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Genetic engineering in the conflict of contradictions

Farmers in Germany can use Bt-maize to combat the European corn borer and will most likely soon be able to use this genetically modified maize variety against the Western corn rootworm as well. The history of Bt-maize is a strange mix of opportunities, risks, scientific contradictions, market authorisations and recalls. It is also an excellent example of why the public scepticism towards genetically modified organisms (GMO) is growing.

Western corn rootworms are devastating maize pests. (Photo: Mihaly Czepo/biosicherheit.de)
German farmers received some very bad news on the 23rd July 2007. A Western corn rootworm (Diabrotica virgifera virgifera) specimen was discovered close to the city Lahr in Baden-Württemberg. The dreaded pest had finally reached Germany. This beetle feeds on the leaves, pollen and seeds of maize plants; its larvae bore into the plants’ roots and stems. The plants break, interrupting the transport of water and nutrients, and the plants eventually die. Such damage might lead to a crop shortfall of up to 30 per cent.

The USA produces the largest quantities of maize worldwide, amounting to approximately 320 million tons in 2008. The economic damage caused by the Western corn rootworm in the USA amounts to approximately 800 million US dollars per year. Experts estimate that in future the Western corn rootworm in Germany could cause around 25 million euros’ of damage.

Severe damage is also caused by European corn borers

Inconspicuous in appearance but highly dangerous for corn cultures: European corn borers. (Photo:Dr. R. Kaiser-Alexnat/BBA Darmstadt)
So far so bad. The Western corn rootworm is not the only pest that affects corn crops in Germany. When European corn borers (Ostrinia nubialis) infest corn fields, a loss of 50 per cent of the corn harvest may result. The larvae of the butterfly start to bore into the stalks and move into the lower stem sections and roots for hibernation. The devastating action of the larvae leads to broken stalks, damaged roots, spoilt corn ears even before the corn matures.

In southern Germany, the European corn borer is an old acquaintance that is now spreading across large areas. The example of Bavaria shows that at the beginning of the 1980s, the European corn borer was only found in two small areas close to Deggendorf and Würzburg. In 2005, the insect had already infested 180,000 hectares of the entire maize cultivation area in Bavaria (416,000 ha).

The European corn borer is also widespread in Baden-Württemberg, where it is present on approximately 41 per cent of all cornfields. In 2007, the corn borer was found in 27 out of the 28 collection sites between Lake Constance and Odenwald region. Over the last few years, the corn borer has spread into other areas - for example in 2004, it was discovered in the north east of Germany, and in 2006 in Lower Saxony.

Bacterial proteins to combat the pest

Genetically modified corn varieties produce a protein that is toxic for European corn borer larvae. (Photo: Dr. R. Kaiser-Alexnat/BBA Darmstadt, biosicherheit.de)
European corn borers have not only become known as destroyers of plants. They have gained even greater publicity because of the efforts to engineer genetically-modified maize (Bt-maize) to combat these insects. The letters Bt stand for Bacillus thuringiensis, a small bacterium, just two to five micrometres long, used by organic farmers worldwide as a biological insecticide. A specific Bt gene is inserted into the maize to produce a protein which is toxic for the larvae of the corn borer. Approximately 50,000 different Bt strains are known, many of which are able to produce Cry, a protein that is toxic for some insect larvae. 169 protein variants are known; some of these variants are species-specific.

Plans existed to exploit the species-specific toxicity of the Bt strains by introducing the gene of a specific Cry protein into corn plants. The method works and the genetically modified Bt-maize produces high enough quantities of the toxin to kill approximately 98 per cent of the European corn borer larvae.

Risk debate

However, the new technology has also received criticism, in particular from conservationists, organic farmers and consumer associations. The Bacillus genes and hence the Cry proteins are not restricted to specific plant segments, but are present in the cells of the entire plant, including pollen cells. Maize pollen is mainly distributed by the wind. This might lead to the risk of the foreign genes being transferred to conventional, i.e. non-genetically modified maize varieties. This might have far-reaching consequences. Opponents of Bt-maize cultivation believe that this will facilitate the uncontrolled spread of the Cry protein genes.

As this gene enables maize plants to fight off European corn borers, the genetically modified plants have a selection advantage and might be able to displace conventional maize varieties. For opponents of genetic engineering, the undisturbed coexistence of conventional and genetically modified plants is unfeasible since they believe it impossible to prevent the transfer of genes between the plants.

Coexistence but with a great distance between the corn varieties

Scientists are carrying out coexistence investigations in order to analyse the potential of the unwanted transfer of the Bt genes between neighbouring fields with traditional and GM plants. This is done by cultivating a central area with Bt-maize, which is surrounded by fields with conventional maize varieties. After the vegetation period, molecular genetic methods and selection experiments are used to assess the proportion of genetically modified traits (outbred plants) in the surrounding (conventional) maize fields.

