Biopesticides
Plants, growing in the wild or in cultivation, face numerous threats from insects, bacteria, viruses, and fungi, as well as from other plants. Biopesticides are inert substances or living organisms that can help protect plants from such threats. Chemical pesticides can offer similar protection but, by contrast, are neither alive nor made by living organisms.
A variety of chemicals produced by plants help ensure that parasites, predators, plant feeders, and herbivores seldom increase in number sufficiently to destroy the plant populations they prey upon. Chemicals found in very low concentrations in certain plants have been found to help keep locusts from feeding on those plants, and some trees produce nearly 1,000 different chemical compounds that help them resist herbivores and parasites.
Plant predators are themselves subject to attack by predators, parasites, and microbes, all of which can indirectly help protect a plant and therefore are also considered biopesticides. An oak tree may have about 100 species of insect herbivores feeding on it. In turn, there can be up to 1,000 species of predators, parasites, and microbes feeding on the herbivores. The microbes, parasites, and predators attacking the herbivore populations are considered “biopesticides,” as are any protective chemicals produced by the tree
Such living biopesticides play a vital role in agriculture and nature, helping to control insect pests, plant pathogens, and weeds. Numerous organisms, including viruses, fungi, protozoa, bacteria, and nematodes , as well as insects, such as parasitic wasps, can attack pest insects and weeds. In some cases, biologists search around the world to find natural organisms to help control an insect, a plant pathogen , or weed populations.
More than 95 percent of all crops have some degree of pathogen resistance bred into them, with resistance to fungi, bacteria, and viruses being most common. Most of this resistance was either added by farmer selection or plant breeder selection, rather than through genetic engineering. It is because of this natural resistance that has been bred into the crops that only 12 percent of the pesticides used in U.S. agriculture are fungicides.
Some viral resistance, however, has been bred into a number of crops through insertion of viral genes into the plant chromosomes. These genes may lead to the plant’s producing viral proteins—biopesticides of a sort—that hamper a virus’s own actions. This pathogen-derived resistance has been successfully used to protect Hawaii’s papaya crop from the devastating papaya ringspot potyvirus. The viral gene was inserted into the papaya genome using a “gene gun,” which shoots viral genes into papaya embryo cells.
Some crops (e.g. corn) are being engineered to contain both herbicide tolerance and the BT toxin. Generally, the use of herbicide-tolerant crops will likely increase the use of herbicides. This has the potential to increase environmental pollution since it might increase the farmers’ reliance on chemicals rather than mechanical and other means of weed control.
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