What alternatives to chemicals does Rachel Carson propose in Silent Spring for pest control?

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In many of the chapters of Silent Spring, author Rachel Carson ends by speaking of methods of pest control that are alternatives to using toxic chemicals.

One example is seen in Chapter 9 in which Carson speaks of the problem of keeping the budworm controlled; budworm caterpillars are considered serious pests because of the amount of damage they can do to plant life by feeding. Instead of spraying toxic chemicals to kill budworms, Carson proposes the method of natural parasitism, which is attributed to first being proposed by Erasmus Darwin in 1800. Since all insects have "many natural enemies," including microbes and other insects, E. Darwin proposed controlling insects by using other insects to kill the pest insect.

In Chapter 17, Carson proposes using what she calls biotic controls, which is the use of biology to solve problems related to living organisms. In this scientific field, specialists use their "understanding of the living organisms they seek to control" and of the "whole fabric of life" to develop control solutions.

One method of biotic control is sterilizing male insects. Carson states that G. A. Runner reported in 1916 the successful sterilization of the cigarette beetle using X-rays. Lab studies in the 1920s reported successfully sterilizing a dozen different insect species using both X-rays and gamma rays. In 1954 Texas Department of Agriculture scientists began a field experiment of releasing screwworms over the island of Curacao and sterilizing them, leading to the eradication of all induced infestation. Upon success of the field experiment, in 1957-58, a similar program was initiated to sterilize and eradicate screwworms in the southeast of the United States since screwworms contributed to a loss of $20 million in livestock profits each year. The program was so successful that an animal infestation of screwworms has not been reported since 1954. Carson also reports that since then, laboratories have been experimenting with using chemicals rather than radiation to produce insect sterilization. While some of the chemicals are dangerous, scientists hope that experiments with the current dangerous chemicals will lead to the discovery of safer chemicals to use for the same purpose.

Other studies concern the use of insects' own "venums, attractants, [and] repellents" as insecticides (Ch. 17). For example, in the 1960s, a study was conducted using the female gypsy moth's sex attraction chemical to draw and trick the gypsy moth into harmlessly copulating with such things as "chips of wood, vermiculite, and other small, inanimate objects" (Ch. 17). Still other studies concern using a substance to prevent the larvae from maturing into adulthood. And, yet another study investigated the use of bacteria to infest insect species with disease.

As the chapter continues, Carson continues to report many alternative means, many of which are very natural, to eliminate pest infestation.

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Carson proposes an alternative approach to pest control that poses no risks to both the environment and humans. These alternatives are called "biotic controls", and are divided into three specific methods.

The first method would use chemicals found within the insects themselves to repel the insects or trap them. Instead of using a poisonous and harmful chemical, it uses the insect itself to control the pest population. This is an environmentally acceptable means of pest control.

The second method would require sterilizing male insects and introducing them into the pest population. This would gradually reduce the volume of the pest population.

The third method uses both natural bacteria and insect predators to kill off pests. Allowing insects to kill each other off does not harm the environment the way pesticides do.

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