Fig 5. Similarity in chemical composition of tree bud resin from poplar tree species and bee-collected resins (“ocher”, “orange”, “red” and “yellow”).

Bee-collected resins did not unambiguously correspond to any of the other sampled tree species. Ordination Figure (D) is based on Bray-Curtis dissimilarities between samples (stress value = 0.18). Different letters indicate different tree species: Pb: Populus balsamifera; Pt: Populus tremula; Px₁-Px₃: three different chemotypes of Populus x canadensis. Different symbols represent different resin types: closed diamond: “ocher”; closed triangle: “orange”; open triangle: “red”; star: “yellow”. A–C and E–G) Exemplary chromatograms of hexane extracts from tree buds (left) and bee-collected resins (right): A) P. balsamifera; B) P. x canadensis (chemotype Px₁); C) P. tremula (chemotype Px₃); E) “red” bee-collected resin; F) “orange” bee-collected resin; G) “ocher” bee-collected resin; chromatograms display retention times in minutes on the x-axis and mass current (mc) on the y-axis; pictures in chromatograms show examples of resin foragers carrying the respective resin chemotype.