Supplementary material for: Testing the peak-end rule in bumblebees: lack of preference for a higher-reward sequence when the final reward is disappointing

ABSTRACT The peak-end rule describes the tendency to evaluate experiences by their most intense and final moments, rather than considering the entire experience as a whole. While this cognitive bias is well-established in humans, studies on nonhuman animals are very limited. Bumblebees make foraging decisions largely based on past experiences, but whether peak-end effects influence their subsequent flower choices is still unknown. Here, we trained individual Bombus terrestris workers on two artificial flower types, blue and yellow, over 12 consecutive foraging bouts. One flower type offered a sequence of three high-quality rewards (25 μL drops of 50% w/w sucrose solution: “consistent” sequence), while the other provided the same sequence but ended with an additional, lower-quality reward (25 μL drop of 20% w/w sucrose solution: “poor end” sequence). We then tested the bees' flower type preference in a final binary choice. Bees showed a strong preference for blue flowers, both in their initial and overall visits. Across all visits during a 1-minute period, they also favoured flowers associated with the “consistent” sequence, though this preference was significant only when these flowers were yellow. Interestingly, despite offering more sucrose per foraging bout, bees did not favour the “poor end” sequence flower. This study is, to our knowledge, the first to investigate peak-end effects in an insect. How bees evaluate sequential rewards when foraging remains largely unexplored, yet could provide valuable insights into nectar distribution and plant-pollinator co-evolution.摘要 峰终定律（peak-end rule）描述了人们依据体验中最强烈的瞬间与最终时刻来评估整体体验的倾向，而非全面考量整个体验过程。尽管这种认知偏差在人类身上已得到学界广泛证实，但针对非人类动物的相关研究仍极为有限。熊蜂的觅食决策在很大程度上依赖过往经历，但峰终效应是否会影响它们后续的花朵选择仍未可知。本研究在连续12次觅食趟次中，对单只地熊蜂（Bombus terrestris）工蜂开展训练，使其接触蓝色与黄色两种人工花卉类型。其中一类花卉提供三次高品质奖励序列：25微升的50% w/w蔗糖溶液，即"恒定奖励"序列；另一类花卉提供完全一致的奖励序列，但最终会额外添加一次低品质奖励：25微升的20% w/w蔗糖溶液，即"劣质终局"序列。随后，我们通过最终的二元选择试验，检测这些工蜂对花卉类型的偏好。结果显示，无论是初始访花还是总访花次数，工蜂均表现出对蓝色花卉的强烈偏好。在1分钟观察期内的所有访花行为中，它们同样青睐与"恒定奖励"序列相关联的花卉，不过这种偏好仅在该花卉为黄色时才具有统计学显著性。有趣的是，尽管每次觅食趟次中"劣质终局"序列提供的总蔗糖量更高，但工蜂并未表现出对该序列花卉的偏好。据我们所知，本研究是首个在昆虫类群中探究峰终效应的实验。目前学界对蜂类在觅食过程中如何评估序列性奖励的研究仍较为匮乏，但相关研究可为花蜜分布格局以及植物-传粉者协同进化提供极具价值的见解。