First, it was a lone scientist in Iowa warning that pests were becoming resistant to genetically-modified corn that was designed to prevent their infestation.

Then the EPA issued a report on how GM corn was losing its effectiveness on corn rootworms.

Now, a group of plant scientists are speaking up, urging the EPA to act "with a sense of some urgency” to mitigate the problem.

NPR and Reuters reports that 22 scientists have written to the EPA, asking regulators to help mitigate the problem with biotech corn and further asking farmers to quit or alter their use of the products.

“The stakes are high,” wrote Carey Gillam for Reuters, “U.S. corn production is critical for food, animal feed and ethanol production, and farmers have increasingly been relying on corn that has been genetically modified to be toxic to corn rootworm pests.”

NPR’s Dan Charles writes that the scientists’ letter lays out “some of the implications of this discovery, and they are potentially profound.”

 The rethinking that's laid out in this letter, in fact, goes beyond what the EPA is able to do under current law. For instance, the researchers want seed companies to stop routinely inserting anti-rootworm genes into their most productive hybrid seed lines. According to the letter, this practice means that farmers "often have few options" apart from rootworm-protected seeds — even in some areas where rootworms don't pose a serious problem.

When farmers plant hybrids that contain the same gene, year after year, it dramatically increases the chances that this gene quickly will become useless, because insects will become resistant to it.

The researchers are calling on farmers in some parts of the country to stop planting corn with anti-rootworm genes altogether, or to plant such corn only intermittently.

Harvest’s Clay Masters has been out in fields of genetically modified corn where rootworms have shown resistance. Click here to read his report.