Recency preference of odour memory retrieval in honeybees

Free-flying honeybees (Apis mellifera) were trained on tasks in which they had to choose one of three odours for a reward of sugar water. In acquisition, the bees learned this task in about five trials of training. Unrewarded retention tests showed that the odour memory was retained after 24-h delay. These findings are unsurprising. Integration experiments were then performed in which the bees had to learn two successive tasks of odour discrimination with conflicting demands. In task 1 (20 trials), one of three odours provided sugar water while the other two provided tap water. In task 2 (ten trials), which followed task 1 immediately, a different odour provided the reward. The bees were given unrewarded tests immediately after training on task 2 and then tested again after 10 min, 22 h or 24 h. The 22-h delay coincided with the circadian time for the start of task 1 training, while the 24 h coincided with the circadian time for the end of the task 2 training. Bees strongly preferred the rewarded odour for task 2 on immediate testing and after a 10-min delay. After delays of 22 and 24 h, they still preferred the rewarded odour for task 2. We conclude that the most recently acquired odour memory dominates behaviour in honeybees. The close association between floral odour and reward availability under natural circumstances may predispose honeybees to rely more on the most recently rewarded odour cue rather than on circadian time.