INSECTICIDE RESISTANCE AND RESISTANCE MANAGEMENT Evaluating Resistance to Bt Toxin Cry1Ab by F 2 Screen in European Populations of Ostrinia nubilalis (Lepidoptera: Crambidae) H. ENGELS, 1 D. BOURGUET, 2 L’. CAGA ´ N ˇ , 3 B. MANACHINI, 4 I. SCHUPHAN, 1 T. J. STODOLA, 5 A. MICOUD, 6 C. BRAZIER, 6 C. MOTTET, 6 AND D. A. ANDOW 5 J. Econ. Entomol. 103(5): 1803Ð1809 (2010); DOI: 10.1603/EC10055 ABSTRACT The large-scale cultivation of transgenic crops producing Bacillus thuringiensis (Bt) toxins have already lead to the evolution of Bt resistance in some pest populations targeted by these crops. We used the F 2 screening method for further estimating the frequency of resistance alleles of the European corn borer, Ostrinia nubilalis (Hu ¨ bner) (Lepidoptera: Crambidae), to Bt maize, Zea mays L., producing the Cry1Ab toxin. In France, Germany, and Italy, 784, 455, and 80 lines of European corn borer were screened for resistance to Mon810 maize, respectively. In Slovakia, 26 lines were screened for resistance to the Cry1Ab toxin. The cost of F 2 screen performed in the four countries varied from US$300 to $1,300 per line screened. The major difference in cost was mostly due to a severe loss of univoltine lines during the screen in Germany and Slovakia. In none of the screened lines did we detect alleles conferring resistance to Mon810 maize or to the Cry1Ab toxin. The frequency of resistance alleles were 1.0  10 Ð3 , 1.6  10 Ð3 , 9.2  10 Ð3 , and 2.6  10 Ð2 in France, Germany, Italy, and Slovakia, with 95% probability, respectively. The average detection probability over all lines was 90%. Making the assumption that European corn borer populations in these countries belong to the same genetic entity, the frequency of alleles conferring resistance to the Cry1Ab produced by the Mon810 maize in western and central Europe was 1.0  10 -4 , with a 95% conÞdence interval of 0 Ð3.0  10 -4 . KEY WORDS European corn borer, Bt maize, Mon810, resistance management, HDR strategy Transgenic crops producing Bacillus thuringiensis (Bt) toxinsÑreferred to as Bt cropsÑare widely planted in the United States, India, Argentina, Brazil, Canada, China, and Spain (James 2009). For example, maize (Zea mays L.), which provides control of lepidopteran and coleopteran maize pests, has been planted on 200 million ha during the last decade, corresponding to 30.5% of the global biotech area (James 2009). Large-scale cultivation of these Bt crops is exerting a tremendous selection pressure on target pest species, which prove to evolve Þeld resistance (Matten et al. 2008; Kruger et al. 2009; Tabashnik et al. 2008, 2009), diminishing the beneÞts of these crops. The risk of target pests becoming resistant to Bt crops has led to the development of several strategies to manage transgenic crops (Gould 1998, Roush 1998, Shelton et al. 2002, Vacher et al. 2003, Zhao et al. 2005, Tuytuynov et al. 2008). Among these the most widely accepted and implemented strategy is the “high-dose/ refuge” (HDR) strategy (Alstad and Andow 1995). This strategy has two components. First, the Bt crops need to produce Bt toxin at high concentration, with the expectation that this concentration would be suf- Þcient to kill most if not all heterozygous individuals. The other part of this strategy is refugesÑthe occur- rence of non-Bt plants, crops, or weeds, preserving a pool of susceptible individuals. The HDR is expected to work best when high dose of toxin is expressed in plant tissue, resistance alleles are rare (initial frequen- cies 10 -3 ), and functionally recessive and refuges are close to Bt plants, so that nearly all resistant sur- vivors from the Bt plants will mate with susceptible individuals from refuge plants to produce heterozy- gous offspring that cannot survive on Bt plants the following generation (Alstad and Andow 1995). Several techniques have been used to estimate the frequency of resistance alleles in natural populations, including in-Þeld screening (Venette et al. 2000) and screening of Þeld-collected egg masses or larvae (Sieg- fried et al. 2007). When resistance alleles have not been identiÞed and are believed to be rare and re- cessive, Andow and Alstad (1998, 1999) and Andow and Ives (2002) suggest that the most efÞcient method 1 Institute for Environmental Research (Biologie V), Aachen Uni- versity, 52074 Aachen, Germany. 2 Corresponding author: Centre de Biologie pour la Gestion des Populations (CBGP), UMR INRA-IRD-CIRAD-Montpellier SupA- gro, Campus International de Baillarguet, 34988 Montferrier sur Lez, France (e-mail: bourguet@supagro.inra.fr). 3 Department of Plant Protection, Slovak Agricultural University, 94976 Nitra, Slovakia. 4 Department of Animal Biology University of Palermo, 90123 Pal- ermo, Italy. 5 Department of Entomology, University of Minnesota, St. Paul, MI 55108. 6 Unite ´ Re ´ sistance aux Produits Phytosanitaires, AFSSA, 69364 Lyon, France. 0022-0493/10/1803Ð1809$04.00/0  2010 Entomological Society of America Downloaded from https://academic.oup.com/jee/article/103/5/1803/790807 by guest on 15 July 2022