Nanomechanical properties of elytra derived from irreversible and reversible color-changing beetles

The color-changing and nanomechanical properties of elytra of Harmonia axyridis Pallas and Dynastes tityus were studied in this paper. The irreversible color change of Harmonia axyridis Pallas is related to pigments and microstructures of cuticle. And nanoindentation results demonstrate that the strong interactions of protein matrix of black spot region may lead it to be harder than orange region. Additionally, the black spot region has anisotropic mechanical properties. As to reversible color change of Dynastes tityus, measurements on structure morphology of elytra indicate that the color-changing from yellow-green to deep-brown mainly results from water absorption with sponge structure. Er and H display an increasing tendency from epicuticle (EPI) to endocuticle (ENDO). The relatively low Er and H of elytron surface play a role in buffer, and the increasingly higher strength is to keep its shape and stability.