Long-term study: Cultivation of Bt maize does not affect earthworms
Earthworms are not affected by genetically modified Bt maize even after several years of cultivation. In a 4-year study, ecologists from the USA and Switzerland have investigated the effects of different Bt maize lines on the earthworm populations. For most of the four earthworm strains that were present in the test fields it was irrelevant whether Bt or conventional maize was growing on the trial area. To validate these results, however, the researchers suggest that the investigations should be continued using other earthworm strains.
Earthworms play an important role in maintaining soil fertility. They help to decompose plant remains in the soil and on the surface and to loosen the structure of the soil. With their study, scientists from the University of Minnesota, together with colleagues from the Universities of New York (USA) and Neuchtel (Switzerland), wanted to obtain additional information on the possible effects of Bt-maize on earthworms.
Earthworms can take up Bt proteins through ingesting plant remains and from Bt protein-containing secretions of the maize roots. In the USA, Bt maize varieties are grown on 57% of the area under cultivation.
Up to now the results of nine laboratory studies and four field trials are available that predominantly show that these animals show no impairment through Bt maize cultivation. In two laboratory studies, however, slight negative effects on the earthworms were observed. The animals grew somewhat more slowly. The effect first occurred only after a test duration of about 200 days.
If this result were confirmed, it could lead in the long term to a reduction in the number of earthworms. Therefore, the American-Swiss research group wanted to monitor how several years of Bt maize cultivation affected the earthworm populations. The results have now been published in Soil Biology and Biochemistry.
In the field trials, three Bt maize varieties that contain the Bt toxins Cy1Ab and Cry3Bb1 were compared with non-genetically modified original lines. One variant of the Bt protein is directed against particular butterflies, and the other against the corn root borer , a destructive beetle. This protein is formed in comparatively high concentrations in the roots of the maize and from there enters the soil.
Within each of the 1600 m2 test areas, four types of earthworm were found, three strains of the genus Aporrectodea and the common earthworm (Lumbricus terretris).The scientists measured the biomass of the different developmental stages of the earthworms. No significantly significant differences were seen between the areas with Bt maize and those under conventional maize.
However, the researchers recommend further studies since, depending on the area in the USA, Europe or other areas, different types of earthworms could be present in the maize fields. Therefore, before cultivation, laboratory tests should be carried out to determine whether the strains found in that region could be in principle impaired by the Bt toxins.
Article courtesy of www.gmo-safety.eu
The authors of the study are scientists who have been concerned for a long time with the question of the effects of genetically modified plants on the soil and the organisms living there. Dr. David Andow (University of Minnesota, photo) has also worked for the Federal Agency for Nature Conservancy. In 1999, Prof Guenther Stotzky (University of New York), another author of this study published an article in Nature showing that Bt proteins are secreted by the roots of the Bt maize into the soil.
