Agricultural Pest Out-Evolves GM Crop

The corn rootworm has become resistant to a genetically modified maize variety that produces an insecticidal toxin.

By | March 19, 2014

The adult stage of the western corn rootworm searches for pollen on corn silk.WIKIMEDIA, USDA - TOM HLAVATYScientists had been warning agrichemical companies and US corn farmers for years that the western corn rootworm (Diabrotica virgifera virgifera) would evolve resistance to insecticide-producing genetically modified (GM) maize varieties if the modified trait wasn’t deployed more thoughtfully. Now, a PNAS paper published this week (March 17) details just how problematic that rising resistance has become in corn fields across the nation. “Unless management practices change, it’s only going to get worse,” Iowa State University entomologist Aaron Gassmann, who led the study, told Wired. “There needs to be a fundamental change in how the technology is used.”

First grown on a wide scale in 1996, the GM maize—called Bt corn for the bacterial toxin gene it incorporated from Bacillus thuringiensis—raised yields and drove down populations of corn rootworm and other pests. But little more than a decade later, populations of rootworms that were resistant to Bt corn cropped up in Iowa, Illinois, Nebraska, South Dakota, and Minnesota.

The problem was that farmers were growing too much Bt corn without planting sufficiently large refuges of non-Bt corn so that the insects there would remain susceptible to the toxin and that susceptibility could be kept alive through the pests’ mating with rootworms from populations feeding on Bt corn. Even though independent researchers warned that resistance would evolve, farmers and the companies that created and sold the GM maize failed to heed their advice, often ignoring even the US government’s guidelines regarding refugia. “Resistance was caused because the farmers did not plant the required refuges and the companies did not enforce the planting of refuges,” Cornell University entomologist Elson Shields told Wired.

Another problem that led to the rise of resistance in corn rootworms was that farmers grew Bt corn year after year instead of rotating other crops, a decision mainly driven by high corn prices. Not growing corn continuously naturally decreases populations of rootworms and other corn pests. Nicholas Storer, a global science-policy leader for biotechnology at Dow AgroSciences, told Nature that modern technologies must be paired with traditional agricultural practices, such as crop rotation, to maximize the benefits of GM organisms. “Crop rotation was the primary tool to combat rootworm before Bt came along,” he said. “We need to keep it up.”

The corn rootworm scenario should serve as a cautionary tale for the rise of resistance in other insect species if GM traits, such as Bt toxin production in corn, are not cultured more wisely on the landscape. Other such traits “will fall under the same pressure,” Shields told Wired. “And the insect will win. Always bet on the insect if there is not a smart deployment of the trait.”

And when insects like the rootworm win, farmers will resort to using pesticides, thus negating one of the key benefits of GM crops designed to combat pests using toxin-producing genes.

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Avatar of: Seth Crosby

Seth Crosby

Posts: 16

March 19, 2014

Is the resistance permanent? If the worms were given a Bt vacation, would the resistance be diluted? Perhaps the resistant bugs are more sensitive to pesticides...or are weaken in other ways? It seems sometimes a new genetic advantage often comes at a cost.

Avatar of: Dr Edo

Dr Edo

Posts: 30

March 19, 2014

The same underlying human mechanisms were at work in California when the War Department released DDT following WW-2. There were ample warnings that it would seek fats but this was ignored. It was not until other states embargoed California butter that anything was done about it. The same can be said of cattle and over grazing in Botswana or Swaziland----to much profit incentive, or the rape of the Sacramento Delta by early placer gold mining and mercury which is still corrupting the Sacramento/Bay waterways. It's just human nature.

March 19, 2014

Why is this a shock, funny enough birds can still eat the new bugs...except you keep shooting them and cutting down hedges.

Price of a hedge > gm crops

Avatar of: vm123456


Posts: 61

March 20, 2014

the 4th paragraph of the article says that hybrid agriculture - mixing industrial farming with select traditional techniques - might work. win iwn situation

Avatar of: vm123456


Posts: 61

March 20, 2014



the 4th paragraph of the article says that hybrid agriculture - mixing industrial farming with select traditional techniques - might work. no need to go back to the dark ages where we had organic agriculture but we also had famine. Best of both worlds


Avatar of: vm123456


Posts: 61

Replied to a comment from Seth Crosby made on March 19, 2014

March 20, 2014

to minimize resistance you should cycle between GM pestdicides. GM is ideally suited to this since you can plant crop strains that are otherwise exactly the same but produce different pestdicides within one growing season

unfortunately the anti GMO proapganda has poisoned the reputation of GMO such that many bright young people shun careers there reducing the number of scientists available. Also investors seeing less customers due to propaganda will hesitate to invest so there are less companies in the game

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