A method of pest control, brought about by living organisms, which are conventionally separated into parasitoids (parasites that kill their hosts as they complete their development), predators and diseases. The activities of these agents of biological control reduce the numbers of the pests and/or the extent of their damage, to below accepted economic injury levels. This definition includes natural as well as applied (brought about by human intervention) pest and/or crop damage reductions. The practice of biological control usually comprises three basic strategies: importation, conservation and augmentation.
Importation (also called classical biological control). This consists of importing and releasing exotic natural enemies that are known to control the exotic pests in their native region. The long-term aim of importations is to establish a stable natural enemy-pest interaction that would maintain the pest’s population below the economic injury level. Ideally the natural enemy should be able to subsist and multiply on the pest (and/or on available alternate food), and to occupy a similar range of habitats.
Conservation This consists of helping the natural enemies to survive in the field by manipulating the environment. It consists of alleviating or eliminating factors that harm the enemies and/or of adding essential resources. As pesticides are the dominant adverse environmental factor, they should either be totally avoided or, if absolutely necessary, be restricted to chemicals that do not harm the natural enemies. Another approach is the use of natural enemies that are resistant to pesticides. The addition of essential components includes providing the natural enemies with refuges as well alternate food, such as nectar and pollen.
Augmentation This refers to increasing the populations of effective natural enemies by making essential resources available or by repeated releases. This might become necessary if the original release has been numerically insufficient, if the increases in the natural enemies in the field occur too late to suppress pest infestations, or after the resident natural enemy population has been wiped out by chemical applications. Ideally the natural enemies are introduced into the system either before the target-pest arrives or while its numbers are still low.
These main components of biological control entail direct aggression of natural enemies against the pest. However, natural enemies can also bring about reductions in pest numbers and/or damage by transmitting pathogens, by competing with the pest for resources without causing plant injury or by reducing the pests’ incidental damage (e.g. feeding on honeydew and sootymold.
The application of disease-inducing microorganisms (viruses, bacteria, entomopathogenic fungi, entomopathogenic nematodes and protozoa) against pests, depends on suitable environmental conditions (especially high humidity) or on protecting these microorganisms from radiation and arid conditions.
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