Brood thermogenesis effects on the thermal dynamics in stingless bee nests (Melipona scutellaris)

Stingless bees (Apidae, Meliponini), a group of mainly tropical, highly social bees, rely predominantly on passive thermoregulatory mechanisms for maintaining a nest-microclimate suitable for brood development. Even so, temperatures in the brood region are usually above temperatures in the nests’ periphery, which cannot be explained through passive thermoregulation alone. In the present study, we investigated temperature variations in nests of Melipona scutellaris throughout the year as well as the effective contribution of brood thermogenesis to the thermal dynamics under experimental simulations. The incubation temperatures in this stingless bee species varied significantly with ambient laboratory temperature. Thus, despite a constant temperature excess in the brood area, colonies did not control incubation temperature in a strict homeostatic manner but rather showed a heterothermic behaviour. At ambient temperatures of 25–32.5 °C, brood thermogenesis increased the temperature in the combs’ close surroundings by up to 4 °C, therewith explaining part of the temperature excess in the brood area. The residual thermal increase by almost 7° at ambient temperatures of 15 °C was, presumably, attributed to active heating by the adults. The elevated metabolic activity of the pupae between 25 and 32.5 °C suggests a lower thermal range for brood development in M. scutellaris. The adaptive advantages of both colony heterothermy and reduced incubation temperatures in the threatened native habitat of this stingless bee species, the Atlantic Rainforest in north-eastern Brazil, are discussed.