Egg - The white or cream colored egg is spherical and about 1.5 mm in diameter when first laid in turf. By the time it hatches, the egg has doubled its original size.
Larva - The grayish-white, slightly curled grub has a yellowish-brown head and measures about 26 mm long when mature. It can be distinguished from other white grubs by two rows of spines which form a "V" on the underside of its last abdominal segment.
Pupa - The cream colored pupa, approximately 13 mm long and 6 mm wide, gradually turns light brown and finally develops a metallic green cast.
Host Plants - Adult Japanese beetles infest over 275 different plants including most vegetable crops. Shade and fruit trees, ornamental shrubs, small fruits, garden crops, weeds, and field crops often are damaged also. The grubs are serious pests of lawns, other grasses, and nursery stock.
Damage - Gregarious in nature, Japanese beetle adults are often found feeding in masses on flowers, foliage, or fruit of a few plants leaving others nearby uninfested. On most hosts, including okra, leaves are skeletonized and mature fruit is damaged. Injury to corn occurs when beetles feed heavily on the silks and ear tips, sometimes reducing pollination and predisposing the ear to other insect damage and fungal infections. In localized spots, larvae injure the developing root systems of grass crops or weeds.
Life History - The grubs overwinter in cells within 13 cm of the soil surface. In spring they move upward, almost to ground level, where they complete feeding and pupate. The three larval instars complete development in about 140 days. Adults emerge as early as mid-May in eastern North Carolina and as late as July in New England. Throughout summer they attack the fruit and foliage of many plants including silks of corn. In North Carolina, peak emergence occurs during July. Soon after emerging females deposit 40 to 60 eggs in small batches 5 to 8 cm deep in the ground. Under extremely dry conditions, many eggs and larvae perish. However, during warm, set summers populations thrive and eggs hatch about 2 weeks after deposition. Newly emerged larvae feed until cold weather forces them into hibernation. Only one generation occurs each year.
Control of this pest is rarely necessary on okra or on vegetable crops which are sprayed regularly for control of other insect pests. Some plants in border rows may appear heavily infested due to the tendency of these beetles to congregate. Field tests in Virginia have shown that much Japanese beetle damage to corn can be avoided by planting so that silking occurs before July 20 or after August 1. Should excessive populations develop, consult the current North Carolina Agricultural Chemicals Manual.
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