Corn plants in Iowa that were genetically modified by Monsanto Co. to be resistant to pests are being attacked by these very bugs, marking the first time a major Midwest bug has developed a resistance to genetically modified crops, the Wall Street Journal reported.

Iowa State University entomologist, Aaron Gassmann, discovered that western corn rootworms in four northeast Iowa fields have evolved to become resistant to the natural pesticide produced by Monsanto's genetically modified corn plants.

"These are isolated cases, and it isn't clear how widespread the problem will become," said Dr. Gassmann. "But it is an early warning that management practices need to change."

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Dr. Gassmann says the Iowa fields infested with the Cry3Bb1 toxin-resistant rootworms have been growing Monsanto's Bt-expressing corn continuously for more than three years. In his study, Dr. Gassmann collected rootworm beetles from four Iowa cornfields with plant damage in 2009. He then fed containing Monsanto's Cry3Bb1 toxin to the larvae, which he found to have a survival rate three times that of control larvae that ate the same corn. 

Monsanto said its rootworm-resistant corn seeds are working as expected "on more than 99% of the acres planted with this technology" and that it is still too early to judge the impact of Gassman's study on farmers.

However, these findings from Dr. Gassman may provide even greater incentive among biotechnology rivals to develop a new generation of genes that would be resistant to further insect adaptations. Technologies like RNA interface may be able to make crops deadly to insects that eat them, essentially ingesting genetic code that turns off a vital gene.