Exotic insect pests worldwide are many. They are accidental biotic contaminants. Classical biological control (CBC) agents can be considered as deliberately introduced biotic contaminants that, when successful, reduce the overall biomass of contamination and often bring considerable self-sustaining economic relief to farming communites.Although the introduction of exotic agents would seem to be contrary to conservation philosophy, there are no quantified instances to date where the introduction of arthropod agents has been shown to have harmed a specific conservation programme or has been categorically damaging to native fauna. There is only limited anecdotal evidence that introduced parasitoids may have damaged certain specific native taxa. CBC in some cases actually assists conservation by reducing the level of exotic pests in nature reserves.As CBC is an important socio-economic method of pest control, especially for tropical farmers, and as the taxonomic groups and life-histories of its targets are so different from those insects of endangered status, the two approaches are not in conflict. But as CBC is virtually irretrievable, it must continue to be carried out carefully and selectively only by truly responsible CBC agencies using appropriate quarantine facilities.Tourists and general travellers pose a greater threat to native faunas than do the activities of such CBC agencies. It is well known that vertebrate agents and certain invertebrates, especially snails, can be devastating to certain native biotas. Additionally, and in view of the impending world-wide biotic diversity crisis, even traditional agents such as insect pathogens, insect parasitoids, and insect and mite predators, should be viewed with extreme caution—especially when oligophagous, and unquestionably when polyphagous.
Classical biological control of insect pests of trees: facts and figures
