Environmental issues involved in biological control of rangeland grasshoppers (Orthoptera: Acrididae) with exotic agents.

Within the field of biological control, there is a strategy that involves the attempt to control a native pest species with an exotic biological control agent. This strategy has been termed neoclassical biological control, and its ecological foundation differs markedly from other forms of biological control. Neoclassical biological control with a parasitic wasp and an entomophagous fungus from Australia is now being applied to rangeland grasshoppers in the western United States. Available evidence suggests that the costs of such a strategy greatly exceed the benefits. Although the probability of successful establishment may be low, if such an agent is established there are a number of possible nontarget impacts. Adverse effects include competitive suppression or extinction of both native biological control agents and nontarget acridids, which comprise the vast majority of extant grasshopper species. Suppression of nontarget acridids may result in loss of biological diversity, existing control of weed species, release of otherwise innocuous acridid species from competitive regulation, disruption of plant community structure, suppression of essential organisms vectored by grasshoppers, and disruption of food chains and other nutrient cycling processes. These impacts are particularly serious given that an established exotic agent is essentially permanent and spatially unbounded. Given that the value of the rangeland resource depends upon the largely unknown ecological processes that underlie its sustainable productivity, there are a number of management techniques that offer a greater probability of success with a markedly lower likelihood of ecological and economic disruption than does neoclassical biological control.