Appetitive but not aversive olfactory conditioning modifies antennal movements in honeybees

In honeybees, two olfactory conditioning protocols allow the study of appetitive and aversive Pavlovian associations. Appetitive conditioning of the proboscis extension response (PER) involves associating an odor, the conditioned stimulus (CS) with a sucrose solution, the unconditioned stimulus (US). Conversely, aversive conditioning of the sting extension response (SER) involves associating the odor CS with an electric or thermal shock US. Each protocol is based on the measure of a different behavioral response (proboscis versus sting) and both only provide binary responses (extension or not of the proboscis or sting). These limitations render the measure of the acquired valence of an odor CS difficult without testing the animals in a freely moving situation. Here, we studied the effects of both olfactory conditioning protocols on the movements of the antennae, which are crucial sensory organs for bees. As bees' antennae are highly mobile, we asked whether their movements in response to an odorant change following appetitive or aversive conditioning and if so, do odor-evoked antennal movements contain information about the acquired valence of the CS? We implemented a tracking system for harnessed bees' antennal movements based on a motion capture principle at a high frequency rate. We observed that differential appetitive conditioning had a strong effect on antennal movements. Bees responded to the reinforced odorant with a marked forward motion of the antennae and a strong velocity increase. Conversely, differential aversive conditioning had no associative effect on antennal movements. Rather than revealing the acquired valence of an odorant, antennal movements may represent a novel conditioned response taking place during appetitive conditioning and may provide a possible advantage to bees when foraging in natural situations.