A controversial GM wheat trial in the UK has failed after more than £2 million of public money was spent protecting it from eco-saboteurs.
The so-called "whiffy wheat" project to create a genetically engineered crop that wards off aphids by releasing an alarm signal scent cost £732,000.
But this was dwarfed by the extra £2,238,439 spent on fencing and other security measures for the field trial after threats of destructive attacks by anti-GM activists.
Campaign group GM Freeze claimed the scientists had wasted taxpayers' money in a pointless bid to "outwit nature".
Both the the trial itself and the steps taken to keep out the vandals, as well as earlier laboratory work, were wholly Government-funded through the Biotechnology and Biological Sciences Research Council.
After success in the lab, the genetically modified wheat turned out to be ineffective at repelling aphids in the outdoor trial conducted at the Rothamsted Research institute in Harpenden, Herts.
Disappointed scientists believe the insect pests may have become blase about the pheromone scent signal and learned to ignore it - much like people closing their ears to a constantly sounding car alarm.
Lead researcher Professor John Pickett said: "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."
The wheat was engineered with a gene derived from the peppermint plant that enabled it to release a pheromone called (E)-beta-farnesene (EbetaF).
Aphids use the alarm to alert each other to the presence of threats such as parasitic wasps and ladybirds. In the wild, the scent causes the insects to flee from danger - and also attracts predators that recognise the aphid signal.
In laboratory tests the GM wheat produced the pheromone in significant quantities without its appearance or growth being affected, and successfully repelled aphids.
But in the field trial there was no statistical difference in the number of aphids infesting GM and conventional wheat.
The findings are reported in the online journal Scientific Reports, part of the Nature publishing group. The outcome, following five years of work, is a blow to the scientists, who nevertheless have vowed to press on with the research.
Rothamsted researcher Dr Toby Bruce said: "In science, we never expect to get confirmation of every hypothesis. Often it is the negative results and unexpected surprises that end up making big advances - penicillin was discovered by accident, for example.
"This trial has ended up yielding more questions than answers, but that means we have more work to do to understand the insect-plant interaction and to better mimic what happens in nature."
Prof Pickett said it may be necessary to engineer the wheat to release the pheromone only when the aphids arrive, rather than continuously.
The scientists also pointed out that when the trial took place in 2013 there was a wet summer with low aphid numbers, which may have made it more difficult to obtain a statistically significant result.
GM Freeze, an umbrella group representing a number of campaign organisations including the Soil Association and Friends of the Earth England, said the trial result was clear evidence of "the folly of focusing public resources on the development and promotion of GM crops".
It condemned the "waste" of public money on a trial "confirming the simple fact that when GM tries to outwit nature, nature adapts in response".
Liz O'Neill, director of GM Freeze, said: "A basic understanding of evolution tells us that GM offers, at best, a sticking-plaster approach to complex and evolving problems.
"We know that pests are very good at adapting to their environment but, like the aphids in the trial, those promoting GM as the first-choice solution to our food and farming needs stopped listening to nature's alarm signals as soon as they became inconvenient."
Rothamsted Research said £444,000 was spent on fencing to keep out both unwanted animals and humans, and an additional £1,794,439 on other security measures "in response to threats of vandalism and attempted criminal damage by anti-GM activists".
Dr Bruce said: "The cost of security associated with this trial was three times the cost of the science experiment, and that's largely due to the real threat that these experiments come under.
"In order to develop these kind of approaches the major cost is associated with the threat of vandalism, which unfortunately we've come up against, and it's a great pity so much money had to be spent on security because if we didn't face that threat of vandalism a great deal of money could have been saved."
In a statement Rothamsted Research denied that the trial had failed in scientific terms despite the GM wheat not working as an aphid repellent outside the laboratory.
"The experiment itself was successful, because it allowed us to test the hypothesis of whether the GM wheat could repel aphids in the field," said the research institute.
"It provided a conclusive answer that the wheat had failed to repel aphids, but that is not the same as a failed experiment or failed science."