Pollinator-friendly management does not increase the diversity of farmland bees and wasps

In order to reverse declines in pollinator populations, numerous agri-environment schemes have been implemented across Europe, predominantly focused on increasing the availability of floral resources. Whilst several studies have investigated how bees and wasps (aculeates) respond to management at the scale of the scheme (i.e. within the flower patch) there has been little assessment of how schemes affect diversity at the farm scale. In the current work we assessed whether farms implementing flower-rich schemes had richer aculeate communities than farms without such habitats. A total of 104 species of bee and 44 species of aculeate wasp were recorded. Farms providing flower-rich habitats had significantly greater floral abundance but there were no differences in the total number of aculeate or flowering plant species recorded compared to farms without these habitats. After accounting for differences in sample size, and contrary to expectations, farms without flower-rich habitats were significantly richer in aculeate and flowering plant species. Bumblebees (Bombus spp.) and honeybees (Apis mellifera) foraged strongly from sown flowers, but the majority of bee species preferred wild plants that are not included in flower-rich schemes such as Heracleum sphondylium, Hypochaeris radicata and Tripleurospermum inodorum. The creation of pollinator-friendly habitats has not increased the diversity of flowering plants and such schemes will consequently only benefit a limited suite of aculeate species. If diverse aculeate communities are to be retained and restored on farmland, agri-environment schemes that provide foraging and nesting resources for a wider range of pollinator species must be developed.