ABSTRACT
As demonstrated throughout the previous chapters, the development of transgenic plants offers a powerful and attractive new method for managing insect pests. From an environmental standpoint, transgenic crops have clear advantages over the pesticides they could replace (Roush, 1994). However, transgenic crops seem now in 1996 to be at a stage of development rather similar to that of synthetic insecticides in the late 1940s, shortly after the first uses of DOT on crops. Throughout the late 1940s, there was great enthusiasm for the new and stunningly effective insecticides, but there were already a few cases where insects had evolved resistance to DDT after only a few years of use (Metcalf, 1980). Insecticide resistance had been raised as a concern more than 30 years earlier (Melander, 1914), but even through the mid-1950s, relatively few people considered resistance to be a serious threat to control of any pest. In those heydays of pesticide discovery, the general attitude seemed to be that resistance could be overcome by ever newer pesticides. However, by the 1970s, it had become very clear that at least some major pests were evolving resistance faster than new and environmentally acceptable insecticides could be discovered and brought to market (Georghiou, 1986; Metcalf, 1980). It is noteworthy that two of the first three Bacillus thuringiensis transgenic crops registered in the USA, cotton and potatoes, are targeted at markets essentially created by the recurrent evolution of resistance to insecticides in the pink bollworm (Pectinophora gossypiella), two cotton bollworms (Heliothis virescens and Helicoverpa armigera), and the Colorado potato beetle (Leptinotarsa decemlineata).
