Mosquito preparations begin in April, Farnsworth said, with treatments designed to kill larvae. For those that do survive and pupate into mosquitoes, chemical fogging awaits. (Photo taken from the Center of Disease Control and Prevention’s Public Health Image Library)

To help limit the spread of West Nile Virus and other mosquito-borne diseases, teams in Pierre and Fort Pierre have begun chemical “fogging” to kill adult mosquitoes. The insecticides used in the fogging efforts will help keep the vampiric insects’ numbers low, but residents of the capital area should be aware that the chemicals can be toxic to people and pets as well.

In Fort Pierre, City Superintendent Vern Thorson said his fogging teams used a chemical brand known as “Anvil 2+2,” whose active ingredients are chemicals known as “d-phenothrin” and “Piperonyl butoxide (PBO). PBO is considered relatively safe by the Environmental Protection Agency, but exposure to d-phenothrin can cause a number of health detriments.

Many of these detriments, according to a 2016 report by the National Pesticide Information Center, are minor so long as exposure to the chemical is brief. They include skin, eye, and throat irritation, as well as dizziness and headaches. Pets briefly exposed to substances containing d-phenothrin may also experience “vomiting, diarrhea, excess salivation, twitching, tremors, or seizures if eaten or applied to the skin,” the report read. Cats are especially vulnerable.

Longer exposure to, or inhalation of, d-phenothrin-containing chemicals can seriously — even fatally — damage the nervous and respiratory systems of both people and pets, according to a 2003 report in the Journal of Pesticide Reform. D-phenothrin can also block the production of testosterone in the body, and a 2012 article in the São Paulo Journal of Medicine linked the substance to cases of gynecomastia — a condition wherein men develop feminine breasts.

Fogging teams in Pierre use another insecticide brand known as “Duet,” Pierre Parks Director Tom Farnsworth said.

“Duet,” like “Anvil,” utilizes d-phenothrin and PBO as its main ingredients, as well as another chemical known as “prallethrin.” Prallethrin, like d-phenothrin, can cause irritation in people and pets in brief exposures and more serious conditions in long exposures.

Anvil and Duet are approved by the EPA for insecticide purposes, but according to their respective EPA chemical profiles, both d-phenothrin and prallethrin also have negative ecological effects. Both are highly toxic not just to adult mosquitoes, but to honey bees and many aquatic animals as well.

To protect themselves and their pets, Thorson said all residents of Fort Pierre should stay at least 200 feet away from the fogging trucks as they move through town. Farnsworth went one step further. He said that during the height of summer, residents may want to stay inside with their windows shut, between about 9 p.m. and 1 a.m., if they see a fogging truck come through.

“The mosquitoes are most active around 9 p.m., to about midnight, 1 in the morning,” he said.

Farnsworth and Thorson both said that fogging cannot take place every night.

“It depends on the weather,” Thorson said. “We can only really go out if the wind is blowing less than 10 miles per hour.”

“You can have a calm day and the winds will come up around 8, 9 at night. It really defeats the purpose,” Farnsworth said.

Thorson said his crew of foggers would be fogging on the nights leading up to the Fourth of July, and would continue to monitor mosquito numbers afterwards. Farnsworth’s team in Pierre sends him weekly estimations of the mosquito population, based on the number of the insects that they catch in traps planted around town. These allow them to track how effective their insecticide efforts have been, and also lets them know which areas in town may need more attention.

However, Farnsworth said it was impossible to know where fogging teams would be on any particular evening, if fogging can even occur.

“We tend to put a release out publicly early on; that we have started our control program,” he said. “But I can’t tell you each night in advance if we’re going to go out.

This year, Farnsworth added, mosquito numbers have been relatively low — but both men said they were more than just a summer nuisance. West Nile Virus, while not usually fatal except among the elderly, can cause a wide array of afflictions. These include muscle weakness, headaches, skin rash, swollen lymph nodes and disorientation. In more severe cases in can also cause paralysis, seizures and coma.

According to the Center for Disease Control and Prevention, South Dakota is one of the most West Nile-infected states in the country. More than 2,400 cases of the disease have been reported in South Dakota since it first emerged in 2002, and many milder cases likely go unreported.

“It’s something I wouldn’t wish on anyone,” Farnsworth said.


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