1University of Turku, Department of Biology, FIN-20014, Turku, Finland.
2Department of Chemistry, FIN-20014, Turku, Finland.
Concentrations of two groups of phenolic compounds, and two phenolic-related traits, of mountain birch (Betula pubescens ssp. czerepanovii) leaves correlated negatively with growth rate of its main defoliator, larvae of E. autumnata: hydrolysable tannins (HT), protein precipitation capacity of tannins, proanthocyanidins (PA) and leaf toughness. Multiplicity of factors of suitability resulted from two causes: i) high among tree variability in the flushing phenology and maturity of leaves, and ii) activation of biosynthesis of different phenolics at different phases of leaf growth and development. It was shown that suitability of young leaves to larvae depended on concentrations of HT, presumably because of their ability to reduce digestibility of nutritive compounds. In the process of leaves maturation, the concentrations of HT decrease and PA form the next barrier limiting larval growth. In the third step, suitability of mature leaves depends on their toughness, which seems to be related to active transformation of soluble phenolics into insoluble cell wall-bound form. Formation of birch leaf phenolics, as determinants of leaf suitability to insect will be considered in relation with leaf growth and regulation of phenolic metabolism in woody plants.