Description and life cycle
Japanese beetle adults have metallic green bodies with coppery brown wing covers surrounded with 12 white tufts of hair. Eggs are pearly white, elliptical, and 1∕16 inch in diameter. The softbodied grubs are whitish with a brown head, “C” shaped, and are 1 inch long at maturity.
Japanese beetles overwinter in the soil as grubs and complete their growth in early spring. Adults emerge in greatest numbers during July and are active for a month. The gregarious beetles are most active on warm, sunny days on favorite hosts. Adults enter the ground in early evening. Females lay 40 to 60 eggs that hatch in 2 weeks. Grubs feed on organic matter and fine grass roots until late fall. They reach maturity in early spring and, after spending 3 to 4 weeks in the pupal stage, emerge as adults. There is only one generation per year.
Adults feed on leaves and fruit. They chew leaf tissue between veins and leave a lacelike skeleton. Severely injured leaves soon turn brown and often drop. Fruit of early ripening peach trees may be gouged in irregular, shallow patches.
Monitoring and management
Fruit and foliage may be protected from damage by spraying at regular intervals when beetles first cause unacceptable injury. Because sprayed trees can be reinvaded, they should be inspected weekly when adults are present.