Bt-Maize: No effects on organisms in water detected in field trials
Does genetically modified Bt-maize endanger water ecosystems? NABU (the Nature and Biodiversity Conservation Union of Germany) hosted a symposium on 17 December 2009 in Berlin, at which the US American ecologists Emma Rosi-Marshall and Jennifer Tank presented their new research results. Two years ago their first study on the effects of Bt-maize on caddis flies resulted in hefty political and scientific debates, particularly in Europe.
Does open water represent a "blind spot" in the safety assessment of Bt-maize? When Bt-maize is cultivated, pollen and plant material find their way into the local water systems. The criticism of the environmental and nature conservation organisations is that the possible effects of Bt-maize on the water ecosystem has until now not been adequately explored. The Agricultural Minister Ilse Aigner also justified the ban on cultivation of Bt-maize imposed by her in April 2009 on the grounds, among others, of the 2007 study by American ecologists.
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The group of Emma Rosi-Marshall (currently at the Cary Institute of Ecosystem Studies, Millbrook, NY) and Jennifer L. Tank (University of Notre Dame, Indiana) demonstrated in laboratory analyses that the larvae from caddis flies were affected by Bt protein. These insects, which live in or on water, are related to lepidopteron (moths and butterflies). Since Bt-maize forms a variant of the Bt‑protein to act against certain types of butterflies, in particular the European corn borer , caddis flies are considered to represent a suitable indicator for effects on water organisms. That an effect is seen in trial feeding in the laboratory does not prove that a particular organism, in this case caddis flies, would actually be affected in their natural habitat. Pivotal is whether the caddis flies come into contact there with the Bt-protein and whether they consume so much that they are affected. The authors of the Caddis fly study have therefore subsequently carried out field trials and have found no evidence that caddis flies are affected by Bt-maize. |
At the NABU symposium in Berlin, the ecologists Emma Rosi-Marshall and Jennifer Tank presented initial, not-yet-published results of these current investigations. They have expanded their experiment protocol to also include a third variety of caddis fly. Their original findings were confirmed: feeding with Bt-maize increased the mortality rate in one strain of caddis fly, and reduced growth rates were seen in another type.
However, again, these laboratory findings were not confirmed in the field trials, according to Rosi-Marshall and Tank in Berlin. They have examined 12 streams and drainage channels in an American maize-growing area over several years. In contrast to central Europe, 'sweet corn' is the primary maize crop in the USA. During harvesting all plant material except the maize corns themselves are left on the field. When cultivating Bt-maize, considerable amounts of harvest residues can end up, in particular, in the drainage channels.
Despite the high proportion of Bt-maize cultivated, Rosi-Marshall and Tank have up to now found no clear evidence that would indicate that the caddis flies are affected by the Bt-maize. Both scientists suspect that these drainage channels near the maize fields may be strongly polluted as a result of the intensive agricultural cultivation that this might hide the effects of the Bt-maize.
Rosi-Marshal and Tank want to publish their current finding in spring at the latest.
The working group of ecologist Christopher M. Swan at the University of Maryland has already published their investigations, made between 2004 and 2006, of the detrimental effects of Bt-maize on several areas of surface water. These included many species of animals, such as insects and various other invertebrates that are found in such water ecological systems. Swan and his colleagues could not detect any differences between Bt-maize or conventional maize with regards to either the number of species present or the number of animals of a particular species. In addition, whether Bt or other forms of maize were cultivated in the fields near these water systems had no influence on the speed and course of the microbial decomposition of plant material.
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