QUANTITATIVE VARIATIONS OF TAXIFOLIN AND ITS GLUCOSIDE IN PINUS-SYLVESTRIS NEEDLES CONSUMED BY DIPRION-PINI LARVAE

The relationships between quantitative variations of 2 flavanonols in Scots pine needles and Diprion pini larvae mortality were studied. Tho se 2 compounds were characterized as taxifolin (T) and its glucoside ( TG) after hydrolysis and analysis by TLC, HPLC and spectrophotometry. Quantitative differences between 30 clones were more important for TG than for T, nevertheless clones which presented a content of taxifolin higher than 1.5 mg g-1 DW showed a T/TG ratio equal to or greater tha n 0.5 (fig 2). Quantitative changes were also observed throughout the year. The amount of taxifolin peaked in autumn as those of its glucosi de decreased (fig 3). Darkness also induced a gradual increase of T bu t no significant effect on TG (fig 4). Storage of twigs during feeding tests and insect defoliation both induced a strong glucosilation of t axifolin in needles (table I). High rates of mortality of Diprion pini larvae were associated with the presence of T and TG both in needles and faeces (table II). Preliminary experiments of feeding bioassay wit h needles supplemented by taxifolin showed a significant reduction of larval development but no direct effect on larval mortality (table III ). Regulation processes between taxifolin and its glucoside, which cou ld involve glucosidases and/or transferases, are discussed for the gen etic and environmental factors studied.