Allegheny County ramps up mosquito control. Could it harm local ecosystems?

On a warm night in late July, two public health workers were on a mission: killing mosquitoes to prevent the spread of West Nile virus in the Pittsburgh region.

They climbed into a pickup truck parked on a residential street in Morningside — one of several neighborhoods where mosquitoes had recently tested positive for the virus.

Nick Baldauf took the wheel. A vector control specialist, he oversees the Allegheny County Health Department’s Mosquito-Borne Disease Control Program . A Pennsylvania Department of Environmental Protection [DEP] employee sat beside him to control the powerful sprayer mounted atop the truck bed. As they drove off, it fogged the street with an insecticide that kills flying mosquitoes on contact.

Their work is routine this time of year, but it’s taken on fresh urgency: Pennsylvania is getting warmer and wetter , creating conditions in which mosquitoes thrive and prolonging the disease transmission season.

The Health Department identified its first two human cases of West Nile virus earlier than usual this year: It announced on July 16 that a Baldwin resident had been hospitalized due to symptoms of the disease. Later that month, a county spokesperson said the department had learned that a Sewickley man fell ill in late June and is recovering. Allegheny County has been fluctuating among the top five counties ranked by West Nile virus activity in the state this summer.

“Since 2018, this is one of the worst years we’ve seen,” Baldauf said. “Normally, this is what we might see in September or late August, and we’re seeing human cases in July.”

Baldauf was in a hurry; they had no time to waste if they were to complete their route through Stanton Heights, Garfield, the Hill District, Perry South and Fineview. They would treat Allegheny Commons Park and the Mexican War Streets, too, if there was time.

But municipal mosquito spraying is controversial — especially among conservation advocates who worry about the effects of broad-spectrum insecticides , which can kill a wide range of insects, on local ecosystems.

After Baldauf and his team sprayed such an insecticide in Schenley Park last August, Greenfield resident Valerie Warhol contacted the county Board of Health to express concern for the park’s monarch butterfly population and other beneficial insects.

“Schenley Park is not just a typical urban park,” they wrote to board members. “It’s a natural environment with a functioning ecosystem, and insects (whether we like it or not) are the foundation of that ecosystem.”

Warhol, who works for a fungal biodiversity and conservation nonprofit , said they support the county’s efforts to curb mosquito-borne diseases. But they want parks — which have high concentrations of pollinating insects — to be no-spray zones .

PublicSource spoke with experts to weigh the pros and cons of mosquito spraying. They include county officials, academics, conservation and anti-pesticide advocates, and mosquito control professionals. Some said spraying contributes to the global collapse in insect populations , which affects all life on earth, including humans. Others said spraying can be part of responsible programs to manage the world’s deadliest animal , which could become deadlier with climate change. Both sides insist they have scientific proof .

The only consensus? The county wouldn’t need to spray as much if more people knew how to keep mosquitoes from breeding near their homes.

‘We’re trying to prevent people from getting sick’

West Nile virus can spread to humans through an infected mosquito’s bite. There’s no vaccine to prevent the disease and it can’t be treated with medication. Most people don’t get sick , while some develop mild flu-like symptoms.

Rarely, the virus causes severe disease that can be fatal. It happened here in September: An Elliott woman in her 80s was hospitalized due to fever and weakness. She later died, according to a county press release.

Baldauf said the county makes every effort to curtail mosquito breeding , which takes place in standing water. Experts say it’s the most effective way to reduce viral transmission and prevent an outbreak.

With guidance and funding from the DEP, the Health Department:

• Treats about 50 wetlands every spring with either the bacterial larvicide Bti , or methoprene , a hormonal growth regulator that keeps larvae from maturing into biting adults
• Also treats more than 13,000 catch basins , which are a known source of culex mosquitoes — the main transmitter of West Nile virus
• Enforces the housing code when residents report discarded tires , unmaintained swimming pools and other sources of standing water
• Sends a larval technician to investigate and address mosquito problems in neighborhoods
• Teaches people to treat, or get rid of, standing water near their homes

After a mild winter, Baldauf started seeing mosquito larvae around St. Patrick’s Day — several weeks ahead of the typical seasonal pattern. It’s why the county treated wetlands in March instead of April this year.

