The European Corn Borer (Ostrinia nubilalis) is a significant agricultural pest that targets corn and other thick-stemmed plants, causing substantial economic losses across major growing regions. Although the insect is a moth, the larval stage is responsible for all crop damage by boring into the plant structure. Its destructive tunneling activity has made the European Corn Borer a primary focus of pest management strategies since its introduction to North America in 1917.
Life Stages and Habitats
The European Corn Borer develops through four stages: egg, larva, pupa, and adult moth. The mature larva is the overwintering stage, sheltering inside corn stubble or plant debris until spring prompts pupation. Adult moths emerge from late spring into summer to mate, and females deposit eggs in flat, overlapping masses on the underside of corn leaves.
The destructive larval stage begins when eggs hatch, typically within three to seven days. Larvae are creamy white to pinkish-gray, measuring about one inch long, identifiable by a dark head and rows of small, dark spots. Depending on geography and climate, the borer produces one to four generations per year. While corn is the primary host, larvae also infest other thick-stemmed plants, including peppers, beans, cotton, and certain weeds.
How the Borer Damages Crops
The consequences of infestation stem from the larvae’s internal feeding and tunneling. Early-stage larvae feed on leaves in the corn whorl, creating a characteristic “shothole” damage pattern as the leaves unfurl. The most severe damage occurs when larvae bore into the stalk, tassel, ear shank, and the ear itself.
Tunneling through the stalk compromises the plant’s structural integrity and its ability to transport water and nutrients, reducing grain weight. This internal damage leads to “lodging,” where the weakened stalk snaps or falls over, hindering mechanical harvesting. Damage to the ear shank can cause the entire ear to drop before harvest. Direct feeding on kernels reduces yield and makes fresh market sweet corn unmarketable. Furthermore, bore holes create entry points for secondary pathogens, such as fungi that cause ear rot, contaminating the grain and posing health concerns.
Managing Infestations
Controlling European Corn Borer populations relies on a combination of strategies, with genetic engineering providing the most impactful solution. Bt corn contains a gene from the soil bacterium Bacillus thuringiensis, which produces a protein toxic to the borer larva upon ingestion. This genetic control method has dramatically reduced borer populations since its commercial introduction in 1996, mitigating the pest’s economic threat.
To preserve the effectiveness of Bt technology, growers must implement an Insect Resistance Management (IRM) plan that includes planting a non-Bt “refuge” area. The refuge is corn without the Bt trait, ensuring susceptible moths survive to mate with any resistant moths emerging from the Bt crop. This process dilutes resistance genes in the overall population, slowing the evolution of resistance. Many modern seed products simplify this by blending refuge seed directly into the bag.
Cultural control methods focus on sanitation to eliminate overwintering larvae and reduce the following season’s population. Shredding corn stalks after harvest, especially if cut close to the ground, can kill up to 80% of the larvae inside the stubble. Plowing under crop residue is also effective, though this practice must be balanced against the risk of soil erosion.
Biological and chemical controls are used in specific situations, particularly in non-Bt fields or high-value crops like sweet corn. Natural enemies, such as Trichogramma parasitic wasps, attack the borer eggs before they hatch, offering a non-chemical means of control. Chemical insecticides are an option, but timing is constrained: they must be applied before newly hatched larvae bore into the stalk, after which the pest is protected inside the plant structure.