Western and northern corn rootworms overwinter as eggs in the soil. Corn rootworm begins development at 44F and hatches from overwintering eggs typically in early to mid-June at 800 degree days. One generation occurs per year in Wisconsin and the North Central Region. Larvae pass through three instars as they feed on corn roots. Peak feeding occurs for several weeks after hatching (between 1300-1700 degree days) and pupation occurs in mid-July. Adults emerge 5-10 days after pupation. Emergence is observed from mid-July to mid-August between 1800-2200 degree days. Egg laying begins two weeks after adult emergence and adults remain active until the first killing frost. Western corn rootworm generally completes development 4-5 days before NCR.

Western corn rootworm is the predominant species in most of WI. While northern corn rootworms also occur in WI, the western corn rootworm hatch map can be used for a state estimate of corn rootworm overwintered egg hatch and larval development (western and northern).