Insect Exoskeleton: Its Ultrastruture and Potential Applications

Insect cuticle is a complex biocomposite material consisting of three major morphologically distinct layers, the waterproofing envelope, the protein-rich epicuticle and the chitin/protein-rich procuticle. Structural cuticular proteins (CPs) and the polysaccharide chitin are the major components of the exo- and endocuticular layers that comprise the procuticle. During cuticle tanning (sclerotization and pigmentation), CPs are cross-linked by quinones derived from the oxidation of catechols, resulting in hardening of the exoskeleton. However, the factors that lead to synthesis and assembly of cuticular regions with differing mechanical properties are not well understood.To gain a better understanding of the development and differentiation of rigid cuticle, we performed transmission electron microscopic (TEM) analysis of elytral cuticle (highly sclerotized and pigmented forewing) from 2 d-old pupae to 9 d-old adults of the red flour beetle, Tribolium castaneum. In 2-3 d-old pupae, pupal cuticle separated from the underlining epidermal cells (apolysis), and outermost envelope and protein-rich epicuticle begun to form. A numerous horizontal chitinous laminae and vertical pore canals were evident in the procuticle of 4-5 d-old pupae. By one day after adult eclosion, less-compact horizontal chitinous laminae were deposited, followed by block-type cuticular layers with no horizontal laminae were formed by 9 days. These results will lead to a) a better understanding of insect cuticle formation, structure and mechanics, b) the potential for development of novel insect control agents that target cuticle physiology, and c) the production of biomimetic materials with physical properties like those of the insect exoskeleton for use in biomedical or other technological devices.This work was supported by NRF (NRF-2012R1A2A1A01006467).