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Field tests on managing resistance to Bt-engineered plants. Nature Biotechnology 18, 339-342.
| Shelton A.M., Tang, Juliet D., Roush, Richard T., Metz, Timothy D., Earle, Elizabeth D. (2000).
| Several important crops have been engineered to express toxins of Bacillus thuringiensis (Bt) for insect control. In 1999, US farmers planted nearly 8 million hectares (nearly 20 million acres) of transgenic Bt crops approved by the EPA. Bt-transgenic plants can greatly reduce the use of broader spectrum insecticides, but insect resistance may hinder this technology. Present resistance management strategies rely on a "refuge" composed of non-Bt plants to conserve susceptible alleles. We have used Bt-transgenic broccoli plants and the diamondback moth as a model system to examine resistance management strategies. The higher number of larvae on refuge plants in our field tests indicate that a "separate refuge" will be more effective at conserving susceptible larvae than a "mixed refuge" and would thereby reduce the number of homozygous resistant (RR) offspring. Our field tests also examined the strategy of spraying the refuge to prevent economic loss to the crop while maintaining susceptible alleles in the population. Results indicate that great care must be taken to ensure that refuges, particularly those sprayed with efficacious insecticides, produce adequate numbers of susceptible alleles. Each insect/Bt crop system may have unique management requirements because of the biology of the insect, but our studies validate the need for a refuge. As we learn more about how to refine our present resistance management strategies, it is important to also develop the next generation of technology and implementation strategies.
In 1999 US farmers planted nearly 20 million acres of Bt crops, which appeared to greatly reduce the use of broader spectrum insecticides in Bt cotton. Some data indicate that this gain might be short-lived due to the development of resistant insects. , In this study Bt broccoli together with the diamondback moth, the only insect to develop Bt resistance in the field, were used. This model system was used to assess the current resistance management strategy of using refuges to generate sufficient numbers of susceptible individuals, to cross with any resistant insects during mating. It was shown in both greenhouse and field experiments that a separate refuge, composed of non-Bt broccoli, delays the onset of resistant insects compared to a refuge, where non-Bt plants are grown mixed with Bt plants. Spraying of this separate refuge to prevent economic loss reduces its potential to dilute resistance. In the greenhouse, where no 'immigration' of susceptible insects was possible, rapid development of resistance was observed.
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