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NABU study

Bt maize pollen: a threat to nature reserves?

According to Germany’s Berliner Zeitung newspaper, in the future the German state of Brandenburg is to specify a minimum separation distance of 800 metres between fields of genetically modified plants and nature reserves. The environment ministry plans to agree corresponding recommendations with the farmers’ union. In February NABU, the German Society for Nature Conservation, had called for a 1000 metre separation distance to protect particularly rare butterflies from transgenic plants.

Cabbage white
Bt maize produces a protein which is effective against its chewing pest, the European corn borer. Since the corn borer is a moth, other moths or butterflies could also be at risk.

Distance from field edge Average pollen/ cm²
1 m 120
10 m 35
100 m 9.7
300 m 5.3
500 m 4
1000 m 2.8

BfN study: In a study commissioned by the Federal Agency for Nature Conservation, pollen drift was measured at different sites in Germany and Switzerland. At around a thousand metres the predicted value with a confidence interval of 95% lies between 0.32 and 24 grains of pollen/cm2, with an average of 2.8 grains of pollen /cm2.

As well as artificial pollen traps, NABU also uses honey bees as natural pollen collectors in its investigations.

The state of Brandenburg’s proposals regarding general requirements for separation distances from nature reserves comes in response to a lengthy legal dispute between the authorities and a farmer who had planted genetically modified Bt maize in a nature reserve in the district of Märkisch Oderland. Permission to grow the maize was eventually refused and the crop was destroyed.

In March the Ministry for Rural Development, Environment and Consumer Protection, in conjunction with the regional farmers’ association, issued a ‘joint position’ on plant genetic engineering, in which they advise farmers to contact the relevant local nature conservation authority in good time so that any nature conservation concerns can be identified. The joint position states that it is not possible to make cultivation recommendations at this stage because of the liability provisions, which represent a one-sided risk for German farmers.

With almost 2000 hectares under cultivation (46% of the German total), Brandenburg has more fields and bigger fields of genetically modified Bt maize than any other federal state in Germany.

NABU study: ‘Significant maize pollen contamination’

NABU is basing its separation distance of 1000 metres on the results of a study which it conducted in summer 2007 at the request of the Brandenburg State Office for the Environment. From mid July until early August 2007 the transfer of maize pollen to the Ruhlsdorfer Bruch nature reserve was measured and evaluated using pollen traps. ‘Significant’ maize pollen levels were found at all the measuring locations in the reserve. During the flowering period up to 175 grains of pollen/cm2 were recorded in the neighbouring area, and as much as 10 grains of pollen/cm2 at a distance of 120 metres. The share of Bt maize pollen in the pollen samples at the various pollen trap locations ranged from 7 to 44%. The possibility of butterflies coming into contact with Bt maize pollen at a distance of 100 metres cannot be ruled out, claims NABU.

According to an expert assessment at different sites in Germany and Switzerland carried out on behalf of the Federal Agency for Nature Conservation, maize pollen can be found in pollen traps even at distances of a thousand metres; on average 2.8 grains of pollen/cm2.

On the basis of these figures, NABU concludes that there is a potential threat to species diversity in nature reserves, although their reasoning is not fully understood. They simply refer to the results of a study conducted by researchers at the Federal Biological Research Centre for Agriculture and Forestry (BBA) (renamed the Julius Kühn Institute (JKI) in 2008). The study, which involved feeding Bt maize pollen to caterpillars, showed that the larvae of the diamond-back moth and the cabbage white and peacock butterfly were susceptible to pollen from Bt176 maize. However, MON810 maize, which is the variety approved for cultivation, produces significantly less Bt toxin in the pollen than Bt176. Correspondingly, the diamond-back moth (the most sensitive species) showed no indication of harm when fed with pollen from the MON810 strain, even at rates of 80 grains of pollen per caterpillar. The researchers refer to further studies in which no effects were found when different species of butterfly were fed with MON810 pollen. They conclude that “These studies indicate that the toxin concentrations in the pollen from the transgenic maize strain MON810 are generally so low that Bt-sensitive larvae are not noticeably harmed, even when they consume large quantities of the pollen”.

Various safety research projects with MON810 have investigated the potential effects on caterpillars in land adjacent to maize fields, and have found no effects so far. The survival of the caterpillars in the field depends on a range of natural and agricultural factors. Bt pollen is just one of many.

Honeybees: natural pollen collectors

To investigate the extent to which bees from the nature reserves visit maize fields to collect pollen, two bee colonies each were set up at two sites in the nature reserve. To record the maximum transfer rate, two bee colonies were also established in the adjacent maize growing area. Evaluation of the pollen sacs revealed that maize pollen made up 0.1 to 0.3 percent of the total amount of pollen gathered by the bees. In turn, Bt maize pollen made up between 3 and 49 percent of this tiny quantity of maize pollen. Considering that, according to a Swiss study in 2006, only around 2.5% of the bee larvae’s total protein requirement comes from pollen grains, it is unlikely that Bt pollen will have a harmful effect on bees.