Wednesday, 14 March 2012

GM goes Green: aphid repelling wheat could reduce the need for pesticides

This summer, field trials of genetically modified (GM) wheat will be held at Rothamsted Agricultural Research Station, where I happen to be doing my PhD. I'm not involved in the field trials in any way, and do not work directly with the scientists who have developed the GM wheat. However, I find the research incredibly exciting, both in terms of the underlying science and the possible implications for sustainable agriculture.

So, the science bit.

Aphids (greenfly) are an important pest of crops. They cause direct damage by feeding from the plant, and also transmit plant viruses. The main method of controlling aphids is to spray crops with insecticides. Unfortunately, these insecticides often kill other insects, including natural enemies of aphids such as ladybirds and parasitoid wasps (they lay their eggs inside live aphids - think bodysnatchers). Overuse of insecticides is also increasing the numbers of resistant aphids, in the same way that overuse of antibiotics selects for resistant strains of infectious bacteria in humans.

When in danger, aphids produce an alarm chemical called (E)-β-farnesene (EBF), which repels other aphids. Some plants, such as mint, also produce this chemical, cleverly keeping aphids at bay.

Scientists at Rothamsted have genetically engineered wheat to synthesise EBF. Laboratory tests have shown that the EBF emitting wheat not only repels aphids, but also attracts their natural insect enemies. This could provide a means of controlling aphids on wheat without the need for heavy pesticide sprays, working with the aphids' natural enemies, rather than against them.

With a 70% increase in global food demand predicted by 2050, and increased concern over the effects of pesticides, herbicides and fertilisers on the environment, you might think that a field trial to test the effectiveness of this GM wheat under farm conditions would be welcomed. However, a number of concerns have been raised about the field trials, both by anti GM campaigners and the general public. I've tried to address some of them below.

The first that I came across was put forward by my Mum, an avid gardener and allotment keeper.
She asked me,  "Where will all the aphids go?"

Since this is a small scale field trial on the Rothamsted Farm site (eight 6m x 6m plots), it is very unlikely that any displaced aphids would manage to leave the farm or damage the crops of other farmers. The trial's own Q&A page suggests that the aphids might move to wild grasses, where they would be eaten by predators such as ladybirds and parasitoid wasp larvae. The field trial will be used to evaluate what effect the GM wheat might have on these insect communities.

If the EBF emitting wheat were ever to become a commercially available crop, then farmers could potentially use a "push-pull" method - planting an attractive crop around the wheat to 'pull in' the aphids repelled by the EBF. This could limit any potential damage of neighbouring wheat crops by the repelled aphids.

A concern raised about GM crops in general, rather than this trial in particular, is what effect do they have on the environment?

As previously outlined, a possible outcome from this research is the reduced need for pesticides to control aphids. I personally believe that the benefit to the environment gained from this would far outweigh any risks. However, in order to assess any possible risks, such as persistence of the modified genetic material in the environment, and unforeseen effects on insect communities, further research is required, which is why a farm scale field trial is so important.

This small scale field trial itself is unlikely to cause environemntal impacts beyond the trial site. It has been approved by the Advisory Commitee on Releases to the Environment (ACRE), who have advised a number of measures which will further limit any health or environmental impacts.

Another general concern about GM crops is that the GM seed market is monopolised by multinational agrochemical companies whose primary aim is to make money.

This is where this research really is special. It was funded entirely by the Government's Biotechnology and Biological Sciences Research Council, with no sponsorship from agrochemical companies. All results from the trial will be freely available and the idea has not and will not be patented. The researchers also make it very clear on their Q&A page that what they're testing is not a finished commercial product, and that as scientists they are simply looking for evidence that their technology works.

In addition to these general concerns, anti-GM campaign groups have also voiced objections to this particular field trial. They warn that the GM wheat contains a synthetic cow gene.

