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Assessing Biological Controls
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14016 |
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Section : |
NATURAL SCIENCE
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| Issue
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2 / 1988 |
4,291 Words |
| Author
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Allen M. Young
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The gypsy moth has eaten its way across North America, its voracious caterpillars defoliating millions of square miles of hardwood forests. The caterpillars of the European corn borer moth devastate annual corn harvests to the tune of millions of dollars a year. Fruit flies in the American tropics blemish and destroy fruit crops from melons to mangoes. Exotic weeds invade our gardens and natural habitats and choke our native species of plants.
Each continent and island across the globe is a beachhead of new invasions of pests. Throughout much of this century, we have sought to control pests with artificially synthesized chemical pesticides, only to create other problems with drastic long-range consequences. As an alternative, we have looked to biology to control pest species of plants and insects. Can the biological control of pests help humankind to manage pest populations? Many researchers believe preserving a region's delicate ecological balance remains a challenge.
Origins and Perspective
Pest infestation is a direct result of human activity, usually a consequence of alteration in the natural landscape. Through the complex processes of evolutionary adaptation, the vast majority of species in nature are highly integrated into an intricate, biologically balanced network. Each species occupies a specific ecological niche, and when natural habitats, such as forests, are cleared away through human activity, the resulting assemblages of species are usually much simpler than before. Thus when a tropical rain forest is destroyed and replaced with a cattle pasture or corn field, far fewer species of both plants and insects thrive in the cleared area. Such greatly altered habitats are ideal targets for invasions of exotic species introduced from other parts of the world.
The introduction of exotic pests is almost always irrevocable. Moreover, the more biological diversity that is destroyed in an area, the greater the chance for pests to take over. Pests are genetically programmed to build up very dense populations in their new homes, and in virtually all cases, exotic species that become pests in their new habitats have left their natural enemies behind in their native habitats. From a human perspective, they are out of control, a condition that quickly becomes obvious when pests invade our turf, crops, and homes. Pests often have few natural competitors in their adopted homes, compounding the problem even further. Although pests readily become established outside of their natural geographical ranges, their natural enemies and competitors do not.
Whenever monocultures of crop species or trees replace ecologically complex natural forests, there is a need for pest control. Plants cultivated as crops or ornamental fruit and shade trees have been selectively bred for certain characteristics deemed as desirable by humankind. But there is an immense biological price tag associated with the selective breeding of plants.
In nature, plant species have evolved a natural resistance against attack by pests. Each living plant is a marvelous, miniature pharmaceutical laboratory, synthesizing substances that ward off the attack of plant-feeding insects and other arthropods. Many plants, including the wild "cousins" of food crops, fruit trees, and garden ornamentals, produce these natural repellents and pesticidal
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