The value of parasitoids in biological control.
During the last 10 years there has been increasing concern about the dangers of ill-advised introductions of biological control agents. Once an exotic species has established, its effects are difficult to predict and are irreversible. Biological control agents that are not host-specific may therefore pose threats to at-risk species, and constraints have been applied to the types of organisms that may be used. The requirement for increased host specificity means that exotic polyphagous predators are less appropriate for introduction, and more research emphasis has been placed on oligophagous organisms such as many parasitoid species. This restriction in the range of candidates available for use makes it imperative to optimize the impact of new and existing biological control agents. It is contended that the usefulness of deemed "unsuccessful" biological control agents may be overlooked. Such control agents may reduce the density dependent-related resilience of a pest population, thus improving the chances of "success" of other controls. To recognize and exploit such situations, a comprehensive understanding of the population dynamics of the pest and control agent is needed. Once again, other opportunities to enhance control, such as habit manipulation, may emerge.