Corn borer

The Corn borer is a destructive crop insect whose history in the United States illustrates how chemical pest control can undermine both its immediate target and established methods of controlling other pests. In eastern Illinois, dieldrin applied against the Japanese beetle was followed by a sharp increase in corn borer larvae. That reversal mattered because the corn borer already caused far greater estimated annual damage than the beetle, and decades of effort to limit it through introduced parasites were put at risk when the sprays killed its natural enemies.

The Illinois Reversal

After a devastating dieldrin treatment of farmland in eastern Illinois aimed at controlling the Japanese beetle, farmers found that corn borers had increased enormously in the treated area. Corn growing within the sprayed area contained almost twice as many larvae as corn grown outside it. The comparison made the outcome concrete: the difference followed the boundary of the treatment, and the attempted control of one insect had been accompanied by a surge in another.

Farmers did not need to know the biological mechanism to recognize the poor bargain. The estimated annual damage caused by the Japanese beetle in the United States was about $10 million; damage attributed to the corn borer was about $85 million. The figures sharpen the reversal. A program directed at the less costly pest had coincided with a much larger threat to crops, shifting the practical consequences of the intervention onto farmers growing corn.

A Pest with a Longer History

The corn borer had been accidentally introduced from Europe in 1917. Within two years, the United States government had mounted an intensive program to locate and import parasites that could help control it. This early reliance on biological methods formed a long-running counterpoint to the later dieldrin treatment: control did not have to mean applying a broad lethal chemical, but could involve bringing the pest’s enemies into the agricultural system.

By the time of the Illinois episode, 24 parasite species had been brought from Europe and the Orient at considerable expense. Five were recognized as distinctly valuable in controlling the corn borer. The effort therefore represented more than a single experiment; it was an accumulated investment in biological control, built up over decades after the insect’s arrival.

The Cost to Natural Control

The sprays jeopardized that earlier work because they killed enemies of the corn borer along with other organisms. The text links the increased numbers of larvae to a wider weakness in chemical control: an intervention aimed at a named pest could also remove the organisms that had been helping to keep another pest in check. The result was not simply a failure to eliminate the Japanese beetle, but a disruption of relationships on which corn borer control depended.

This account places the Illinois increase within the book’s broader criticism of indiscriminate spraying. Chemical treatment is shown not as an isolated tool acting on a single species, but as an intervention in an ecological system where organisms affect one another. The nearly doubled larval count, the disparity in estimated crop losses, and the threatened parasite program together make the cost legible: an immediate campaign against one insect could compromise both farmers’ crops and a slower, established alternative for managing another.