T-R PHOTO BY MIKE DONAHEY Japanese beetles eat everything but the veins on the plants they like. The iridescent insects will devour many types of garden plants and trees, and are hard to eradicate. Their eating behavior creates “lacy” leaves like those pictured here from a northwest Marshalltown home Friday.

Lacy, brown leaves are the calling card a small, iridescent insect that many Central Iowa gardeners are all too familiar with: the Japanese beetle.

The small, invasive beetles are back with a vengeance in the area after a few relatively mild summers, and Marshall County Conservation Naturalist Emily Herring said she’s been getting calls about the insects recently.

“They’re a little bit smaller than a dime, and they’ve got a green, metallic head and thorax, and brown, metallic wings; they have little black-and-white stripes on their abdomen as well,” she said. “They’re very shiny, and usually if you see one, you’ll see multiple.”

The “lacing” effect the bugs leave behind on plant leaves is due to their eating preferences.

“The tell-tale for them is that lacy leaf, they eat all of the plant except for the veins,” Herring said.

Iowa Department of Agriculture and Land Stewardship State Entomologist Robin Pruisner said the insects are hard to manage now that they’re established in the state.

“I call the Japanese beetles ‘tough little tanks,'” she said. “They were first found in the United States in 1916 in New Jersey … in Iowa, they were first reported in 1994.”

Since then, the Japanese beetle has spread to about 69 of the state’s 99 counties, and their territory is growing. Pruisner said the beetles continue to spread westward across the country like a slow-moving storm system.

“I call it the fire that burns out front, so the front of that infestation, as it moves westward, tends to be the worst,” she said. “That front, so to speak, is right over top of Iowa right now.”

Because the insect population will continue to move west, Pruisner said the summertime infestations should become milder in the future. Eastern states that formerly had large numbers of beetles now have much smaller populations.

Herring said the beetles can be fought with insecticide, but the effectiveness depends on whether the insects can be reached. It can be hard, for instance, to apply insecticide at the top of a Linden trees, which Japanese beetles target.

Pruisner said one management method to avoid is Japanese beetle traps.

“The traps have a lure in them, and they end up luring more beetles into an area than the trap actually catches and kills,” she said.

In the case of Linden trees, both Pruisner and Herring said it’s sometimes best to leave the insects alone. If the tree is healthy, the beetles don’t usually do fatal damage.

“What we often tell people to do is, when you’re making plant decisions, try and stay away from those most-preferred host, or mix them up with other things,” Pruisner said.

A comprehensive list of targeted plants can be found at the Iowa State University website, and it includes raspberry plants, roses, crabapple and apple trees, and others. For the full list, visit https://hortnews.extension.iastate.edu/2010/7-14/japanesebeetle.html

Herring said she’s noticed fewer beetles as the summer goes on, and said they may go dormant in the late summer and early fall.

Pruisner summed up the how many Central Iowans likely feel about the beetles’ damage to garden plants and trees.

“It’s very frustrating,” she said.