Structural Design Variations in Beetle Elytra

Beetles typically use their protective wing coverings or elytra to shield their membranous hindwings from the environment. Elytra in some terrestrial species have evolved a greater protective role capable of shielding the organism from powerful antagonistic predators. The structure-function relationships of these biological composites identify how architectural and chemical variations of the cuticle are tuned to create light-weight, impact resistant composites. Specifically, the elytral structures of a tree dwelling beetle capable of flight, Trypoxylus dichotomus, and a terrestrial beetle incapable of flight, Phloeodes diabolicus, are compared to understand how their varied environmental needs forged the elytra to facilitate fight or resist fatal predator strikes. Mechanical and microstructural analysis reveals P. diabolicus has a harder, stiffer elytra that incorporate through-thickness fibers to resist greater mechanical stresses imposed by bending and puncture. Conversely, the elytra of T. dichotomus have a compliant structure with large voids that facilitates localized deformation. Variations in flexural strength and puncture resistance remain attributed to P. diabolicus possessing a thicker cuticle with a greater degree of cross-linking and an increased amount of endocuticular layers. These findings may provide useful insight into the design and manufacturing of composite materials for use in light-weight or energy-absorbing applications.