Female bees have evolved a variety of specialized mechanisms for collecting and transporting pollen, the principal food source for all Apoidea larvae.  Among the most important of these numerous and diverse adaptations, are scopae.  These are dense regions of branched, electrostatically charged hairs located on the hind leg or ventral portion of the abdomen, into which pollen grains are packed for bulk transport.  Some specialist bees, those that collect pollen from just a few related host plants, have been reported to have scopal hairs specially adapted to their host plant pollen, but few studies have addressed this within a phylogenetic context.  Here we present preliminary results from a comparative study of representatives of five specialist bee genera, Alepidosceles, Diadasia, Diadasina, Melitoma and Ptilothrix, and their host plant pollens.  We examined scopal hairs and host pollens using a combination of light microscopy and SEM techniques.   Qualitative (e.g. unbranched vs. branched hairs, type of branching) and quantitative (e.g. hair length, branch length, branch spacing) characteristics of the scopae were measured in taxa affiliated with Cactaceae and Malvaceae hosts.  

Results/Conclusions

Differences in scopal hair structure suggest that adaptive change occurs during or following host-switching events.  The most likely parameter driving these changes is the size of host pollen grains, which range in diameters from 50-300 microns.  Future studies involving additional emphorine taxa will provide additional opportunities to more rigorously test adaptive hypotheses.