Cuticle formation and pigmentation in beetles

• Published in: Current opinion in insect science 2016-10, Vol.17, p.1-9
• Main Authors: Noh, Mi Young, Muthukrishnan, Subbaratnam, Kramer, Karl J, Arakane, Yasuyuki
• Format: Article
• Language: English
• ISSN: 2214-5745; 2214-5745
• DOI: 10.1016/j.cois.2016.05.004

•Tyrosine metabolism is responsible for insect cuticle coloration and hardening.•Hard and rigid beetle cuticle has a distinctive morphology and ultrastructure.•There is unique localization and cross-linking of specific CPs in the rigid cuticle.•Biomimetic materials inspired by the beetle exoskeleton are being developed. Adult beetles (Coleoptera) are covered primarily by a hard exoskeleton or cuticle. For example, the beetle elytron is a cuticle-rich highly modified forewing structure that shields the underlying hindwing and dorsal body surface from a variety of harmful environmental factors by acting as an armor plate. The elytron comes in a variety of colors and shapes depending on the coleopteran species. As in many other insect species, the cuticular tanning pathway begins with tyrosine and is responsible for production of a variety of melanin-like and other types of pigments. Tanning metabolism involves quinones and quinone methides, which also act as protein cross-linking agents for cuticle sclerotization. Electron microscopic analyses of rigid cuticles of the red flour beetle, Tribolium castaneum, have revealed not only numerous horizontal chitin-protein laminae but also vertically oriented columnar structures called pore canal fibers. This structural architecture together with tyrosine metabolism for cuticle tanning is likely to contribute to the rigidity and coloration of the beetle exoskeleton.