Western bean cutworm biology & life cycle
Western bean cutworm (WBC) is a common pest of corn. It goes through four stages of development – egg, larvae, pupa, and adult (moth). The insect overwinters as larvae or pre-pupae in the soil. In June and early July the larvae pupate and emerge from the soil as moths. The moths mate, and the females deposit eggs in clusters of up to 200 eggs on the upper side of pre-tasseled corn leaves. Once the corn crop is in tassel or beyond, they prefer to lay their eggs on the underside of dry bean leaves or later-planted corn fields still in pre-tassel stages in July and August. In ideal conditions with warm weather, this can occur earlier in the season. Eggs hatch in about five to seven days.
The new larvae are the most damaging – they seek out the whorl of the corn plant to begin feeding on the newly emerged tassel and pollen. As the ear shoots emerge, the larvae migrate there and enter through the tip or side husk to feed on silks and developing kernels. Numerous WBC can be found in a single ear. And because the larvae are very mobile, they can disperse from the original egg site to other plants in the vicinity both up and across corn rows.
Besides yield loss, WBC can also be associated with quality concerns (mould or mycotoxin development) as ear feeding allows an entry point for secondary infections. Mature larvae drop to the ground when fully developed and burrow into the soil to overwinter as pupa in earthen chambers.