Functional biodiversity in an agricultural landscape: a floristic and syrphidologic study of Biodiversity Promotion Surfaces (BPSs)

Description of the subject. This study focuses on the vegetation and Diptera Syrphidae found in biodiversity promotion surfaces (BPSs) of the "extensive meadows" type, within an agricultural context. Objectives. The objective was to test the influence of the "size" and "botanical quality" factors of BPSs on the syrphifauna that develops there. It also aimed to highlight the relationships between vegetation and hoverflies, and to emphasize the potential for the biological control of these surfaces. Method. Twelve BPSs were selected on the basis of their size (< 3,000 m(2) vs > 9,000 m(2)) and their level of botanical quality, defined on the basis of indicator plant species. Vegetation inventories were conducted in each of the BPSs. Hoverfly sampling was carried out via the two emergence traps and one Malaise trap that were installed on each site. Results. Regardless of their size or level of botanical quality, BPSs are home to and attract mostly aphidiphagous hoverflies in the larval stage. Yellow and white flowers, as well as those producing nectar, influence the richness and abundance of hoverflies. Conclusions. The potential of BPSs to shelter and attract aphidiphagous hoverflies shows that they are able to offer a biological control service against pests in adjacent crops.