A major field trial of GM wheat that is designed to repel aphids has found the crop is no better protected against the pests than conventional wheat.

The results come from two years of trials that compared aphid attacks on standard wheat plants with those suffered by a GM version modified to release a natural aphid repellant.

The publicly-funded trial ran under heavy security at Rothamsted Research in Hertfordshire in 2012 and 2013 after it was targeted by anti-GM campaigners who threatened a day of direct action to trash the crops.

The research cost of the trial was £730,000, but that figure is dwarfed by a further £400,000 spent on fencing to protect this and future trials, and an extra £1.8m used to combat threats of criminal damage and vandalism.

Scientists created the GM wheat strain in the hope that it would deter aphids, which devour the crops and can leave them with infections. They modified the wheat to produce a natural pheromone which aphids release when under attack from predators. The “aphid alarm” makes the bugs flee to safety.



Aphids are not the only organisms that release the odour though. More than 400 plants have evolved to secrete the same substance, called E-beta-farnesene, or EBF, including peppermint. The chemical doubles up as an attractant for some insects that kill aphids, such as parasitic wasps.

Prior to the field trial, lab tests at Rothamsted found that the pheromone worked as a highly-effective aphid repellant. The work bolstered researchers’ hopes that the trial would demonstrate the crop’s resilience against aphids in the wild. An aphid-resistant wheat crop could have huge benefits for farmers and the environment because the plants would no longer need to be sprayed with insecticides.

“The disappointing thing is that when we tested it in the field, we didn’t find any significant reduction in aphid settlement in the test plots,” said Toby Bruce, who worked on the trial. Details of the trial are published on Thursday in the journal Scientific Reports.

The crop’s failure to resist the bugs has not surprised everyone. Jonathan Gershenzon at the Max Planck Institute for Chemical Biology in Jena, Germany, found in 2010 that GM plants designed to release EBF did not repel aphids, at least under lab conditions. The reason, he suspects, is that the plants released the chemical continuously rather than in short pulses.

Commenting on the Rothamsted trial, Gershenzon told the Guardian: “I would have bet that it wouldn’t work based on our published study.”

“Our major conclusion was that this strategy doesn’t work in nature because the aphids get used to the continuous release of their alarm pheromone and thus learn to ignore it. Or, they’re programmed to respond only to bursts of it, which would be the natural situation when one of their sisters is attacked. Or both,” he said.

“I can imagine that the authors were misled because the application of the alarm pheromone ‘worked’ in laboratory experiments to repel aphids. Like many workers before them they probably applied the pheromone in an unnatural way so that the dose was much higher than seen under more natural conditions. So it was very important that they were able to test this in the field, to answer a basic scientific question as well as to look for agricultural benefits.”



“This was a noble, but expensive try,” he added. One drawback of Gershenzon’s study was that it was carried out in the lab in still air, so the results cannot be extrapolated with any confidence to fields where the wind blows.

John Pickett, who led the Rothamsted trial, agreed that how the pheromone is released may be crucial to protect the plants. “We now know that in order to repel natural aphid populations in the field, we may need to alter the timing of release of the alarm signal from the plant to mimic more closely that by the aphid, which is a burst of release in response to a threat rather than continuous,” he said.

Gershenzon said he had expected the GM wheat to fare better than conventional wheat in the field trials, by attracting aphid predators to the crops. But, he added, that might only happen when enough aphid enemies were present, a factor influenced by the vagaries of weather and neighbouring vegetation. “Perhaps they were just unlucky,” he said.

Helen Wallace at the campaigning group, GeneWatch, argued that the field study was a waste of taxpayer’s money. “With GM crops, it’s always jam tomorrow and never jam today,” she said.

Threats from anti-GM campaigners to destroy the experimental crops caused the final bill for the trial to rise from £732,000 to £3m.