Colony-level macronutrient regulation in the red imported fire ant, Solenopsis invicta

Amounts and ratios of dietary macronutrients (proteins [P] and carbohydrates [C]) may have a profound effect on an insect’s lifetime performance and fitness. Many insects are capable of reaching and defending an optimal ‘nutritional target’ of these disparate resources by actively regulating consumption of each macronutrient. This ‘intake target’ may be dynamic depending on an insect’s physiological condition. Colonies of eusocial insects comprised of many individuals and having overlapping generations with different physiological requirements, provide a unique opportunity to study macronutrient regulation in insects. Using a geometric approach representing dietary macronutrient content in Cartesian space, we investigated performance and macronutrient regulation of Solenopsis invicta colonies presented with three different dietary choice treatments, each with two resources differing in total P and C content. Colony reproduction was greatest on treatments with high P content, and worker mortality was lowest on treatments with high C content. The P:C intake target for each dietary treatment was highly dynamic, the coordinates of which were significantly related to worker mortality and larval eclosion rates. Depending on colony demographics, workers collected and recruited to the resource with macronutrient content corresponding to a colony’s physiological condition: workers from colonies with developing brood selectively collected resources high in P, and workers from colonies with little to no developing brood selectively collected resources high in C. Results indicate that workers, given a choice of resources differing in macronutrient content, selectively collect those best matching colony-level macronutrient requirements.