- Pest Type: Insect
- Crops Affected: Corn
- Scientific Name: Ostrinia nubilalis
- Pest Order: Lepidoptera
Crop damage is caused by the larvae. First generation borers feed on the leaf surfaces and on leaves in the whorls of plants, producing a "shot hole" appearance. Small larvae also bore into leaf midribs, causing them to break. When about half grown, the borers enter the stalks. Second generation borers often feed on pollen and leaf collars or sheaths before boring into ear shanks, stalks and cobs. Second generation damage consists of leaf girdling, stalk breakage, ear drop, and direct feeding damage to the grain, particularly on the ear tips. Stalk breakage and lodging can be severe, especially in years when harvest is delayed by bad weather.
The life cycle consists of four stages: egg, larva, pupa and adult. The European corn borer overwinters as a full grown larva inside corn stalks, shanks, cobs, or plant debris in the fields. In May or early June, the overwintering larvae pupates. The adult emerges from the pupa in 9-15 days, mates, and seeks early planted corn for egg laying. Female moths lay from 15-45 eggs in masses on the undersides of leaves. Each female moth lives for 1-2 weeks and may lay a many as 400 eggs. Eggs hatch in 4-9 days, generally in late June, and this first generation of larvae begin to feed. Feeding continues until these larvae pupate in July. A second brood of moths emerges from the pupae in July and August. Again, females mate and begin laying eggs on the undersides of corn leaves, selecting late-planted or late-maturing fields. Eggs hatch and the larvae feed until full grown, then overwinter in the corn stubble. Given very favorable weather conditions, some of the second generations larvae may complete their life cycle in time for a partial third generation.
Insecticides for first generation corn borer control must be applied after most of the eggs have hatched but before borers imbed in the stalks. Second generation eggs are generally deposited over a longer period of time, and upon hatching, borers may immediately seek protection; thus, control of second generation borers is often more difficult and requires precise timing. Worksheets have been developed in many areas, to determine whether it will be profitable to treat a field to control corn borers. Transgenic corn hybrids which produce B.t. toxin are another means of protection against European corn borer. Talk to your local advisers for control recommendations in your area.