"Beneficial" bugs are not beneficial to everything.
A British researcher says it was once thought that "good" bugs would kill the "bad" bugs without environmental damage usually associated with pesticides.
However, he says, biological control is not risk-free. The introduction of new insects can indirectly affect other animals.
For example, flies that feed on weed seeds in Australia were so successful, the populations of a bird species which also relied on the seeds, suffered.