![]() The perception of airborne sounds by honeybees is presently understood to be limited to the brief pulses (less than 50 ms) made by waggle-dancing workers in several species of Apis. Thus, bee-produced signals are collectively termed ‘vibroacoustic’ because they are often transmitted within colonies simultaneously as both airborne sounds and substrate vibrations, and mode of perception is not always clear. Honeybees perceive sounds either as air-particle movements detected by Johnston's organs in their antennae or as substrate-borne vibrations detected by subgenual organs in their legs. Honeybees (genus Apis) are an important model system for exploring signal use within a social group because of the diversity of ‘sounds’ that colony members exchange to coordinate their activities. Acoustic monitoring is an excellent way to gain valuable insights into the signals that social groups exchange as they detect predators and coordinate defensive responses, particularly in environments where sound is a well-used modality and visual observation is challenging. ![]() ![]() The emerging picture is that one needs to know an animal species well in order to understand how group members communicate when faced with predatory threats. Finally, antipredator signals may be multimodal, which can refine their influence on recipients, aid communication in noisy environments and help group members respond appropriately when attacks come from multiple types of predators. These signals may be discrete or graded, meaning they may have distinct features that discriminate them from other signal types or they may vary on a continuum with intermediate forms. Signals produced in response to predators may encode predator type, level of urgency or both. Importantly, for social animals that respond collectively to predators, signals organize group-level defences. Furthermore, selection should favour signal diversity in species that are hunted by predators that differ in attack strategy, the degree of danger they pose to prey or prey response. Signal meaning can be revealed by immediate responses to predation threats, both in the production of signals by alarmed individuals and the response of group members to those signals. Predation is a major selective pressure for animals that live in conspicuous social groups, and the rich antipredator signalling that it drives can reveal the intricacies of social communication. ![]() One of the most intriguing features of animal sociality is the evolution of shared signals that convey information and coordinate activity among group members. Apis cerana workers flexibly employ a diverse alarm repertoire in response to attack attributes, mirroring features of sophisticated alarm calling in socially complex vertebrates. Concurrent observations of nest entrances showed an increase in worker activities that support effective defences against giant hornets. ![]() Workers making antipredator pipes exposed their Nasonov gland, suggesting the potential for multimodal alarm signalling that warns nestmates about the presence of dangerous hornets and assembles workers for defence. Antipredator pipes share acoustic traits with alarm shrieks, fear screams and panic calls of primates, birds and meerkats. soror predators were directly outside of nests, in part because of frenetic production of antipredator pipes, a previously undescribed signal. soror workers in particular-triggered dramatic increases in signalling rates within colonies. Apis cerana colonies produced hisses, brief stop signals and longer pipes under hornet-free conditions. We compared vibroacoustic signalling and defensive responses of Apis cerana colonies that were attacked by either the group-hunting giant hornet Vespa soror or the smaller, solitary-hunting hornet Vespa velutina. Asian honeybees use an impressive array of strategies to protect nests from hornet attacks, although little is understood about how antipredator signals coordinate defences. ![]()
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