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Metabolism of 14 C‐labelled pentagalloylglucose by Epirrita autumnata and Agriopis aurantiaria (Lepidoptera: Geometridae) and implications for the nutrition of geometrid defoliators
Author(s) -
Salminen JuhaPekka
Publication year - 2018
Publication title -
austral entomology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.502
H-Index - 39
eISSN - 2052-1758
pISSN - 2052-174X
DOI - 10.1111/aen.12323
Subject(s) - frass , lepidoptera genitalia , gallic acid , betula pubescens , chemistry , tannin , hemolymph , botany , metabolism , bark (sound) , biochemistry , biology , food science , ecology , antioxidant
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 scarce umber Agriopis aurantiaria . The aim was to determine yet unknown metabolic patterns of the widely distributed hydrolysable tannins in these model lepidopteran species. Pentagalloylglucose was applied in [ U ‐ 14 C]‐labelled, leaf‐painted form in the larval diet. During the 24 h experiment, the radioactivity was distributed between all larval fractions studied, e.g. hemolymph, gut, the rest of the body, CO 2 exhaled and frass excreted. Detailed chemical analyses and subfractionation of the larval fractions revealed that both species significantly modified the structure of pentagalloylglucose; it was the main 14 C‐active component in none of the larval fractions. E . autumnata and A . aurantiaria were able to partially hydrolyse pentagalloylglucose as evidenced by the presence of 14 C‐labelled gallic acid in the gut and in frass. The production of 14 CO 2 by these two species showed that they were either able to liberate CO 2 from the COOH moiety of gallic acid or that they were able to use some parts of the pentagalloylglucose even as an energy source. Also newly formed, not yet characterised tannin metabolites were 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 earlier speculated and that there is a great variation within and between insect species in their ability to metabolise these polyphenolic plant metabolites. All this should be taken into account especially in attempts trying to explain insect performance on a leaf diet solely by correlations with the foliar tannin levels: the metabolic fate of tannins might be more important determinant of insect performance than the ingested amount of tannins per se.