Biological Control and Refuge Theory

Abstract

REFERENCES tions arising from the intluences of host and parasitoid phenologies (3). Single values cannot characterize host-parasitoid interactions, and maximum values are unlikely to be typical over longer times or in different areas (4). 4) Contrary to the prediction made by Hawkins et al., successful biological control can result from the use of agents that are characterized by low rates of parasitization in their native habitat (5). Natural enemies that are rare in their native habitat may have superior potential as control agents when released in exotic habitats (6). 5) Hawkins et al. attribute seven cases of high parasitization (above 60%) in unsuccessful biological control projects to climatic mist,natch between parasitoids and hosts. We question how such high rates of parasitization could be achieved if clima tic factors "reduce parasitoid reproduction, survivorship, or host synchrony ..." (1, p. 1431). Variation in the susceptibility of insects to predators, parasitoids, and disease is important. Mechanisms for encapsulating parasitoids, hiding from predators, and resisting disease influence the impacts of natural enemies in native and exotic habitats, but measuring refuge size from the observed maximum parasitization of successful biological control programs does not yield new understanding or predictability to the practice of biological control. 1. B. A. Hawkins, M. B. Thomas, M. E. Hochberg, Science 262, 1429 (1993). 2. B. P. Beirne, Can. Entomo/. 107,225 (1975). 3. R. G. van Driesche, Environ. Entorno/. 12, 1611 (1983). 4. A. McPhee, A. Newton, K. B. McRae, Can. Entomo/.120, 73 (1988); l. A. Pearsall and S. J. Walde, Eco/. Entorno/. 19, 190 (1994). 5. J. Ro)and, in Popu/ation Dynamics of Forest /nsects, A. D. Watt, S. R. Leather, M. D. Hunter, N. A. C. Kidd, Eds. (Intercept, Andover, United Kingdom, 1990), pp. 289-302. 6. J. Myers, C. H. Higgins, E. Kovacs, Environ. Entorno/. 18, 541 (1989)