Evolution will find a way (Image: John Shireman/Getty Images)

YOU can’t keep a bad pest down. Corn rootworms in the US may have developed resistance to a protective chemical made by a genetically modified corn. The US Environmental Protection Agency announced last week that it plans to investigate the pest’s resilience.

Corn rootworms are one of the most damaging agricultural pests in the US. They impair corn’s ability to absorb water and nutrients from the soil, says Michael Gray of the University of Illinois in Urbana. The economic impact of the insects, in terms of crop damage and the cost of pesticides, used to be around $1 billion a year, until the biotechnology firm Monsanto introduced its rootworm-killing variety of corn in 2003.

Gray recently showed that western corn rootworms on two Illinois farms have developed resistance to Cry3Bb1, an insecticide produced by Monsanto’s genetically modified YieldGard corn (PLoS One, doi.org/d5mqwn).


Resistant rootworms could further damage corn crops that have already suffered the hottest, driest summer the US Midwest has experienced in more than 70 years. Corn prices are at a record high despite US farmers planting the largest corn acreage since 1937, according to the Department of Agriculture.

YieldGard was planted on more than 150,000 square kilometres of US farmland last year. In an official statement, Monsanto says there is no evidence that the insecticide-resistant rootworms are spreading.