History and future of introduction of exotic arthropod biological control agents in Spain:: a dilemma?

The first documented introduction of an exotic invertebrate biological control agent (IBCA) in Spain occurred in 1908. Sixty-four additional species have been introduced since then. Information, both previously recorded and original data, on the species introduced for pest control is summarized. Most of the introduced IBCAs focused on citrus pests and homopterans clearly predominate among target phytophagous species. Success has been more frequent for IBCAs used in seasonal inoculative strategies (50.0% of cases) than in classical biological control programs (17.1% of cases). Concerns about potential non-target effects of such species are increasing, but post-release evaluation has often been insufficient to draw any conclusions about them. Most of the beneficial species introduced in Spain were parasitoids (n = 53), and the remaining species were predators (n = 12). Only four parasitoids are considered specialized monophagous natural enemies. The mean number of host species parasitized by parasitoids is 15.2, whereas the mean number of prey species attacked by predators is 21.2. Therefore, polyphagy appears to be quite common among the IBCAs that have been introduced in Spain. The rationale guiding many of these introductions in the past would not be acceptable nowadays. Since classical biological control is such a valuable strategy for pest control, straightforward protocols to evaluate exotic candidate species are urgently needed.