Western Corn Rootworm

Common: Northern, Western

Scientific: Diabrotica longicornus barberi, Diabrotica virgifera virgifera

Crop Hosts: Corn and other grasses.

Identification and Life Cycle: Both species overwinter as diapausing eggs at the base of the corn plant. The number of eggs ranges from 200 to 1,000 per female, which can translate into 10 to 50 million eggs per acre. After hatching, the larvae move to roots of corn and are typically full grown by early July when they leave the roots and pupate in cells in the soil. The adults emerge in July and August, deposit eggs in September and early October and are killed by the frost. The adult northern corn rootworm is 2/10-of an inch long and green or yellowish in color. The adult western rootworm is somewhat larger and is yellow-brown with 3 prominent black stripes on the dorsum.

Geographical Distribution: The northern rootworm is found in more northerly corn-growing states. The western rootworm is the superior competitor and is found throughout the corn- growing states.

Damage and Treatment: Root injury by the worm results in growth retardation and the plant may fall over after a heavy rain because of the poor root system. Also, adults feed on newly formed corn silks and may clip them, producing ears with few kernels.

Treatment should be made when insect populations and/or damage levels reach economic thresholds. Refer to local University Extension Pest Management Guidelines for specific state thresholds.