Bt maize is a GMO crop designed to produce its own insecticide. Its introduction allowed US maize farmers to grow the crop in the same field year after year without a break.
It was supposed to repel and kill pests but within three and a half years the corn rootworm developed resistance.
The GMO industry answer was to produce more genetically engineered toxins and to “stack” them in combination of two or three in the maize plants.
Now the Iowa research team has found that pest resistance to the original toxin is being transferred to the newer engineered strain.
Pests are overcoming GMO technology with surprising speed
“That’s two of the three toxins on the market now,” says Gassmann. “It’s a substantial part of the available technology.”
It is not surprising that pests have developed resistance but the speed and extent is unexpected.
Genetically engineered maize producing the Bt toxin Cry3Bb1was first approved for use in the United States in 2003.
From the start 2% of the Corn Rootworms survived feeding on the toxic corn.
That 2% was enough to establish a healthy, resistant breeding population.
 Within 6 years rootworm damage was widespread across US GMO maize crops.
 In 2011, damage had spread to maize containing a second genetically engineered toxin mCry3A.
Gassmann’s research has shown that this is due to cross-resistance and that corn rootworms that had become resistant to Cry3Bb1 are also resistant to mCry3A.
It’s a vicious treadmill for farmers; we have previously covered it here.
Non-GMO maize grown to protect GMO maize
For some time the GMO seed companies have been urging farmers to plant ‘refuges’ of non-GMO maize within their fields to act as a breeding ground for susceptible root worms.
But as corn rootworm resistance has developed and spread recommendations on the size of “refuges” have come to verge on the ridiculous – up from 10-15% of the overall crop to closer to 40%.
So in order to prolong the effectiveness of genetically engineered maize plants and to make GMO cropping viable- you have to grow non-GMO maize.
Traditionally farmers throughout the world have used crop rotations; growing a range of different crops to keep soil healthy, prevent loss of nutrients and prevent plant diseases and pests from becoming established.
But the GMO companies and GMO researchers told them that with GMO crops they would no longer need crop rotations and in the US this has led to the widespread abandonment of sound farming practices
This has been the biggest driver behind the development of rootworm resistance.
Abandoning good farming practice
If maize is grown in the same field year after year, it applies the perfect selection pressure for pests to evolve resistance. Take away maize monocropping and the problem is controlled.
Typically the companies have been quick to blame farmers – even though they advised them that rotations were unnecessary.
Nicholas Storer, a global science-policy leader for biotechnology at Dow AgroSciences in Washington DC, says that the study illustrates that if GMO crops are not used as part of an integrated pest-management policy, resistance can develop quickly in an individual field.
But In response to the growing resistance Dow - working with Monsanto - is now adding more insecticide genes to its maize which can only make the problem worse.
Gassmann’s study shows that the combination of multiple toxins is less effective once resistance arises to one of the toxins.
Farmers should not rely on GMO technology to fight pests, and should instead periodically change the crop grown on a field to help disrupt the pest’s life cycle.
“The rootworm can’t survive if the corn’s not there,” Gassmann says.
Even the man from Dow acknowledges this; “crop rotation was the primary tool to combat rootworm before Bt came along,” he said in an honest moment, “We need to keep it up.”
So why would anyone need GMOs?
Meg Noble