FLORAL USE BY 2 SYMPATRIC BUMBLE BEE SPECIES (BOMBUS-TERRICOLA AND BOMBUS-TERNARIUS) - EFFICIENCY CONSIDERATIONS

The purpose of this study was to explain a peculiarity of resource use by two sympatric bumble bee species. In one study area, pronounced re source partitioning was observed: Bombus terricola Kirby was confined to Asclepias syriaca L. and Bombus ternarius Say to Apocynum androsaem ifolium L., and yet in another area both species frequented Apocynum. Measurements of floral characteristics and forager behaviour on Apocyn um led to an hypothesis regarding floral use by two bumble bee species : B. terricola is relatively inefficient at flying between flowers, an d so tends to visit Apocynum only in areas where the plants are closel y spaced. Half of the patch of Apocynum was clipped so as to decrease flower density, with the expectation that, as a result, the frequency of B. terricola relative to B. ternarius would be reduced. The predict ion was confirmed. The results underscore the role of context in flora l use by bees.