Spider communities in Bt maize and conventional maize fields

Investigations on spider communities in maize fields were conducted in Oderbruch (Brandenburg, Germany) from 2000 to 2002 and near Halle/Saale (Saxony-Anhalt, Germany) in 2000. Pitfall traps (10 per maize variety) were used to compare spider communities in Bacillus thuringiensis (Bt), isogenic and conventional maize. The collected data were analysed using canonical community ordination (CANOCO). In addition, species were classified into wandering and web-spinning spiders, because the latter are thought to be more exposed to Bt pollen. In all fields the spider coenosis was composed of species typical for open-land habitats (e.g. Oedothorax apicatus, Erigone atra, Pardosa agrestis). Web-spinning spiders, dominated by Linyphiidae, accounted for more than 90 per cent of the catches. No negative effect of Bt maize was observed on web-spinning spiders, as their abundance was similar in all three maize varieties. Ordination analysis showed that maize variety had no impact on the spider community while other factors such as field characteristics and yearly changing environmental conditions were of great importance for community composition.