Invasive gypsy moths expected in Lower Michigan, aerial treatments planned

Gypsy moths were first discovered in Michigan in 1954

Gypsy moth caterpillars have spiky hairs and a pattern of blue and red dots. You may find beads of frass (caterpillar droppings) under trees. (Michigan DNR)

The Michigan DNR says gypsy moth activity is expected across Lower Michigan this year after heavy defoliation last year by caterpillars.

The DNR said Michigan residents across the state may start to notice the loss of leaves on oak, aspen and maple trees again this year.

Gypsy moths are an invasive species, a term for non-native pests that can cause harm to native species and ecosystems. In its caterpillar life stage, the insect is a voracious leaf eater. Large numbers of gypsy moth caterpillars caused widespread defoliation in the state from the mid-1980s to the early 1990s. A large population in 2020 may lead to more caterpillars hatching this spring in localized areas across Lower Michigan.

Related: 11 invasive species to watch out for in Michigan

Last year, defoliation was heaviest in Alcona, Alpena, Montmorency and Oscoda counties, with more localized outbreaks from Manistee south into Newaygo County. Department of Natural Resources forest health experts say it is likely that gypsy moth caterpillar populations will crash in some areas while they thrive in others. Heavy defoliation likely will become visible within the next month in localized outbreak areas and persist through mid-July.

“Gypsy moth caterpillars rarely kill trees in Michigan,” said James Wieferich, DNR forest health specialist. “Only stressed trees suffering from problems like drought, old age or root damage are at high risk. In most cases, gypsy moth caterpillars are more of a nuisance in residential areas on houses and in yards than in the woods.”

The leaf-eating caterpillars are hairy, up to 2 inches long and have a pattern of blue and dark-red spots. Male moths are dark buff in color and fly; females are white with black, wavy markings and do not fly.

Gypsy moths were first discovered in Michigan in 1954. By the 1980s and 1990s, large gypsy moth populations cycled through Michigan, defoliating up to a million acres in some years, said Scott Lint, DNR forest health specialist. (Learn more about gypsy moths here from MSU Extension)

Aerial treatments

Macomb County has started aerial treatments to help suppress growth of gypsy moths across the area. The Macomb County Gypsy Moth Suppression Program was established in 1993 and is administered by Michigan State University (MSU) Extension. Here’s how the treatment works:

The main defense is an aerial application of Bacillus thuringiensis var. kurstaki (Btk), used to reduce high populations of gypsy moth caterpillars at sites that meet certain guidelines for treatment. Btk is a naturally occurring bacterium found in the soil and is not harmful to pets, birds, fish, plants, beneficial insects, or humans. Btk specifically targets only caterpillars of a certain age. It is applied when the caterpillars are young (usually in May) to insure the greatest impact in reducing numbers. Alternative mechanical techniques, such as tree banding, egg mass scraping, and hormone traps to help reduce populations. The Suppression Program recommends the use of a combination of methods.

More info: Aerial view maps of spray blocks in Macomb County municipalities that have been affected with gypsy moth infestation this year.

A video (below) shows aerial treatments underway this morning in Romeo.

Other Michigan communities have aerial treatment programs, including Bay County, Rochester Hills, Clare County, Kentwood, and several others across Western and Northern Michigan.

Michigan communities considering a gypsy moth spray program should seek licensed pesticide applicator businesses familiar with the complex pesticide laws, including notification and permitting requirements.

A list of Michigan businesses licensed to apply pesticides is available at Michigan.gov/MDARDPABL. Additional information about pesticide laws and regulations is available at Michigan.gov/MDARDPestCert.

Related: 5 invasive plants to watch out for in Michigan


About the Author:

Ken Haddad is the digital content and audience manager for WDIV / ClickOnDetroit.com. He also authors the Morning Report Newsletter and various other newsletters. He's been with WDIV since 2013. He enjoys suffering through Lions games on Sundays in the fall.