Japanese Beetle

Encyclopedia Article

Description of Japanese beetles

The Japanese beetle is a well-known pest of turfgrass and landscapes in the eastern United States. JB has been reported from 66 different counties in Iowa since 1994, predominantly in the east-central region of the state.  Click here to see the current distribution map.

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. 

Japanese beetle
Japanese beetle 

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. 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

Birch, gray
Elm
Grape
Hollyhock
Horsechestnut 
Linden2, American
Lombardy poplar
London planetree
Malus spp. (crabapple1, etc.)
Maple, Norway, Japanese
Mountain ash 
​​​​​​​Prunus spp. (flowering cherry, etc.)
Rose
Sassafras
Walnut, black
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
​​​​​​​Boxelder
Boxwood
Conifers (arborvitae, spruce, pine, fir, yew, juniper)
Dogwood
Euonymus
Green ash
Hickory, shagbark
Holly
Lilac
Magnolia
Maple, red, silver
Mulberry
Oak, white, red, scarlet, black
Persimmon
Poplar, white
Sweet gum
​​​​​​​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.  

Category: