Review Special feature: biological control: theory and practice

Population Ecology

, Volume 48, Issue 4, pp 297-305

First online:

Biological control: lessons from a study of California red scale

  • William W. MurdochAffiliated withDepartment of Ecology, Evolution and Marine Biology, University of California Email author 
  • , Susan L. SwarbrickAffiliated withDepartment of Ecology, Evolution and Marine Biology, University of California
  • , Cherie J. BriggsAffiliated withDepartment of Integrative Biology, University of California

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A 20-year study of suppression of California red scale, a world-wide pest of citrus, by the parasitoid Aphytis melinus has established that the interaction is dynamically stable and that the mechanisms leading to control and stability operate at a local scale: spatial processes are not important. Key features appear to be an invulnerable class in the pest and rapid development of the parasitoid compared with the pest, as well as the fact that the parasitoid is an in situ specialist on the pest. Although another parasitoid species and two predator species are also present, they play at most a negligible role in pest control. These features—long-term persistence, suppression by a single natural enemy, an invulnerable stage in the pest and rapid development in the natural enemy—appear to be common in other coccid pest systems. By contrast, in temporary crops where the pest and enemy populations are open (i.e., sustained over the long run mainly by immigration) and non-persistent locally, as is frequently found in aphid pests, we expect that multiple generalist enemies are required for control and, of course, that spatial processes are important. There are very few well-studied examples of such systems, but these support our expectations. In these cases, it also appears that neither rapid enemy development nor an invulnerable pest stage is important for successful control.


Parasitoids Predators Population regulation Insect pests Invulnerable stages Development times