How risky is biological control?

The potential harmful effects of non-indigenous species introduced for biological control remain an important unanswered question, which we addressed by undertaking a literature review. There are few documented instances of damage to non-target organisms or the environment from non-indigenous species released for biological pest control, relative to the number of such releases. However, this fact is not evidence that biological control is safe, because monitoring of non-target species is minimal, particularly in sites and habitats far from the point of release. In fact, the discovery of such impacts usually rests on a remarkable concatenation of events. In addition to trophic and competitive interactions between an individual introduced species and a native one, many effects of introduced species on ecosystems are possible, as are numerous types of indirect interactions. Predicting such impacts is no mean feat, and the difficulty is exacerbated by the fact that introduced species can disperse and evolve. Current regulation of introduced biological-control agents, particularly of entomophages, is insufficient. At the very least, strong consideration should be given to the likely impact of both the pest and its natural enemy on natural ecosystems and their species, and not only on potential costs to agriculture, silviculture, and species of immediate commercial value.