Host resistance to the fir engraver beetle. 1. Monoterpene composition of Abies grandis pitch blisters and fungus-infected wounds

Abstract

The monoterpene hydrocarbons of the cortical blister oleoresin of Abies grandis were compared, using gas chromatography, with those obtained from lesions that formed as a response of the tree to inoculation with cultured Trichosporium symbioticum, a fungus which is transmitted by the fir engraver beetle Scolytus ventralis. The resins from each source differed both quantitatively and qualitatively. Three terpenic compounds (tricyclene, camphene, and bornyl acetate) that are normally present in primary resin were not found in secondary resin. However, resins that formed in response to the inoculation contained higher concentrations of myrcene in three quarters of the trees and delta³-carene in one quarter of the trees that were sampled than resin from pitch blisters, which contained only trace amounts of these two compounds. These results suggest that conifers respond to fungus infection by producing monoterpenes which are more toxic, repellent, and (or) inhibitory to bark beetles and their associated fungi (e.g. myrcene and delta³-carene) at the expense of attractive or less biologically active compounds (e.g. camphene) which are present in the preformed resin system.