FARGO — The recent mass death of monarch butterflies killed by aerial spraying of insecticide to control mosquitoes in the Fargo area has triggered a debate about the necessity of spraying and possible risks to human health.
Heavy rains in mid-August created ideal conditions for a major mosquito hatch, which led to aerial spraying later that month that resulted in the mass deaths of monarch butterflies — collateral damage in the fight against West Nile virus.
Local officials and residents have been discussing Cass County Vector Control’s aerial spraying program since the Aug. 26 incident.
John Strand, a Fargo city commissioner, isn’t comforted by assurances from vector control officials and others that the mass die-off of monarch butterflies shouldn’t have occurred. He worries that the dead monarchs could be a warning, like the “canary in the coal mine.”
“To me that’s the moment of asking questions,” he said. “Are there other unintended consequences, including human health?”
Strand is calling for a review to see whether Cass County’s aerial spraying program is more aggressive than other cities in the region and to examine the pros and cons of aerial spraying, which public health officials say is an important tool in preventing West Nile virus.
“Not everybody sprays like we do,” Strand said.
Mayor Tim Mahoney, a physician who serves on the vector control board, agrees with Strand that there should be public input on whether to forego spraying during the monarch migration. The public could be notified so they could take steps, and spraying could be postponed until after the migration, he said.
Already, Mahoney said, “You have to have a lot of dialogue whether to spray. It all has to be signed off.”
Mahoney and Strand want to conduct a public forum this fall. “Let’s have a discussion,” he said. “We have to try to see if there’s another way of doing it.”
More than 80% of people who are infected by West Nile virus never develop symptoms, although others catch West Nile fever and a small number — less than 1% — develop neurological problems that can result in serious illness or death, said Ben Schram, West Nile surveillance coordinator for the North Dakota Department of Health.
People are upset about the monarch deaths and want to prevent a recurrence, Strand said. Ben Prather, director of Cass County Vector Control, said the die-off occurred during the butterflies’ migration.
More should be done, Strand said, to monitor the migration so vector control can avoid spraying when the butterflies are most vulnerable. He said he’s heard from many residents who don’t want to see more mass casualties of butterflies, important pollinators, due to mosquito spraying.
Safe for humans?
Ron Miller, a retired Fargo pediatrician, also has raised concerns about potential human health consequences and believes the “carpet bomb” aerial spraying to control mosquitoes is unnecessary — done more so people can be comfortable outdoors than for valid public health reasons.
Individuals should assume greater responsibility for protecting themselves against mosquitoes and other insects, he said. In very low doses, permethrin, the insecticide that vector control uses to spray for mosquitoes, repels insects.
“It’s very safe to put it on your clothing,” he said. Or people can use other insect repellents as directed, such as DEET.
As for aerial spraying of permethrin, he questions whether we know enough to be confident about safety. “I don’t think the answer to that is known. It’s thought to be safe,” he said.
But experts once thought another insecticide, DDT, was safe, before it was banned because of the widespread harm it caused to birds and other species as well as concerns about human health.
“There’s no question it works,” Miller said of permethrin. “The problem is, it kills all insects, including butterflies.”
North Dakota is a state with high prevalence rates of West Nile virus, Schram and Prather said, and aerial spraying is a safe and effective way to control mosquitoes to prevent the spread of the virus.
West Nile virus cases vary widely from year to year in North Dakota. Three cases have been reported so far this year and nine cases were reported last year, but 204 cases were reported in 2018, including 60 involving neurological symptoms, which can include disorientation, headaches or even paralysis, Schram said.
West Nile virus deaths in North Dakota peaked at five in 2003, with two each reported in 2016 and 2017, he said.
But Miller maintains that the health risk is exaggerated and cites figures from the North Dakota Department of Health showing cases in Cass County are rare. There were no cases last year, 16 in 2018, four in 2017, 21 in 2016 and none in 2015.
Also, Miller said, case reports alone don’t tell the full story, since serious illness from the virus is rare. He argues that having fewer cases of mild West Nile virus doesn’t justify spraying and that targeted spraying to protect vulnerable populations, including the elderly, would be a wiser choice.
“It’s like carpet-bombing,” he said of aerial spraying. “It is hard to know if a child who plays in an aerial-sprayed yard will develop an illness later in life.”
'Our short summers'
Vector control only resorts to aerial spraying when mosquito trap counts are high, with two to five applications common, Prather said. Mosquito trap counts in recent years are much lower than before, he said.
“We want people to enjoy the outdoors during our short summers,” Prather said.
The first line of defense in mosquito control is working to prevent formation of stagnant ponds, where mosquito larvae hatch. Efforts focus on eliminating pooling spots and treating them with larvicide to kill the mosquitoes before they hatch.
Still, aerial spraying sometimes is needed, but officials strive to keep it from becoming routine, relying on larvicide to do most of the work, Prather said. Larvicide is “virtually nontoxic, even to other insects,” he said.
Even aggressive larvicide treatments can be swamped by heavy rains, however, requiring aerial spraying, Prather said.
Permethrin, a neurotoxin that was synthesized in 1977 and first approved for spraying, on cotton, in 1979, is one of the least toxic insecticides, he said. It is used in agriculture, to spray crops and protect livestock, as well as in households, including as an insect fogger.
A study found no observable effects of permethrin dosages equivalent to a 30-pound dog receiving 1.5 grams daily over three months. For a person to ingest a 1.5-gram dose, one would have to consume all the permethrin sprayed by an ultra-low volume ground fogger over an area equal to three-fourths of a football field, according to information cited by Cass County Vector Control.
Lethal doses of permethrin and DEET are lower than common substances including albuterol, simethicone, acetaminophen and salicylic acid, the active ingredient in aspirin, according to World Health Organization acceptable daily intakes cited by vector control.
Nonetheless, Mahoney said officials have directed Prather to see whether there are less toxic alternatives to permethrin.
Miller still isn’t satisfied that science has demonstrated that even low doses of permethrin are safe over the long term.
“The annals of the history of medicine are resplendent with a variety of chemicals thought at the time to be safe” and later found to be toxic or cause cancer, he said. “The risks of many chemicals used as this one was are truly unknown.”
Also, Miller said, it hasn’t been shown whether aerial spraying makes a “meaningful difference” in preventing severe West Nile virus cases.
Mahoney, who said Prather has presented “piles of research” showing permethrin is safe, said the vector control program, established in 1988, has popular support.
“In our community mosquitoes can be a great bane,” he said. Spraying, he said, is “a comfort for the people.”