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The mechanisms that maintain reproductive division of labor in social insects are still incompletely understood. Most studies focus on the relationship between adults, overlooking another important stakeholderthe juveniles. Recent studies show that not only the queen but also the brood regulate worker reproduction. However, how the two coordinate to maintain reproductive monopoly remained unexplored. Here, we disentangled the roles of the brood and the queen in primitively eusocial bees (Bombus impatiens) by examining their separated and combined effects on worker behavioral, physiological and brain gene expression. We found that young larvae produce a releaser effect on workers, decreasing oviposition and aggression, while the queen produces both releaser and primer effects, modifying worker behavior and reproductive physiology. The expression of reproduction-and aggression-related genes was altered in the presence of both queen and brood but was stronger or the same in the presence of the queen. We identified two types of interactions between the queen and the brood in regulating worker reproduction: (1) synergistic interactions regulating worker physiology, where the combined effect of the queen and the brood on worker physiology was greater than their separate effects; (2) additive interactions, where the combined effect of the queen and the brood on worker behavior was similar to the sum of their separate effects. Our results suggest that the queen and the brood interact synergistically and additively to regulate worker behavior and reproduction, and this interaction exists at multiple regulatory levels.

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8The mechanisms that maintain reproductive division of labor in social insects are still 9 incompletely understood. Most studies focus on the relationship between adults, overlooking 10 another important stakeholder in the gamethe juvenile offspring. Recent studies from various 11 social species show that not only the queen, but also the brood regulates reproductive division of 12 labor between females, but how the two coordinate to maintain reproductive monopoly remained 13 unexplored.14 Our study aims at disentangling the roles of the brood and the queen in regulating worker 15 reproduction in primitively eusocial bees. We examined the effects induced by the brood and 16 queen, separately and together, on the behavioral, physiological and brain gene expression of 17 Bombus impatiens workers. We found that young larvae induce a releaser effect in workers, 18 decreasing egg laying and aggressive behaviors, while the queen induces both releaser and primer 19 effects, modifying worker aggressive and egg laying behavior and reproductive physiology. The 20 expression of reproduction-and aggression-related genes was altered in the presence of both 21 queen and brood, but the effect was stronger or the same in the presence of the queen. 22We identified two types of interactions between the queen and the brood in regulating worker 23 reproduction: (1) synergistic interactions regulating worker physiology, where the combined 24 effect of the queen and the brood was greater than each of them separately; (2) additive 25 interactions regulating worker behavior, where the combined effects of the queen and the brood 26 are the gross sum of their separated effects. In these interactions the brood acted in a manner 27 similar to the queen but to a much smaller extent and improved the quality of the effect induced 28 by the queen. Our results suggest that the queen and the brood of primitively eusocial bees 29 coordinate synergistically, additively, and sometimes even redundantly to regulate worker 30 behavior and reproduction, and the interaction between them exists in multiple regulatory levels. 31 32

Among social insects, task allocation within its group members remains as one of the paramount pillars of social functionality. Division of labor in many eusocial insects is maintained by behavioral flexibility that can shift according to the needs of the colony they reside in. Workers typically, over time as they age, shift from intranidal nurses to extranidal foragers. If the needs of the colony change, either from the needs of the adults or the brood therein, workers shift their behavior in order to compensate for the need of a particular task to be done. This shift, either accelerating towards a behavior associated with an older worker, or regressing back into the nest, is not clearly understood in social insects outside of honeybees. In this study, evaluated how brood type affected the red imported fire ant, Solenopsis invicta, worker task reversion and acceleration. Through observation of worker behaviors performed over multiple time-points per day, we discovered that worker task reversion and acceleration does occur within this ant species. Furthermore, the type of brood influenced the rate at which this occurred, with larvae having the strongest effect of all types. Finally, there was a propensity for workers to maintain their new behavior throughout the experiment. This study shows that the needs of brood within a social insect colony can influence the behavior workers perform, reversing the age polyethism that is common among social insect species.