Providing foraging resources for solitary bees on farmland: current schemes for pollinators benefit a limited suite of species.
Abstract
Changes in agricultural practice across Europe and North America have been associated with range contractions and a decline in the abundance of wild bees. Concerns at these declines have led to the development of flower-rich agri-environment schemes as a way to enhance bee diversity and abundance. Whilst the effect of these schemes on bumblebee species (Bombus spp.) has been well studied, their impact on the wider bee community is poorly understood. We used direct observations of foraging bees and pollen load analysis to quantify the relative contribution that sown flowers (i.e. those included in agri-environment scheme seed mixes) make to the pollen diets of wild solitary bees on Higher Level Stewardship farms (HLS) implementing pollinator-focused schemes and on Entry Level Stewardship farms (ELS) without such schemes in southern England, UK. HLS management significantly increased floral abundance, and as the abundance of sown flowers increased, these sown plants were utilized for pollen by a greater proportion of the solitary bee species present. However, the overall proportion of pollen collected from sown plants was low for both direct observations (27.0%) and pollen load analysis (23.3%). At most only 25 of the 72 observed species of solitary bee (34.7%) were recorded utilizing sown plants to a meaningful degree. The majority of solitary bee species did not collect pollen from flower species sown for pollinators. Total bee species richness was significantly associated with plant species richness, but there was no difference in the total species richness of either bee or flowering plant species between HLS and ELS farms. Synthesis and applications. Our results show that the majority of solitary bee species present on farmland in the south-east of England collect most of their pollen from plants that persist unaided in the wider environment, and not from those included in agri-environment schemes focused on pollinators. If diverse bee communities are to be maintained on farmland, existing schemes should contain an increased number of flowering plant species and additional schemes that increase the diversity of flowering plants in complementary habitats should be studied and trialled.