Insights into the evolution of bark beetle–fungus mutualisms: The alder bark beetle and its association with a Neonectria canker pathogen

Associations between herbivorous insects and microorganisms range from weak commensal relationships to highly evolved phytopathogenic mutualisms.  Understanding the potential for herbivorous insects to encounter, acquire, and carry fungi, including phytopathogens, among host plants is of critical importance given increasing evidence of climate change-induced range shifts and anthropogenically-assisted introductions of both insects and fungi into coevolutionarily naïve systems.  Alniphagus aspericollis, the alder bark beetle, is an unusual bark beetle in that it infests and kills a hardwood tree, red alder (Alnus rubra) and, unlike most tree-killing (i.e. primary) bark beetles, is not regularly associated with ophiostomatoid fungi.  Instead, this beetle is consistently found in association with a Neonectria canker pathogen, which marks a heretofore undocumented type of bark beetle–fungus association that offers a unique opportunity to evaluate novel interactions between insects and fungi and the processes by which mutualisms can evolve.  My research will determine whether the A. aspericollis–Neonectria represents an emergent mutualism, investigate its potential origins, and use this unique system to critically evaluate hypotheses regarding the function(s) of fungi in the evolution of bark beetle–fungal mutualisms, thereby improving our ability to predict the ecological impacts of novel organism interactions.