10.2190/F59H-4BH5-16GV-M7PB F59H4BH516GVM7PB 5 Interdependent Pests: The Economics of Their Control 153 161 20020509 20020509 20020509 20020509 F59H4BH516GVM7PB.pdf http://baywood.metapress.com/link.asp?target=contribution&id=F59H4BH516GVM7PB 2 Clem Tisdell University of Newcastle, New South Wales, Australia Population levels of two or more pest species are frequently interdependent and this has consequences for the optimal control of any single one targeted for control. When the controlled pest species is a predator on another pest or is in competitive relationship with it, the optimal (most economic) control of the target species is smaller than in the absence of the interdependence. On the other hand, if the controlled pest species is the prey of predator that is also a pest, or is in symbiosis with another pest, greater control of the target species is required (from an economic standpoint) than in the absence of this interdependence. Conditions for the most economic control of a targeted pest species are outlined and it is observed that governments sometimes fail to take account of the interdependence of pest populations in their pest control policies. C. A. Tisdell, <i>Wild Pigs: Environmental Pest or Economic Resource</i>, Pergamon Press, Sydney, in press. J. C. Headley, Defining the Economic Threshold, <i>Pest Control Strategies for the Future</i>, National Academy of Sciences, Washington, D. C., pp. 100-108, 1972. C. Tisdell, Simple Economic Models of Pest Control, <i>Research Report or Occasional Paper 33</i>, Department of Economics, University of Newcastle, Australia, May 1977. C. Tisdell, Observations on the Wild Pig Problem in N. S. W., <i>Research Report or Occasional Paper 41</i>, Department of Economics, University of Newcastle, Australia, March 1978.