CLASSICAL BIOLOGICAL-CONTROL OF ENVIRONMENTAL PESTS

Exotic species commonly invade areas of conservation concern. Such spe cies may threaten native species or ecosystems, either attacking indiv idual species, or changing ecosystem characteristics in ways that make them less suitable for the continued existence of one or more native species. Among the potential effects of exotic species are crowding, c hanges in water table levels, fire frequency or intensity, altered soi l fertility or chemistry, and altered levels of predation or disease. Chemical, mechanical and biological methods each may be used to contro l exotic species in some cases. Chemical and mechanical methods are di fficult to apply to large areas and must be repeated periodically to p revent pest resurgence. Classical biological control often has high in itial costs but is permanent in nature and self propagating, such that large areas can be treated economically. Risks of biological control are minimal if agents are appropriately screened to determine host ran ge prior to introduction and in introductions are conducted using appr opriate quarantine procedures. Biological control is a useful approach for control of a variety of kinds of environmental pests that threate n the conservation of native species and ecosystems, including exotic plants, herbivorous and predacious arthropods, other invertebrates, an d in some instance vertebrates.