2.9.2 Decrease in the Rate of Resistance Evolution

Concern over the risk of pest resistance to conventional pesticides led to development of a relatively new field of applied science, called pest-resistance management (NRC 1986). The goal of this field is to determine approaches for developing and deploying pest control tactics in ways that maximize long-term benefits. Pest-resistance management is grounded in concepts and empirical findings from the basic sciences of quantitative genetics and population genetics (NRC 1986). In this regard, it is very similar to the applied science of classical crop breeding. These fields of inquiry rely heavily on statistical inference. A theoretical population geneticist or a crop breeder is therefore unlikely to make a deterministic prediction about the outcome of a natural evolutionary event or the exact characteristics of his or her next new cultivar. For the same reason, scientists investigating pest-resistance management tactics are reluctant to provide regulatory officials or farmers with exact predictions about how many years it will take for a specific pest to adapt to overcome a proposed resistance management plan. However, they can provide information on which of a number of approaches to development and deployment of transgenic and conventional pest-protected plants is likely to be most successful in decreasing the rate of pest evolution to adapt to those plants.

Quantitative comparisons of resistance management approaches for crops protected against insect damage began in 1986 (Cox and Hatchett 1986; Gould 1986a, b). A list of potential approaches has since been developed (Gould 1988a; McGaughey and Whalon 1992; Roush 1997; Tabashnik 1994). Some of the general approaches for resistance management for insect pests are as follows:

  • High dose of a single contained toxin in most plants, with some plants producing no toxin at all and thus serving as a refuge (approach 1).

  • Multiple toxins at high (or in some cases moderate) doses in most plants, with some nontoxic plants serving as a refuge (approach 2).

  • GMPP plants with low doses of a toxin that only slow the growth of the pest, so that pest population growth decreases and natural enemies can become more effective (approach 3).

  • Development of GMPP plants that produce the toxin only when and where it is most critical to protecting the plant (approach 4).

Much of the research aimed at developing these approaches and assessing their expected impacts has focused on transgenic pest-protected plants that produce Bt toxins.

A high dose of a toxin has been defined by the EPA Science Advisory



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