Micromechanical properties of consecutive layers in specialized insect cuticle: the gula ofPachnoda marginata(Coleoptera, Scarabaeidae)and the infrared sensilla ofMelanophila acuminata(Coleoptera,Buprestidae)

Abstract

SUMMARYInsect cuticle is a highly adaptive material that fulfils a wide spectrum of different functions. Cuticle does not only build the exoskeleton with diverse moveable parts but is also an important component of a stunning variety of mechanosensory receptors. Therefore, the mechanical properties of these specialized cuticular systems are of crucial importance. We studied the different cuticular layers of the head part (gula) of the head-to-neck ball articulation of Pachnoda marginata and of the photomechanic infrared (IR) sensilla of Melanophila acuminata on the basis of cross sections. In our study, we combined histological methods (i.e. detection of the different types of cuticle by specific staining) with measurements of hardness (H) and reduced elastic modulus (E r ) by nanoindentation technique. In the gula of Pachnoda we found an unusual aberrance from the well-known layering. Between the epi-and exocuticle, two meso-and one endocuticular layers are deposited which are softer and more elastic than the underlying exo-and mesocuticular layers. The hardest of all examined materials is the cuticle of the exocuticular shell of the internal sphere of the Melanophila IR sensillum with H=0.53 GPa whereas the inner mesocuticular core of the sensillum represents the most elastic and softest layer with values of H=0.29 GPa and E r =4.8 GPa. Results are discussed with regard to the proposed functions.

Biomechanics of substrate boring by fig wasps

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Biomechanics of the stick insect antenna: Damping properties and structural correlates of the cuticle

“…We were able to show that the specialized layering of the flagellar exo-and endocuticle, and in particular the water content, significantly affects its biomechanical properties. As the compliance of endocuticle is thought to be due to its high water content (Mueller et al, 2008;Vincent and Wegst, 2004), this indicates a critical role of the endocuticle.…”

Fracture toughness of locust cuticle

“…Over the past 60years, different insect species and body parts have been tested by engineers and biologists, using various techniques, and it has been shown that the Young's modulus of cuticle can range from less than 1kPa (intersegmental membranes of mature female locusts) to several GPa (tendons) (Vincent and Wegst, 2004). It has also been shown experimentally that variations of the cuticle's fibre alignment, water content and controlled 'tanning' of the material affect the cuticle's static mechanical properties, such as stiffness and hardness, and dynamic mechanical properties, such as damping, over several orders of magnitude (Müller et al, 2008;Klocke and Schmitz, 2011;Dirks and Dürr, 2011;Schöberl and Jäger, 2006;Göpfert and Robert, 2001).…”