ACCUMULATION OF MONOTERPENES AND ASSOCIATED VOLATILES FOLLOWING INOCULATION OF GRAND FIR WITH A FUNGUS TRANSMITTED BY THE FIR ENGRAVER, SCOLYTUS VENTRALIS (COLEOPTERA: SCOLYTIDAE)

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Abstract
The accumulation of monoterpenes during the defensive response by grand fir was quantified over a 28-day period. Monoterpene content increased exponentially with time and varied greatly among trees. Following analysis, sampled trees were observed for 4 years. Those trees which showed an extensive accumulation of monoterpenes in response to artificial inoculation with fungi transmitted by the fir engraver were less likely to be killed during this period than trees which exhibited low levels of secondary monoterpene accumulation. The extent of the defensive response was influenced by host age, disease, crown class, and artificial stress. Following inoculation with fungi transmitted by the fir engraver, the proportions of limonene, myrcene, and Δ-3-carene, present in the monoterpene fraction increased. In previously reported laboratory bioassays, each of these compounds has demonstrated higher toxic or repellent properties, or both, than have the other monoterpenes present in grand fir. Mechanical injury resulted in less pronounced reactions than did fungal inoculation. Necrotic lesion formation is accompanied by an increased concentration of short-chain hydrocarbons, followed by a decline to normal levels. Necrotic lesion formation and monoterpene synthesis represent at least two independent activities during the wound response.