Tree-killing bark beetles in conifer forests vector symbiont fungi that
are thought to help the beetles kill trees. Fungal symbionts emit
diverse volatile blends that include bark beetle semiochemicals involved
in mating and host localization. In this study, all 12 tested fungal
isolates biosynthesized beetle semiochemicals when growing in medium
amended with linoleic acid. Semiochemicals produced included the
spiroacetals chalcogran, trans-conophthorin and exo-brevicomin but also
2-methyl-3-buten-1-ol, the main aggregation pheromone component of the
spruce bark beetle Ips typographus. Accumulating evidence show that the
fatty acid composition in conifer bark can facilitate colonization by
bark beetles and symbiotic fungi, whereas the fatty acid composition of
non-host trees can be detrimental for beetle larvae or fungi. We
hypothesize that beetles probe the fatty acid composition of tentative
host trees to test their suitability for beetle development and
production of semiochemicals by symbiotic fungi.