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Bad time to relax resistance management requirements

Posted by Andrei_Alyokhin on 12 Aug 2011 at 17:47 GMT

This is an unfortunate, but entirely expected, development. The field failures reported by the growers and the more than 50% survival on Bt plants are rather disconcerting. Furthermore, resistance levels are likely to increase as selection continues.

Another big reason to be concerned is that there is considerable geographic separation among the problem fields (in particular, P4 seems to be completely isolated). So, we are not dealing with a single pocket of resistance.

In light of what appears to be an increasing number of cases of pest resistance to Bt crops, it is particularly disconcerting to see a continuous and unjustified relaxation of refuge requirements by the EPA. With the introduction of pyramided plants, refuge requirements for rootworms have been reduced to 5% blends of transgenic pyramided seed with non-transgenic seed. That decision is a recipe for disaster. Not surprisingly, it was made against the recommendations of an independent Scientific Advisory Panel convened by the EPA.

There is no sound scientific justification for reducing the refuge size (Nature Biotechnology 29, 577–578 [2011]). Furthermore, when one toxin in the pyramid has already failed (as is the case for the populations tested in this article), the pyramid is compromised because there is only one toxin remaining to kill the pests. So, even if a 5% refuge is sufficient for truly pyramided crops (and we do not know that), it is highly unlikely to be efficient when the pyramid is no longer a pyramid.

No competing interests declared.

Correct refuge size for rootworms

Andrei_Alyokhin replied to Andrei_Alyokhin on 15 Aug 2011 at 15:12 GMT

The correct refuge size for rootworms in blended seed is, of course, 10%. Five percent is a refuge size for caterpillars. Still, relaxation of refuge requirements is a bad idea.

No competing interests declared.