The “River Disease” (RD), a disorder impacting honeybee colonies located close to waterways with abundant riparian vegetation (including Sebastiania schottiana, Euphorbiaceae), kills newly hatched larvae. Forager bees from RD-affected colonies collect honeydew excretions from Epormenis cestri (Hemiptera: Flatidae), a planthopper feeding on trees of S. schottiana. First-instar honeybee larvae fed with this honeydew died. Thus, we postulated that the nectars of RD-affected colonies had a natural toxin coming from either E. cestri or S. schottiana. An untargeted metabolomics characterization of fresh nectars extracts from colonies with and without RD allowed to pinpoint xanthoxylin as one of the chemicals present in higher amounts in nectar from RD-affected colonies than in nectars from healthy colonies. Besides, xanthoxylin was also found in the aerial parts of S. schottiana and the honeydew excreted by E. cestri feeding on this tree. A larva feeding assay where xanthoxylin-enriched diets were offered to 1^st instar larvae showed that larvae died in the same proportion as larvae did when offered enriched diets with nectars from RD-colonies. These findings demonstrate that a xenobiotic can mimic the RD syndrome in honeybee larvae and provide evidence of an interspecific flow of xanthoxylin among three trophic levels. Further, our results give information that can be considered when implementing measures to control this honeybee disease.

“河流病” (RD) 是一种影响靠近水道且河岸植被丰富（包括Sebastiania schottiana、大戟科）的蜜蜂群落的疾病，它会杀死新孵化的幼虫。来自受 RD 影响的蜂群的觅食蜜蜂从Epormenis cestri（半翅目：Flatidae）收集蜜露排泄物，这是一种以S.schottiana树为食的飞虱。用这种蜜露喂养的一龄蜜蜂幼虫死亡。因此，我们假设受 RD 影响的菌落的花蜜含有来自E. cestri或S. schottiana的天然毒素. 对来自有和没有 RD 的菌落的新鲜花蜜提取物的非靶向代谢组学表征允许将黄木素确定为一种化学物质，在来自受 RD 影响的菌落的花蜜中的含量高于来自健康菌落的花蜜。此外，在S. schottiana的地上部分和E. cestri以该树为食分泌的蜜露中也发现了黄木素。甲幼虫喂养测定，其中花椒油富集日粮提供给1^日龄幼虫表明，当提供富含 RD 菌落花蜜的饮食时，幼虫的死亡比例与幼虫的死亡比例相同。这些发现表明，异生素可以模拟蜜蜂幼虫的 RD 综合征，并提供黄木素在三个营养级之间的种间流动的证据。此外，我们的结果提供了在实施控制这种蜜蜂疾病的措施时可以考虑的信息。