Carbohydrate regulation in relation to colony growth in ants

SUMMARY Ants and all social insects are faced with a nutritional challenge: the food entering the colony is brought by only a small number of its workers but is shared among all members of the colony. In this study, we investigated how ants maintain carbohydrates supply at both a collective and an individual level in response to changes in the concentration of available sucrose solution, colony demography and larval growth. We manipulated the concentration of sugar solutions available to ant colonies (dilute, medium and concentrated solutions) over extended periods and measured the capacity of colonies to maintain sugar supply through compensatory feeding. First, we demonstrated that ants regulated carbohydrate intake at a collective and individual level. Initially, ants consumed most and recruited fastest in response to more concentrated than to dilute sugar solutions, but over time this pattern reversed, such that the number of ants that fed and the volume ingested by each ant was a negative function of sugar concentration in the diet. Second, we found that ants became better at regulating their carbohydrate intake with the production of larvae in the nest. When the number of larvae was experimentally doubled, the ants regulated their consumption of carbohydrates more accurately than when the number of adult workers was doubled, suggesting that larvae play an important role in providing nutritional feedback to workers. Finally, we showed that ants defended a carbohydrate `intake target' by allowing them to select among sugar solutions of different concentration.