Fungal Interactions and Host Tree Preferences in the Spruce Bark Beetle Ips typographus.

Sifat Munim Tanin,Paal Krokene,Dineshkumar Kandasamy

doi:10.3389/fmicb.2021.695167

Abstract

The spruce bark beetle Ips typographus is the most damaging pest in European spruce forests and has caused great ecological and economic disturbances in recent years. Although native to Eurasia, I. typographus has been intercepted more than 200 times in North America and could establish there as an exotic pest if it can find suitable host trees. Using in vitro bioassays, we compared the preference of I. typographus for its coevolved historical host Norway spruce (Picea abies) and two non-coevolved (naïve) North American hosts: black spruce (Picea mariana) and white spruce (Picea glauca). Additionally, we tested how I. typographus responded to its own fungal associates (conspecific fungi) and to fungi vectored by the North American spruce beetle Dendroctonus rufipennis (allospecific fungi). All tested fungi were grown on both historical and naïve host bark media. In a four-choice Petri dish bioassay, I. typographus readily tunneled into bark medium from each of the three spruce species and showed no preference for the historical host over the naïve hosts. Additionally, the beetles showed a clear preference for bark media colonized by fungi and made longer tunnels in fungus-colonized media compared to fungus-free media. The preference for fungus-colonized media did not depend on whether the medium was colonized by conspecific or allospecific fungi. Furthermore, olfactometer bioassays demonstrated that beetles were strongly attracted toward volatiles emitted by both con- and allospecific fungi. Collectively, these results suggest that I. typographus could thrive in evolutionary naïve spruce hosts if it becomes established in North America. Also, I. typographus could probably form and maintain new associations with local allospecific fungi that might increase beetle fitness in naïve host trees.

Highlights

Microbial symbionts of invasive insect herbivores often promote successful establishment and development in host plants in novel habitats (Wingfield et al, 2010, 2016; Hulcr and Dunn, 2011; Frago et al, 2012)
There were no significant differences in lesion lengths produced by conspecific fungi associated with I. typographus (E. polonica and G. penicillata) and allospecific fungi associated with D. rufipennis (E. rufipennis and L. abietinum)
Previous studies have shown that this European species can successfully colonize and breed in evolutionary naïve North American spruce species such as Sitka spruce [Picea sitchensis (Bongard) Carrière], white spruce (P. glauca) and black spruce (P. mariana; Økland et al, 2011; Flø et al, 2018)

Summary

Introduction

Microbial symbionts of invasive insect herbivores often promote successful establishment and development in host plants in novel habitats (Wingfield et al, 2010, 2016; Hulcr and Dunn, 2011; Frago et al, 2012). Invasive insects could form novel associations with native microbes that promote their establishment in naïve habitats (Himler et al, 2011; Jiggins and Hurst, 2011; Zhao et al, 2013). Many insects have invaded novel forest ecosystems worldwide and some of these species cause great ecological and economic disturbances (Aukema et al, 2010). Ips typographus is a tree-killing bark beetle that primarily colonizes Norway spruce [Picea abies (L.) Karst.], the economically most valuable forest tree species in Europe (Schroeder and Cocoş, 2018). Outbreaks of I. typographus and other tree-killing bark beetles have killed hundreds of millions of trees in recent years, with devastating economic impacts in commercial production forests (Raffa et al, 2008; Hlásny et al, 2019)

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