Changes in volatile terpene and diterpene resin acid composition of resistant and susceptible white spruce leaders exposed to simulated white pine weevil damage

Induced (traumatic) resin in white spruce (Picea glauca (Moench) Voss) lead ers resistant or susceptible to the white pine weevil (Pissodes strobi Peck ) was analyzed for volatile terpenes and diterpene resin acids after simula ted white pine weevil damage. Leaders from 331 trees were wounded just belo w the apical bud with a I-mm diameter drill, coinciding with the natural ti me of weevil oviposition in the spring. Leaders were removed in the fall, a nd the bark and xylem from the upper and lower regions of the leader extrac ted and analyzed by gas chromatography. Unwounded trees had low amounts of resin in xylem compared with bark. In re sponse to wounding, volatile terpenes and diterpene resin acids increased i n the upper xylem (area of wounding), with resistant trees showing a greate r increase than susceptible trees. Wounding caused monoterpenes in particul ar to decrease in the lower region of the leader (away from the drilled are a) in greater amounts in susceptible trees than in resistant trees. In resp onse to wounding, the proportion of monoterpene to resin acid increased in the upper and lower xylem of resistant trees, and slightly increased in the upper xylem of susceptible trees. Monoterpene-enriched resin is more fluid than constitutive resin, and probably flows more readily into oviposition cavities and larval mines, where it may kill immature weevils, Loss of resi n components in the lower xylem suggested catabolism and transport of these materials to the site of wounding; however, energetic and regulatory data are necessary to confirm this hypothesis. This study provides a basis for m easuring the ability of a tree to undergo traumatic resinosis that could be used to screen for resistance to white pine weevil.