The Western rootworm beetle, one of the most serious threats to corn, has developed resistance to Monsanto's Bt-corn and entire crops are being lost.
Farmers from several Midwest US states have reported root damage to corn that was specifically engineered with a toxin to kill the rootworm. Iowa State University recently completed a field study.
The study found that fields identified by farmers as having severe rootworm feeding injury to Bt maize contained populations of western corn rootworm that displayed significantly higher survival on Cry3Bb1 maize in laboratory bioassays than did western corn rootworm from fields not associated with such feeding injury. In all cases, fields experiencing severe rootworm feeding contained Cry3Bb1 maize. Interviews with farmers indicated that Cry3Bb1 maize had been grown in those fields for at least three consecutive years. There was a significant positive correlation between the number of years Cry3Bb1 maize had been grown in a field and the survival of rootworm populations on Cry3Bb1 maize in bioassays. However, there was no significant correlation among populations for survival on Cry34/35Ab1 maize and Cry3Bb1 maize, suggesting a lack of cross resistance between these Bt toxins
Bacillus thuringiensis – Bt – is a bacterium that kills insects. Different proteins are engineered into cotton as well as corn plants.
According to USDA figures two-thirds of all US corn is genetically and the majority of that is Bt-corn. Monsanto has the biggest market share in the US, reporting about 35% in 2009.
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