Social behavior and colony trajectory in bumble bees are shaped by the brood

A hallmark of sociality is reproductive division of labor, mediated by pheromones, between reproductive and sterile females. While the role of the queen in regulating worker reproduction in social insects attracted much of the attention in selected model organisms, the role of the brood and its pheromones remained poorly studied.

Here, we used bumblebees to understand the various roles of brood in maintaining and manipulation the structure of a social colony. Findings show that the brood regulates workers’ behavior and physiology in various ways. Young larvae were shown to inhibit egg laying behavior in workers whereas pupae induced the opposite effect. Both effects are dose-dependent, not influenced by relatedness or the previous experience of workers and are mediated by both unique behaviors exhibited by the brood and chemical signals produced by young larvae and pupae. We further show that the impact of the queen on worker reproduction is partial without the brood, and that the presence of brood regulates large-scale processes at the colony level such as the beginning of the competition phase and the production of sexuals. Despite the various impacts brood has on workers, a transcriptome analysis of workers’ brains in response to young larvae demonstrate weak impacts on gene expression in comparison with the impact of the queen. These studies overall point to a significant impact of the brood on the social behavior of bees and demonstrate the need to examine the effects of brood and the chemical mechanisms underlying these effects more thoroughly across other species.