Gypsy moth spraying program begins in western Wisconsin

By: - April 27, 2020 9:26 pm
Gypsy moth (Photo courtesy of 123RF free stock photos)

Gypsy moth (Photo courtesy of 123RF free stock photos)

Over the next month, if you notice a yellow plane spaying areas of your county, don’t worry. The Department of Agriculture, Trade and Consumer Protection (DATCP), will begin an aerial spraying operation in May to control populations of invasive gypsy moths (Lymantria dispar dispar). Planes will begin spraying as early as 5 A.M in some areas.

“Aerial spraying is the most efficient and effective treatment method to help slow the spread and delay the impacts associated with gypsy moth outbreaks,” said Christopher Foelker, DATCP’s gypsy moth program manager. “It’s important to slow this invasive pest. Well-established gypsy moth populations cause damage to forests which impacts natural resources, wildlife, tourism and the timber industry.”

The majority of the spraying will take place across 18 counties in Wisconsin’s western regions. Spraying will also take place in areas where the gypsy moth population is low, in an attempt to stifle the insect’s western advance. Operations in southern Wisconsin will begin by mid-May, and conclude after spraying campaigns in the northern part of the state in July.

A web page is maintained by the DATCP providing maps of “Slow the Spread Treatment Sites,” (STS), which detail where western spray operations will occur. The first wave of spraying will include the counties of Bayfield, Buffalo, Burnett, Chippewa, Crawford, Douglas, Dunn, Grant, Green, Iowa, Lafayette, Polk, Richland, Rusk, Sawyer, Trempealeau, Vernon and Washburn.

In truth, the state has a limited window of time to conduct effective sprays. DATCP is aiming for when caterpillars hatch and feed among the trees. Plans come in low, utilizing a spray treatment called Bacillus thuringiensis var. kurstaki, or (Btk). It’s a naturally occurring bacterium, normally found in dead or decaying material in soil. According to a Purdue University research paper, Btk was first isolated in 1902 from a diseased silkworm larva, and has maintained a commercial presence in the United States since 1958. It works by triggering the caterpillar’s gut to release endotoxins, poisoning the digestive system.


Mammals, including humans, have different environments in their stomachs than insects like the gypsy moth. Normally, the high levels of acidic fluids destroys Btk before it can cause any infection. It also does not normally affect birds or fish. However, it also is ineffective against adult moths, as well as butterflies, honey bees and some other insect species, according to a page maintained by the Canadian government.

The Wisconsin Department of Natural Resources (DNR) states that gypsy moths were introduced to North America in 1869, by an amateur entomologist. These moths are ravenous, and have defoliated millions of acres of trees in forests and urban areas across 20 states. According to the DNR, gypsy caterpillars feed on over 300 species of trees. “During outbreaks, they may defoliate entire stands of trees or forests,” reads the page.

That’s why controlling or eliminating their population is crucial. Gypsy moths have been found in every Badger State county, and the eastern two-thirds of the state is considered infested and quarantined. This quarantine prohibits the movement of items which could transport their eggs, caterpillars, or adults. Spay operations in the western part of the state are proactive, and meant to limit their numbers before they take over completely.

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Isiah Holmes
Isiah Holmes

Isiah Holmes is a journalist and videographer, and a lifelong resident of Milwaukee, Wisconsin. Holmes' video work dates back to his high school days at Wauwatosa East High, when he made a documentary about the local police department. Since then, his writing has been featured in Urban Milwaukee, Isthmus, Milwaukee Stories, Milwaukee Neighborhood News Services, Pontiac Tribune, the Progressive Magazine, Al Jazeera, and other outlets. He was also featured in the 2018 documentary The Chase Key, and was the recipient of the Sierra Club Great Waters Group 2021 Environmental Hero of the Year award. The Wisconsin Freedom of Information Council also awarded Holmes its 2021-2022 Media Openness Award for using the open records laws for investigative journalism. Holmes was also a finalist in the 2021 Milwaukee Press Club Excellence in Journalism Awards alongside the rest of the Wisconsin Examiner's staff. The Silver, or second place, award for Best Online Coverage of News was awarded to Holmes and his colleague Henry Redman for an investigative series into how police responded to the civil unrest and protests in Kenosha during 2020. Holmes was also awarded the Press Club's Silver (second-place) award for Public Service Journalism for articles focusing on police surveillance in Wisconsin.