Effect of Time Elapsed after Sacrifice on the Stiffness of Male Beetle Head Horns

抄録

Many researchers have conducted mechanical experiments on beetle exoskeletons (cuticulae) because there is much to learn about their structure and strength. Although the time elapsed between the moments the beetles are sacrificed and the moments in which mechanical experiments could be conducted influences the mechanical properties of the cuticula, it has not been given enough importance in previous studies. This study experimentally clarified the relationship between the elapsed time and stiffness. Cantilever specimens were fabricated from the head horns of male beetles (Trypoxylus dichotomus), and bending tests were conducted 3, 16, and 65 days after the sacrifice. The humidity at the experiments were also recorded because the stiffness of the cuticula depends on the moisture content. Even though humidity during the experiment varied over a wide range of -31 to +23 % for 16 and 65 days compared to 3 days after sacrifice, the change in stiffness for 16 and 65 days compared to 3 days after sacrifice was only -12 to +6 %. The results provide clear numerical guidance when referring to stiffness data from previous studies in which the time since sacrifice was not clear, and when starting future studies discussing stiffness of cuticula.