Guarding Vibrations—Axestotrigona ferruginea Produces Vibrations When Encountering Non-Nestmates

SIMPLE SUMMARY: Stingless bees visit flowers to collect pollen and nectar which is stored in their nest. These stores are highly valuable and help the colony to overcome times of resource scarcity. The bees protect the collected nectar and pollen against robbers of all kind. It should be advantageous for a colony if it can recognize intruders and chase them away. In this context, the communication with nestmates might be crucial. The most important signals that stingless bees use are chemicals and vibrations. Communication between nestmates has been mostly studied in the context of foraging. Little is known about communication in the context of defense. We tested if vibrational signals play a role in nest defense and nestmate recognition of the African stingless bee Axestotrigona ferruginea. Stingless bees produce distinct vibrations in the context of foraging and guarding. Foraging vibrations most likely contain food source information whereas guarding vibrations might be used to alarm nestmates. ABSTRACT: Flower visiting stingless bees store collected pollen and nectar for times of scarcity. This stored food is of high value for the colony and should be protected against con- and heterospecifics that might rob them. There should be high selective pressure on the evolution of mechanisms to discriminate nestmates from non-nestmates and to defend the nest, i.e., resources against intruders. Multimodal communication systems, i.e., a communication system that includes more than one sensory modality and provide redundant information, should be more reliable than unimodal systems. Besides olfactory signals, vibrational signals could be used to alert nestmates. This study tests the hypothesis that the vibrational communication mode plays a role in nest defense and nestmate recognition of Axestotrigona ferruginea. Substrate vibrations induced by bees were measured at different positions of the nest. The experiments show that guarding vibrations produced in the entrance differ in their temporal structure from foraging vibrations produced inside the nest. We show that guarding vibrations are produced during non-nestmate encounters rather than nestmate encounters. This further supports the idea that guarding vibrations are a component of nest defense and alarm communication. We discuss to whom the vibrations are addressed, and what their message and meaning are.