Japanese beetles are one of the most common pests in Northeast gardens. They were accidentally introduced with infested irises from Japan for the 1916 World's Fair. The adults feed on over 300 different plants, "skeletonizing" the leaves and leaving only midribs and other veins. When populations are high, they may defoliate plants. The larvae (grubs) feed on roots and can kill large areas of turf (see white grub factsheet).

Description:

Adults are approximately 10 mm (3/8 inch) long, with a metallic green midsection and head. The wing covers are coppery brown, and tufts of white hairs line the sides of the abdomen.

Life Cycle:

The life cycle is completed in one year, with ten months spent as a grub in the soil and two months as an adult. Females deposit eggs in soil, usually in turf, during the summer (primarily in July). Grubs feed on roots near the soil surfaces until cold weather arrives, then move to about 15 cm (6 inches) below the surface of the soil to they hibernate for the winter. Grubs move nearer the surface in the spring and resume feeding. They pupate in May and June, emerging in early July as adults.

Damage:

Roses, fruit trees, beans, tomatoes, and corn are among the favorite foods of the adult Japanese beetle. Adults feed during the day, especially in warm weather and on plants in full sun. They chew on the flowers and the leaves, which soon wilt and drop. Large populations can completely defoliate a plant. There are several similar species, such as Oriental and Asiatic garden beetles, which also eat landscape plants. Oriental and Asiatic garden beetles feed mostly during the night on flowers, but cause little damage as adults (the larvae can seriously damage roots, particularly of grasses).

Control:

Light infestations can be controlled by knocking the adults into a pail of soapy water early in the morning, while they are still sluggish. The plants can also be sprayed with Neem, which is approved for organic gardens and acts as a feeding repellant.

Commercially available Japanese beetle traps use two chemical lures to attract the beetles: one lure is a Japanese beetle sex pheromone that attracts male beetles; the other lure consists of a blend of three chemicals which emulates a floral scent and attracts males and females. One study has shown that using these traps in an individual yard may not be effective. Traps will exert some degree of control, but the number of traps to use, and how effective they are, remains a topic of debate among entomologists. Using these traps in a small residential yard may be counter-productive, as they may attract more beetles into the yard than they kill. Traps may be effective, however, in a home yard surrounded by forest, on a golf course or in a residential community where all neighbors simultaneously trap Japanese beetles, or in other sites where the traps do have the potential to suppress the local beetle population.

By Marion Gold, Steven Alm and Meggan Gould, 1999. Photo copyright Lisa L. Gould.