Definition and Scope of Biological Control

Biological control is a form of pest control that uses living organisms (parasitoids, predators, or herbivorous arthro pods) to suppress a pest's density to lower levels. There are four kinds of biological control, two of which - classical biological control and augmentative biological control - are discussed in this article and two others - conservation biological control and biopesticides - that are discussed in Biological Control Models.

Classical biological control is the deliberate importa tion and release of new species of natural enemies with the intention of suppressing the densities of a target weed or insect permanently over the whole of its range in the country receiving the natural enemies. Target pests are typically invasive species and the introduced natural ene mies are those specialized agents that attack it in its native range. Classical biological control is a major tool in reducing impacts of invasive species, both in crops and natural areas.

Augmentative biological control is pest suppression in greenhouses or outdoor crops through the purchase and release of commercially reared natural enemies. This approach is used against pest insects and mites, but not against weeds. Natural enemies used include both preda tors and parasitoids. The value of this approach depends on efficacy and cost ofthe natural enemy. This approach is most effective in greenhouse crops.

Biological control has important advantages com pared to other methods of pest control. Classical biological control is often cheaper and less polluting than use of pesticides, because pest control is relatively permanent and does not require annual retreatment. Initial costs of classical biological control are high, for discovery, importation, testing, and initial release of new natural enemies. However, costs drop to low or even zero levels in later years, while the benefits of the pest control achieved continue to accrue for years. For augmentation biological control, results are temporary and costs reoccur annually, as with pesticides. Augmentative biological control may be either more or less expensive than other approaches depending on details such as the cost of natural enemy production by commercial insectaries that sell beneficial organisms, and efficacy of other control tactics. Both of these types of biological control are harmless to people and vertebrates, giving the approach a distinct advantage over pesticides, which must be actively managed for safe use to mitigate harm to humans and other nontarget organisms. Risks of both augmentative and classical bio logical control to nontarget insects or, for weed biocontrol projects, to plants can exist, but these risks can be managed to low levels by careful screening of species being considered for release in new areas. Biological control as a scientific endeavor has a history of about 125 years of effective use (beginning in the 1880s), over which time new information, techniques, and technologies have increased our ability to use biological control agents with increasingly greater understanding and effectiveness.

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