Japanese Beetle
Adult -The 12-mm-long beetle is shiny metallic green with coppery-brown wings (Color Plate 3W). Six small patches of white hairs appear along the sides toward the rear of the insect. The male and female look alike, but the male is generally smaller and has sharper spines on its forelegs.
Egg -The whitish egg is ellipitcal, becoming more spherical as the embryo develops. It has a diameter of about 2 mm.
Nymph -The larva, about 25 mm long when fully grown is a C-shaped, white grub with a yellowish-brown head. It is usually found in a cell underground. There are three larval stages.
Pupa -The pupa is about 13 mm long and 6 mm wide. It may be pale cream, tan, or green depending upon its age. .
Host Plants -Over 300 plants are known food sources for the Japanese beetle. The adults are particularly fond of roses, and they prefer white and yellow flowers to the darker colors.
Damage -Both the larvae and adults have chewing mouthparts. The grubs consume roots of turf grasses, whereas the adults feed on leaves, buds, flowers, and fruits. Since the adults do not eat the leaf veins, infested leaves become skeletonized. Flowers and buds have ragged edges after beetles have been feeding.
Life History -Japanese beetles overwinter as larvae, pupate in late spring, and emerge as adult beetles about 2 weeks later. Adults usually appear in mid-May. They are gregarious, often feeding together in masses on flowers, foliage, and fruits of plants in bright sunlight. They fly in broad daylight. Populations diminish during August. The female selects poorly drained soil in which to deposit her eggs. She burrows 7 to 8 cm into the ground and lays several eggs at a time, continuing for a period of days until she has laid 40 to 60 eggs. They hatch approximately 2 weeks later. Though a dry summer usually reduces the number of live larvae, a severe decrease in rainfall in the fall or spring hardly affects the population because older larvae are resistant to dry conditions. After entering a quiescent prepupal stage, the larvae pupate. The beetles tend to become well established in areas of grazing, general agriculture, truck crops, and fruit-growing. They are usually not found in heavily forested land. Though it takes 2 years for a generation to develop in the beetles' northern limit, 1 year is required in most areas.
Insecticides will not completely protect roses, which unfold rapidly and are especially attractive to beetles. When beetles are first noticed on roses, buds should be nipped and the bushes sprayed to protect the leaves, then when the beetles become scarce, the bushes can be allowed to bloom. To protect a limited number of rose blooms, nets or perforated bags can be tied around the blossoms. For specific chemical controls, see the current state extension service recommendations.