Japanese Beetles Emerging; Identification Key to Management

Japanese Beetles Emerging; Identification Key to Management

Japanese beetle

Figure 1. Japanese beetle (Popillia japonica Newman)

False Japanese beetle

Figure 2. Sand chafer, also known as the false Japanese beetle (Strigoderma arboricola)

Japanese beetle adults (Figure 1) are beginning to emerge in southeast and south central Nebraska. Their distribution has been increasing in Nebraska the last several years and they are being seen in corn and soybeans more frequently, in addition to feeding on landscape trees and shrubs. (See distribution map from Nebraska Department of Agriculture, Figure 3.)

NDA Map of Japanese Beetle distribution in Nebraska
Figure 3. Distribution of Japanese beetle in Nebraska (Source: Nebraska Department of Agriculture)

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

Similar to corn rootworm beetles, they will scrape off the green surface tissue on leaves before silks emerge, but prefer silks once they are available. Japanese beetles feed on corn silks, 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."

Be aware that Japanese beetle numbers are often highest on field margins, so scout across the whole field before making a treatment decision. Japanese beetle adults are about ½ inch long and have a metallic green head and thorax. A key characteristic 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 (Figure 2) 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 and 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