Altitudinal variation in foliar chemistry and anatomy of yunnan pine, Pinus yunnanensis, and pine sawfly (Hym., Diprionidae) performance

Host plant characteristics associated with the larval feeding performance of a pine sawfly were examined across an altitudinal gradient in south-western China. Neodiprion xiangyunicus (Xiao and Huang) larval performance (e.g. larval mass and potential fecundity) and defoliation intensity increased at higher altitudes along an altitudinal gradient in Sichuan, China. Needle chemistry and anatomy of yunnan pine, Pinus yunnanensis (Franch.), also varied across along an altitudinal gradient. In general, total sesquiterpene levels decreased with increasing altitude, oxygenated monoterpenes increased with increasing altitude, and total monoterpenes did not vary significantly across the altitudes. Concentrations for 16 of the 28 individual terpenes varied significantly between at least two of the three altitudes; the vast majority (75%) of these differences were for sesquiterpenes. Foliar nutrition, morphology and anatomy also varied by altitude. Foliar nitrogen and needle dry biomass were significantly lower in trees at the high altitude site. Needle epidermal thickness and diameters of resin ducts were significantly thicker and wider, respectively, in trees at the middle altitude than at the top and bottom altitudes. These results suggest that a combination of foliage chemistry and morphology rather than any single plant trait probably determines the observed patterns of insect herbivory.