Biochemical transformation of birch leaf phenolics in larvae of six species of sawflies

Abstract

We investigated the biochemical transformation of individual phenolic compounds of mountain birch leaves in larvae of six birch-feeding sawfly species: Amauronematus amplus, Pristiphora alpestris, Nematus brevivalvis, Priophorus pallipes, Arge sp. and Nematus viridis by comparing the phenolic residues in larval faeces to those of their leaf diet. Partial hydrolysis of hydrolysable tannins, isomerisation of chlorogenic acid and glycosylation of flavonoid aglycones were observed in all studied species. Moreover, we found considerable among-species variation in the composition of phenolic compounds in larval faeces. In addition to foliar phenolics, seventeen non-foliar phenolic metabolites, including eight phenolic acids and nine flavonoid glycosides were detected from the faeces. Of the non-foliar phenolic acids, four were egested species-specifically and only two by all six sawfly species. We also detected differences in the ratios of chlorogenic acid isomers in the faeces of different species, which can indicate different physiological conditions in the guts of studied larvae. In addition to the qualitative differences, quantitative differences were detected in the egestion of chlorogenic acids, possible o-quinone precursors in the larvae. Detected differences, either qualitative or quantitative, could not be explained by seasonal changes in the content of compounds in the leaf diet.