Locust oviposition: stress softening of the extensible intersegmental membranes

Abstract

The mechanical properties in simple extension of the extensible intersegmental membrane of the mature female locust have been studied. The testing machine is described. The main feature of biological importance is stress softening (the Mullins Effect) of the membrane. The filler to which this phenomenon is due is probably mainly the chitin fraction. Stress softening allows the locust to extend the membranes elastically and yet require a much smaller restoring force to retract the membranes. Consequently there is no need for the locust to hold on to the sides of the hole with her ovipositor valves, nor to increase the internal pressure, to maintain the membranes extended: the weight of the abdomen is sufficient. Other features resulting from stress softening are that successive egg pods are laid deeper, and that the membrane is much toughened. The subject of toughness in biological materials is enlarged upon, and the practice of ‘conditioning’ discussed briefly