Rootworm Resistance Emerges to Two Types of Bt Toxins in GM Maize

http://www.biosafety-info.net/article.php?aid=1056

Publication date: March 27, 2014

THIRD WORLD NETWORK BIOSAFETY INFORMATION SERVICE Dear Friends and Colleagues  Researchers from Iowa State University have discovered that the western corn rootworm has developed resistance to two of the three types of Bacillus thurinigiensis (Bt) toxin produced by genetically modified (GM) maize.   GM maize containing the Bt toxin, Cry3Bb1, to resist the rootworm was first approved in 2003 in the U.S. In 2009 and 2010, rootworm damage appeared in the crops, evidence of evolved resistance. In 2011, severe rootworm damage was seen in GM maize containing a second Bt toxin, mCry3A. The researchers also found cross-resistance between the two toxins, possibly because the toxins share structural similarities and some binding sites in the insect’s gut. They also point out that the Bt maize does not produce enough toxin to fully control the rootworms. Thus rootworm resistance evolves rapidly where the same maize variety is grown every year, as has been observed in Iowa.  Industry has responded with ‘pyramiding’ their GM seeds to produce two different Bt toxins to attack the rootworm, to delay resistance development, but the researchers caution that this is at best a temporary measure. They recommend increasing refuge size and reverting to the proven age-old practice of crop rotation to disrupt the pest’s life cycle.