Complete Metamorphosis

Biological Control of Insects

Humans have been competing with insects for food since the development of agriculture. To limit the damage that insects do to our food crops, we have developed a variety of poisons that kill a broad range of insects. However, these poisons may kill beneficial as well as harmful insects; they persist in the environment, accumulating in animals at higher levels in the food web; and they select for strains of insects that are resistant to the poisons.

These drawbacks have led scientists to develop biological controls of insect pests. One type of biological control is the use of natural predators or parasites that attack specific kinds of insects. For example, the bacterium Bacillus thuringiensis is used to control cabbage worms, tomato worms, and other moth larvae.

Biological control also includes methods that interfere with the reproduction of insects. In the sterile-male approach, for instance, large numbers of male insects sterilized by radiation are introduced into an area. The females lay eggs that never develop, so the population size of the next generation is smaller. Used over several generations, this technique can nearly eliminate some pest species in selected areas.

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