Thieves or friends: Are specialist bees more efficient at removing pollen than generalists?

Background/Question/Methods

Specialist bees take advantage of a very limited set of floral hosts compared to generalists that forage in the same system, thus it is suspected that they have evolved to exploit these hosts very efficiently. Though bees are generally thought of as pollinators the relationship between specialist bees and their host plants comes into question. Because specialists are expected to be especially good foragers they might act as pollen thieves relative to other visitors if they do not make up for the excess pollen removed by depositing more pollen on stigmas.  To investigate this I studied the pollinators of Physalis longifolia [Solanaceae] and investigated pollen removal versus fruit-set in Physalis’ generalists [Halictidae] and its specialist (Colletes latitarsis), which sometimes sonicates the flower (which lacks poricidal anthers) when collecting pollen. 

Results/Conclusions

Colletes removed significantly more pollen than Dialictus but not more than Halictus or Augochlorella. Further Colletes did not remove more pollen when sonicating than during other visits. Colletes induced fruits set in Physalis around 90% of the time, whereas Halictids were less likely to induce fruit set.  These data imply that sweat bees act as pollen thieves in the Physalis system, taking more pollen than they contribute to pollination. Colletes does not remove more pollen than generalists in a single visit, but more data is needed to determine whether or not Colletes is actually a more efficient forager, and what advantages it gains from being a specialist in this system.