitis mosquito — Culex tarsalis — and the common house mosquito — Culex pipiens — are considered more worrisome because they are opportunistic feeders that bite humans as well as other animals. Both Culex species can carry West Nile virus and St. Louis encephalitis virus, while Culex tarsalis can also impart Western equine encephalitis virus.

Tracking where species are concentrated helps district scientists figure out which habitats to target with specific control measures and prioritize appropriate applications.

The district’s surveillance program consists of 36 traps spread out across the wetlands. During the peak of summer, one carbon dioxide trap that mimics human breathing with a battery-powered computer fan can lure up to 40,000 mosquitoes into its netting in a day.

Back at the district’s headquarters, 2215 N. 2200 West, the bugs are frozen, counted with the help of imaging software, and a small sample is broken up into species by hand.

“We are the eyes of the operation,” seasonal lab employee Kelsey Fairbanks said. “No one knows where to treat or where to go if we don’t know what species there are.”

The lab can relay data on the number of mosquitoes in each trap, broken down by species, to Faraji, the executive director, on the same day the traps are collected from the field. Faraji then draws up the district’s plans for treatment.

Keeping the bugs in check

District employees use three types of interventions to kill mosquitoes: physical, biological and chemical.

They prefer to target the youngest larvae because they can use biological pesticides that hamper their growth and don’t harm other organisms. Placing fish that eat larvae in pools and ponds is another example of a biological control.

Hardman, the rural supervisor, said April 10 was the first day the district used a pesticide this season. He had been inspecting pools for larvae for weeks prior, but that week was the first time he had found juveniles.

That, according to Nate Byers, the district’s molecular biologist, meant shifting to “larviciding” — the term for killing juveniles — as quickly as possible, to get them before they can fly and require other control methods.

“The adulticiding, we will hold off for considerably longer,” Byers said. “We try to limit the amount of adulticiding we do. Larviciding is better. Prevention is better.”

The physical controls generally work better in the urban environments that the district serves, like dumping out standing water so juveniles can’t hatch in the first place. The surveillance traps are another example of a physical intervention.

Avoiding chemical pesticides, where possible

The district limits its use of chemical pesticides, for efficiency and environmental reasons. To deal with juveniles that have reached the later stages of their development, staffers can deploy a hormone that stops larvae from growing or coat standing water with a mineral oil that cuts off mosquitoes’ access to oxygen.

It’s only when the district targets adult populations that they use more traditional pesticide sprays, whether via airplane or drone in the wetlands or with backpacks on foot or bike in urban areas.

The advocacy group Utah Physicians for a Healthy Environment has long criticized the district for using those sprays, which contain toxins that can damage human nerve systems, even in small amounts. On its website, the group implores residents to submit a no-spray request to the district for their property.

The district does not test the products it uses for safety, only efficacy. Instead, it relies on the federal Environmental Protection Agency to set standards for using the pesticides and reducing risk for humans and other organisms.

Depending on the specific habitat staffers are targeting, employees can use ATVs or a large snowcat-like tracked vehicle for control measures. The district also contracts with an airplane spraying company to address larger areas. A nascent drone program helps Hardman’s team intervene more quickly and covered 4,000 acres last year.

Back at the labs

Much of the district’s most important work happens at its offices. There, after the mosquito sorting process, scientists run virus identification tests — with methods similar to those used to track COVID-19 — to see how disease is spreading within the population.

“This tells us where in the city and in what species of mosquito West Nile virus is circulating,” Byers said, pointing to a test run last August.

Other office spaces are used to test new products for their efficacy in killing mosquitoes. The district also has a robust research program largely powered by Utah State University students and grant money. That research has helped the district implement new techniques, like 3D-printing its own traps.

Mosquito control isn’t limited to the wetlands, though. District employees also place mosquito-eating fish in ornamental ponds across Salt Lake City, inspect tree holes that collect water for larvae and treat thousands of stormwater catch basins.

There are 13 full-time employees at the district, which hires temporary workers — many of them college students — for much of its basic work during peak mosquito season.

A changing landscape

The district told city leaders and residents last fall that it needed to raise property taxes to boost a tight budget that was getting eaten up by persistent inflation and to compensate its employees appropriately.

The district has also lost out on revenue from the new industrial growth that still requires service, because of the Utah Inland Port’s taxing authority.

The mosquito season is growing longer in the Salt Lake Valley due to climate change and rising temperatures, forcing the agency to spend more on equipment and materials.

At the same time, the agency is expanding its facility to open up more space for testing and research. Officials also sought the tax increase so the district could buy its own helicopter and build a hangar to better support its aerial operations instead of relying on the more imprecise planes flown by district contractors.

The Westside Coalition criticized the plan last fall in a letter to district officials, pointing out that officials said they planned to use the last tax increase in 2021 to pay for the helicopter. Faraji said the helicopter has now been purchased.

The helicopter, officials say, is key in the district’s ongoing effort to control mosquitoes efficiently and effectively in a range of habitats — another piece of artillery in the never-ending — and ever-extending — battle against the biting bugs.

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