Learning performance of foraging bumblebees (Bombus terrestris) under manipulation of inter-visit time intervals (Hymenoptera: Apidae)

Short-term information affects feeding choices in bees. When making rapid successive choices, bees tend to forage in a flower-constant manner, and perform well in delayed matching-to-sample learning tests. Flower constancy and learning performance decline when consecutive choices are more than five seconds apart. It was suggested that visual stimuli associated with the last-encountered food source are retained in the bees' working memory, and prime their next choice. The contents of the working memory may either fade, or be replaced by other visual input, within a few seconds. To distinguish between these possibilities, the visual input available to bees between consecutive feeding choices was controlled. Bombus terrestris (Linnaeus 1758) bumblebees, foraging on differentially-rewarding artificial feeders of different colors, were exposed to either 1.5 seconds or 15 seconds of darkness following each feeder visit. The bees did not fly in the dark, therefore these treatments differed in the time elapsed between successive feeding choices, but not in the visual input available to the foragers during this time. The bees' feeder choices were compared to the choices of untreated controls. Control bees chose rewarding feeders significantly more often than bees from both darkness treatments. Shifts between feeders of different colors, and choices of non-rewarding feeders, were associated with long time-intervals between visits in the control treatment, but not in the darkness treatments. The results support previous evidence that short-term information, when available, improves the learning performance of bees. The similarity in the bees' foraging performance in the two darkness treatments suggests that the decay of working memory may involve acquisition of new visual data. Alternative interpretations for the similar results in the two darkness treatments are discussed.