Major niche shift for a group of tree-killing bark beetles

How a shift in fungal symbionts allowed a major niche shift for a group of tree-killing bark beetles

Most tree-killing bark beetle species use fungi to more efficiently extract nutrients from tree phloem for development and reproduction. However, one group of tree killers exhibits a unique feeding strategy. These species use outer bark. Not only is this a major shift in behavior, but outer bark poses a significant challenge for survival. Bark is dry and composed primarily of lignin and cellulose, two compounds that animals, including insects, and indeed most fungi, cannot metabolize. Moving from phloem, an already challenging substrate, to exploiting bark is an extreme strategy that would require, not only acquiring new fungi capable of using this dramatically different resource, but ones that can provide the beetle a balanced, complete diet and moisture. Western pine beetle larva

Radical shifts in resource use by insects have often been achieved by forming associations with microbes. By ‘partnering’ with microbes, insects access new genomic variation instantaneously allowing them to exploit new adaptive zones without having to evolve new capacities themselves. We are investigating how shifts in fungal symbionts associated with bark beetles have supported their massive success as ‘apex predators’ in forest ecosystems through a comparative study of phloem- and bark-inhabiting species. 

Image: Western pine beetle larva nestled in fungal layer in feeding chamber in bark