![]() Because these crops need fewer pesticides, there is less harm to beneficial insects and other animals. Some studies have shown that crops that have been genetically modified to resist pests result in greater biodiversity in fields. The corn plants can now make the protein, killing caterpillars that eat them. Scientists inserted these bacterial genes into the genome of corn plants. For instance, some bacteria have genes that code for proteins that are toxic to certain caterpillars. In one type of genetic modification, transgenic technology, genes from one organism can be inserted into another, different organism. This has led to new varieties of crops like cotton and corn that are highly resistant to damaging herbivores. Geneticists can also use other methods to introduce new traits into crop plants. This has led to new crop varieties that are both high yielding and resistant to herbivore damage. ![]() Through traditional breeding, geneticists can breed crop plants by performing crosses among natural plant varieties. These may be plant chemicals that are toxic to herbivores or proteins that kill or deter them. Just as strains of plants vary for traits like seed color or fruit size, they also vary in the defense compounds that they make. Today, new pesticides are rated not only for their ability to control herbivores, but also for their off-target impacts on other wildlife, as well as their potential risk to humans. For this reason, some pesticides like DDT have been banned in most countries. Likewise, pesticides may also harm other wildlife on land or in water, and they may impact human health. They often kill predatory insects, which would have otherwise eaten the pest species. Another downside is that pesticides kill indescriminately. This leads to a cycle where farmers continually need new, effective compounds. While pesticides can be highly effective in combating herbivores, many herbivores have evolved resistance to them. Chemists have also developed many other synthetic pesticide compounds that have no related chemical structures in nature. Synthetic analogs include pyrethroids and neonicotinoids, the most widely used pesticides in many agricultural areas. These compounds are stronger and more stable than their natural counterparts. Still others bind to and inactivate proteins that are essential for basic life functions, such as energy production, metabolism, feeding, and reproduction.Ĭhemists have developed synthetic analogs of plant-derived pesticides. Others block key enzymes that insect or mite larvae need to grow and develop. Some, such as pyrethrins and nicotine, disrupt the nervous system of arthropods, causing paralysis and then death. ![]() Farmers have been using naturally occurring compounds-such as pyrethrins from Chrysanthemum flowers or nicotine from tobacco-for centuries to kill insects on crop plants, or even head lice on humans.Ĭompounds that act as pesticides have diverse chemical structures with different modes of action. The application of pesticides is widely used to limit herbivore damage to crops. But these practices don’t work as well against insects that can fly long distances. They tend to work against herbivores with limited mobility in one or more life stages. Whether they work or not depends on the biology of the particular pest species. Practices like crop rotation have long been used to control herbivores. Removing weeds can thus reduce potential reservoirs of crop pests. ![]() Some insect herbivores also live on weeds in or near fields. The pests cannot emerge to damage new plants. For major cereal crops, for example, farmers can plow the soil to bury stubble underground. Getting rid of leftover plant material after harvesting, like stems infested with overwintering insect larvae, can also reduce the numbers of herbivores the following year. The original crop plant can then be grown the next year. These kinds of insects die off during the in-between years when the field is planted with a crop that they don’t prefer. This strategy tends to work well against specialists like potato beetles and corn root worms. Farming practices, like rotating crops and keeping fields weed-free, can reduce pest damage.Ĭrop rotation is the practice of planting a field with a different crop from one year to the next, in a repeating cycle.
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