The US Environmental Protection Agency has posted a report on a government website that suggests pests in several states are developing resistance to genetically modified maize created by agribusiness Monsanto. The Bt maize was engineered to kill insects by releasing a toxin (the Bt toxin, from a soil-dwelling microbe), but scientists have expressed fears that the maize may be losing its effectiveness against rootworms.

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Evidence collected from four states shows rootworms are developing resistance to the insecticide engineered into the company’s maize, the Environmental Protection Agency said in its statement, posted on Wednesday but dated 22nd November.

In its statement, the EPA said Monsanto is not adequately monitoring for signs that pests are developing resistance to its modified plants; the agency examined Monsanto's current monitoring program, following reports from entomologists and documented cases of crop damage due to rootworms in Iowa, Illinois, Minnesota and Nebraska, and concluded the company’s program "is ineffective and likely to miss early resistance events."

In July and August two studies from Iowa State University and the University of Illinois showed rootworms have evolved resistance to the Bt insecticide in a number of Midwestern states. Nevertheless a Monsanto spokesperson said the company continues to believe there is no scientific confirmation of resistance to its Bt corn.

Although it would only go so far as to say evidence pointed to "suspected resistance" in rootworms, the EPA recommended Monsanto begin surveying fields earlier for evidence of damage. No EPA officials were available for further comment.

Today, Bt corn accounts for around a third of the maize grown in the USA, according to USDA estimates, but the technology has proven highly controversial; earlier this year, scientists in Canada found traces of Bt toxin in the blood of 93 per cent of pregnant mothers and 80 per cent of umbilical cords, which they put down to mothers consuming animal products from livestock fed Bt corn.

The EPA memo revealed "Resistance is suspected in at least some portions of four states in which ‘unexpected damage’ reports originated." It recommend Monsanto extend its testing to cover Colorado, Minnesota, South Dakota and Wisconsin as well as Nebraska, Illinois and Iowa because of concerns about the performance of Bt corn in all seven states.

Corn rootworm larvae destroy plant roots before developing into adult beetles. The bug is amongst the most devastating corn pests in the USA; the USDA estimates the pest costs farmers about $1 billion a year in damages and chemical pesticides. If the resistance is proven to be a growing problem, farmers will once again have to resort to using chemical pesticides to tackle the bug, negating any benefits of growing the more expensive biotech corn.

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