Host location by visual and olfactory floral cues in an oligolectic bee: innate and learned behavior

Oligolectic bees collect pollen from only a few related plant taxa, and our understanding of both the bees' innate and learned behavior in host-plant recognition is incomplete. For the oligolectic bee Chelostoma rapunculi, whose host plants are within Campanula, we conducted choice tests on foraging-naïve individuals to investigate the bee's innate preference for visual and olfactory floral cues of its host plants over those of nonhost plants. In addition, we tested both foraging-naïve and foraging-experienced individuals to determine the relative importance of these 2 sensory modalities in the bee's innate and learned host-flower location. Visual and olfactory cues of Campanula trachelium flowers, both separately and combined, attracted significantly more foraging-naïve bees than equivalent cues of nonhost plants. Furthermore, for both foraging-naïve and -experienced bees, the visual cues of host plants were more attractive than the olfactory ones, and the 2 cues combined attracted more bees than either alone. In foraging-naïve bees, visual and olfactory cues alone elicited almost exclusively approaches, whereas after the bees gained foraging experience, landings became more frequent in response to visual cues but not to olfactory cues; in both bee groups, the combination of visual and olfactory cues was most effective in promoting landings. We conclude that Ch. rapunculi has an innate preference for the floral cues of its host plants over those of nonhost species and that both foraging-naïve and foraging-experienced bees integrate visual and olfactory cues to find their host flowers, with a slightly greater reliance on visual cues in bees with foraging experience.