Environmental Engineering Reference
In-Depth Information
characteristics, and farmers who have encountered it
call it a
superbug.
This tiny white insect escaped from
poinsettia greenhouses in Florida in 1986 and has be-
come established in Florida, Arizona, California, and
Texas.
It is known to eat at least 500 species of plants but
does not like onions and asparagus. The silverleaf
whitefly has no natural enemies. Dense swarms of
these tiny insects attack plants, suck them dry, and
leave them withered and dying.
U.S. crop losses from this insect are greater than
$200 million per year—and growing. Scientists are
scouring the world looking for natural enemies of this
superbug. Stay tuned.
velop genetic resistance, but at a slower rate than in-
sects. Since 1945, about 1,500 species of insects, mites,
weeds, plant diseases, and rodents (mostly rats) have
developed genetic resistance to one or more pesticides.
Because of genetic resistance, many insecticides
(such as DDT) no longer do a good job of protecting
people from insect-transmitted diseases in some parts
of the world. Genetic resistance can also put farmers
on a
pesticide treadmill,
whereby they pay more and
more for a pest control program that often becomes
less and less effective.
Some insecticides kill natural predators and parasites
that help control the populations of pest species.
Wiping
out natural predators, such as spiders, can unleash
new pests, whose populations their predators had pre-
viously held in check, and cause other unexpected ef-
fects (Connections, p. 125). Of the 300 most destructive
insect pests in the United States, 100 were once minor
pests that became major pests after widespread use of
insecticides. Mostly because of genetic resistance and
reduction of natural predators, pesticide use has not
reduced U.S. crop losses to pests (Science Spotlight,
below).
Pesticides do not stay put.
According to the USDA,
only 0.1-2% of the insecticide applied to crops by aer-
ial spraying or ground spraying reaches the target
pests. Also, less than 5% of herbicides applied to crops
reach the target weeds. In other words, 98-99.9% of the
pesticides and more than 95% of the herbicides we ap-
ply end up in the air, surface water, groundwater,
bottom sediments, food, and nontarget organisms,
including humans and wildlife (Figure 9-16, p. 197).
Science: Disadvantages of Modern
Synthetic Pesticides
Pesticides can promote genetic resistance to their
effects, wipe out natural enemies of pest species,
create new pest species, end up in the environment,
and sometimes harm wildlife and people.
Opponents of widespread pesticide use believe that
the harmful effects of these chemicals outweigh their
benefits. They cite several serious problems with the
use of conventional pesticides.
They accelerate the development of genetic resistance to
pesticides by pest organisms.
Insects breed rapidly, and
within five to ten years (much sooner in tropical areas)
they can develop immunity to widely used pesticides
through natural selection and come back stronger than
before. Weeds and plant disease organisms also de-
How Successful Have Synthetic Pesticides Been
in Reducing Crop Losses in the United States?
Pesticides have not
been as effective in
reducing crop
losses in the
United States as
agricultural ex-
perts had hoped, mostly because of
genetic resistance and reductions in
natural predators.
When David Pimentel, an expert
in insect ecology, evaluated data
from more than 300 agricultural
scientists and economists, he
reached three major conclusions.
First,
although the use of syn-
thetic pesticides has increased
33-fold since 1942, 37% of the U.S.
food supply is lost to pests today
compared to 31% in the 1940s. Since
1942, losses attributed to insects
almost doubled from 7% to 13%,
despite a 10-fold increase in the use
of synthetic insecticides.
Second,
the estimated environ-
mental, health, and social costs of
pesticide use in the United States
total $4-10 billion per year. The
International Food Policy Research
Institute puts this figure much
higher, at $100-200 billion per year,
or $5-10 in damages for every dol-
lar spent on pesticides.
Third,
alternative pest manage-
ment practices could halve the use of
chemical pesticides on 40 major U.S.
crops without reducing crop yields.
Numerous studies and experi-
ence show that pesticide use can be
reduced sharply without reducing
yields. In fact, yields may actually
increase. Sweden has cut pesticide
use in half with almost no decrease
in crop yields. Campbell Soup uses
no pesticides on tomatoes it grows
in Mexico, and yields have not
dropped. After a two-thirds cut in
pesticide use on rice in Indonesia,
yields increased by 15%.
Critical Thinking
SCIENCE
SPOTLIGHT
Pesticide proponents argue that
although crop losses to pests are
higher today than in the past, with-
out the widespread use of pesti-
cides losses would be even higher.
Explain why you agree or disagree
with this position.
