Encyclopedia of Evolution.pdf - Online Reading Center

Many insect species are now becoming resistant to all major
classes of insecticides. An insect that is resistant to one pesticide
is often resistant to other related, chemically similar pesticides.
In addition to promoting the evolution of resistant strains of
bacteria, animals, and weeds, the over-use of chemicals in medicine,
insect control, and agriculture has resulted in the buildup
of toxicity in the environment and in the food chain.
The evolution of pesticide resistance in insects and rat
populations has implications both for public health and for
agriculture. Pesticide sprays are heavily used to control many
species of insects, such as the mosquitoes that spread diseases
like malaria and yellow fever. Insect pests (such as weevils
and caterpillars) cause millions of dollars of agricultural yield
loss. When the sprays become less effective (because many,
though not all, of the insect populations evolve resistance),
public health officials may respond by increasing the applica-
resistance, evolution of
A U.S. soldier sprays DDT on a civilian shortly after World War II. Originally, DDT was effective against mosquitoes that spread malaria and lice that carry
typhus. The World Health Organization claims that the use of DDT saved million lives. However, shortly after the widespread use of DDT began, insect
populations began to evolve resistance to it. (Courtesy of the Centers for Disease Control and Prevention, Public Health Image Library)
tion of sprays, which has two effects: greater environmental
contamination, and more evolution of resistance.
The evolution of herbicide resistance in weeds also
portends greater agricultural yield loss (due to competition
between weeds and crops) and greater environmental
contamination from stepped-up herbicide applications. In
recent years, crops (such as maize, soybeans, and potatoes)
that have been genetically engineered to resist herbicides have
come on the market, and large acreages are now devoted to
them. Farmers can now spray massive amounts of herbicides
on their fields, to kill the weeds, without fear of killing the
crops. This encourages the heavy use of herbicides—which is
precisely what the companies that sell the seeds of these crops
want, since the herbicides are manufactured by the same
companies that sell the seeds. Unfortunately, this will result
in even greater environmental contamination.