Biological Limits on Agricultural Intensification: An Example from Resistance Management

When the application of pesticides places selective evolutionary pressure on pest populations, it can be useful to plant refuge areas—crop areas intended to encourage the breeding of pests that are susceptible to the pesticide. Renewed interest in refuge areas has arisen with recent advances in biotechnology and genetically modified (GM) crops. In this paper, we use a simple model of the evolution of pest resistance to characterize the socially optimal refuge strategy for managing pest resistance. We demonstrate some interesting analogies with other models of renewable resource management, such as those of fisheries. Among the analogous results are findings that maintaining what we might call "maximal sustainable susceptibility" is typically not economically optimal and that the stock of pesticide effectiveness maintained is a declining function of the discount rate. The former result is in contrast to some existing studies based solely on biological considerations. We also examine the land use consequences of the enhanced agricultural productivity that results from the use of GM crops. Arguments are frequently encountered to the effect that GM crops could reduce the total area required for agriculture and thereby increase the quantity of land conserved for natural habitat. We show that the situation may not be as simple as standard arguments portray it. If refuge areas are used to manage resistance, then more land will be devoted to agriculture than would be the case were it simply a matter of adopting a technology that offered the same yield per hectare without requiring the management of a biological stock such as pest susceptibility.