Data for: Phytochemical shift from condensed tannins to flavonoids in transgenic Betula pendula decreases consumption and growth but improves growth efficiency of Epirrita autumnata larvae

<p>Despite active research, antiherbivore activity of specific plant phenolics remains largely unresolved. We constructed silver birch (<em>Betula pendula</em>) lines with modified phenolic metabolism to study the effects of foliar flavonoids and condensed tannins on consumption and growth of larvae of a generalist herbivore, the autumnal moth (<em>Epirrita autumnata</em>). We conducted a feeding experiment using birch lines in which expression of dihydroflavonol reductase (<em>DFR</em>), anthocyanidin synthase (<em>ANS</em>) or  anthocyanidin reductase (<em>ANR</em>) had been decreased by RNA interference. Modification-specific effects on plant phenolics, nutrients and phenotype, and on larval consumption and growth were analyzed using uni- and multivariate methods. Inhibiting <em>DFR</em> expression increased the concentration of flavonoids at the expense of condensed tannins, and silencing <em>DFR </em>and <em>ANR </em>decreased leaf and plant size. <em>E. autumnata </em>larvae consumed on average 82% less of DFRi plants than of unmodified controls, suggesting that flavonoids or glandular trichomes deter larval feeding. However, larval growth efficiency was highest on low-tannin DFRi plants, indicating that condensed tannins (or their monomers) are physiologically more harmful than non-tannin flavonoids for <em>E. autumnata </em>larvae. Our results show that genetic manipulation of the flavonoid pathway in  plants can effectively be used to produce altered phenolic profiles required for elucidating the roles of low-molecular weight phenolics and condensed tannins in plant–herbivore relationships, and suggest that phenolic secondary metabolites participate in regulation of plant growth.</p>