Back in 2000 and 2001, the Julius Kühn Institute in Braunschweig dealt with the problem by carrying out coexistence trials. Project leader Dr. Joachim Schiemann and his team found out that the proportion of outbreds accounted for less than one per cent no more than 10 metres from the original GM maize field.

Other field trials in 2004 and 2005 showed that a distance of 75 metres was sufficient to be far below the legal threshold limit of 0.9 per cent. If food contains more than 0.9 per cent of genetically modified organisms, it must be declared as “genetically modified”. In many investigations, for example in the field trials carried out in Bavaria in 2004, the maximum permissible value was already achieved at distances around 20 metres from the GM plants.

Protective barriers, wind and crops

Further investigations have taken account of the influence of additional hemp, barley, wheat or ryegrass plantings. Areas that are planted with other plants might lead to different micro-climatic conditions and which might also favour the flight of corn pollen. The cultivation of conventional maize varieties to shield the Bt-maize fields might affect the outbreeding frequency. Such protective areas act as a barrier and also increase the proportion of genetically unmodified pollen during pollen flight phases.

In 2005, the Bavarian Agricultural Research Institute carried out such coexistence trials at four sites in Bavaria. The final report recommends a safety margin of 100 metres between Bt-maize and conventional maize fields.
Investigations carried out in Forchheim in 2006 led to similar results. The scientists collected corn seeds at approximately 300 sites in a conventional maize field and counted the seeds that carried the Bt gene. The researchers showed that the maximum permissible value of 0.9 per cent was achieved at a distance of 100 metres. A distance of 150 metres is sufficient to reduce the proportion of Bt-maize in bordering conventional maize fields to below 0.1 per cent.
Experimental setup of the coexistence trial in Forchheim in 2006 and 2007. Genetically modified maize was cultivated in the yellow framed area labelled ‘Donor’ (left); conventional maize was planted in the large area to the right. In between these two are
Experimental setup of the coexistence trial in Forchheim in 2006 and 2007. Genetically modified maize was cultivated in the yellow framed area labelled ‘Donor’ (left); conventional maize was planted in the large area to the right. In between these two areas there were zones of different size that were planted with crops. The green arrow indicates the prevalent wind direction. (Photo: LTZ Augustenberg)
It is not only the direction of the wind, surrounding plants and distance between the fields that lead genes from genetically-modified maize to get into the genome of traditional varieties. An important parameter, which is often not taken into account when discussing outbreeding (arising from gene flow from GM to non-GM plants), is the limited fertilisation capacity of maize pollen. In terms of propagation, maize is under time pressure. Once the maize pollen has been released, it is only able to fertilise female plant parts for a limited period of time – this is assumed to range from between a couple of minutes to half an hour.

Coexistence of maize seems possible

Based on these facts it can be assumed that the coexistence of different cultivation forms (GM, traditional and organic) is possible if specific distances are observed, at least as far as maize is concerned.

In the amendment of the German Genetic Engineering Law of 25th January 2008, the German Bundestag paved the way for easier cultivation of GM crops. If the Bundesrat agrees, then Germany will set the distance between GM crops and conventional crops at 150 metres and 300 metres will be required for the coexistence of GM and organic crops.

Toxin specificity is controversial

The opponents of genetic engineering have further reasons to oppose genetically modified maize. The Bt toxin produced by Bt corn plants is said to only affect certain animal species, but it still remains to be clarified whether its specificity is high enough to affect only the European corn borer. Moreover, care must be taken not to let the toxin reach the food chain by way of predator-prey relationships and thus damage other species. This possibility was investigated on green lacewing larvae who feed, amongst other prey, on European corn borers. The results of the investigation are not consistent, but it cannot be excluded that the Bt toxin has a potential indirect effect on green lacewing larvae.
An ichneumon fly (right) hatching from an aphid mommy. Since European corn borers can also be infested by ichneumon flies, they might potentially also be damaged by Bt maize. (Photo: Dr. Jörg Leopold, University of Göttingen, biosicherheit.de)
The parasitic interactions between European corn borers and other animal species are also of great importance, for example for ichneumon flies that lay their eggs in the clutch of European corn borer eggs. If the corn borer becomes extinct locally or regionally, this might also have consequences for ichneumon flies. Such ecological and eco-toxicological issues need to be clarified before genetically modified organisms such as Bt-maize are planted in fields.