Warming weather could also be driving high viral levels in mosquito samples: The county regularly traps and ships adult mosquitoes to a state lab in Harrisburg for testing . When viral levels reach an action threshold , the county sprays etofenprox (brand name Zenivex E20 ) — an insecticide that targets biting adults in areas where those traps were set.

“If this continues as it has been, we’re probably going to be spraying once a week,” Baldauf said. Just 10 days later, he drove the truck through Crafton , Ingram and other neighborhoods west of Downtown. On Monday, he treated Arlington , Beltzhoover and other neighborhoods near the South Side.

“We don’t want to be out here spraying,” he said, noting beekeepers and those on the state’s list of people hypersensitive to pesticides are given advance warning.

“But we’re trying to prevent people from getting sick.”

Could mosquito spraying harm ecosystems?

Warhol is a nature photographer who takes groups on “bug safaris” in Pittsburgh’s urban farms and community gardens.

In September, they gave this reporter a tour of Bartlett Meadow in Schenley Park. It was dotted with goldenrod and New England aster — fall blooms for pollinators like the honey bees, Skipper butterflies and several moth species that Warhol pointed out.

“I feel like it’s really counterproductive when we’re spraying” in parks, they said. “It has a bigger impact on the ecosystem because those are areas where insects are breeding and feeding more readily than they probably are in an urban or suburban neighborhood.”

Baldauf said that’s unlikely. The county is spraying “the safest stuff on the market” that was recommended by scientists. “I’m a conservationist myself and I don’t want to use something that’s harmful,” he added. Despite Warhol’s concerns, the Health Department will spray etofenprox on a route through Schenley Park tonight.

Etofenprox poses a very low risk of toxicity to humans and other mammals, according to the Environmental Protection Agency . The county sprays at night — when bees and many other pollinators are less active. And the sprayer creates droplets large enough to stick to a mosquito, but small enough to bounce off anything larger like a butterfly, Baldauf explained.

It’s an argument backed by vector control groups and pesticide industry professionals.

Most mosquito control programs spray insecticide at an ultra-low volume , which minimizes the impact on non-target species, said Dan Markowski, technical advisor to the American Mosquito Control Association . And the product breaks down in sunlight, lowering the amount of toxic residue on foliage.

But Warhol isn’t buying it.

They said moths, fireflies and other nighttime pollinators could be vulnerable during spraying. Many sleeping insects are out in the open at night, such as butterflies that attach themselves to stems or leaves while dormant. And etofenprox can bind strongly to the wax that coats the leaves of almost all plants, prolonging its degradation on those surfaces.

“That means the caterpillars are going to be eating this insecticide that’s on the leaves and it will likely kill them,” Warhol said.

A bird conservation advocate agreed that nighttime pollinators could be affected, which could have ripple effects in bird populations, such as the common nighthawks that feed after dusk.

“Even when these products are used with the best intentions … in a highly targeted manner, they certainly do have the potential to affect non-target invertebrates,” said Hardy Kern, director of government relations of the birds and pesticides campaign at the American Bird Conservancy . “And these non-target invertebrates are really important food sources for birds.”

The group isn’t opposed to “the thoughtful use of pesticides” when they’re needed to protect human health, he added.

The insect apocalypse

Humans tend to hate insects , but we couldn’t survive without them. They pollinate the plants we eat, break down organic waste and form the base of the food web .

Our antipathy toward them is a major barrier to their conservation: Research shows insect populations plunged by 45% in the last four decades. The collapse is linked to human activity such as deforestation, urbanization, agricultural conversion and other types of habitat destruction. Pesticides could be contributing to the problem, though the agriculture industry likely plays a much bigger role than municipal mosquito spraying.

