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Assessment of fitness costs in Cry3Bb1 resistant and susceptible western corn rootworm (Coleoptera:Chrysomelidae) laboratory colonies
Citation:
OSWALD, K., B. French, C. Nielson, AND M. BAGLEY. Assessment of fitness costs in Cry3Bb1 resistant and susceptible western corn rootworm (Coleoptera:Chrysomelidae) laboratory colonies. JOURNAL OF APPLIED ENTOMOLOGY. Wiley-Blackwell Publishing, Hoboken, NJ, 136(8):730-740, (2012).
Impact/Purpose:
This research effort is designed to provide the risk assessment community with modern genetic tools for evaluating long-term risks of genetically modified (GM) crops. Molecular population genetic data can potentially reveal information about long-term trends in both pest populations targeted by plant-incorporated pesticides (PIPs) and non-target populations. EPA regulations require specific pest management strategies to slow the evolution of resistance in target pest populations in order to prolong the environmental benefits of GM crops (i.e., reduced use of chemical pesticides). A key component of this research effort will be to provide detailed information on pest biology, including gene flow and mating patterns in the wild (within species and between closely related species), geographic and chromosomal distribution of resistance alleles, and the additive and non-additive effects of genetic variation on resistance under selective pressures in the field. These data will be used to improve and validate models of insect resistance development with the goal of implementing best agricultural practices for delaying or preventing the development of pest resistance. These methods will be evaluated as a necessary component in the process of developing novel PIPs. In comparison to pest populations, the exposure of non-target populations to toxins from GM crops like Bt-corn (i.e. corn expressing an insecticidal protein derived from the bacterium Bacillus thuringiensis) and the long term population-level effects of these exposures are very poorly understood. Short-term field studies have failed to detect significant population effects on non-targets. However, sensitive methods to evaluate the exposures of non-targets to GM crops and long term population effects are lacking. Genetic methods we have developed for aquatic indicator species can be adapted to the assessment of non-target insect populations in order to provide baseline population data and a cost-effective methodology for monitoring long-term population trends. These methods will be evaluated as a routine monitoring tool for the assessment of GM crop safety on non-target species. Together with the research on pest populations, the monitoring of non-targets will be used to determine the current and future safety of GM crops. An important aspect of this biotechnology research effort is that it focuses on the comparison of GM crops to traditional farming practices. To effectively compare the risks and benefits of GM crops, they must be evaluated relative to realistic alternatives, which includes the effects of traditional industrial scale farming and its concomitant use of pesticides. Planned research will begin to assess the effects of traditional pesticides (i.e. organophosphates, carbamates, etc.) on non-target communities and compare them to the effects of GM crop use. One of the rationales for the approval of GM crops such as Bt corn and cotton is that they are predicted to reduce the use of traditional chemical pesticides which, if true, would represent an ecosystem benefit. Planned non-target studies will compare the effects of traditional agricultural practices, such as chemical pesticide use, to novel GM crop practices in terms of impacts to the long-term sustainability of non-target organisms. This effort will include threatened and endangered non-targets insects. Pesticide run-off into streams and rivers is an important environmental issue and we will address this issue by comparing the use of GM crops to the use of traditional chemical pesticides on our nation's streams and rivers.
Description:
Maize production in the United States is dominated by plants genetically modified with transgenes from Bacillus thuringiensis (Bt). Varieties of Bt maize expressing Cry3Bb endotoxins that specifically target corn rootworms (genus Diabrotica) have proven highly efficacious. However, development of resistance to Bt maize, especially among western corn rootworm (Diabrotica virgifera virgifera) populations, poses a significant threat to the future viability of this pest control biotechnology. The structured refuge insect resistance management strategy implemented in the United States for Bt maize adopts a conservative approach to managing resistance by assuming no fitness costs of Bt resistance, even though these can strongly influence the dynamics of Bt resistance within numerous agricultural pest species. To investigate the effects of Bt resistance on fitness components of western corn rootworm, we compared survivorship, fecundity, and viability of five Bt resistant laboratory lines reared on MON863 (YieldGard Rootworm), a variety of Bt maize that expresses Cry3Bb1 endotoxin, and its nontransgenic isoline. Analysis of performance on the isoline maize demonstrated no fitness costs associated with Bt resistance. Resistant lines reared on Bt maize displayed higher fecundity compared to those reared on isoline. Adult emergence of resistant lines reared on MON863 was not significantly delayed compared to resistant and control lines reared on the isoline, but delayed emergence of 4-6 days was observed for the susceptible line reared on MON863. These data will be valuable for formulating improved insect resistance management strategies for a principal agricultural pest of maize.