According to Greenpeace, there are several scientific studies which suggest that the Bt toxin also puts at danger butterfly species such as peacock butterflies and swallow-tails, but also earthworms, sciarids, green lacewings, honeybees and threadworms. The situation is difficult to judge, because other studies claim that the Bt toxin does not endanger species other than the European corn borer. For three years, Prof. Ingolf Schuphan coordinated a research alliance investigating eleven research projects dealing with the potential effects of Bt-maize on species diversity. The scientists examined approximately one million beetles, spiders, bugs, cicada, larvae and microbes. In an interview with “biosicherheit.de” Schuphan concluded: “If Bt had effects on the agro-biodiversity, then these happen by chance and are so small that they can hardly be distinguished and such variations will stabilise with time.

Low toxin concentrations in the soil

ELISA tests are used to determine the Bt concentration in the soil. (Photo: biosicherheit.de)
But what happens to the Bt toxin once it has killed a European corn borer? Researchers at the Julius Kühn Institute dealt with this issue and investigated the concentration of the Bt toxin Cry1Ab of the genetically modified corn variety MON810 in different plant parts and in the soil. Cry1A is a Bt toxin that specifically affects European corn borers. In the soil, close to the roots, the scientists measured a maximal Cry1A concentration of 1.9 nanogrammes per gramme of dried soil.

After the harvest, Crya1A concentration in roots amounted to three to eight microgrammes, which is more than a thousand times higher compared to the concentration measured in the soil. It seems that only a small proportion of Bt toxin gets into the soil surrounding the roots. However, the project leader, Christoph Tebbe, points out that the statements derived from the Cry1Ab measurements are only valid for this particular toxin and cannot yet be transferred to other Bt toxins without further clarification.

Alternative methods

The fight against the corn borers is not new for the farmers in Germany. Over the years, several strategies have been developed to reduce the devastating effects of corn borer attacks on maize fields. The Bt toxin, considered safe to humans, mammals and most insects, has been a popular pesticidal spray since the 1960s. Bt toxin is approved for corn borer treatment because the chance of unintended side effects arising are low. The toxin is destroyed by UV light and is hence only effective for a short time once sprayed over the plants.

European corn borer populations can also be reduced by their natural enemies such as Trichogramma ichneumon flies. The use of these flies is however very time-consuming as it is necessary to apply the flies manually at exactly the right time.

Insecticides are the most popular agents used and are associated with certain risks. Ploughing the soil after the harvest is another effective option. This destroys the larvae which have retreated into the roots for hibernation.

Scientific investigations have focused on the efficiency of the aforementioned methods. The scientists found that Bt-maize varieties and ploughing are the most effective. On average, these two methods helped protect 98 per cent of the plants. Insecticides are 84 per cent effective, biological treatment with Trichogramma saves 68 per cent of the plants. Bt toxin, which is sprayed onto the plants, protects approximately 30 per cent of the maize plants.
This shows that there are effective possibilities to combat European corn borers without Bt-maize. However: “The decision on which method is chosen depends on the many pros and cons,” said Dr. Ulrich Kraft from the Agricultural Technology Centre Augustenberg, adding that “it is necessary to ascertain which undesired effects a chemical pesticide has compared to Bt-maize, and what effects ploughing on hillside fields, for example soil erosion, may have.”

Authorisation withdrawn

Should we therefore go for Bt-maize? There is definitely no general consensus on this question. The uncertainty about negative ecological side effects and open questions relating to the effects on organisms, has led to political action against this maize variety in recent years.

On 3 May 2007, the Federal Office for Consumer Protection and Food Safety announced that MON810, a Bt-maize variety produced by Monsanto, must no longer be sold. Monsanto had to present a plan in which potential environmental effects of MON810 could be assessed. Only when Monsanto presented its monitoring plan in December 2007, could MON180 maize again be approved for sale.

In autumn 2007, the French government delayed the authorisation for cultivating MON810 maize. A committee, which was put in place by the French government, dealt with the scientific facts and concluded that there “are open questions related to the effect of the cultivation and trade of MON810 on the environment, health and economy”.

The list of open questions will become longer because the seed producers are applying for the marketing authorisation to grow a number of genetically-modified varieties - for example in Germany, Bt-maize varieties against the spreading European corn borer. This is the same plant, but equipped with a different Bt toxin gene. For the consumers this means that the concerns about the safety of genetically modified plants will further increase. Based on current knowledge, it is impossible to transfer the research results gained with certain plants and Bt toxins to other plants and toxins. The maze of contradictory scientific findings and their interpretation is becoming more obscure, the greater the number of genetically modified plants that become available. It is clear that those convinced of the benefits of genetically modified maize still have a battle on their hands to win over those with a more sceptical attitude.

chb - 26.02.2008
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