Mayela Lopez/AFP/Getty ImagesControlling Agricultural Pests
LEARNING OBJECTIVES
- Distinguish between narrow-spectrum and
broad-spectrum pesticides. - Relate the benefits of pesticides in disease
control and crop protection. - Summarize problems associated with pesticide
use, including genetic resistance, ecosystem
imbalances, bioaccumulation and biological
magnification, and mobility in the environment. - Describe alternative ways to control pests.
A
ny organism that interferes in some way with
human welfare or activities is a pest. Some
weeds, insects, rodents, bacteria, fungi, nem-
atodes (microscopic worms), and other pest
organisms compete with humans for food; other pests
cause or spread disease. People try to control pests, usu-
ally by reducing the size of the pest population. Using
pesticides is the most common way of doing this, particu-
larly in agriculture. Pesticides can be grouped by their
target organisms—that is, by the pests they are supposed
to eliminate. Insecticides kill insects, herbicides kill
plants, rodenticides kill rodents such as rats and mice,
and fungicides kill fungi (Figure 14.14).
Benefits of Pesticides
Pesticides can effectively control organisms, such as insects,
that transmit devastating human diseases. Fleas and lice
carry the microorganism that causes typhus in humans.
Malaria, also caused by a microorganism, is transmitted to
millions of humans each year by female Anopheles mosqui-
toes. Pesticides help control the population of mosquitoes,
thereby reducing the incidence of malaria.
Pesticides also protect crops. It is estimated that pests
eat or destroy more than one-third of the world’s crops.
Given our expanding population and world hunger, it is
easy to see why control of agricultural pests is desirable. Pes-
ticides—applied heavily primarily in the United States and
other highly developed countries—reduce the amount of
a crop lost through competition with weeds, consumption
by insects, and diseases caused by plant pathogens (micro-
organisms, such as fungi and bacteria, that cause disease).
Why are agricultural pests found in such great num-
bers in our fields? Part of the reason is that agriculture is
usually a monoculture, in which the field cultivated with a
single species represents a simple ecosystem. In contrast,
forests, wetlands, and other natural ecosystems are com-
plex and contain many species, including predators and
parasites that control pest populations, as well as plant
species that pests do not use for food. A monoculture
reduces the dangers and accidents that might befall a pest
as it searches for food. In the absence of many natural
predators and in the presence of plenty of food, a pest
population thrives and grows, damaging more of the crop.Problems with Pesticides
The ideal pesticide is a narrow-spectrum pesticide that
kills only the intended organism and does not harm
other species. The perfect pesticide would readily break
down into safe materials such as water, carbon dioxide,
and oxygen. The ideal pesticide
would stay exactly where it was
put and would not move around
in the environment. Unfortu-
nately, no pesticide is perfect.
Most pesticides are broad-spec-
trum pesticides. Some pesticidesbroad-spectrum
pesticide A
pesticide that kills a
variety of organisms,
including beneficial
organisms, in addition
to the target pest.Bananas being sprayed with fungicide before
Ã
«iÌÊÌÊ}ÀViÀÞÊÃÌÀiÃÊUÊ}ÕÀiÊ£{°£{