Extreme ecological stoichiometry of a bark beetle–fungus mutualism

1. Ecological stoichiometry theory was applied to investigate how a consumer contends with an extreme elemental mismatch between its food and its body via symbiotic facilitation. 2. The beetle Dendroctonus brevicomis LeConte develops in bark, a substrate extremely low in nitrogen (N) and phosphorus (P). Its survival there depends on interactions with mutualist and antagonist fungi. 3. This study found that mutualists transfer N and P from sapwood and phloem into bark, where beetles feed, whereas the antagonist moves these elements only to phloem, resulting in starvation of the insect. However, even with mutualists, N and P concentrations remained low in bark, resulting in low N and extremely low P concentrations in the beetle. 4. The N:P ratios found in D. brevicomis larvae were the highest thus far reported for beetles and among the highest for insects and invertebrates. This suggests that the beetle has evolved additional, nutrient-sparing adaptations.