Post-release evaluation of non-target effects of biological control agents.

Abstract

In this chapter, post-release evaluation of non-target impacts of introduced biological control agents is discussed, with emphasis on parasitoids used for biological control, but examples are also given for insect pathogens and herbivores for weed biological control where they provide illustrative examples and useful comparisons. The scope of non-target effects of biological control agents is discussed in relation to: direct effects on native non-target species; direct effects on beneficial or valued exotic species; direct effects on non-target pest species; competition with, or displacement of other natural enemies; and indirect effects on the same or other trophic levels. Three case studies from recent and on-going research on post-release impacts are presented. These include first, a classical biological control release of the braconid, Microctonus aethiopoides, introduced to control a pest weevil in New Zealand. Secondly, examples of inundative application of entomopathogenic nematodes are given which highlight aspects of non-target effects on insect populations in the field, competition between endemic and exotic species at the application site, and post-application persistence or dispersal. The third case study describes indirect effects of biological control of spotted knapweed in North America. Finally, a summary of possible approaches to post-release monitoring and impact assessment of a biological control release is presented.