Comparing methods to evaluate the effects of Bt maize and insecticide on spider assemblages

In a field study, potential adverse effects of Bt maize on plant-dwelling spiders (Araneae) were assessed in 2001 in Bavaria, South Germany. Spider assemblages were recorded in Bt maize fields and conventional maize fields, with and without (pyrethroid) insecticide application. In addition, the efficacy of several sampling techniques to collect plant-dwelling spiders was tested (beating sheets, suction sampling, plant removal, stem eclectors). A total of 29 species and 14 families were identified. Juvenile spiders of the families Theridiidae, Linyphiidae, Tetragnathidae and Araneidae dominated the catch. The sampling methods differed in their capture efficiency with regard to abundance, family composition, species richness and power to detect effects. Suction samplers performed best, and are recommended for monitoring plant-dwelling spiders in maize. Bt maize had no substantial effects on species richness and abundance of spiders, whereas insecticide application reduced spider densities.