Contamination and management of resistance evolution to high-dose transgenic insecticidal crops |
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Authors: | Paul R Glaum Anthony R Ives David A Andow |
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Institution: | (1) Department of Zoology, UW-Madison, Madison, WI 53706, USA;(2) Department of Entomology, University of Minnesota, St. Paul, MN 55108, USA |
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Abstract: | For maize and cotton, transgenic varieties that express toxins derived from Bacillus thuriengensis (Bt) are now planted in several countries. To slow resistance evolution, the “high-dose/refuge” strategy is broadly implemented
in which resistance is recessive and some fields (or areas within fields) are planted exclusively with Bt crops and other
fields planted exclusively with non-transgenic refuge crops for susceptible insects. This strategy, however, could potentially
be undermined by contamination. Here, we investigate general models of resistance evolution for high-dose events in which
fields are contaminated due to the inadvertent mixing of seeds, volunteer plants, or pollen flow between Bt and non-Bt varieties
coupled with seed-saving by farmers. Contamination of the refuge by Bt plants increases selection for resistance, thereby
speeding resistance evolution. Nonetheless, in most situations this effect is small. Contamination of Bt fields by non-transgenic
plants might be expected to have the opposite effect and always reduce the rate of resistance evolution. While this is often
the case, it is not always so. If larvae move among plants within a field, then high movement rates may reverse the effect
of contamination of Bt fields to slow resistance evolution. Furthermore, if the dispersal rates of adult females between Bt
and refuge fields are low, then contamination of Bt fields may speed resistance. These results suggest that contamination
has the potential to undermine the efficacy of the high-dose/refuge strategy, yet depending upon the particular pest and situation,
contamination may not be a concern. |
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