The expansion of Schistocerca gregaria at the imaginal ecdysis: The mechanical properties of the cuticle and the internal pressure

Abstract (1) At the imaginal ecdysis of Schistocerca , the cuticle is viscoelastic rather than elastic. (2) The cuticle becomes softer just before emergence. It is suggested that this is due to an ‘eclosion hormone’. The softening permits the extrication of the appendages and an increase in the size of the locust. (3) The stiffness of the cuticle increases transiently at the end of emergence. (4) In the later part of wing expansion, the cuticle becomes elastic and its stiffness again increases. (5) Maximum pressures are recorded about 10 min into emergence, and pressures in the gut are greater than those in the tracheal system. (6) From these results it is concluded that the expansion of the wings initially depends on the high haemolymph pressure and low stiffness. Only in the last 15 min of wing expansion do the processes involved in autonomous expansion become important.