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Genetically modified Bt maize: No impact on insect communities

Plant varieties, weather and farming methods affect the maize ecosystem

For three summers in a row, Eva Schultheis and her team at RWTH Aachen University caught countless insects on the maize trial field and then identified the species in the laboratory. They wanted to find out whether the insect communities found in genetically modified Bt maize are different from those found in conventional maize. They found differences between the years and between individual maize varieties, but were unable to detect any influence of the genetic modification. Extensive investigations in the laboratory with the rice leaf bug, which was chosen as a representative species, also failed to find any negative Bt maize effects. GMO Safety spoke to Eva Schultheis about her research work.

Eva Schultheis from the Institute of Biology III (Plant Physiology) at RWTH Aachen University on the maize trial field. A net was used to catch insects over a 120 m stretch per plot on three occasions during the growing season.

There were a total of 40 plots on the trial field growing four different maize varieties: genetically modified Bt maize that produces three different Bt proteins and, as a control, three conventional varieties, including the parent variety of the Bt maize (isogenic variety). The Bt maize produces three different Bt proteins, two of which target the European corn borer while the other targets the Western corn rootworm.

Sticky trap

Sticky traps: One of these traps was set up on each plot at a height of one metre in the herbaceous layer and exchanged about once a week for a period of ten weeks.

Insects being shaken from the male flowers at the top of the maize plants

Shake samples: Insects were shaken from the male inflorescences of 25 plants per plot. All the insects were placed in alcohol, taken to the laboratory and identified to species level.

A full-life-cycle test was conducted in the laboratory on insects bred in the laboratory.

Model organism: Trigonotylus caelestialium, a common mirid bug.

GMO Safety: You investigated whether genetically modified Bt maize has a harmful effect on insect communities in the maize field. The Bt maize in question produces three Bt proteins which specifically target two maize pests: the European corn borer and the Western corn rootworm. The question was whether they might also harm non-target organisms. In your research you concentrated on particular insects. Which ones were they?

Eva Schultheis: We recorded the insect community found on our trial field from 2008 to 2010 – both in the herbaceous layer and in the male inflorescences. When analysing the results, we concentrated on groups of organisms that come into contact with the Bt protein from the Bt maize, i.e. ones that feed on the plants or ones that prey on the organisms that feed on the plants and therefore ingest the proteins indirectly. We wanted to find out whether there are differences in the insect communities – both in terms of species composition and abundance. We wanted to see whether these insects are adversely affected by Bt maize.

GMO Safety: What methods did you use in the field?

Eva Schultheis: We caught the organisms we found in the maize field over a period of around ten weeks in each growing season from 2008 to 2010. To do this we used three different techniques. To trap organisms in the herbaceous layer we took samples using the net on three occasions in the year. The second technique involved sticky boards. These are A4 plastic sheets coated in non-attracting insect glue. The third technique involved shake samples. We shook the male inflorescences and caught the insects that were between the anthers and the pollen.

GMO Safety: That sounds like a lot of work. What was the reward for your efforts? What did you discover?

Eva Schultheis: In conclusion, we can say that we were unable to detect a Bt effect, in other words we found no evidence that cultivation of the genetically modified Bt maize variety had an impact. But we did discover a range of other effects. We identified a varietal effect. For many of the groups of organisms there was a difference, even at species level, in the Benicia variety, which was one of our conventional control varieties. That one was always a bit different – sometimes the results were higher, sometimes lower than the others. In addition, we demonstrated that there were differences from one year to the next. This is important if you want to define an ecological base line, for instance if you want to develop a monitoring system for approved Bt maize. Of course, differences between the years depend on the weather. We were able to demonstrate that very clearly and also show that different farming methods have an impact, e.g. field irrigation.

GMO Safety: In the laboratory you focused on a specific species – a mirid bug that you selected as a model organism. What makes this particular mirid bug a good model organism?

Eva Schultheis: Our “pet”, Trigonotylus caelestialium, a mirid bug, is interesting because it ingests the Bt proteins from the plants, which means it is to them. It is also very abundant in the field, which means it appears in large numbers. The bugs are easy to catch, simple to identify and you can keep them and breed them in the laboratory. What is particularly interesting is that this mirid bug is found almost all over the world. It is found in Canada and the USA, in Russia, in various Asian countries and in Central Europe, which means it can be used worldwide.

GMO Safety: You built up your own breeding programme with this species of mirid bug and conducted various tests on the insects in the laboratory. What were you investigating in these laboratory tests?

Eva Schultheis: First of all we caught mirid bugs in the field and brought them into the laboratory. The first step then was to establish a method of breeding them on maize. We were successful and managed to breed up to four generations per year. In a second step we conducted a full-life-cycle test, in other words, we documented the development of the bugs from egg laying to hatching and nymphal development to adult insect and egg laying again, on all four of the maize varieties we were studying.

We also conducted various feeding trials. For instance, we observed whether there are differences in feeding behaviour between varieties. To do this, we measured the area eaten by a bug each day. Then we kept the bugs on Bt maize for a while and then transferred them to conventional maize to see whether the Bt proteins in the bug stay there and accumulate or whether they are excreted again. That would be important in the food chain, if the insects were accumulating large quantities of Bt proteins.

GMO Safety: And did you notice any abnormalities?

Eva Schultheis: We did not observe any differences in the feeding experiments that investigated feeding quantities. In the feeding trials where we started by keeping the bugs on Bt maize and then moved them to conventional maize we were able to see that the Bt proteins had completely disappeared from the bugs after six hours, so we can assume that there is no accumulation of Bt proteins in the bugs that could have impacts on the food web.

In the full-life-cycle test, we investigated a number of different factors and we can say that there are differences between the different varieties. This is visible in the nymphal development time, for instance. But there is no clear effect caused by the Bt variety. Rather, the Bt variety always behaves in a very similar way to the near-isogenic variety, whereas there are differences between these and the Benicia variety and the second control variety.

GMO Safety: You also investigated whether the Bt proteins remain active once they have been ingested by the insects. Why did you do this and how?

Eva Schultheis: We wanted to know whether the Bt proteins ingested by the insects play a role in the food web. For this to be the case, the proteins would of course have to be active. This is why we took a bioassay that had been established here in the laboratory and adapted it to the target organism, the European corn borer. We then concentrated extracts from our mirid bugs and fed them to corn borer larvae. We were able to demonstrate that 17 per cent of the corn borer larvae we used in the test died as a result. So we can say that the proteins are bioactive. However, these extracts contain all three Bt proteins and only two of them are active against the European corn borer, so we would need to see where this value fits in tests with individual proteins.

In summary, we can say that the mirid bug we selected to be our representative species really is suitable as a model organism. It represents a link between the field and the laboratory and other trials with this organism could be envisaged.

GMO Safety: Thank you for talking to us.

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