Corn earworm (Heliothis zea), Lepidoptera

Corn earworm biology & life cycle

Corn earworms do not overwinter in Ontario; moths migrate north from southern United States in the spring.

Moths prefer to fly on warm, cloudy days and most often at dusk. First generation moths emerge at approximately the same time as corn silking. Moths mate and then female moths lay eggs on green corn silks. Each moth can live up to 12 days and can lay as many as 2,500 eggs.

Hatched larvae feed on fresh silks, then bore down through the silk channel to the developing ear where they continue to feed. At maturity, the larvae drop to the ground and dig or burrow a small cell into the soil, pupate and re-emerge two to three weeks later.

There can be two to three generations of this pest each season. Pupae that form in the fall remain in the soil and overwinter in that stage.

Identifying Corn earworm

Corn earworm: eggs

Eggs are dome shaped and about 0.8 mm in diameter.

Corn earworm: larvae

Larvae vary in colour from bright green to pink, brown or black with a lighter underside. They have alternating light and dark bands along the body. The head is usually yellow, but can also be brown to orange; legs are black and the skin is coarse with many thorn-like projections. Unlike the European Corn Borer (ECB), the larvae of corn earworm are not spotted. Mature larvae reach a length of 38-50 mm. Larvae fist feed on corn silk, interfering with pollination. Older larvae feed on kernels at the tips of the ears.

Corn earworm: Pupae

Larvae drop to the ground and form a silk-lined cocoon in the soil where the insect pupates. Pupae are about 20-30 mm long, 6 mm wide, and reddish-brown to dark brown.

Corn earworm: adult

Adults are 20 mm long with a wingspan of 38 mm. Adult corn earworm moths are robust, have a wingspan of 25-38 mm and are usually light grayish-brown to rust-tan to yellowish-olive colour, with a prominent marking on the forewings. The eyes of the moths are usually green. They are typically active at dusk or on warm cloudy days. Adults are larger and darker than ECB adults.

Corn earworm: management

Fields should be inspected when the corn crop is flowering for the presence of adults and larvae. Insecticide controls are available for infested fields.