Staphylinidae and Carabidae overwintering in wheat and sown wildflower areas of different age.

Species richness and abundance of staphylinid and carabid beetles overwintering in winter wheat fields and 1- to 3-year-old wildflower areas were investigated during 2000/2001 on 16 study sites in Switzerland. Abundance and species richness of overwintering staphylinids significantly increased with successional age of the wildflower areas and were always higher in older wildflower areas than in winter wheat. A similar but less distinct pattern was observed for the abundance and species richness of carabid beetles. The influence of habitat parameters (vegetation cover, fine sand content, organic matter, pH, soil pore volume, surrounding landscape structure, habitat area) on the staphylinid and carabid assemblages based on the number of individuals per species and site was analysed using canonical correspondence analysis. Vegetation cover was the most significant parameter significantly characterizing both staphylinid and carabid assemblages. The amount of vegetation cover explained 15.7% of the variance, fine sand content accounted for 13.3% and surrounding landscape structure for 10.9% of the variance in the staphylinid assemblage. In the carabid assemblage, vegetation cover was the only significant factor, explaining 24.7% of the variance. This study showed for the first time that the significance of wildflower areas as a reservoir for hibernation for generalist predatory beetles increases with progressing successional age.