Many researchers have hailed transgenic insecticidal crops-plants modified to produce insecticidal proteins derived from genes of the bacterium Bacillus thuringiensis (Bt)-as the most important technological advancement in insect pest management since the development of synthetic insecticides (Vaeck et al. 1987, Koziel et al. 1993, Perlak et al. 1990, 1993). At least 18 transgenic insecticidal crops have been field-tested in the United States, and three (corn, cotton, and potato) have been widely planted (Andow and Hutchison 1998, Federici 1998, Gould 1998, USDA 1999). But as the commercial availability of these crops has grown, so too has controversy over how to assess and manage the risks posed by this method of pest control.The widespread planting of millions of hectares of transgenie crops with high levels of insecticidal proteins raises concerns that pest populations might develop resistance to Bt toxins and that food webs might be disrupted (Gould 1998, McGaughey et al. 1998, Marvier 2001). Indeed, the US Environmental Protection Agency (EPA) .requires industry to maintain populations of susceptible (nonresistant) insect pests to slow development of resistant populations. Nor are concerns limited to the United States: Anxiety over the safety of food and products derived from transgenic crops have created tensions among international trading partners (Balter 1997, Butler and Reichhardt1999, Masood 1999).In this article we focus on transgenic insecticidal corn (Bt corn) developed for selected lepidopteran species that feed on above-ground portions of the corn plant. Over 2.8 million hectares of Bt corn were planted in the United States in 1998, limited only by seed availability (Andow and Hutchison 1998); an estimated 9.7 million hectares of Bt corn were planted in 1999. Thus, although acreage declined to approximately 6.2 million hectares in 2000, Bt corn is now the most common management tactic for the European corn borer, Ostrinia nubilalis, throughout the corn-growing regions of the United States.The potential benefits of transgenic insecticidal corn include savings in resources devoted to scouting for pest insects, reduced applications of broad-spectrum insecticides, increased or protected yields due to season-long control of O. nubilalis (Rice and P&her 1998), protection of stored corn from lepidopteran insect pests (Giles et al. 2000), and lower mycotoxin levels due to a reduction in fimgal plant pathogens associated with O. nubilalis feeding (Munkvold et al. 1997,1999).Balanced, against these potential benefits are possible draw-backs. Such disadvantages of genetically modified crops can, in general, be grouped into three categories: (1) selection for resistance among populations of the target pest, (2) exchange of genetic material between the transgenic crop and related plant species, and (3) Bt crops' impact on nontarget species. The potential for O. nubilalis to develop resistance to toxins in Bt corn has been discussed in several publications (Gould 1998, McGaughey et al. 1998, Huang et al. 1999). Although the transfer of genetic material between Bt corn and its wild relatives can be a concern (Snow and Pahna 1997, Bergelson et al. 1998, Traynor and Westwood 1999), the potential for that transfer is limited to Mexico and Central America, where the wild species are located (Galinat 1988).