Biological Control Agents: Invasive Species Or Valuable Solutions?

To a large degree, the most serious insect and weed pests around the world are non-native, invasive species. Classical biological control, the introduction of natural enemies of invasive species to limit their populations, is a possible mechanism for alleviating the impacts of non-native pests. Whether introducing more non-native species in this way is a good approach depends on the positive and negative impacts of the potential control agents relative to the economic and environmental damage caused by the pests. Many classical biological control programs are deemed to be successful and contribute positively to ecosystem services by reducing the need for insecticides and herbicides as well increasing agricultural production, improving soil moisture conditions, and increasing native biodiversity. Recently, non-target impacts of some species of biological control agents have received considerable attention, which has impeded new classical biological control initiatives. However, analyses of the effectiveness of pre-release screening of agents shows that biological control has been very effective, particularly for weed control programs. Only 1-2 % of released agents have caused some damage to non-target species, and few have been shown to become invasive in the sense of being introduced, established, and having negative impacts in the new ecosystem. Clearly, generalist predators and parasitoids with multiple generations a year and multiple hosts should not be introduced because the potential for non-target impacts will be high. Host plant testing and specificity are important for choosing weed control agents, but must be viewed in the ecological context of species distributions and phenologies. However, the costs of lost opportunities from overly restrictive regulations must also be considered in evaluations of potential future classical biological control programs.