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Microbial Pesticides
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16696 |
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Section : |
NATURAL SCIENCE
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10 / 1989 |
2,005 Words |
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Anthony M. Shelton and H. Alan Wood
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Since the publication of Rachel Carson's Silent Spring, there has been a growing awareness and concern surrounding the potential hazards of the 3.5 billion pounds of pesticides used in the United States each year. Through the media, the public has been bombarded with reports that a particular pesticide residue was found on a food crop or is contaminating a source of drinking water. In the spring of 1989 the pesticide Alar gained such widespread notoriety that U.S. grocers prominently displayed "Alar free" signs in their produce section.
Actual and perceived hazards of pesticide residues have led to a general lack of confidence in the safety of all pesticides and the implementation of many new federal standards for their use. However, our present agricultural system, with its built-in dependence on chemical pesticides, carries enormous resistance to movement toward more environmentally neutral alternatives. Our agricultural system requires chemical pesticides for it to continue to produce abundant and low-cost foods with high nutritional value, and with the cosmetic properties demanded by most consumers. Although many may argue that it is highly desirable to produce the nation's food crops without chemical pesticides, this is not presently feasible. Despite the current use of pesticides in agribusiness, plant pests destroy an estimated 20 to 30 percent of our food crops each year. To meet the challenge of pest control without the potential of environmental and health problems, the commercial pesticide industry and agricultural researchers are actively exploring new pesticide strategies.
Among the new pesticide strategies in agriculture and forestry is the use of naturally occurring biological agents, such as insects and fungi that kill weedy plants, fungi that parasitize other fungi, insects that attack other insects, and fungi, bacteria, and viruses that kill harmful insects. Employing fungi, bacteria, and viruses to control insect pests shows particular promise. These naturally occurring microorganisms could be applied as nonpolluting insecticides that would not harm the beneficial insects (such as parasitic wasps and other natural predators) that help keep pest populations in check.
Baculoviruses as Pesticides
Recently, there has been a renewed interest in developing insect viruses, particularly the baculoviruses, as alternatives to chemical insecticides. More than 500 baculoviruses have been described, and 90 percent of these infect and kill caterpillars, many of which are major agricultural pests. Baculoviruses characteristically form a protein coating that protects them from the rigorous external environment, but then dissolves when they enter an insect's stomach. Research is focusing on manipulating the gene that carries the information for forming the protein coating, but its success will depend on understanding the full range of the baculovirus' natural activity.
In many instances, baculoviruses play an important role in the natural regulation of insect populations. One baculovirus preys on the gypsy moth, which defoliates millions of acres of forest land each year in the northeastern United States and now threatens forests in the northwest. When gypsy moth populations become high, the naturally occurring gypsy moth baculovirus becomes epidemic and kills more than 95 percent of the insects. The virus epidemic accounts for the cyclic nature of gypsy moth infestations and is important for the moth's
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