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

Abstract Forest fire is known to positively affect bark beetle populations by providing fire-damaged trees with impaired defenses for infestation. Tomicus piniperda, the common pine shoot beetle, 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 hypothesized to improve substrate quality and detoxify tree defensive chemistry to indirectly facilitate tree colonization by beetles. While some bark beetle species form symbiotic associations with 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 burnt and unburnt sites. In our study system, we find that forest fire significantly impacts the fungal community composition associated with T. piniperda and that fire may also indirectly change nutrient availability in phloem to 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 indicate that vectoring of associated fungal communities is not a strategy associated with the T. piniperda life cycle.