(p-100)PROANTHOCYANIDINS AS A FACTOR OF SUITABILITY OF MOUNTAIN BIRCH LEAVES TO AN HERBIVOROUS INSECT

Svetlana Ossipova^{1, 2}, Vladimir Ossipov^{1, 2} and Erkki Haukioja¹

¹University of Turku, Department of Biology, 20014, Turku, Finland.
²University of Turku, Department of Chemistry, 20014, Turku, Finland.

Proantocyanidins (PA, condensed tannins) are the main phenolic compounds of mountain birch (Betula pubescens ssp. czerepanovii) leaves. They occur in two forms: soluble and bound to structures like cell walls. Concentrations of PA are increased in the process of leaf growth and development and reach their maximum in mature leaves. At leaf senescence, the PA concentrations gradually decrease. Levels of phenolics also vary due to environmental factors, like shading and defoliation of trees. The role of PA as a determinant for the growth rate of larvae of the geometrid Epirrita autumnata was investigated. It was found that these phenolics were the major determinants of leaf suitability during a relatively short time interval in the middle of leaf growth only. In other times, hydrolysable tannins or leaf toughness mainly determined suitability of leaves for the herbivore.