Widespread insecticide spraying to kill mosquitoes potentially carrying the deadly Eastern equine encephalitis virus comes with a negative: It kills other bugs, too — including rare, endangered and highly beneficial ones.

Among those that could be affected is the endangered Mitchell's satyr butterfly, which the Michigan Department of Natural Resources calls on its website "one of the world's rarest butterflies, found only in Michigan and Indiana."

Amid an alarming rise in cases of the mosquito-spread disease in southern Michigan, state health officials are conducting widespread, airborne insecticide spraying for the first time in nearly 40 years.

As of Monday, more than 541,000 acres of southern Michigan had received spraying by airplane, in portions of 14 counties: Allegan, Barry, Berrien, Calhoun, Cass, Jackson, Kent, Lapeer, Montcalm, Newaygo, St. Joseph, Van Buren, Washtenaw and Livingston.

While the organic pyrethrin product used to kill adult mosquitoes is safe for humans and animals, health officials emphasize, it's not safe for other insects. That puts some endangered or threatened butterflies and moths at risk, along with essential, dwindling pollinators such as bees, some scientists worry.

"The issue is complicated," said Logan Rowe, a zoologist and conservation associate with the Michigan Natural Features Inventory, a consortium of scientists providing information to governments and others to promote biodiversity and conserve rare and declining plants and animals.

"The pesticide being used is a broad spectrum pesticide that has the potential to affect any insect it comes in contact with, including the threatened species. ... The main issue I have is that the decision (to spray) was fast, with limited public or scientific input, little time or opportunity to weigh the positives versus the negatives, and with little understanding of the possible nontarget organisms that might be affected."

Rowe cited the example of bumblebee queens that may currently be searching for their overwintering hibernation sites that could be killed by the spraying. Bumblebees are one of several bee species suffering massive population and range declines in Michigan and elsewhere in recent years, for reasons that aren't fully understood. Honeybees contribute $24 billion annually to U.S. agriculture, through pollination and increased crop yields.

Michigan Department of Natural Resources spokesman John Pepin confirmed the existence of threatened and endangered insect species in the general areas receiving spraying, including the endangered Mitchell's satyr butterfly, the state-threatened Silphium borer moth and Persius duskywing butterfly.

"The DNR issued a state threatened and endangered species permit for (mosquito) spraying because of human health and safety concerns," Pepin said.

EEE is a rare disease that is caused by a virus spread by infected mosquitoes. EEE virus is one of a group of mosquito-transmitted viruses that can cause inflammation of the brain, or encephalitis. In the United States, there are typically only about five to 10 human cases reported nationwide each year, according to the U.S. Centers for Disease Control and Prevention. But nine human cases of EEE have been reported in southwestern Michigan, with four fatalities, in recent weeks. Some 33 animals also have tested positive for EEE infection, according to the state health department.

Severe cases of EEE begin with the sudden onset of headache, high fever, chills and vomiting. The illness may then progress into disorientation, seizures and coma. Approximately 33% of patients who develop EEE die, and many of those who survive have mild to severe brain damage, according to the CDC. The infection is about 90% fatal for horses.

The widespread mosquito spraying is the first done in Michigan since 1980, said Lynn Sutfin, spokeswoman for the Michigan Department of Health and Human Services.

"We are considering this a public health emergency," she said. "This is not business as usual."

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The pesticide being applied in nighttime, aerial applications, Merus 3.0, contains 5% pyrethrin, a chemical found naturally in chrysanthemum flowers, which allows the pesticide to be considered organic. The pyrethrin kills mosquitoes — and other insects — through disrupting their nervous systems.

The spray breaks down quickly in sunlight and outdoor exposure, and "binds strongly to soil," Sutfin said. "It's not going to get into our groundwater," she said.

The nighttime spraying helps limit exposures more to mosquitoes, which are active at night, Sutfin said.

"We contacted some beekeepers in the area so they know where this is going on and when, in case they want to take precautions, such as covering their hives with cloth or burlap," she said.

Massachusetts, which has done similar mosquito spraying this year, examined 600 of the state's honeybee colonies after the spraying, and have not had any unusual losses, Sutfin said.

The aerial spraying will continue until all of the areas of Michigan designated as having EEE virus-carrying mosquito activity are treated — 15 counties so far, a number that could still expand — or until there is a hard, mosquito-killing frost, Sutfin said.

"We do not have one of those (frosts) predicted until at least mid-October, according to weather forecasts," she said.

Kalamazoo County, in the heart of the EEE activity area, has opted out of aerial spraying. The number of residents who opted out of having their property sprayed comprised a large enough geographical area that "spraying would no longer be an effective measure to reduce adult mosquito populations in Kalamazoo County," the county health department stated in a release.

Kalamazoo County, along with the cities of Kalamazoo and Portage, are attempting to reduce resident EEE risk by distributing skin-worn insect repellent containing DEET to homeless shelters and senior centers throughout the county. The repellent is also available for free pickup at the Kalamazoo County Health and Community Services Department, as well as at City of Kalamazoo offices.

Rowe expressed concern that aerial spraying could kill natural insect predators of mosquitoes, such as dragonflies and damselflies — "which could make the problem even worse, as mosquitoes will reproduce daily."

"It's difficult to take a stance that some will view as opposing public health. ... In this case, I'm not sure the risk to human health is as severe as some thing, or outweighs the potential negatives, and if I owned property, I would likely opt out" of spraying.

Contact Keith Matheny: 313-222-5021 or kmatheny@freepress.com. Follow on Twitter @keithmatheny.