The Japanese beetle is a serious agricultural pest. It has attractive looks, however, with bronze wing shields and metallic green thorax. The abdomen appears black-and-white striped because of white tufts of hair on the abdominal segments.
Japanese beetles belong to a large family of beetles called scarabs. As with other scarabs, they are oval, stout, and have clubbed antennae with segments that can press tightly together or can be fanned open like a feather.
Like those of most scarab beetles, the larvae are whitish, C-shaped grubs that live underground. The heads are brownish, and they have three pairs of legs.
Learn more about this and other scarab beetles on their group page.
Length: about ½ inch (adults); to about 1 inch (larvae).
Habitat and Conservation
These beetles often feed in groups of up to 25 on a wide variety of plants, especially on the top portions, in the sunlight. They are skeletonizers, feeding only on the soft parts of foliage, leaving only a lacy network of veins behind. Native to Japan, this insect is a serious pest of lawns, gardens, and crops in North America. They have multiyear population booms, which usually subside as natural predators and diseases arise to bring their numbers back into balance.
Adult Japanese beetles chew leaves, preferring plants with pleasant-smelling foliage. They also eat flowers and fruits. They are found on a wide variety of plants, including roses and many other garden flowers, fruit trees, crape myrtles, sassafras, lindens, maples, grapes, beans (including soybeans), and corn. When they eat the tassels and silks of young ears of corn, they can prevent pollination and reduce yield on attacked ears. The larvae eat roots of many kinds of plants.
A nonnative, invasive pest. The Japanese beetle was first discovered in North America in 1916 in New Jersey. Attempts to eradicate it failed, and in 1932 it was found in St. Louis. Today, infestations occur in the eastern US, and the US Department of Agriculture works to hamper its spread to western states. University extension and state agriculture departments help people control the Japanese beetle.
After mating, females burrow a few inches into the soil and lay eggs, 40–60 during a summer. The grubs live underground for about a year, feeding on plant roots, molting as they grow. They descend 4–8 feet into the soil to overwinter. When fully grown, in late spring the larvae pupate for a few weeks. They emerge as adults in mid-June and crawl to the surface to fly, mate, and lay eggs. As adults, they live for about two months. They can fly up to 3 miles for food.
The larvae do especially well in well-watered, lush lawns, such as in golf courses and suburban areas. The adults damage a wide variety of garden and crop plants. Fortunately, there are many ways to control them; but there are no ways to be rid of them.
With their multiyear cycles of population booms, they influence cycles of predator species, whose numbers rise when the beetles are plentiful. The Japanese beetle is not a major pest in its native country, where climate, natural diseases, and native predators help keep its numbers in check.
Scoliid wasps hunt Japanese beetle grubs and the larvae of other scarab beetles.