Old and new insect pests begin bugging Wisconsin

July 7, 2011

by David Tenenbaum

The mosquitoes are back, the Japanese beetles are starting to devour the 300 species of plants they call "food," and a flock of invasive insects are poised to make headlines in Wisconsin, says Phil Pellitteri of the University of Wisconsin-Madison Insect Diagnostic Lab.

Some "insect problems" are minor, says Pellitteri. People who pull out a spray can to kill millipedes may not realize that they may be annoying, but are not harmful.

The Japanese beetle, which attacks a wide range of cultivated plants, including roses, shrubs and grapes, is more serious.

"Japanese beetles are like a superstar in an amateur league," says Pellitteri, due to their broad taste in host plants, their ability to fly half a mile, and their two-month feeding season.  "Many insects are around for only a few weeks, so these have an impact on gardeners unlike anything else."

But as Japanese beetles have expanded into new areas of Wisconsin, they have declined elsewhere. 

An insect with even more potential for harm, the brown marmorated stink bug, may already be breeding in Wisconsin.

"This is like a marriage of the multicolored Asian lady beetle to the Japanese beetle," Pellitteri says. "Last year, the stink-bug population went crazy in New Jersey, causing significant damage in corn, soybean, peaches, cherries, peppers and tomato."

While the Japanese beetle mainly attacks ornamental plants, the stink bug "hits fruits and vegetables, and it's a nuisance as well. A feeding stink bug causes a white blemish on tomatoes and ruins the taste of a raspberry. It causes brown corky spots on apple, and people have concerns about cranberry. This one can cause major fruit loss," Pellitteri laments.

Fruits are also threatened by the spotted-wing drosophila, which, unlike most fruitflies, attacks unripe fruit.

"The female has a saw-like egg laying device that can force growers to put on chemicals just before harvest, which is not where anybody wants to go," Pellitteri says. "This is a big disappointment; has big potential for damage."

Meanwhile, Lyme disease, transmitted by deer ticks, continues to expand in Wisconsin, with a 35 percent increase in human cases in 2010.

"We've never had a decline in cases in the last dozen years," says Pellitteri. 

The emerald ash borer continues to threaten billions of ash trees in Wisconsin, Pellitteri says.

"In some pockets, the ash borer has grown a little bit. Kenosha now has dead trees, and the infestation in Vernon County has reached 20,000 acres, but I was pleasantly surprised last year that we did not have three or four new counties with the ash borer," he says.

The ash borer is finally facing a counterattack, Pellitteri adds.  "Ken Raffa in the UW-Madison entomology department, along with the Department of Natural Resources, has released three parasitic wasps against the emerald ash borer, although we don’t yet know whether they will effectively control this pest."

Nature often tends to restore some form of balance in the long term. For example, the number of pestiferous multicolored Asian lady beetles have begun to decline at some sites.

"This is common with invasives, when they first get here, they have the biggest impact, and in time come into more reasonable balance" as predators and competitors adjust to it, says Pellitteri.

There is other good news from the insect world. Mosquitoes have generally been mild so far this year. The honeybee, one of more than 400 bee species that performs essential pollination services, seems to be defying the worst fears about colony collapse disorder, Pellitteri says.
"Normally we lose 30 percent of honeybee colonies over the winter, and most of the  problem here is due to winter weather and varroa mite, not colony collapse," he says.

And 2011 is shaping up as a banner year for fireflies, Pellitteri adds. Because fireflies feed on millipedes and slugs, "We'd expect that having so much rain last year would have favored their prey, and that seems to have made this a good year for fireflies. I hear people say there are not as many fireflies as when they were kids, but in my memory, we don’t get many years like this one for fireflies."