The Worker Flow at the Hive Entrance Predicts When Nest Cleaning is Intensified in Stingless Bees

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Waste produced by living organisms is commonly disposed of as a prophylactic measure to avoid the spread of diseases and parasite infestation. For social insects, a proportion of workers is allocated to dispose the waste material outside the colony’s nest. However, most nests of social insects have a single entrance, where a high flow of individuals may create congestion, potentially compromising normal foraging activities and colony growth/health. Here, we investigated how two species of stingless bees (Tetragonisca fiebrigi and Plebeia droryana) deal with waste disposal and regular foraging activities, and the impacts of these activities on traffic flow at nest entrances. First, we compared the average traffic of bees assigned to waste removal activities. Following this, we investigated probabilities for waste removal as bee traffic increases. Then, we estimated a cutoff value to predict the likelihood that waste removal activities will be intensified over foraging trips. We found that, on average, the number of bees performing waste removal activities was lower than those undertaking foraging trips for both species. In addition, we observed that as overall bee traffic increases, the number of workers engaged in waste removal reduces or even ceases. Our models indicate that bee traffic of approximately 15 individuals/time is a cutoff score, below which, colonies invest in waste removal and above which, foraging trips are increased. It suggests that both species use the entrances of their colonies in an optimized way by adjusting which tasks should be intensified as the traffic of individuals increases.