Benefits and risks of introducing exotic macro-biological control agents into Europe1

Biological control of insects — the use of natural enemies to reduce pest numbers — has been applied on a worldwide scale for more than 100 years and its use has considerably increased during the past decades as it offers a sustainable, economical and environmentally attractive alternative to chemical pest control. In biological control, locally occurring natural enemies are used or alien species are imported. Until now, introductions of hundreds of species of insect natural enemies have not led to environmental problems when a procedure of selection, importation and release was carefully applied. In contrast, many intentional and unintentional introductions of plants and phytophagous animals have resulted in very negative effects on the environment. Several early biological control introductions, mostly of generalist, large predators (e.g. vertebrates, birds and toads) and usually not supervised by biological control experts, led to unintended negative effects on native species. For insect biological control executed by experts, examples of unintended, harmful effects are not known. Selected natural enemies are usually specific, mono- or oligophagous species of parasitoids and predators. To prevent making mistakes in the future, pre-introductory evaluation of natural enemies is advocated, including a step where their potential negative effects are studied. Examination of the literature, taxonomic research and host acceptance experiments are used in such studies to estimate negative effects.