The significance of social interactions in synchronized swarming flight in a termite

In social insects, individuals of working caste coordinate their actions to manage various collective tasks. Such collective behaviours exist not only in workers but also in winged reproductives (alates). During certain seasons, newly emerged alates fly from the nest to disperse and find mating partners in a synchronized manner. This 'swarming' behaviour is one of the collective behaviours that involve the greatest number of individuals in social insects. However, such synchronization is considered to be caused by the response to specific environmental cues rather than behavioural coordination among colony members. Here, we show that a termite Reticulitermes kanmonensis shows synchronized dispersal flight among alates within the same colony even under the constant temperature environment. Under the semi-field environment with fluctuating temperatures, alates within the same colony synchronized their dispersal flight under higher temperatures, while flight was suppressed under lower temperatures. We observed that termites synchronized their dispersal flights even under constant temperature conditions in the laboratory (20℃), indicating that environmental cues are not always necessary for synchronization. In either case, higher synchronization happened with a larger number of alates. These results suggest that social factors interplay with environmental cues to enable the synchronized swarming flight of social insects.