Cannibalism of pupae by larvae has been documented in many species of insects, but the features of larval cannibalism and pupal defensive mechanisms against larval cannibalism have been largely ignored. Pupae of tenebrionid beetles rotate their abdominal segments in a circular motion in response to the tactile stimulation of appendages, including legs, antennae, maxillary pulps, and wings. When the pupal abdominal rotation responses of Tenebrio molitor and Zophobas atratus were completely blocked by transecting the ventral nerve cord (VNC) of the pupae, the appendages of the paralytic pupae became initial, major targets for attack by larval cannibals. The majority of 20 paralytic pupae was cannibalized by 100 larvae within 6 h, and almost all the pupae were killed within 2–3 days. In contrast, only a few pupae of Z. atratus and several pupae of T. molitor were cannibalized when the VNC was intact. The abdominal rotation response of the pupae thus functions as an effective defense against larval cannibalism.
ventral nerve cord