Spider communities in Bt. maize and not genetically modified maize fields

Investigations on spider communities in maize fields were conducted in Oderbruch (Brandenburg) and near Halle/S. (Sachsen-Anhalt) in 2000 and in the Oderbruch landscape alone in 2001. Pitfall traps (10 per field) were used to perform a field-by-field comparison in neighbouring commercial and Bacillus thuringiensis (Bt.) maize fields (cv.: 'Novelis 270'). The Oderbruch landscape is permanently infested with the European corn borer (Ostrinia nubilalis), whereas the occurrence of this pest at the site near Halle/S. is moderate. Oedothorax apicatus and Erigone atra were dominant species in all of the fields, E dentipalpis only in Halle (2000), Meioneta rurestris and Pardosa agrestis in Oderbruch (2000) and Porrhomma microphthalmum in Oderbruch (2001). Data on the stability and diversity of the spider populations were collected based on O. apicatus, a dominant member of the carnivorous arthropod community, and on the level of a functional group (Araneae). The data were interpreted based on quantitative (activity levels) and qualitative variables (species number, dominance structure, diversity, red list species). The 2-year data did not reveal any clear signs of effects related to Bt-maize growing. On the other hand, the spiders proved to be good indicators of the ecological impact of insecticide use.