Bark beetle nutritional ecology is seldom studied although the acquisition of nutrients is key to these insect’s fitness and population dynamics. Since most bark beetles feed only in phloem, the thickness of the phloem within a tree has often been used as a proxy for the tree’s quality as food. However, while phloem is what the beetles feed in, a substantial portion of their nutrients can come from the sapwood via translocation by symbiotic fungi. Fungal hyphae growing within the phloem fed on by larvae and spores fed on by new adults can provide substantial nutrient subsidies. The symbiotic fungi vary in their ability to provision beetles with elements such as nitrogen and phosphorus. The beetles, in turn, vary in their requirements for these elements. Thus, the level of benefits and dependencies vary and range from low to high and commensal to obligate, respectively. For highly aggressive tree-killing bark beetles that mass attack and colonize trees, high quality provisioning by fungi may be key to this lifestyle by reducing the intra-specific competition that would otherwise result from feeding in a densely-colonized and thus highly limited phloem resource. Recent research applying an ecological stoichiometric approach indicates bark beetle nutritional ecology is an area ripe for exploration and key to understanding many aspects of bark beetle dynamics and evolution.
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