Pollen packing affects the function of pollen on corbiculate bees but not non-corbiculate bees

Female bees store scattered pollens grains from their bodies for transport by different modes of grooming and pollen packing. Species with corbiculae, such as honey or bumble bees, compress grains into dense pellets borne on the hind tibiae. Other species sweep grains into local concentrations of hairs (scopae), typically around the legs (in Halictidae and Andrenidae) or the ventral abdomen (Megachilidae), in which grains remain loose. Do these modes of pollen packing affect the functional value of pollen? We transferred grains from the bodies of four groups of bees—the corbiculate bees: Bombus impatiens and Apis mellifera, and the non-corbiculate bees: Megachile rotundata and Halictus spp.—onto previously unvisited stigmas of Brassica rapa. We wiped corbicular or scopal pollen and body pollen from each bee’s body separately and measured the resulting fruit set and the number of seeds in successful fruits. The type of pollen significantly affected the number of fruits for the corbiculate bee species but not the non-corbiculate bees, and the type of pollen significantly affected the number of seeds in successful fruits for A. mellifera but not B. impatiens, M. rotundata, or Halictus spp. These results suggest that loose scopal pollen is fully functional, but corbicular pollen is sometimes impaired. In some situations, non-corbiculate bees may be more valuable pollinators than corbiculate species because their treatment of pollen leaves its capabilities intact.