Small-scale microcosms to detect chemical induced changes in soil nematode communities — Effects of crystal proteins and Bt-maize plant material

Small-scale laboratory microcosms (30 g soil in 50 ml tubes) were evaluated for their suitability to assess the impact of chemicals on in situ soil nematode communities. For this purpose, appropriate conditions in the microcosms were explored to ensure stable conditions and a homogenous distribution of the nematodes. Then, the microcosms were used to assess the toxicity of insecticidal crystal proteins (Cry1A.105, Cry2Ab2, Cry3Bb1) present in genetically modified maize (MON89034 × MON88017) on in situ nematode communities. Highly abundant and genus rich nematode communities could be maintained over a period of 12 weeks. Due to a low variance between the replicates of the treatments, low detection limits could be achieved. Using meaningful stress indices, such as the maturity indices, the microcosm study revealed dose-dependent effects of the insecticidal Cry proteins that could be verified as toxic effects by comparing with effects of two positive controls (Cu, nematicidal Cry5B). Moreover, toxic effects could be differentiated from organic enrichment effects that were induced by the addition of plant material. With a NOECCommunity of 0.1 mg kg− 1 dry wt, the nematode communities reacted considerably more sensitive to the Cry proteins than a single-species nematode toxicity test (NOEC: 29 mg l− 1). The small-scale microcosm set-up turned out to be a suitable, low-budget tool for assessing the toxicity of chemicals on soil nematodes on community level, representing a link between single-species toxicity tests and large scale outdoor mesocosms.