Figure 1a. Japanese beetle and 1b. False Japanese beetle (Photos by Jim Kalisch)

July 11, 2013

We have received many questions about the Japanese beetles that have been emerging over the past couple of weeks. This introduced insect has been expanding its range in southeastern and south central Nebraska and now is more frequently being found in corn and soybean fields, as well as in yard and gardens.

Japanese beetles can contribute to defoliation in soybeans, along with a complex of other insects, such as bean leaf beetles, grasshoppers, and several caterpillar species.

Japanese beetles also may feed on corn silks, similar to corn rootworm beetles, and may interfere with pollination if abundant enough to severely clip silks before pollination. University of Illinois Extension recommends: “An insecticidal treatment should be considered during the silking period if:

1. there are three or more Japanese beetles per ear,
2. silks have been clipped to less than ½ inch, AND
3. pollination is less than 50% complete.”

Again, similar to corn rootworm beetles, they will scrap off the surface green tissue on leaves before silks emerge, but prefer silks once they are available.

Japanese beetles adults are about ½ inch long and have a metallic green head and thorax. A key characteristic to look for is a series of white tufts of hair on each side of the abdomen.

In some cases people have mistaken the Japanese beetle for its look-alike, the false Japanese beetle, or sand chafer, Strigoderma arboricola, which is a native Nebraska insect found across most of the state. Sand chafers are commonly found along the Platte River valley and other river valleys in Nebraska. False Japanese beetle adults are about the same size as Japanese beetles, but do not have a metallic green head. They may vary in color from coppery brown to black. They may have some white hairs on the side of the abdomen but they are not organized into tufts of hair.

They are often noticed because they have a habit of landing on people; they seem to be attracted to people wearing light-colored clothing. They have not been reported to cause economic damage to crops as adults, although the immature white grub has been reported to cause damage to potato tubers.

Bob Wright
Extension Entomologist