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Photo: Scott Bauer, USDA ARS, Bugwood.org
- For 50 years, corn rootworms have adapted to resist every control measure, from crop rotation, to older broadcasted soil insecticides, foliar insecticides and now some Bt-RW traits. Even the variant Western corn rootworm has proven greater tolerance in its gut to digest soybean foliage.
- High populations of rootworms, known to challenge low-dose RW traits (unlike high-dose Bt corn borer traits), have occurred in both 2011 and 2012. And for 2013, drought-caused soil cracks may have allowed easier and deeper egg laying which could lead to a third year of high infestation, an extended hatch and greater overwintering.
- In lab studies, USDA Entomologist Bruce Hibbard, Columbia, Mo., has shown that the western corn rootworm has developed resistance against all Bt-RW traits, which goes beyond the current field resistance shown against the Cry3Bb1 trait (Monsanto's YieldGard RW, VT Triple products and one of the two RW traits in SmartStax hybrids).
- In field research, rootworms have shown proven resistance to the Cry3Bb1 trait in Iowa and Illinois – so far in a small number of continuous corn fields where the Cry3Bb1 trait was used for numerous years. Greater than expected damage has been reported in northwestern and north-central Illinois, northeastern Iowa, southern Minnesota, northeastern Nebraska and eastern South Dakota. Common features in the affected fields include a history of continuous corn and the use of Cry3Bb1-expressing hybrids for multiple years.