Floral tea polyphenols can improve honey bee memory retention and olfactory sensitivity

Animal-pollinated plants face a common problem, how their defensive anti-herbivore compounds may impair or alter pollinator behavior. Evolution has tailored multiple solutions, which largely involve pollinator tolerance or manipulation, to the benefit of the plant, not the removal of these compounds from pollen or nectar. The tea plant, Camilla sinensis, is famous for the caffeine and tea polyphenols (TP) that it produces in its leaves. However, these compounds are also produced in its nectar, which honey bees readily collect. We examined the effects of these compounds on bee foraging choices, learning, memory, and olfactory sensitivity. Foragers preferred a sucrose feeder with 100 µg or 10 µg TP/ml over a control feeder. Caffeine, but not TP, weakly increased honey bee learning. Both caffeine and TP significantly increased memory retention, even when tested 7 d after the last learning trial. In addition, TP generally elevated EAG responsiveness to alarm pheromone odors. These results demonstrate that not only caffeine, but other secondary plant compounds, can attract pollinators and influence their learning and memory.

以动物为传粉媒介的植物普遍面临一个共性难题：其防御性抗草食动物化合物可能会损害或改变传粉者的行为。进化已催生多种应对策略，大多通过让传粉者产生耐受性或对其进行调控来使植物获益，而非从花粉或花蜜中移除这类防御化合物。茶树（Camellia sinensis）以叶片中合成的咖啡因与茶多酚（tea polyphenols, TP）闻名于世，但这类化合物同样存在于其花蜜中，且蜜蜂会主动采集此类花蜜。本研究针对上述化合物对蜜蜂觅食选择、学习能力、记忆能力以及嗅觉敏感性的影响展开了系统探究。实验结果显示，觅食蜂更倾向于选择添加了100 μg/ml或10 μg/ml茶多酚的蔗糖喂食器，而非空白对照喂食器；咖啡因（而非茶多酚）可轻度提升蜜蜂的学习能力。无论是咖啡因还是茶多酚，均能显著提升蜜蜂的记忆留存率，即便在末次学习试验7天后进行检测，该效应仍可观测到。此外，茶多酚通常可提升蜜蜂触角电图（Electroantennogram, EAG）对告警信息素气味的响应强度。本研究结果证实，不仅咖啡因，其他植物次生代谢产物同样能够吸引传粉者，并对其学习与记忆能力产生调控作用。