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      Field-evolved resistance by western corn rootworm to multiple Bacillus thuringiensis toxins in transgenic maize.

      Proceedings of the National Academy of Sciences of the United States of America
      Animals, Bacillus thuringiensis, chemistry, Bacterial Toxins, pharmacology, Beetles, drug effects, physiology, Plants, Genetically Modified, genetics, microbiology, Zea mays

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          Abstract

          The widespread planting of crops genetically engineered to produce insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt) places intense selective pressure on pest populations to evolve resistance. Western corn rootworm is a key pest of maize, and in continuous maize fields it is often managed through planting of Bt maize. During 2009 and 2010, fields were identified in Iowa in which western corn rootworm imposed severe injury to maize producing Bt toxin Cry3Bb1. Subsequent bioassays revealed Cry3Bb1 resistance in these populations. Here, we report that, during 2011, injury to Bt maize in the field expanded to include mCry3A maize in addition to Cry3Bb1 maize and that laboratory analysis of western corn rootworm from these fields found resistance to Cry3Bb1 and mCry3A and cross-resistance between these toxins. Resistance to Bt maize has persisted in Iowa, with both the number of Bt fields identified with severe root injury and the ability western corn rootworm populations to survive on Cry3Bb1 maize increasing between 2009 and 2011. Additionally, Bt maize targeting western corn rootworm does not produce a high dose of Bt toxin, and the magnitude of resistance associated with feeding injury was less than that seen in a high-dose Bt crop. These first cases of resistance by western corn rootworm highlight the vulnerability of Bt maize to further evolution of resistance from this pest and, more broadly, point to the potential of insects to develop resistance rapidly when Bt crops do not achieve a high dose of Bt toxin.

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          Most cited references20

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          Sustainability of transgenic insecticidal cultivars: integrating pest genetics and ecology.

          F. Gould (1998)
          This review examines potential impacts of transgenic cultivars on insect population dynamics and evolution. Experience with classically bred, insecticidal cultivars has demonstrated that a solid understanding of both the target insect's ecology and the cultivar's performance under varied field conditions will be essential for predicting area-wide effects of transgenic cultivars on pest and natural enemy dynamics. This experience has also demonstrated the evolutionary capacity of pests for adaptive response to insecticidal traits in crops. Biochemical and genetic studies of insect adaptation to the Bacillus thuringiensis (Bt) toxins expressed by currently marketed transgenic cultivars indicate a high risk for rapid adaptation if these cultivars are misused. Theoretical and practical issues involved in implementing strategies to delay pest adaptation to insecticidal cultivars are reviewed. Emphasis is placed on examining the "high dose"/refuge strategy that has become the goal of industry and regulatory authorities.
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            Adaptation and invasiveness of western corn rootworm: intensifying research on a worsening pest.

            The western corn rootworm, Diabrotica virgifera virgifera LeConte, is an established insect pest of maize (Zea mays L.) in North America. The rotation of maize with another crop, principally soybeans, Glycine max (L.), was the primary management strategy utilized by North American producers and remained highly effective until the mid-1990s. In 1995, widespread and severe root injury occurred in east-central Illinois and northern Indiana maize fields that had been annually rotated with soybeans on a regular basis for several decades. The failure of this cultural tactic from a pest management perspective was attributed to a behavioral adaptation by a variant western corn rootworm that had lost fidelity to maize for egg laying. In 1992, an infestation of western corn rootworm was found within a small maize field near the Belgrade Airport. By 2007, the presence of this insect pest had been confirmed in 20 European countries. More recent molecular studies have confirmed that at least three separate invasions (until 2004) of western corn rootworms have occurred in Europe, increasing the risk that rotation-resistant western corn rootworms will be introduced into a new continent. Although biological control and use of conventional resistant maize hybrids have not achieved widespread success in the management of western corn rootworms in North America, these tactics are being evaluated in Europe.
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              A meta-analysis of effects of Bt cotton and maize on nontarget invertebrates.

              Although scores of experiments have examined the ecological consequences of transgenic Bacillus thuringiensis (Bt) crops, debates continue regarding the nontarget impacts of this technology. Quantitative reviews of existing studies are crucial for better gauging risks and improving future risk assessments. To encourage evidence-based risk analyses, we constructed a searchable database for nontarget effects of Bt crops. A meta-analysis of 42 field experiments indicates that nontarget invertebrates are generally more abundant in Bt cotton and Bt maize fields than in nontransgenic fields managed with insecticides. However, in comparison with insecticide-free control fields, certain nontarget taxa are less abundant in Bt fields.
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                Author and article information

                Journal
                24639498
                3986160
                10.1073/pnas.1317179111

                Chemistry
                Animals,Bacillus thuringiensis,chemistry,Bacterial Toxins,pharmacology,Beetles,drug effects,physiology,Plants, Genetically Modified,genetics,microbiology,Zea mays

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