© 2007 The Authors Entomologia Experimentalis et Applicata 126: 115–121, 2008 Journal compilation © 2007 The Netherlands Entomological Society 115 DOI: 10.1111/j.1570-7458.2007.00642.x Blackwell Publishing Ltd Selection for Cry1F resistance in the European corn borer and cross-resistance to other Cry toxins Eliseu J.G. Pereira 1 , Bruce A. Lang 2 , Nicholas P. Storer 3 & Blair D. Siegfried 1 * 1 Department of Entomology, University of Nebraska, Lincoln, NE 68583, USA, 2 Mycogen Seeds, 301 Campus Drive, Huxley, IA 50124, USA, and 3 Dow AgroSciences LLC, 9330 Zionsville Road, Indianapolis, IN 46268, USA Accepted: 27 September 2007 Key words: Ostrinia nubilalis, Bacillus thuringiensis, Bt maize, resistance management, Lepidoptera, Crambidae Abstract Evolution of resistance by insect pests is the greatest threat to the continued success of Bacillus thuringiensis (Bt) toxins used in insecticide formulations or expressed by transgenic crop plants such as Cry1F-expressing maize [( Zea mays L.) (Poaceae)]. A strain of European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), obtained from field collections throughout the central US Corn Belt in 1996 was selected in the laboratory for resistance to Cry1F by exposure to the toxin incorporated into artificial diet. The selected strain developed more than 3000-fold resistance to Cry1F after 35 generations of selection and readily consumed Cry1F expressing maize tissue; yet, it was as susceptible to Cry1Ab and Cry9C as the unselected control strain. Only a low level of cross-resistance (seven-fold) to Cry1Ac was observed. These lacks of cross-resistance between Cry1F and Cry1Ab suggest that maize hybrids expressing these two toxins are likely to be compatible for resistance management of O. nubilalis. Introduction The European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), is one of the most important pests of maize [( Zea mays L.) (Poaceae)] in the USA and Europe, and has been the target of several different management strategies (Hudon et al., 1989; Mason et al., 1996). Since 1996, genetically modified maize expressing the Cry1Ab toxin from Bacillus thuringiensis (Bt) Berliner has been successfully used for suppression of European corn borer populations in the USA. More recently, Cry1F-expressing maize (Chambers et al., 1991) derived from genetic transformation event TC1507 (see profile at http://www.agbios.com) was commercially deployed in the USA for control of European corn borer in 2003. Cry1F-expressing maize hybrids as well as other Bt-expressing hybrids represent an important alternative to conventional insecticides in terms of environmental safety and have increasingly been shown to have negligible effects on non-target organisms (Hellmich et al., 2001; Shelton et al., 2002; Naranjo et al., 2005). The development of Bt resistance in target pests threatens the continued effectiveness of Bt technology, both as transgenic Bt plants and all other Bt-based products. Laboratory selection experiments have shown the wide- spread potential for development of resistance to Bt toxins among insect pest species (Tabashnik, 1994; Ferré & Van Rie, 2002) including O. nubilalis (Huang et al., 1997; Bolin et al., 1999; Chaufaux et al., 2001; Siqueira et al., 2004). Resistance to Bt formulations used in a pest-management setting has also been reported in field populations of Plutella xylostella (Tabashnik, 1994) and in greenhouse populations of Trichoplusia ni (Janmaat & Myers, 2003). Although Bt crops have been commercially available for 10 years, field resistance has yet to be documented, suggesting that resistance management strategies have been effective or that changes in resistance allele frequency remain below the limits of detection (Tabashnik et al., 2003; Bates et al., 2005). Among the theoretical strategies for resistance manage- ment, the high-dose/refuge and pyramiding of more than one toxin with different target sites have been most widely cited (Roush, 1997, 1998; Gould, 1998; Zhao et al., 2003). However, the assumptions of proposed resistance management strategies are difficult to validate without well-characterized resistant strains. Laboratory-selected resistant strains * Correspondence: Blair Siegfried, Department of Entomology, 202 Plant Industry Building, University of Nebraska, Lincoln, NE 68583, USA. E-mail: bsiegfried1@unl.edu