The Invasive Japanese Beetle May Have Finally Ended Their Reign in South Wisconsin

by Lucy Ji, age 16

Just a couple years ago, the Japanese beetle terrorized Wisconsin’s farmlands and natural vegetation. After many years of havoc, southern Wisconsin seems to have moved past the worst of the invasion.

The Japanese beetle is an invasive species, a non-native species that negatively impacts the balance of the environment. It was first found in 1916 around the southern part of the United States. Gradually, the species spread throughout the entire eastern half of the country. These beetles are easily identified through their distinctive metallic green shell. This pest feeds on hundreds of species of fruits, flowers and crops including Norway maple, birch, crabapple, mountain ash, and countless other native plants. The adult beetles tear through the leaves and foliage while the grubs feed on the roots at ground level. If either of these becomes damaged, it can inhibit nutrient uptake of the plant.

Fortunately, according to Phil Pellitteri, a UW-Madison entomologist, there are two natural forces reducing the population. One cause of the diminishing beetle count was the lack of rain last year. The heat dried out the lush lawns of Madison where the beetles made themselves at home. The second reason has to do with “the natural cycle of invasive insects” and how long Japanese beetles have been around.

“One could argue it is coming into some sort of balance now,” Pellitteri said.
Studies conducted by UW soil science professor Phil Barak show that beetle populations have been declining at a rate of 50 percent per year. Today, Pellitteri estimates the population is less than ten percent of what it was at the beginning of their cycle.

Unfortunately, this trend is not occurring outside the Madison area. “When I talk to the people up in Green Bay,” he said, “they’re about three or four years into a Japanese beetle problem and it is just a stinker like it was here ten years ago.”

Pellitteri predicts that the beetle population should not increase in the future and, if anything, the count should decline even further.

[Source: Wisconsin State Journal, Wisconsin Horticulture]