Invasive gypsy moth population continues to decline

By: - December 10, 2019 3:56 pm
Gypsy moth (Photo courtesy of 123RF free stock photos)

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

The Department of Agriculture, Trade and Consumer Protections’ (DATCP) most recent trapping season for gypsy moths (Lymantria dispar dispar) suggests that the invasive species’ population is continuing to decline in Wisconsin. In 2017, 108,808 moths were captured, followed by a little over 76,000 in 2018. For 2019, the numbers continued to drop to 52,396 captured moths.

Although not a form of population control, the traps are an effective means of measuring the insect’s population. The invasive moth species originates from Europe, and began spreading into North America after it was first introduced in 1869. Gypsy moth caterpillars feed on leaves from a variety of trees and shrubs, particularly oaks. With their ravenous appetite, the caterpillars can cause severe defoliation if left unchecked.

Upon entering the adult phase of their life cycle, the creatures single-mindedly seek mates. Male moths fly, while females do not, meaning that the DATCP population data is based entirely on the male segment of the species. After laying masses of eggs, the female moth dies. The eggs then lay in wait for the following spring when they hatch, feed, grow and turn into new moths before beginning the cycle again.

Trapping males also helps guide where to direct spraying programs to reduce the moths’ numbers the following year. In 2019, about 76,288 acres across 14 Wisconsin counties were successfully treated. Spray sites for next year, however, haven’t yet been determined.

Wisconsin’s cold winters have not been kind to the gypsy moth. According to a DATCP press release, this might be driving the invasive species’ continued decline — especially over the last couple of years, when snowfall has been less consistent. Gypsy moths use snow as insulation when they hunker down for the winter. The protection also helps secure and hide their egg masses.

DATCP encourages Wisconsin residents to help push the invasive insect out wherever possible. Removing egg clusters is a crucial thing ordinary citizens can do, without the need for sprays. The clusters can be found on trees, vehicles, fences, playground equipment, buildings or any such outdoor items. The bulb-shaped egg masses are a bit bigger than a quarter, flat with a velvety texture and can hold anywhere from 500 to 1,000 eggs.

“For the second straight year, there were several days of severe winter temperatures cold enough to kill gypsy moth eggs throughout Wisconsin,” said Michael Falk, trapping coordinator for the program. “These cold temperatures, in combination with our treatments, have helped decrease gypsy moth catches by about one-third since 2018, and one-half since 2017. However, moth populations can rebound quickly given the right environmental conditions.”

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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.