Forest fire influence Tomicus piniperda associated fungal communities and phloem nutrient availability of colonized Pinus sylvestris. Tomicus and fire

Forest fire is known to positively affect beetle populations by providing fire-damaged trees with impaired defences for infestation. Tomicus piniperda, the common pine shoot borer, breeds and lays eggs under the bark of stressed pine trees and is considered a serious forest pest within its native range. Wood-colonizing fungi have been hypothesised to improve substrate quality and detoxify tree defensive chemistry to indirectly facilitate tree colonization by beetles. While some beetle families form symbiotic associations with beneficial fungi and actively vector their partners when colonizing new trees, T. piniperda does not have mycangia or body hairs for specific vectoring of fungi. To explore the T. piniperda associated fungal community for signs of specific association we used ITS-metabarcoding to separately characterize fungal communities associated with surface and gut of male and female beetles. We also characterized the temporal changes in fungal community and nutrient status of pine phloem with and without beetle galleries. Sampling was performed two years after a natural forest fire and included both burned and unburned sites. In our study system, we find that forest fire significant impact the fungal community composition associated with T. pinierda and that fire may also change nutrient availability in fungal-colonised phloem of beetle galleries. We conclude that T. piniperda can vector fungi to newly colonized trees but the absence of positive effects on substrate quality and minimal effects of sex, indicating that vectoring of associated fungal communities is not a strategy associated with the T. piniperda life cycle.