Effects of Bt-corn decomposition on the composition of the soil meso- and macrofauna

Genetically modified Bt-corn is able to fight main insect pests on corn very specifically and currently varieties against the European corn borer (Ostrinia nubilalis) and the Western corn rootworm (Diabrotica virgifera virgifera) are available. A transgenic corn plant, however, expresses not only Bt-proteins, it also differs from the near-isoline in the amount of major plant components such as cellulose or lignin which in turn affect the degradability of dead plant material. In a 9 months litter bag field study we therefore investigated the decomposer community on decaying leaf material for nine corn varieties (2x Cry1Ab, 1x Cry3Bb1, their untransformed corresponding near-isolines and three conventional varieties). Monthly the degradation of leaf material was analysed and the meso- and macrofauna was extracted. Nearly 67% of the decomposer community consisted of Collembola, Acari contributed 24% and Clitellata 6% to the total abundance of animals. Twelve taxa of other arthropods added less than 4%. All corn varieties were likewise used as food resource by decomposers, thus the Bt-proteins obviously did not affect the soil organisms. Decomposer communities and degradation speed did not differ between the nine corn varieties, thus there was no evidence for any effect related to the genetically modification or any variety effect at all.