Part 2 of our "Resistance Reality" story, featured in the Farm Journal 2012 Seed Guide. Click here to start reading from the beginning.
In particular, the entomologists are concerned about the extent to which the Bt toxin Cry34/35Ab1 is deployed in hybrids.
It is in germplasm that belongs to Dow AgroSciences, DuPont Pioneer, Monsanto and Syngenta.
"We want Steve Bradbury to be aware of some very specific concerns regarding the durability of 34/35, that it’s potentially being compromised," says Mike Gray, University of Illinois Extension entomologist and one of the letter’s co-authors.
Cry34/35Ab1 is a pivotal toxin. It is the material most technology providers are using to build a bridge away from the first-generation Bt products in the marketplace to new ones in the development pipeline. Scientists believe damage to the rootworm control integrity of Cry34/35Ab1 would have significant ramifications for U.S. corn production, based on its widespread use in hybrids grown throughout North America.
Cry34/35Ab1 is used in combination with the Cry3Bb1 toxin in hybrids branded as SmartStax, sold by Dow AgroSciences, and Genuity SmartStax, sold by Monsanto. The SmartStax brand also includes the new refuge-in-a-bag style corn hybrids introduced on a large-scale basis to farmers this year. The Dow products are sold under the brand Refuge Advanced powered by SmartStax, and the Monsanto brand is Genuity SmartStax RIB Complete.
Scientists contend that SmartStax hybrids could be at risk in those fields where the Cry3Bb1 trait has failed and rootworm resistance has occurred. In those areas, the burden of rootworm control would still be based on only a single toxin, Cry34/35Ab1, rather than the combined strength of the two toxins.
The scientists’ letter to EPA asks the agency to address the risks Cry34/35Ab1 faces.
"It is crucial that susceptibility to Cry34/35Ab1 be preserved, in part because it has now been approved in pyramid with mCry3A and is the common toxin in two different pyramids from two registrants. A third registrant is also seeking to register mCry3A + Cry34/35Ab1," the scientists write.
No field-evolved rootworm resistance has been reported in corn hybrids containing either mCry3A or Cry34/35Ab1.
The Bt issues point to a broader concern EPA must address more effectively—how to appropriately regulate and manage resistance to genetically modified products within the industry, says University of Nebraska–Lincoln Extension entomologist Jeff Bradshaw.
Continue: "Reduced Refuge Obligation" >>