The combined effect of color and odor on flower choice behavior of bumble bees in flower mimicry systems

Abstract

Food-deceptive flowers are pollinated by animals that expect a reward but are cheated. Such plants profit from their similarity to rewarding plants and should develop signals that hinder discrimination. We use artificial rewarding model flowers and nonrewarding mimicking flowers that present similar visual cues. We test how additional scent cues change flower choice of the mimic by bumble bees (Bombus terrestris) in two situations: (1) both flower types are simultaneously present and can be compared by the pollinator, and (2) both flower types are encountered successively in the absence of each other. We find that in situation 1, discrimination learning is greater if scents are used as cues for identifying the mimic, whether the mimic has a different scent or if it is scentless while the model is scented. In situation 2, a generalization task, a scented mimic is avoided faster than a scentless one. Discrimination of the mimic is poorest if it has the same scent as the model, thus demonstrating a potential for scent mimicry, which has not yet been proved to exist among differently rewarding flowers. Thus, the best strategy for a mimic would be to have the same scent as the model, but this strategy may not be used due to evolutionary constraints. Alternatively, if there are several potential models, then having no scent would be a better strategy than mimicking just one of the models. In situation 1 flower discrimination by color cues is enhanced in the mere presence of scent, compared to unscented controls, even if the scent does not provide a distinguishable cue itself. The results indicate that the presence of scent may enhance color discrimination by improving attention towards visual cues and/or that combined color/odor cues may lead to better memory formation and retrieval.