Evaluating the cues that coordinate a shift towards the robbing foraging tactic in the honey bee (Apis mellifera)

In a social species like the honey bee ( Apis mellifera ), changes in foraging strategy require shifts in several groups of specialized workers that are involved in collecting, storing, and processing food. In cases of extreme food shortage, honey bee colonies can switch to a high-risk, high-reward foraging tactic known as honey robbing, which involves stealing mature honey from other colonies. Colonies engaged in honey robbing show a corresponding increase in defensive behaviors displayed by specialist guard bees, presumably because the conditions that provoke robbing also increase the risk of colony invasion. Previous studies suggest aggressive behaviors displayed by robbing forager nestmates modulate guard defensiveness. In the current study, we evaluated which aspects of the robbing experience likely alter forager aggression, and in turn, guard defensiveness. We trained colonies to visit feeders containing either raw honey or a sucrose solution and examined whether food type, experience of conflict at the feeder, or other abiotic cues that reflect the time of the season best explain variation in guard defensiveness. We found little evidence that food type influences forager interactions with guards. Rather, conflict at the feeder is the best predictor of increased aggressive interactions, even when accounting for the effects of seasonal change. Thus, intraspecific conflict at the food resource during robbing may drive shifts in individual forager aggression, activating guard defensiveness as one component of a syndrome of colony-level changes required to accommodate the robbing foraging tactic. Significance statement Honey bees possess an extreme foraging tactic that they employ under conditions of resource scarcity. This tactic, honey robbing, requires coordinated changes among worker bees to accommodate enhanced food collection, processing, and storing, as well as nest defense. In a previous study, we showed that robbing foragers show unusually high aggression, and that this shift may trigger greater defensiveness from nestmate guards once foragers return home. Here, we explored the cues that coordinate the change in defensive effort from guards and find that forager conflict at the food resource is a strong predictor of guard defensiveness. These results suggest that guards use behavioral cues from their own foragers to estimate their risk of attack and increase their defensiveness accordingly.