Fungal associates of the tree-killing bark beetle, Ips typographus, vary in virulence, ability to degrade conifer phenolics and influence bark beetle tunneling behavior

The bark beetle Ips typographus carries numerous fungi that could be assisting the beetle in colonizing live Norway spruce (Picea abies) trees. Phenolic defenses in spruce phloem are degraded by the beetle's major tree-killing fungus Endoconidiophora polonica, but it is unknown if other beetle associates can also catabolize these compounds. We compared the ability of five fungi commonly associated with I. typographus to degrade phenolic compounds in Norway spruce phloem. Grosmannia penicillata and Grosmannia europhioides were able to degrade stilbenes and flavonoids faster than E. polonica and grow on minimal growth medium with spruce bark constituents as the only nutrients. Furthermore, beetles avoided medium amended with phenolics but marginally preferred medium colonized by fungi. Taken together our results show that different bark beetle-associated fungi have complementary roles in degrading host metabolites and thus might improve this insect's persistence in well defended host tissues.The collaboration between TZ and AH was funded by the Deutsche Forschungsgemeinschaft (Grant HA7617/1-1 awarded to AH). Field work was funded by the Swedish Research Council Formas (Grant 229-2011-890 awarded to TZ) and the Research Council of Norway (Grant 221479/F20 awarded to PK). The chemical analyses were funded by the Max Planck Society.http://www.elsevier.com/locate/funeco2020-04-01hj2019Forestry and Agricultural Biotechnology Institute (FABI)Zoology and Entomolog