In order for the wheat to synthesise EBF, two genes were synthesised and put into the wheat. Niether were taken directly from other organisms. The first is most similar to the gene in mint responsible for synthesis of EBF. The second is a gene found in many organisms, including plants such as maize and tomato. The version of the gene synthesised by the scientists happens to be most similar to the version found in cows, but is also very similar to that found in plants. Therefore to refer to the gene as a "cow gene" is a little misleading.  As already said, the wheat being tested in the field trials is not a finished commercial product and the researchers have stated that "alternative [genes] would need to be used in a commercial variety that is able to produce (E)-β-farnesene" suggesting that the 'cow-y' version of the gene might not be used at all.

This also goes for objections that the GM wheat contains an antibiotic gene and a herbicide tolerance gene.

Both these genes were merely used to aid the insertion of the EBF synthesis genes into the wheat, and to check that the insertion of these genes had been successful. The antibiotic resistance gene is very unlikely to be transferred to infectious bacteria, and the herbicide tolerance gene is not being used to allow blanket spraying of the crop with herbicides, nor is it likely to confer herbicide resistance to wild grass species or nearby wheats, as wheat is self pollenating and the pollen is not easily wind dispersed.

Campaign groups also warn that the aphid repellent effects will wear off.

This doesn't surprise me. While one might hope that solutions to agricultural problems such as drought and salinity could perhaps be permanent, no scientist would assume this of a control strategy, GM or not, against living threats to crops, such as insect pests and diseases. This is because these life forms are constantly evolving new mechanisms to sidestep plant resistance, often faster than the plants can evolve new resistance strategies. The struggle between plant and pest can be seen as an evolutionary arms race, and pests that can sidestep plant defences will have a selective advantage over those that can't. This is one area where GM technology could be very beneficial; conventionally breeding a resistance trait into a commercially viable, high yielding wheat line can take many years, by which time the pest or pathogen may have already become immune to this trait. Insertion of a resistance trait into a plant using genetic modification is relatively quick in comparison, and more than one gene can be 'stacked' to give resistance to a wider range of crop pests.

On a pedantic note, the loss of responsiveness of the aphids to EBF was not shown on wheat, but rather on Arabidopsis, a little cress plant used to model crop plants the same way we use mice to model humans when studying disease. The species of aphid used was also different to the one which most commonly invades wheat. The aphids were reared on EBF emitting Arabidopsis, in the absence of natural enemies which are attracted to EBF. In order to assess whether this would indeed happen, on EBF emitting wheat, under farm conditions, in the presence of natural enemies which would be a danger to any EBF habituated aphids, a field trial is needed.

A final argument (last one I promise!) is that non-GM approaches have been effective in protecting crops  from pests/parasites, so we don't need GM.

GM freeze presents an impressive list of these non-GM breakthroughs. However, some of them, just like EBF emitting wheat, are still in the research stage. Others have led to resistance to one particular pest or pathogen, but there could be a potential cost in terms of resistance to others. However, my intention here is not to pick at the pitfalls of any of these case studies. Several of them are also funded by the BBSRC, indicating that it is willing to fund research into both GM and non-GM avenues of crop protection. This is because our best chance of protecting crops against pests, limiting chemical inputs and meeting the global demand for food production does not lie in an "either/or" approach, but rather in "both/and". It has long been agreed by agricultural scientists and farmers that the best strategy for controlling pests and diseases of crops is an Integrated Pest Management (IPM) approach, rather than focusing on one aspect of control. In my opinion the best IPM approach would use all the ecological and scientific tools available, including GM.


  1. Does the amount of EBF produced by mint vary throughout the year? I grow mint in my garden, and it's always covered with aphids in early spring.

    1. That's a very good question and you're not the first person to ask it. I'll try to find out for you over the next week or so.

    2. Peppermint doesn't produce EBF in high enough quantities to repel the aphids very efficiently, which is presumably why the researchers had to synthesise versions of the genes that would lead to sufficient EBF production to repel, rather than just copying the mint genes. Hope that helps.