Environmental Engineering Reference
In-Depth Information
Science: Other Ways to Control Pests
A mix of cultivation practices and biological and
ecological alternatives to conventional chemical
pesticides can help control pests.
Many scientists believe we should greatly increase the
use of biological, ecological, and other alternative meth-
ods for controlling pests and diseases that affect crops
and human health. A number of methods are available.
A variety of cultivation practices can be employed
to fake out pest species. Examples include rotating the
types of crops planted in a field each year, adjusting
planting times so major insect pests either starve or get
eaten by their natural predators, and growing crops in
areas where their major pests do not exist. Also, farm-
ers can increase the use of polyculture, which uses
plant diversity to reduce losses to pests. Homeowners
can reduce weed invasions by cutting grass no lower
than 8 centimeters (3 inches) high. This height pro-
vides a dense enough cover to keep out crabgrass and
many other undesirable weeds.
Genetic engineering can be used to speed up the
development of pest- and disease-resistant crop strains
(Figure 10-28). Controversy persists over whether the
projected advantages of increased use of genetically
modified plants and foods outweigh their projected
disadvantages (Figure 10-19).
We can increase the use of biological control by im-
porting natural predators (Figures 10-26 and 10-29),
parasites, and disease-causing bacteria and viruses to
help regulate pest populations. This approach is non-
toxic to other species, minimizes genetic resistance,
and can save large amounts of money—about $25 for
Figure 10-29 Natural capital: biological pest control. The wasp
pupae (white) will kill this tobacco hornworm.
every $1 invested in controlling 70 pests in the United
States. However, biological control agents cannot al-
ways be mass-produced, are often slower acting and
more difficult to apply than conventional pesticides,
can sometimes multiply and become pests themselves,
and must be protected from pesticides sprayed in
nearby fields.
Sex attractants (called pheromones ) can lure pests
into traps or attract their natural predators into crop
fields (usually the more effective approach). These
chemicals attract only one species, work in trace
amounts, have little chance of causing genetic resis-
tance, and are not harmful to nontarget species. How-
ever, it is costly and time-consuming to
identify, isolate, and produce the specific
sex attractant for each pest or predator.
We can also use hormones that disrupt an
insect's normal life cycle (Figure 10-30),
thereby preventing it from reaching matu-
rity and reproducing. Insect hormones have
the same advantages as sex attractants. But
they take weeks to kill an insect, often are
ineffective with large infestations of insects,
and sometimes break down before they can
act. In addition, they must be applied at ex-
actly the right time in the target insect's life
cycle, can sometimes affect the target's
predators and other nonpest species, and
are difficult and costly to produce.
Some farmers have controlled certain
insect pests by spraying them with hot water.
This approach has worked well on cotton,
alfalfa, and potato fields and in citrus
groves in Florida, and its cost is roughly
equal to that of using chemical pesticides.
Figure 10-28 Science: the results of one example of using genetic engineering
to reduce pest damage. Both tomato plants were exposed to destructive cater-
pillars. The normal plant's leaves are almost gone (left), whereas the genetically
altered plant shows little damage (right).
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