Quantitative variation of different monoterpenes around galleries of Ips typographus (Colleoptera: Scolytidae) attacking Norway spruce

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Abstract
Oxygenated and hydrocarbon monoterpenes present in gallery walls in the phloem at different phases of an attack by Ips typographus and associated microorganisms on Norway spruce trees were quantified. The concentration of monoterpene hydrocarbons rose rapidly at the onset of beetle attack and reached a maximum in the phloem surrounding nuptial chambers that were recently prepared by males. Thereafter, amounts decreased rapidly and then increased again in late attack phases. During the attack, the variation in the amounts of monoterpene hydrocarbons in the gallery walls was partly reflected by some oxygenated monoterpenes, such as myrtenol, present in the same tissue. Borneol, verbenone, terpinene-4-ol, and α-terpineol were present in low quantities in the early phases of attack, but large amounts of these compounds were found in gallery walls during later phases. The bark beetle semiochemicals, cis- and trans-verbenol, had their concentration maxima in gallery walls of finished nuptial chambers. Results of the present study suggest that some bark beetle semiochemicals are produced extraneously to the beetle by microorganisms such as yeasts. A simple model for the production of oxygenated monoterpenes in early and late Ips typographus attack phases is presented.