CDFA is scheduled to begin treatments this month for two Japanese beetle infestations in California, in the Carmichael-area of Sacramento County and in the Bay Area community of Sunnyvale. The following interviews are with four people with experience or knowledge about a potentially devastating pest that requires an estimated $460 million a year for ongoing control programs in the eastern US. In California, the approach is to eradicate Japanese beetle infestations so control programs aren’t necessary.
The adult beetle is a broadly oval insect nearly 1/2-inches long and about 1/4-inch wide. The body is a bright metallic green; the legs a darker green. The wing covers are a coppery brown and extend almost to the tip of the abdomen. There are two small tufts of white hairs just behind the wing covers and five patches along each side. The larva (grub) resembles those of many other beetles which feed on plant roots. It is white, from 1/16 to 1/4-inch long with three pairs of legs.
History and Economic Importance
The Japanese beetle is originally from Japan, and was first found in the U.S. in 1916 in New Jersey. It is not a serious pest in Japan where there are relatively few large grassy areas favorable for its reproduction, and the action of predators, parasites, and pathogens keep the beetle numbers low. In the U.S. however, a favorable climate, large areas of permanent turf for reproduction, and ineffectual natural enemies favor increased population densities. It is considered a serious pest of turf, and adults damage a wide variety of both ornamental and agricultural plants.
The Japanese beetle is native to the main island of Japan. The beetle is currently found in coastal and adjacent states from Maine to Alabama with small infestations westward to beyond the Mississippi River.
Females lay eggs in small clusters of one to four eggs within cells two to four inches below the soil surface. Each female may lay 40 to 60 eggs in her lifetime. Eggs hatch in 10 to 14 days. Larvae feed on many types of plant roots, but are fond of grasses. They move deeper into the soil at the onset of winter, and return to the root zone in the spring to feed. Larvae develop through three instars. Pupation takes place in earthen cells later in the spring, and adults emerge after eight to 20 days. There is usually one generation per year, although larvae can take up to two years to develop in unfavorable conditions such as wet, damp soils. The adults emerge from May to September and feed on foliage, flowers and fruit. The exact timing of emergence depends upon geographical location and weather.
Hosts and Damage
A wide range of plants are attacked in the U. S. by the adult beetles, which skeletonize leaves by eating around the larger veins and chew on flowers. Hosts include small fruits, tree fruits, truck and garden crops, ornamental shrubs, vines, and trees. Feeding studies show a host range in excess of 300 plants in 79 plant families. Among the preferred plants are grape, apple, cherry, peach, plum, rose, and corn. Corn is injured by eating the silk which interferes with formation of kernels. Soft fruits such as grapes, berries, and stone fruits may be completely consumed. Medium to high densities of larvae will cause patches of dead grass.