Short- and long-term modulation of forager motivation by colony state in bumble bees

Abstract

The question of how animals make decisions has been intensely studied by ethologists, behavioural ecologists, psychologists and neuroscientists alike. Foraging bumble bees are an excellent system to study decision making because, as eusocial insects, foragers are solely focused on the task of collecting food for the colony. Bumble bees are generalist foragers of ephemeral resources that do not store food long term and are thus expected to show flexible adjustments in foraging motivation in response to stored food. However, their feeding behaviour at resources as a function of stored food has not been explored. Here, we present results demonstrating that bumble bees ( Bombus impatiens ) show flexible adjustments in foraging motivation in response to colony food stores across different timescales. First, bumble bees showed decreased foraging motivation as the colony accumulated food over the course of a day. Second, bees that developed in colonies with full food stores showed persistently lower motivation than bees developing in colonies with impoverished food stores even days after those food stores were removed. We further demonstrate that this persistent low motivation may be explained by the lower amount of abdominal lipids in nutrient-depleted colonies. Our results provide evidence for a mechanism that may mediate the social control of individual foraging motivation, an important step in the evolution of eusociality. • We examined bumble bee feeding behaviour at resources as a function of stored food. • We tested bees from provisioned and unprovisioned colonies. • Bees showed flexible foraging based on colony food stores across timescales. • Bees from provisioned colonies showed lower foraging motivation. • This low foraging motivation may be explained by lower abdominal lipid levels.