A farmer processes corn cobs.
A farmer processes corn cobs. - 
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Steve Chiotakis:
A type of genetically-modified corn by agricultural and chemical-company Monsanto may be developing a resistance to the exact bug it's supposed to resist. New research out of Iowa State University says it raises worries that biotech crops could spawn superbugs.

Marketplace's Eve Troeh reports.

Eve Troeh: Western corn rootworms are tough little bugs.
Monsanto genetically engineered a type of corn that keeps them at bay. It's worked for more than a decade, so well that some farmers plant it year after year. You're not supposed to do that, because it gives the worms time to learn how to survive. The study found that farmers who grew the Monsanto corn three years in a row got infested by worms that turned into "super bugs."

Darin Newsom: These types of adaptations could start to reduce yield, and start to cause the problems that we were looking to avoid.

Darin Newsom is senior agriculture analyst at DTN. He says corn prices are booming because of more demand to feed animals, to send overseas, and to make ethanol. It's tempting for farmers to stick with corn.

Newsom: We are seeing more acres put back-to-back on corn because we simply need a supply of corn, year in and year out.

He says any news that could lead to less corn -- like a superbug -- means prices will likely rise even more. Monsanto encourages farmers not to use the same type of modified corn back-to-back.

I'm Eve Troeh for Marketplace.

Follow Eve Troeh at @evetroeh