Assessing the value of annual and perennial forage mixtures for bumblebees by direct observation and pollen analysis

The value of introduced seed mixtures in providing forage for bumblebees on farmland was assessed by direct observation of individuals and analysis of pollen loads. Two mixtures of perennial grasses and wildflowers were compared with an annual mix of mostly seed-bearing crops over three years. Foraging bees showed contrasting patterns of visitation depending on species. Longer-tongued Bombus species preferred the perennial mixtures in which Trifolium pratense was dominant, whilst shorter-tongued Bombus and honeybees, Apis mellifera, visited mainly Borago officinalis in the annual mix. These patterns were supported by analysis of pollen loads from B. pascuorum and B. terrestris, both species showing a high degree of flower constancy to sown species. The relative specialisation of different bee species towards certain plant families, and the flowering phenology of seed mix components, must be considered in the design of agri-environment measures to conserve these and other pollinators.