Effects of resin flow and monoterpene composition on susceptibility of lodgepole pine to attack by the Douglas-fir pitch moth, Synanthedon novaroensis (Lep., Sesiidae)

Resin flow differed significantly among three of six clones of lodgepole pine seed orchard trees, but did not differ among the clones categorized as susceptible or resistant to attack by the Douglas-fir pitch moth. A stepwise regression analysis identified δ-3-carene, cyclohexene, and α-terpinolene as significant compounds, explaining 49.9% of the variation in the number of attacks per tree. δ-3-Carene alone explained 41.8% of the variation in the regression, and analysis of variance showed that resistant clones consistently had high relative amounts (>17.9%) of this compound, whereas susceptible clones had low amounts (<10%). The significant effect by cyclohexene and α-terpinolene in the stepwise regression appeared to be due to a correlation between α-terpinolene and δ-3-carene in several clones, and that cyclohexene was only present in one clone, rather than any discernable biological relationship. Limonene co-eluted with β-phellandrene, so its role must be determined by additional study.