) - The U.S. Environmental Protection Agency is calling on



to beef up its monitoring of a genetically-engineered corn product that appears to losing effectiveness against bugs.

In a report released Nov. 30, the EPA noted that rootworms in four states -- Iowa, Illinois, Nebraska and Minnesota -- seem to be building up a tolerance to the corn, which is supposed to be lethal for the bugs.

The EPA called Monsanto's monitoring efforts in this area "inadequate."

The U.S. Department of Agriculture estimates the bugs cause about $1 billion a year in damages.

Shares of Monsanto were down 3.2% to $70.86 in midday action on Friday. Year-to-date, the stock is up a little more than 5%.


Written by Alexandra Zendrian in New York


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Alexandra Zendrian