The Japanese beetle is native to Japan and was introduced into the United States before 1916. It now occurs throughout much of the Eastern United States from Maine to Georgia and west to the Missouri River. In Michigan, it occurs in scattered locations in the Lower Peninsula south of a line from Saginaw to Muskegon.
The adult beetles are about 1/2 inch long and broadly oval with a shiny metallic green forebody and copper-colored wing covers. There are six small patches of white hairs on the side of the abdomen.
The immatures (larvae) are typical C-shaped white grubs. They are distinguished from other white grubs by the V-shaped arrangements of spines on the raster (underside of abdominal tip). The grubs are 1 inch long when mature.
The insect overwinters as a partially grown larva. In the spring they move closer to the soil surface and feed on grass roots. The grubs mature in late May or June and pupate in the soil. The adults begin to emerge in late June and early July. Peak adult activity, including mating and egg-laying, occurs over the following 4-6 weeks. The beetles begin to die off during the late summer. After mating, the female beetles deposit 40-60 eggs in the soil. The emerging grubs feed on grass roots until fall, when they move downward in the soil. There is only one generation per year.
Both adults and larvae may cause economic damage. Adults have been reported to feed on the foliage, flowers, or fruit of over 275 plant species. The beetles are active during the day and feed gregariously. The white grubs favor the roots of grass plants and can cause serious damage to turf grasses by "root pruning."
Control measures for adult Japanese beetles should be initiated as soon as beetles appear, but before serious damage occurs. Dusts or sprays of Sevin, Malathion, methoxychlor, Rotenone, or Diazinon may be used according to label instructions.
The beetles also can be controlled by hand collecting. Place a container or sheet beneath infested plants and dislodge the beetles. Do this when the beetles are still lethargic. Kill the beetles by placing them in a container filled with a mixture of water and kerosene. In the 1930's, traps were developed for survey work. Today's traps, which employ a combination sex pheromone and floral lure, can be used to capture large numbers of beetles. Be sure to place the traps away from vulnerable host plants!
Healthy, vigorous plants are most able to overcome beetle injury, so be sure all plants are provided with proper care. Also, dispose of any over-ripe or diseased fruits, as these tend to attract beetles.
Larvae (white grubs) of Japanese beetles can be controlled by applications of either pesticides OR milky spore disease. (These methods are mutually exclusive and cannot be used in combination.) Registered grub insecticides include Diazinon, Dursban, or Dycarb. Refer to the label for rates and methods of application.
Milky spore disease (Bacillus popilliae) is a biological control of Japanese beetle grubs. However, it may require up to 2 or 3 seasons to become firmly established in the soil (at which time it becomes self- inoculating). It generally works best at high grub population densities.