Soldier morphogenesis in a nasute termite: discovery of a disc-like structure forming a soldier nasus.

Nasute termites belonging to the subfamily Nasutitermitinae, have a soldier caste that possesses a frontal projection (nasus) on the head, from which defensive substances are secreted. In the course of caste differentiation of the processional nasute termite Hospitalitermes medioflavus, the most dynamic morphogenesis occurs in the stage of moulting from male minor worker to presoldier (the stage preceding the soldier stage). We examined the presumptive nasus epithelium in minor workers and determined that the nasus develops rapidly just prior to the moulting to presoldiers. The rapid growth is associated with two folding layers of cuticle and epithelium, which we termed the soldier-nasus disc, and resembles the imaginal discs found in holometabolous insects.