Laboratory observations reveal that mature Vespa mandarinia larvae continue calling at night

Vespa hornet larvae produce a rhythmic 'rasping' sound by rubbing their mandibles against the cell walls of their nests. The call is thought to be a larval provisioning cue. However, detailed observations of larval calls have been limited to a few species, and it is not known whether the call can be influenced by the external environment, such as light and time of day, or by internal larval states, such as feeding. We conducted laboratory observations of larval calls under workerless conditions to investigate the effects of 1) larval stage and size, 2) daily variation, 3) light conditions, and 4) feeding on sound production. Vespa mandarinia larvae produced sounds regardless of their status, such as position, light condition, time of day, and worker absence. During mastication, the larvae stopped calling. A key finding of this research is the novel discovery that larvae produce sounds at night, which is a previously undocumented behaviour.