Japanese beetle, common name for a destructive beetle, Popillia japonica, of the scarab beetle family. Accidentally imported to the United States from Japan, it was first discovered in New Jersey in 1916 and is now widespread in the northeastern states, where it is a serious pest of lawns, orchards, and gardens. The adult is about 1/2 in. (13 mm) long with a metallic-green head and thorax and reddish-brown wing covers. Metamorphosis is complete (see insect). The eggs are laid in the ground; the small white larvae, called grubs, feed on the roots of grasses, sometimes killing them, and hibernate during the winter. Pupation occurs in the spring, and the adult emerges in midsummer, feeding on and destroying leaves, flowers, and fruits. Many methods of control have been tried, especially those involving the insect's natural enemies—e.g., parasitic wasps and flies, some of them imported from Japan; bacteria that cause the "milky disease" of grubs; and certain parasitic nematodes. None, however, have been entirely successful in controlling the spread of the beetle. Japanese beetles are classified in the phylum Arthropoda, class Insecta, order Coleoptera, family Scarabaeidae.
See bulletins of the U.S. Dept. of Agriculture.