Streuungen von Bodenfallenfängen der Spinnen in konventionellen und Bt-Maisfeldern und ihr ihr Einfluss auf die Bewertung des guten ökologischen Zustandes

Variation of spider pitfall trappings in conventional and Bt maize fields and its uses for the evaluation of a good ecological state A study on the influence of Bt maize cultivation on non-target arthropods delivered long-term data on-spider pitfall trappings. In 2000-2007, data of 23 field-to-field comparisons of conventional/ isogene maize (KV) and Bt maize (BT) were accumulated (2000-2001: 1 per year, 2002-2004 : 2 per year, 2005-2007: 5 per year). Each data set contains the catches of two fields with 6 pitfall traps each over a period of 4 weeks starting on BBCH 61 . Statistical analysis was based on the sums of spider communities. The species presenting the highest activities were Oedothorax apicatus and Erigone atra. Analysis started by establishing variations (standard deviation, coefficient of variation) and means within the KV and BT sampIes. Variation within the fields (n=6) was low and between the years of study significantly higher than variation between KV fields or BT fields within any given year. A corridor of a good ecological state was defined using the 10% and 90% quantile variation of KV in the years 2001-2007. This led to a three steps model which evaluates the influence of Bt maize on non-target arthropods. The model incorporates the variation in KV as well as a significance test of KV and BT. Spiders are used as indicators for non-target organisms.