Research Color modulates olfactory learning in honeybees by an occasion-setting mechanism

A sophisticated form of nonelemental learning is provided by occasion setting. In this paradigm, animals learn to disam-biguate an uncertain conditioned stimulus using alternative stimuli that do not enter into direct association with the uncon-ditioned stimulus. For instance, animals may learn to discriminate odor rewarded from odor nonrewarded trials if these two situations are indicated by different colors that do not themselves become associated with the reward. Despite a growing interest in nonelemental learning in insects, no study has so far attempted to study occasion setting in restrained honeybees, although this would allow direct access to the neural basis of nonelemental learning. Here we asked whether colors can modulate olfactory conditioning of the proboscis extension reflex (PER) via an occasion-setting mechanism. We show that intact, harnessed bees are not capable of learning a direct association between color and sucrose. Despite this incapac-ity, bees solved an occasion-setting discrimination in which colors set the occasion for appropriate responding to an odor that was rewarded or nonrewarded depending on the color. We therefore provide the first controlled demonstration of bimodal (color–odor) occasion setting in harnessed honeybees, which opens the door for studying the neural basis of such bimodal, nonelemental discriminations in insects. The capacity to learn relationships between events in the environ-ment is of central importance for adapting successfully to a com-plex and changing world. Animals can learn that an originall