Japanese Beetle (JB)

Popillia japonica

Written by: 

Jaime Pinero

Overview

Both as adults and as grubs (the larval stage), JB is a destructive plant pest. Adults feed on the foliage and fruits of several hundred species of fruit trees, ornamental trees, shrubs, vines, and field and vegetable crops. Adults leave behind skeletonized leaves and large, irregular holes in leaves. The grubs develop in the soil, feeding on the roots of various plants and grasses.

The adult JB is 1/4 to 1/2 inch in length and has a shiny, metallic-green body with bronze-colored outer wings. The beetle has six small tufts of white hair along the sides and back of its body under the edges of its wings. Their eggs are yellowish-white, elliptical or spherical in shape, and are laid about 3 inches into the soil in grassy areas, often in closely cut grass. The grubs can be recognized by the distinctive C-shape they take when curled up. They are white or cream in color, have three pairs of legs, and a hard brown head. The grub stage is about 10 months long. They then go into a brief pupa or resting stage in late spring where they change into a beetle.

Biology

The JB has only one generation per year, but these beetles emerge over a long period from early July through late August and they live for over 30 days. JB overwinters as third-instar larvae in the soil, approximately 12 to 18 inches deep. As soils warm in the spring, larvae migrate to the top 1 to 2 inches and resume feeding on grass rootlets. Larvae begin pupation by mid-June. Warm, sunny days draw beetles out in larger numbers. During the feeding and mating period, females intermittently leave plants, burrow about 3 inches into the ground nearby host plants and lay a few eggs. This cycle is repeated until the female lays 40 to 60 eggs. Larvae migrate downward before the soil freezes to overwinter.

Monitoring

Traps are available for JB but are only effective for monitoring the initial adult emergence. Adults may be monitored by quietly moving into the tree, jarring several branches, and observing how many fly off. Direct fruit counts are the most effective way of assessing the level of damage. Since feeding may be "clumped" or unevenly distributed, care should be taken in looking at a representative sample before making a spray decision. If feeding exceeds 1 percent, then treatment is justified. 

Management

Control of adults can be difficult. Insecticides can reduce damage, but applications may need to be repeated every three to four days since new migrations of beetles can occur daily. Insecticide options include broad-spectrum and reduced-risk. Do not spray when trees are in bloom.

Mass trapping systems have been developed for use against JB under certain situations e.g., organic orchards, in rural areas. Contact Dr. Jaime Piñero at jpinero@umass.edu for more information about mass trapping as an organic management method for Japanese beetles.