Influence of farming system on ground beetle communities at local and landscape scales

The beneficial effect of organic farming on the abundance and species richness of auxiliary communities (i.e., communities of organisms providing ecosystem services as pest regulation) in agroecosystems has been repeatedly evidenced. However few studies have intended to characterize its actual contribution in terms of natural enemies’ production. In this study, we carried out an analysis of the abundance and species composition of carabid beetles communities in fields managed according to the rules of organic and conventional farming. We aimed at identifying the relative contributions of the two farming systems to the production of auxiliary ground beetles at local and landscape scale. Twenty winter wheat fields (Triticum aestivum) were selected in Brittany (west of France), ten managed under organic farming and ten under conventional agriculture. In each fields, pitfall traps and emergence arena were installed to sample, respectively, circulating(including both individuals having overwintered in field and individuals having immigrated from the surroundings of field)and emerging (individuals having over wintered in field) individuals in those fields. Analyses of the samples showed that the structure of carabid communities was mainly driven by the type and availability of food resources. Results suggest that organic farming rather act as a sink than as a source in spring because of its attractiveness for carabid beetles. However, the best quality of habitats provided by organic crops in spring and probably also by marginal areas associated with this system throughout the year, probably contributes to make organic farming a source at other periods of the year and at the scale of multiannual dynamics.