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 n
on-indigenous species released for biological pest control, relative t
o 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 r
elease. In fact, the discovery of such impacts usually rests on a rema
rkable concatenation of events. In addition to trophic and competitive
interactions between an individual introduced species and a native on
e, many effects of introduced species on ecosystems are possible, as a
re numerous types of indirect interactions. Predicting such impacts is
no mean feat, and the difficulty is exacerbated by the fact that intr
oduced species can disperse and evolve. Current regulation of introduc
ed biological-control agents, particularly of entomophages, is insuffi
cient. At the very least, strong consideration should be given to the
likely impact of both the pest and its natural enemy on natural ecosys
tems and their species, and not only on potential costs to agriculture
, silviculture, and species of immediate commercial value.