Ecological, physiological, and evolutionary drivers of stoichiometry in insects.

The elemental composition of organisms links physiology to biogeochemical cycles, yet the relative contributions of evolutionary divergence, ecology, and allometry to stoichiometric variation remain incompletely resolved. Here, we integrate a global insect stoichiometric database spanning 223 species with a comprehensive phylogenetic backbone to evaluate the relative importance of hypothesized ecophysiological drivers of carbon (C), nitrogen (N), and phosphorus (P) stoichiometry within a multivariate framework. We found a strong phylogenetic signal in stoichiometric ratios and in P and N content, with evolutionary divergence (phylogenetic structure) accounting for approximately half of the explained variation in P-based ratios, exceeding the contribution of any individual ecological predictor. Phylogenetically corrected models recover trophic enrichment across successive trophic levels, consistent with previously documented patterns, and positive scaling between body mass and both C:P and N:P, in line with the general predictions of the Growth Rate Hypothesis. Temperature was the strongest ecological predictor of insect stoichiometry, with positive effects on C:P and N:P ratios and a negative effect on C:N, highlighting the thermal underpinnings of previously observed geographic patterns. Finally, our models recover higher P and lower C in terrestrial insects relative to their aquatic counterparts, contrary to classic expectations that invoke differences in structural constraints and autotrophic composition across habitats. Together, our work shows that variation in insect stoichiometry emerges from the interacting influences of evolutionary divergence and ecological and physiological variation, which can be disentangled through appropriately scaled, phylogenetically informed analyses.