Flower constancy in the hoverflies Episyrphus balteatus (Degeer) and Syrphus ribesii (L.) (Syrphidae)

The causes and consequences of flower constancy have been thefocus of many studies, but almost all have examined the foragingbehavior of bumblebees, honeybees, or butterflies. We test whetherconstancy occurs in an overlooked group of pollinators, thesyrphid flies. Foraging sequences of wild flies of two species,Episyrphus balteatus and Syrphus ribesii were examined whenvisiting flowers in seminatural plant communities and in artificialarrays of two color morphs of Lobularia maritima planted ata range of frequencies. Both species exhibited marked floralconstancy when foraging in the mixed-plant community. Becauseall groups of pollinating insect so far examined exhibit constancyat least under some circumstances, we suggest that this is thepredominant strategy used by pollinators and that there is probablya common explanation. Neither syrphid species exhibited constancyto different color morphs within a plant species, in contrastto previously published studies of Hymenoptera foraging amongpolymorphic flowers, which all describe positive frequency-dependentselection. Possible explanations for this discrepancy are discussed.We argue that constancy in these syrphids is unlikely to resultfrom learning constraints on handling ability, currently themost widely accepted explanation for flower constancy, becausethey forage primarily for pollen which is easily located inmostflowers they visit.     

Evidence for Handedness in Bumblebees

We describe a simple study of how bumblebees (Bombus spp.) behave when visiting florets which are arranged in a circle around a vertical inflorescence. In four species of bees, individuals showed a tendency for rotation in the same direction around each inflorescence on successive visits, i.e., each individual tended to go either clockwise or anticlockwise. Similar behavior has also been observed in mammals including humans. The implications of this tendency to repeat tasks in the same way are discussed, particularly in relation to our understanding of the phenomenon known as flower constancy. In humans, the tendency for individuals to turn in a particular direction is strongly related to handedness. In three of the four bee species there was a significant overall tendency for the bees to rotate in a preferred direction, suggesting that they too may exhibit handedness.