Last week it was reported that a GM wheat variety that was found to deter aphids in laboratory tests failed to do the same in field trials (1). Some opponents of GM technology have called the trial a “waste of over £1 million of public money” and said that the trial “confirms the simple fact that when GM tries to outwit nature, nature adapts in response” (2). Are these fair criticisms?
The GM wheat variety—which was developed by researchers at Rothamstead Research in the UK—can make an insect pheromone called (E)-β-farnesene. This pheromone is normally produced by aphids when they are under threat to warn other aphids so they disperse. Some of the natural predators of aphids (e.g. parasitic wasps) are also able to detect this pheromone and are attracted by it.
(E)-β-farnesene and other insect pheromones have the potential to be used in agriculture as an alternative to pesticides, which typically kill beneficial insects too. However, the pheromones evaporate easily at normal temperatures and break down quickly, so application of synthetically made pheromones in fields is costly and technically challenging (1). Therefore, genetically engineering plants to produce the pheromone themselves could be more effective.
To enable the wheat plants to produce (E)-β-farnesene, the researchers introduced the genes that encode two enzymes called farnesyl diphosphate synthase and (E)-β-farnesene synthase, which modify molecules found naturally in the wheat plants. Laboratory tests found that the (E)-β-farnesene produced by these plants deterred three species of aphids and also increased the foraging behavior of a species of parasitic wasp called Aphidius ervi that preys on aphids. Based on these promising results, a field trial was carried out in 2012/3.
Why were the wheat plants able to deter insects in the laboratory but not in the field? The conditions in the environment could have played a role: both summers of the field trial were cold and wet, and researchers observed that the populations of aphids and parasitic wasps in both years were low, well below the threshold levels of infestation that would be reached before farmers would spray the crop with pesticides.
Also, the way in which the wheat plants produced the pheromone is perhaps not ideal. Aphids only produce the pheromone when threatened, but the GM wheat variety produced (E)-β-farnesene all the time. In the field, this could have led to the aphids becoming used to the pheromone—like how fishermen become accustomed to the strong smell of fish—so that the pheromone ceased to act as a deterrent. Therefore, developing different varieties that only make the pheromone at particular points in time (e.g. during aphid attacks) may be more effective.
The researchers have shown that it is possible to produce GM wheat that can make an insect pheromone. Although this variety is ineffective at deterring aphids in the field, it provides useful insights that could be used to develop better varieties in future, or may inform other approaches to deter aphids from attacking crops. “Negative” results are very common in scientific research because it is impossible to be sure of the results of an experiment before you have tried it. Therefore, this field trial was not “a waste of money”, but a normal step in research.
While I agree that “nature adapts” to finds ways around human technologies, this does not mean that we should completely give up on GM technology. After all, we haven’t stopped trying to develop new antibiotics just because some bacteria have developed resistance to some of the existing ones. Our problems with antibiotic resistant bacteria have been exacerbated by the over-use of antibiotics, which have placed bacteria under stronger selection pressures to develop resistance. Similarly, growing a limited number of crop varieties in monocultures places selection pressures on pests to develop resistance to our attempts to deter, or kill them. Using a mixture of different technologies and farming practices is likely to be much more effective in improving crop yields in the long-term. Even if they never make it to market, GM crop varieties are useful for scientific research, which will inform our efforts to improve agriculture in future.
- Bruce, TJA, Aradottir, BGI, Smart, LE, Martin, JL, Caulfield, JC, Doherty, A, Sparkers, CA, Woodcock, CM, Birkett, MA, Napier, JA, Jones HD and Pickett, JA (2015) The first crop plant geneticallyengineered to release an insectpheromone for defence. Scientific Reports.
- BBC News: UK GM wheat ‘does not repel pests’ by Claire Marshall http://www.bbc.co.uk/news/science-environment-33262885