Energy storage and C:N:P variation in a holometabolous insect (Curculio davidi Fairmaire) larva across a climate gradient

Abstract

Increasing empirical evidence has documented variability in elemental composition within species. However, the extent, causes, and pattern of variability in consumer stoichiometry across a large geographical scale are not well understood. Here, we investigated this issue using a holometabolous insect, weevils (Curculio davidi Fairmaire). Larvae of this species store energy needed for diapause, and variable energy requirements across the geographic range of this species could lead to differences in body elemental composition. Our results showed that variability was high (assessed as the coefficient of variation (CV)) in larval body nitrogen (N) and phosphorus (P) (CV, 10% for N and 13% for P) compared to emerging adults (CV, 5% for N and 8% for P). Temperature-related factors explained more variation than other climatic factors and food for carbon (C), N and P in weevil. In warmer regions, larval C concentration was higher, while N and P were lower. The high C content of weevil larvae relative to both their food source and their adult stage was attributed to energy storage. Across the climatic gradient of its geographic range, larval body C content increased with mean annual temperature and decreased with average diurnal temperature range. This finding implies that temperature-related C storage drives the high variability in elemental composition of larvae across the climate gradient, and also effectively dampens the stoichiometric imbalance between consumers and food resources while serving as an energy reservoir for overwintering and metamorphosis.