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
- 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
- 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 nationís 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