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What Does Resistance Mean?

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Silent Spring not only raised public awareness of how pesticides can cause unintentional impacts on non-target organisms, but also summarized growing evidence that insects and other pests can develop resistance to these toxins.

Resistance occurs when a few individuals in a pest population have a genetic mutation that makes them less sensitive to the toxin.

These individuals survive the pesticide, breed, and convey the resistance gene to their offspring, and thus the percentage of resistant individuals continues to grow. After many generations, most of the population may be resistant. This is an example of evolution in action. Widespread use of DDT in agriculture is one reason that insects such as mosquitoes built up resistance to the toxin.

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Plant pests can also become resistant to herbicides. MSU researchers recently found that some horseweed in Michigan is now resistant to glyphosate (Roundup), the most widely used herbicide in America. This is the first confirmation of glyphosate-resistance in weeds in Michigan.

Early signs of chemical resistance in pests were noted by others as well.

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