Watch for Japanese Beetles in Iowa

The Japanese beetle has been one of the most troublesome urban insect pests in the eastern U.S. since it was imported into New Jersey with ornamental plants from Japan about 1916. It has spread on its own and with nursery stock and sod throughout the eastern half of the U.S.

Japanese beetle was in Iowa several years ago (Cedar Rapids, 1970's) but disappeared after a brief time. We may not be so lucky with infestations that were reported in Scott County (Davenport and Bettendorf) last summer. Japanese beetle has been observed in at least five infestations and some are already quite large and well-established.


Part of our response to the discovery of a new insect species within the state is to document its spread and establishment. If you find beetles that you suspect are Japanese beetles, please send specimens to Extension Entomology, ISU, Ames IA 50011 for confirmation and recording as a new county record.

The Japanese beetle measures 1/3 to 3/5 inch long. The head and thorax are greenish bronze and the wing covers are copper/metallic-colored. There are prominent white spots at the tip and along the sides of the abdomen.

The adult beetles are present from late June through mid-August. They feed on the foliage and fruits of over 350 kinds of plants but are best known as pests of fruits, vegetables, garden flowers, trees and shrubs. Their feeding causes scarring on the surface of fruits and chewing damage on the margins of leaves and destruction of flowers. They prefer roses, raspberry, grape, and crabapple. Damage to field crops is usually limited.

The Japanese beetle larva is one of several white grub species living in the soil. They are a serious pest because they feed on the roots of turfgrass. Control of the grub stage in the soil is similar to control of the other annual white grub we typically have in Iowa. Biological controls for Japanese beetle grubs exist -- bacterial milky spore disease and entomopathic nematodes -- but have been either unsatisfactory or marginally effective against this pest in the Midwest.

Control of adult beetles is difficult because they emerge every day for several weeks to a month. Generally, surface sprays of carbaryl (Sevin) or cyfluthrin (Tempo) reduce damage for two to several days, but multiple applications are required to maintain control. Although Japanese beetle traps are widely available for purchase, research conducted in Kentucky suggests that they are not effective in controlling moderate to heavy infestations; and they may attract more beetles into a yard than would occur otherwise.

This article originally appeared in the July 21, 1995 issue, p. 113.


Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on July 21, 1995. The information contained within may not be the most current and accurate depending on when it is accessed.