This thesis contributes to the field of Populus (Salicaceae) research and the establishment of Populus as a model organism exploring secondary metabolites responsible for herbivory defense. In species of the Salicaceae family this defense is represented by phenolic glycosides so called salicinoids. We determined the absolute configuration of salicortin, one of the most abundant salicinoids occurring within the genera Populus, by comparing its chiroptical properties with those of ()-idescarpin, a structurally related compound from Idesia polycarpa. Furthermore, we examined the main fecal (frass) constituents of the Salicaceae specialist C. vinula (Lepidoptera) fed on Populus nigra leaves. Additionally, we investigated salicinoid breakdown in these larvae by feeding experiments with highly 13C enriched salicortin. Subsequently, we investigated the most abundant leaf metabolites of I. polycarpa (Salicaceae) and the influence of an Idesia leaf diet on the performance of the Salicaceae specialist C. vinula and the broadleaf generalist Lymantria dispar.