RELATIONSHIP BETWEEN FOLIAR CHEMISTRY AND SUSCEPTIBILITY OF NORWAY SPRUCE (PINACEAE) TO PRISTIPHORA ABIETINA (HYMENOPTERA: TENTHREDINIDAE)

Abstract

AbstractFollowing a 3-year period of high populations of the little spruce sawfly, Pristiphora abietina Christ, a monophagous species infesting Norway spruce, Picea abies Karst., we compared variations in foliar nutrients (nitrogen, water, soluble carbohydrates, starch) and potential defensive compounds (fiber, quinic and shikimic acids, tannins) of trees that had been subjected to high or very low levels of defoliation. During the time of needle expansion a substantial decline in leaf quality occurred: nitrogen, water, and carbohydrate levels decreased, whereas fiber and starch concentrations increased. Allelochemicals such as tannins and organic acids, however, peaked at bud break and then rapidly declined. More heavily attacked trees had higher nitrogen, water, and fiber contents but lower starch and organic acid concentrations than lightly attacked trees. The needle tannin content was significantly lower in heavily attacked trees throughout the period of larval feeding. Needle tannin levels and the nitrogen to tannin ratios seem to be the most probable traits to distinguish sawfly-resistant from sawfly-susceptible Norway spruce trees.