Entomologist and University of Delaware Professor Doug Tallamy warned of the looming insect apocalypse when he gave a virtual lecture last year to the Audubon Society of Western Pennsylvania . On his list of what to do about it: “Oppose mosquito spraying” and focus on larvicides, public outreach and education.

Tallamy estimates mosquito spraying kills between 10% and 50% of adults, which is nowhere near the 90% needed to get good control. “It means they keep having to come back and back and back” to spray, he said during an interview. “Even if it did get good control, the big problem is all of the non-targets that it kills.”

Asked how the county measures the efficacy of spraying, Baldauf said his team repeatedly sets traps in neighborhoods over time and counts the mosquitoes in each sample.

“We do see lower numbers after the spray events,” he added, noting that specific figures “would be anecdotal at this point.”

While the public adores monarch butterflies, some scientists say we should care about less charismatic insects, too. They’re important prey for fish, birds, amphibians and other arthropods, and whole ecosystems would collapse without them.

“I have no reason to believe [etofenprox] wouldn’t be just as lethal to insects the same size as mosquitoes or smaller,” said Colin Purrington, a retired evolutionary biologist who taught at Swarthmore College and blogs about mosquitoes .

Even if larger insects aren’t killed on contact, it could still harm them by reducing their lifespan or their ability to gather food, he added. “I think the concern about spraying, even at low volumes, is definitely there.”

Teaching people to protect themselves

Despite concerns around conservation, experts on both sides said the county has a solid mosquito control program that prioritizes prevention and uses spraying as a last resort.

“I interact with a lot of municipalities across the country, and many of them are not as thoughtful in their application as Allegheny County seems to be,” said Kern, of the American Bird Conservancy.

The one thing everyone agrees on is that community outreach and education can make a huge difference in the war against mosquito-borne diseases. Baldauf does several events per month, year round, to teach people how to protect themselves and their communities.

“It’s really good outreach because a lot of times, you’d be surprised how many people just don’t even realize mosquitoes are aquatic insects,” he said.

But no matter how much prevention or education the county does, adult mosquitoes will always emerge — especially as climate change widens the insect’s range and lengthens its peak season. If global insect populations keep declining, scientists and policymakers will have to find new ways to balance conservation with safeguarding human health.

“I’m torn about when is the right time to spray something,” said Purrington, the evolutionary biologist.

“I love insects, but I also like people and I don’t know anyone who’s had West Nile virus, but it’s a horrible thing to have, and certainly can be debilitating and can lead to death.”

Venuri Siriwardane is PublicSource’s health and mental health reporter. She can be reached at venuri@publicsource.org or on X, formerly known as Twitter, @venuris .

This story was fact-checked by Briana Bindus.

This reporting has been made possible through the Staunton Farm Mental Health Reporting Fellowship and the Jewish Healthcare Foundation.

How to protect yourself from mosquitoes

• Wear an EPA-registered repellant when spending time outdoors.
• Wear protective clothing, such as long pants and long-sleeved shirts and/or mosquito-repellent clothing and gear
• Eliminate sources of standing water: Check for clogged gutters, kiddie pools, watering cans and trash bins left out in the rain. Find a list of objects that hold water here and here .
• If you can’t eliminate the standing water source, treat it with Bti — a bacterial larvicide available at most hardware stores.
• Make a sugar trap to eliminate mosquitoes indoors. Find instructions here .
• File a complaint with the Allegheny County Health Department if you see standing water sources in your neighborhood, including tire piles and unmaintained swimming pools and landscape ponds.
• Report dead birds between April 1 and Oct. 30 to the Pennsylvania Department of Environmental Protection, which tests for the presence of West Nile virus.
• If you’d like to invite Vector Control Specialist Nick Baldauf to speak at your event, contact the Health Department here .
• Find more tips for controlling mosquitoes here and here .

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