Metabolism of 14C-labelled pentagalloylglucose by Epirrita autumnata and Agriopis aurantiaria (Lepidoptera: Geometridae) and implications for the nutrition of geometrid defoliators

: Juha-Pekka Salminen

Publisher: Blackwell Publishing

: 2018

: Austral Entomology

: 57

: 2

: 255

: 264

: 10

: 2052-1758

DOI: https://doi.org/10.1111/aen.12323

The metabolism of pentagalloylglucose, the immediate biosynthetic precursor of both ellagitannins and

gallotannins, was investigated in larvae of two geometrid species, autumnal moth Epirrita autumnata and scarceumber Agriopis aurantiaria. The aim was to determine yet unknown metabolic patterns of the widely distributedhydrolysable tannins in these model lepidopteran species. Pentagalloylglucose was applied in [U-14C]-labelled,leaf-painted form in the larval diet. During the 24 h experiment, the radioactivity was distributed between all larvalfractions studied, e.g. hemolymph, gut, the rest of the body, CO2 exhaled and frass excreted. Detailed chemicalanalyses and subfractionation of the larval fractions revealed that both species signiﬁcantly modiﬁed the structureof pentagalloylglucose; it was the main 14C-active component in none of the larval fractions. E. autumnataand A. aurantiaria were able to partially hydrolyse pentagalloylglucose as evidenced by the presence of 14C-la-belled gallic acid in the gut and in frass. The production of 14 CO2 by these two species showed that they wereeither able to liberate CO2 from the COOH moiety of gallic acid or that they were able to use some parts ofthe pentagalloylglucose even as an energy source. Also newly formed, not yet characterised tannin metaboliteswere detected especially in the gut, hemolymph and body samples, in both soluble and insoluble forms.These ﬁndings emphasise that the hydrolysable tannin metabolism in insects is much more complex than earlierspeculated and that there is a great variation within and between insect species in their ability to metabolise thesepolyphenolic plant metabolites. All this should be taken into account especially in attempts trying to explain insectperformance on a leaf diet solely by correlations with the foliar tannin levels: the metabolic fate of tannins might bemore important determinant of insect performance than the ingested amount of tannins per se.