New York City mosquito spraying program harms mosquitoes, not humans

Americans have been waging war against blood-sucking, disease-carrying mosquitoes for more than a century.

But some social media users are expressing concern and sharing conspiracy theories that efforts to eradicate the insects are a grave and intentional threat.

A Sept. 20 Instagram post shared a video of a person who said that New York City was spraying a mosquito pesticide, with footage of a truck on a residential street emitting a trail of fumes, while a loudspeaker announcement urged people to go inside.

A caption on the post read, "It’s ok, pesticides are only linked to about 3 dozen neurological disorders and cancers. I’m sure the government has our best interests at heart and it’s all totally safe." 

This post and others like it that suggest New York City is spraying unsafe pesticides into the air were flagged as part of Meta’s efforts to combat false news and misinformation on its News Feed. (Read more about our partnership with Meta, which owns Facebook and Instagram.)

New York City’s health department sometimes sprays pesticides to control the spread of the mosquito-borne West Nile virus. Its trucks play a recorded message advising people to go inside and shut the windows to avoid exposure, department spokesperson Shari Logan confirmed in a statement to PolitiFact.

Although any pesticides pose risks if used improperly, experts say the dosing of chemicals sprayed for mosquito control in New York is considered safe for humans.

Meanwhile, humans face serious risk from mosquitoes — what the U.S. Centers for Disease Control and Prevention has called "the world’s deadliest animal" because of the diseases they carry and spread. 

New York City’s Department of Health and Mental Hygiene sprays adulticides — pesticides to kill adult mosquitoes — when its surveillance shows a high risk to human health from West Nile virus and other mosquito-borne diseases. 

Trucks spray the pesticides in the evenings in residential areas and parks and residents are alerted at least 24 hours ahead of time. The spraying of pesticides by trucks in the U.S. has happened for decades and there are more than 1,100 U.S. vector control agencies, run by cities, states, counties or other jurisdictions. 

The health department said mosquitoes carrying West Nile virus are typically in New York City from May through October, with peak activity in August and September.

The department developed and began using a mosquito surveillance and control plan in 2001, two years after West Nile virus first appeared in the city.

The virus is the leading cause of mosquito-borne illness in the U.S. Although most people who get the virus experience no symptoms, about 1 in 5 develop a fever or other symptoms. About 1 in 150 develop a serious central nervous system illness such as encephalitis or meningitis, and about 1 in 10 of those die, the CDC said.

Preliminary CDC data shows that year to date in 2023, there have been 1,419 cases of West Nile virus in 44 states. That’s up from 1,126 cases in 2022. In New York state, 22 cases of West Nile virus have been reported this year, according to CDC data. The city’s public health department said 59 city residents died from the virus from 1999 through 2022.

The pesticides sprayed in New York City contain pyrethroids or pyrethrins, which belong to one of two classes of adulticides commonly used to spray for mosquitoes in the U.S. Pyrethroids are synthetic chemicals that mimic pyrethrins, which are chemical compounds extracted from chrysanthemum flowers.

Pyrethroids and pyrethrins kill mosquitoes by preventing the insects’ nervous systems from working properly. These chemicals are also in over-the-counter insecticide sprays for homes, flea and tick treatments for pets, and head lice treatments for humans. Pest control companies also use them to spray homeowners’ yards.

Three pesticides made by Clarke, a company that makes mosquito control products, are being used in New York City’s 2023 spraying program: Anvil 10+10, Duet, and Merus. 

Anvil and Duet use synthetic pyrethroids, and Merus uses pyrethrins.

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Scientific studies and product safety data do not show the chemicals used in New York cause cancer and neurological issues in humans at the dosage used in spray trucks.

New York City's health department said in its statement that it sprays very low concentrations of pesticides, and that the pesticides’ health risks are low to people and pets. A spokesperson for one of the pesticide brands the city uses said about a tablespoon of active ingredient treats an acre, an area about the size of a football field.

Since the city began spraying for mosquitoes in 2001, no reported diseases in people or pets have been linked to the pesticides, the department said.

Although the labels of the products used in New York City warn that the pesticides can be harmful and potentially fatal if swallowed or inhaled, and can irritate eyes and skin, none of the products contain cancer-causing ingredients, according to their safety data sheets. 

A CDC webpage said animal studies have shown that pyrethrins and pyrethroids might be capable of causing cancer in people, but the only evidence comes from animals that ate very large amounts of the chemicals for a lifetime.

The main ingredients listed in the pesticides used in New York — Sumithrin, prallethrin and pyrethrins — are determined to be "not likely to be carcinogenic to humans," according to company safety data sheets and the EPA. (Here are the safety data sheets for Anvil, Duet, and Merus.)

Piperonyl butoxide, an ingredient in Anvil and Duet, was linked to slightly higher incidences of benign liver tumors in mice after lifetime high dose exposures, according to product safety sheets. But there is no evidence it causes cancer in humans. Piperonyl butoxide is used in more than 2,500 pesticides to make them more effective.  

Neurotoxic effects are possible from pyrethroids, but Dani Lightle, a pesticide registration research leader at Oregon State University, said an EPA database of reported adverse incidents from these chemicals shows most resulted from accidental misuse by people.

"In short: you’re significantly more likely to poison yourself with a dog flea treatment gone wrong than you are to have impacts from the mosquito fogger truck," Lightle said.

Lightle said those effects, such as muscle tremors or hyperthermia, from pyrethroids happen quickly and symptoms are not long-lasting.

Clarke spokesperson Laura McGowan said the company’s products used in the New York City area have been in use for decades and are registered for public health mosquito control by the EPA.

"The droplets are designed specifically to work on a mosquito’s biology, with droplet sizes so small that several fit on the head of a pin," McGowan said.

Once the droplets touch the ground, the product begins to break down, McGowan added. 

Essentially, the dose makes the poison, Lightle said.

"Salt will kill you if you ingest too much of it, but at a reasonable amount, it’s great on french fries," she said. "The risks presented by any of these chemistries are real if they are misused."

An Instagram post claimed that New York City is spraying unsafe pesticides to combat West Nile virus.

Experts and public health officials say  pesticides sprayed in New York City and other cities to combat mosquitoes don’t threaten humans because of the small amount used. Toxicity is related to dose. 

No diseases have been reported as a result of the spraying program, New York City officials said.

The ingredients in the pesticides used in New York City have not been proven to cause cancer, and any potential neurological effects from the sprays are short-term, a pesticide safety expert said.

We rate the claim False.