European corn borer (Ostrinia nubilalis), Lepidoptera

European corn borer biology & life cycle

The European corn borer (ECB) typically overwinter as fully grown larvae lodged in the stem or cob of the host plant, though they can also be found in other host plants such as large-stemmed grasses and various vegetables. Pupation occurs in early spring and adults emerge in early June to July. Larvae initially feed on the leaves and work their way to the whorl of the plant. Pinholes or shot holes are signs of borers already moving into the plant. Depending on the strain of ECB, growing conditions and the growing region, populations can go through one or two full generations and, in some cases, a partial third generation in a single season.

Identifying European corn borer

European corn borer: eggs

Eggs are small, round, flat, and white when first laid; they are laid in masses and overlap each other like fish scales.

European corn borer: larvae

Newly hatched larvae are 3 mm in length and light brown in colour, with rows of small brown spots. Fully grown larvae are flesh coloured with same rows of brown spots and 25 mm long. Initially there is a shot-hole damage to the leaves, but the larvae later work their way into the tassel, stalk, and ear shank. They may also feed on the silks, kernels and cobs.

European corn borer: Pupae

Pupae are reddish brown in colour, about 25 mm long and pointed at one end.

European corn borer: adult

Adult females are yellowish brown to tan moths with darker, wavy bands across the wings. Wing spans are 25 mm. Male moths are somewhat darker in colour and slightly smaller than the females. Moths are delta-shaped when wings are held at rest. The moths are active at night and hide in weedy grasses during the day.

European corn borer: management

With the widespread use of Bt corn hybrids, ECB populations have been reduced to very low levels in corn and are more likely to be found in other host crops. Only those fields not planted with a Bt hybrid are at risk. No-till fields with high residue are susceptible, along with frequent corn crops in the rotation.

Management strategies for non-Bt corn hybrids:

• Use European Corn Borer Economic Threshold Calculations in Appendix H of this OMAFRA publication, to determine if an insecticide is warranted
• Select non-Bt corn hybrids with resistance or tolerance to ECB feeding
• Shred debris after harvest to destroy borers overwintering in stalks and stubble
• Allow natural enemies to attack immature stages of ECB