Habitat management in calcareous grasslands: effects on the insect community developing in flower heads of Cynarea.
The phytophagous insect communities dwelling in the flower heads of Cirsium acaule and Centaurea scabiosa were studied in mown, sheep-grazed and abandoned calcareous grasslands in Germany. Phytophagous species developing in the stemless Cirsium acaule were not affected directly by mowing or grazing, but by changes in microclimate due to habitat management. The community in Centaurea scabiosa was affected both directly by the removal of flower heads and indirectly by changes in microclimate. The responses of the particular insect species to management were not uniform and depended mainly on life-style and habitat preferences. Mowing reduced species packing and mean densities for a number of univoltine species on C. scabiosa compared with abandoned or sheep-grazed sites. Bivoltine species were only slightly affected. Most species were most abundant in abandoned sites, but 2 species had their focus in mown and sheep-grazed sites. In Cirsium acaule, no differences in species packing were found between managed and unmanaged sites. The densities of the most common species were affected inversely, with the fly Tephritis conura being more abundant in abandoned sites and 2 weevil species (Larinus spp.) more abundant in managed areas.