FLOWER CONSTANCY IN THE HOVERFLIES EPISYRPHUS-BALTEATUS (DEGEER) AND SYRPHUS-RIBESII (L.) (SYRPHIDAE)

The causes and consequences of flower constancy have been the focus of many studies, but almost all have examined the foraging behavior of b umblebees, honeybees, or butterflies. We test whether constancy occurs in an overlooked group of pollinators, the syrphid flies. Foraging se quences of wild flies of two species, Episyrphus balteatus and Syrphus ribesii, were examined when visiting flowers in seminatural plant com munities and in artificial arrays of two color morphs of Lobularia mar itima planted at a range of frequencies. Both species exhibited marked floral constancy when foraging in the mixed-plant community. Because all groups of pollinating insect so far examined exhibit constancy at least under some circumstances, we suggest that this is the predominan t strategy used by pollinators and that there is probably a common exp lanation. Neither syrphid species exhibited constancy to different col or morphs within a plant species, in contrast to previously published studies of Hymenoptera foraging among polymorphic flowers, which all d escribe positive frequency-dependent selection. Possible explanations for this discrepancy are discussed. We argue that constancy in these s yrphids is unlikely to result from learning constraints on handling ab ility, currently the most widely accepted explanation for flower const ancy, because they forage primarily for pollen which is easily located in most flowers they visit.