Controlling Agricultural Pests 365George Grall/NGS Image Collection0Number of resistant insect and mite species
20030040050019501001960 1970 1980
Year1990 2000600Based on data from Mark Whalon, Michigan State University, as reported in Brown, L.R., et al.Vital Signs1994. New York: W.W. Norton & Co.
as biological magnification (Figure 14.16; also see
Figure 4.8).
One of the worst problems associated with pes-
ticide use is that pesticides affect more species than
the pests for which they are intended. Beneficial
insects and other organisms are harmed and killed
as effectively as pest insects. Quite often the stress
of carrying pesticides in their tissues makes organ-
isms more vulnerable to predators, diseases, or
other stressors in their environments. Because the
natural enemies of pests often starve or migrate
in search of food after a pesticide is sprayed in an
area, pesticides are indirectly responsible for a large
reduction in the populations of these natural ene-
mies. Pesticides also kill natural enemies directly
because predators may consume lethal amounts of
a pesticide while consuming the pests. After a brief
period, the pest population rebounds and gets larger
than ever, partly because no natural predators are left
to keep its numbers in check. In some instances, thedo not degrade readily, or they break down into com-
pounds as dangerous as—if not more dangerous than—
the original pesticide. And most pesticides move around
the environment quite a bit.
The prolonged use of a particular pesticide can cause
a pest population to develop
genetic resistance to the pesti-
cide. In the 50 years during which
pesticides have been widely used,
at least 520 species of insects and
mites and at least 84 weed species
have evolved genetic resistance to
certain pesticides (Figure 14.15).
An organism exposed to a chemically stable pes-
ticide that takes years to break down may accumu-
late high concentrations of the toxin, a phenomenon
known as bioaccumulation. Organisms at higher levels
on food webs tend to have greater concentrations of
bioaccumulated pesticide stored in their bodies than
those lower on food webs, through a process knowngenetic resistance
An inherited
characteristic that
decreases the effect
of a given agent (such
as a pesticide) on an
organism (such as a
pest).Peregrine falcons make a comeback
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Peregrine falcons were once an endangered species in the
United States. Bioaccumulation of pesticides such as DDT caused
the birds to lay eggs with extremely thin shells, causing the
chicks’ deaths. With the ban of DDT and similar pesticides,
the falcons recovered.iiÌVÊÀiÃÃÌ>ViÊUÊ}ÕÀiÊ£{°£xÊ
The number of pest species evolving genetic resistance to
pesticides has increased.Interpreting Data
How is this figure similar to Figure 14.10a,
which shows the evolution of resistance
to antibiotics?