Bumblebees and pollination of endemic Onobrychis pindicola (Fabaceae) in the subalpine habitats of Pirin Mts.

Onobrychis pindicola subsp. urumovii Degen & Dren. is an endemic with restricted distribution on Pirin Mts. and Slavjanka Mts. (Balkan Peninsula, SW Bulgaria). It is obligatorily dependent upon insect vectors for pollen transport, being a self-incompatible plant. The aim of this study was: 1) to identify which bumblebees pollinate Onobrychis pindicola, 2) to identify which plants compete for these pollinators with O. pindicola, 3) to use pollen load analysis to assess bumblebee flower constancy and spatial foraging patterns of bumblebee pollinators of O. pindicola. The nectar is accessible to a wide spectrum of bees including short tongued bumblebees and honey bees. Onobrychis pindicola is pollinated most actively by Bombus pyrenaeus. Other bumblebees visited the flowers more or less actively. These were B. lapidarius, B. terrestris and B. pratorum. The bumblebees tended to utilize plant resources in guilds and follow particular plants for foraging. Observed in the field high flower constancy was confirmed by the pollen analysis