Mar 17, 2003

Research Maize

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Strategies against the Western corn rootworm

Western corn rootworm in Europe

The Western corn rootworm was brought to Europe at the start of the 1990s. Since then it has been spreading inexorably and is becoming a problem. To combat the pest, a genetically modified maize plant was developed which has already been approved in the US. Is it also a sensible control strategy for Europe? GMO Safety spoke to Stefan Vidal of the University of Göttingen. He coordinates an EU project dealing with the spread of the Western corn rootworm.

GMO Safety: Mr Vidal, how do you think things will go from here? Do we need to be worried that the Western corn borer will continue to spread in Europe despite the quarantine measures?

Vidal: Yes, definitely, because we don’t yet understand how the Western corn rootworm reached e.g. France and Italy. There are two different dispersal mechanisms – the continual spread from the original focus of the dispersal in Southern Europe in all directions, to Austria via the Danube and then to Bavaria via Passau. Spreading via this route, it is this region of German that it should appear in first. There is also erratic dispersal, which was identified last year e.g. in France, near Paris. From there there will be a concentric dispersal in all directions, so that we can also expect the pests to invade Baden-Württemberg via Alsace. In a few years, maybe even sooner, the Western corn rootworm will settle there too. And finally there is another development in the direction of the Czech Republic, so we can expect to see the beetle in Eastern Germany, Poland and neighbouring regions in the foreseeable future.

GMO Safety: This new Bt maize from Monsanto is, of course, a product for the American market. Do you see this control strategy as a sensible one for Germany too?

Vidal: Yes, definitely, because we can assume that the densities and the damage caused by the Western corn rootworm in the US can also occur in intensive maize cultivation areas in Europe. This will affect certain regions, again e.g. on the Danube in Bavaria, in Baden-Württemberg and in the Tecklenburg region. Various strategies that we have run through show that when maize is grown continually the only sensible strategy is chemical control or the use of transgenic maize.

GMO Safety: That goes against the opinions of some who are saying that maybe just differences in farming practice – more rotation, different crop sequences – are enough to reduce damage.

Vidal: In regions where maize is not grown intensively we have, I believe, fewer problems than in the US. But the regions I have just mentioned are precisely those regions in which we grow one maize crop after another, in some places for years, and this is where there will be problems. Some farmers here will not be able to switch to rotation at all. And there is another point: in Baden-Württemberg there are seed-growing regions, and here too there will be serious problems if the Western corn rootworm makes an appearance.

GMO Safety: There are reports, which sound very interesting, that the Western corn rootworm has adapted to crop rotations, for instance laying eggs in fields of soya on which maize will be planted the following year. What do you think of such speculations?

Vidal: Those aren’t speculations – those are facts, but once again from the US. So far we don’t have this farming practice in Germany, and probably won’t adopt it, but soya is already planted after maize in Italy. If we had this biotype of the beetle, the Italians would face serious problems. The data so far, however, shows that this biotype is not found in Europe.

GMO Safety: Let’s turn to the issue of resistance development. The new Bt maize from Monsanto contains much less Bt toxin than the Bt plants designed to combat the European corn borer. Do you think this is likely to have consequences for resistance development?

Vidal: Yes, the discussions that were held at the EPA, the US licensing authority, because of the lower toxin content in MON863 are about precisely this problem – that resistance is more likely to develop with low-toxin variants than with high-toxin variants like MON810. This led to a discussion in the scientific advisory panel on how large the refugia should be. The EPA has now proposed 20 percent and, to start with, has set this as the size for the next few years. But there was a minority view that proposed asking for 50 percent.

GMO Safety: What is your opinion? Is 20 percent enough or would 50 percent have been not only better but also necessary?

Vidal: For the American situation, with very intensive monoculture-like maize cultivation, I have reservations that a size of 20 percent may not be sufficient to prevent the development of resistance. The Western corn rootworm is a very flexible herbivorous insect which has been able to adapt to a wide range of different cultivation conditions, so I have doubts as to whether it will actually be possible to prevent resistance problems in the US in future. In Europe, where maize cultivation is much more fragmented, I don’t believe a 50 percent rule is necessary.

GMO Safety: One last question: Do you believe that Monsanto intends to have this Bt maize variety approved for Europe as well?

Vidal: Yes, absolutely.

GMO Safety: Many thanks for talking to us.