Description of Japanese beetles
The Japanese beetle (Popillia japonica) is the most destructive insect pest in the landscape and garden. It was 91first found in this country, near Riverton, New Jersey, after arriving in nursery stock from Japan. Japanese beetle infestations slowly expanded southward and westward and are now found from the Atlantic Ocean to the Ricky Mountains. Japanese beetle in the U.S. and Canada
The Japanese beetle did not appear in Iowa until 1994 but is now found in over 3/4ths of the state. Click here to see the current Iowa distribution map.
The Japanese beetle is the "worst landscape pest in America" becase it attacks plants and be a serious pest in both the adult and larval stages. As an adult beetle in mid-summer, the beetles are known to devour the foliage, flowers, and fruit from more than 400 species of plants. The rest of the year the larvae are white grubs that live in the soil and eat the roots from trees, shrubs and turfgrass. Damaged turf wilts, turns tan and dies during August or September after the roots are eaten.
Adult beetles emerge in mid-June through July. They are similar to other Junebugs in general appearance, and 3/8 inch long and 1/4 inch wide. The head and thorax are shiny metallic green, and the wing covers are coppery red. The row of five tufts of white hairs on each side of the abdomen is a distinguishing feature.
Life cycle of Japanese beetles
Japanese beetle larvae are typical white grubs. They are in the soil from August until June where they feed on plant roots (especially turfgrass) and organic matter. The grubs are C-shaped and approximately 1.25 inches when full grown.
Damage caused by Japanese beetles
Adult beetles eat the foliage, fruits and flowers of over 300 plants. Foliage is consumed by eating the tissue between the veins, a type of feeding called skeletonizing. Flowers and fruits are devoured completely, often by a horde of a dozen or more beetles at a time.
Management of Japanese beetles
Control of adult beetles is difficult because they emerge every day for a period of several weeks. Handpicking or screening or high-value plants may be of benefit in isolated situations with limited numbers of beetles. Remove beetles early and often to preserve the beauty of the plant and to reduce the attraction of more beetles. Remove beetles early in the morning while temperatures are cool and the beetles are sluggish. Collect or shake beetles into a bucket of soapy water and discard.
Spot spraying infested foliage of high value plants with carbaryl (Sevin), permethrin (Eight), bifenthrin or cyfluthrin (Tempo) may reduce damage for several days, but multiple applications are required to maintain control. Spraying the adult stage is not an effective strategy for prevention of white grubs.
Several traps using a floral lure and sex attractant are available. Use of these traps is not recommended. 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. The traps may reduce damage and populations when landscapes are isolated from other Japanese beetle breeding areas or when mass trapping (everyone in the neighborhood) is used.
Japanese Beetle Host Plant Preferences
One way to limit the impact of adult Japanese beetle defoliation may be to select plants that the Japanese beetles tend to avoid. The following list of the Japanese beetle's most and least-favored woody plants may be useful to people designing new landscapes in areas infested by this beetle.
Most Favored by Japanese Beetle
Malus spp. (crabapple1, etc.)
Maple, Norway, Japanese
Prunus spp. (flowering cherry, etc.)
Weeds (wild grape, multiflora rose, smartweed, poison ivy)
1Susceptibility of crabapples varies with variety
2Tilia tomentosa 'Sterling' and Tilia americana 'Legend' are less susceptible than other lindens
Least Favored by Japanese Beetle
Ash, white, green
Conifers (arborvitae, spruce, pine, fir, yew, juniper)
Maple, red, silver
Oak, white, red, scarlet, black
Yellow poplar (tuliptree)
Do you live in Iowa and have an insect you would like identified?
The Iowa State University Plant & Insect Diagnostic Clinic will identify your insect, provide information on what it eats, life cycle, and if it is a pest the best ways to manage them. Please see our website for current forms, fees, and instructions on preserving and mailing insects.
Contact information for each states diagnostic laboratory for U.S. residents. If you live outside of Iowa please do not submit a sample without contacting the Plant & Insect Diagnostic Clinic.