London (27.12.11) – In an extensive interview, Mechthild Schuppener of RWTH Aachen University noted that there was no risk to small tortoiseshell (Aglais urticae) and peacock (Inachis io) butterflies from genetically modified Bt maize and that the pollen quantities leading to higher mortality rates in caterpillars in the laboratory were not detected in the field (1).

Using two species of butterflies common on cultivated land, whose caterpillars develop during the flowering period of maize, the workers in Aachen found in laboratory experiments that the caterpillars were indeed sensitive to Bt-maize pollen applied to pieces of stinging nettle leaves, the only type of plant on which the caterpillars feed.

Recognising that there had been little reported information on maize varieties producing more than one Bt protein, the scientists set up experiments to test the possibility of any reinforcement from combined effects; they reasoned that the two proteins could have a cumulative effect.

The caterpillars were indeed sensitive under laboratory conditions, with effects observable at pollen densities of 200-300 grains per sq cm; the higher the pollen doses, the great the effect on the caterpillars. At 1,000 grains per sq cm, the mortality of caterpillars fed pollen from GM-maize was much higher than those on pollen from conventional strains.

Pollen traps set up around maize fields showed that the pollen densities fell rapidly with distance from the maize plants. Right up against the maize field margin, while occasional stinging nettle leaves showed pollen grain densities as high as 200 grains per sq cm, these were isolated instances, with the average density being of the order of only around 30 grains per sq cm. Moreover, the pollen traps had sticky surfaces but stinging nettle leaves are not sticky so that maize pollen is rapidly blown off or washed away by rain.

The Aachen group also looked at two different agricultural landscapes (2): one region in which a lot of maize is grown and another with little. In each case some caterpillars of the small tortoiseshell and peacock butterflies were found during the maize-flowering period, in regions in the vicinity of maize fields and others flourishing a long way away. Thus, while individual caterpillars were exposed to maize pollen, others had no contact with it.

With observed field effects so much less than those in the laboratory, the authors were confident that the risk to the butterflies from this type of Bt-maize is negligible.

Sources:

1. No risk to butterflies from genetically modified Bt maize. GMO Safety (21.9.11) (http://www.gmo-safety.eu/results/1346.butterflies-genetically-bt-maize.html)

2. Mechthild Schuppener, Alan J. Slusarenko & Stefan Rauschen (25.5.10). Potential effects of pollen from stacked Bt maize on non-target Lepidoptera in agrarian systems. Nature Precedings (http://precedings.nature.com/documents/4491/version/1)

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