COMMENTS ON "APPLIED ENTOMOLOGY IN THE TWENTY-FIRST CENTURY"

BY ROBERT METCALF, AMERICAN ENTOMOLOGIST, WINTER 1996.

R. L. Metcalf suggests that crop losses to insects remain as high today as they were before the wide-spread usage of insecticides. He cites a USDA estimate of annual losses for six major crops treated with insecticides at 11.3% in 1900-04, whereas David Pimentel estimates the average annual loss for these crops in 1995 at 13%. The suggestion has been made that the use of modern chemicals has been counterproductive -- pesticides control insect pests but destroy beneficial insects; they led to the abandonment of effective non-chemical control practices; and they led to resistant pest populations that continue to cause crop losses. By focusing solely on crop losses resulting from insects, Drs. Metcalf and Pimentel do a disservice to the enormous positive contribution that modern synthetic chemicals have made to the agricultural food supply.

• Modern synthetic insecticides largely have replaced highly risky, inorganic substances that were used widely for insect control purposes in the good old days. The USDA estimated that in 1904, all commercial apples in the United States were treated with arsenic for insect control purposes, a practice that continued until the introduction of DDT in the 1940s. Perhaps apple loss to insects is the same percentage today as it was in 1904, but it is unarguable that human health is less at risk by replacing arsenic residues with synthetic chemical residues.

• The switchover from older inorganic compounds to modern synthetic insecticides led to an enormous increase in crop production because the new compounds were less harsh on the crop trees and plants. For example, following the switchover from arsenic to synthetic chemicals, for apple insect control, per tree apple yields in eastern states doubled and tripled between 1949 and 1959. The reason: the arsenic sprays (while controlling insects) also damaged the trees and reduced apple production. The modern synthetic insecticides were less harsh on the trees, and apple production doubled as a result. (Perhaps the percent yield losses to insects are the same, but that is a moot point.)

• The introduction of synthetic insecticides paved the way for the production of certain crops in regions and at times of the year for which production previously was impossible. For example, before the introduction of synthetic chemical insecticides, there was no sweet corn industry in Florida because there were no effective means of controlling insects. Regular spraying of synthetic insecticides has made the Florida sweet corn industry the nation�s largest supplier of fresh sweet corn. The production of nectarines in California became feasible only after the regular applications of synthetic insecticides to control previously uncontrollable insect pests.

Drs. Metcalf and Pimentel promote the notion that U. S. crops are "heavily treated with insecticides." Actually, current crop losses to insects may result more from undertreatment with insecticides; if growers sprayed more insecticides, crop losses might decline.

• Pesticide use surveys in Illinois indicate that about 11,000 acres of field corn are treated with an insecticide to control the second-generation of the European corn borer. Research entomologists have conducted field surveys for the past 40 years, which indicate that 10% (or about one million acres) of Illinois field corn acreage incurs damage exceeding spray thresholds for second-generation European corn borer. Now that the insecticide has been engineered genetically into corn plants, the expectation is that corn yields will go up accordingly.

• Recently, a massive increase in the spraying of insecticides has eradicated the boll weevil in states like North Carolina. As a result, not only have crop losses due to insects declined, but cotton acreage and production have expanded.

Leonard P. Gianessi

National Center for Food and Agricultural Policy

1616 P Street, NW, First Floor

Washington, DC 20036

Tel: 202-328-5036� Fax: 202-328-5133