epicuticle

The epicuticle is the outermost layer of the arthropod cuticle, lying above the deeper procuticle. In insects, the cuticle is secreted by epidermal cells during molting and consists of several sublayers, including the epicuticle followed by the procuticle, which itself comprises the exocuticle and endocuticle. The epicuticle is typically thin and rich in lipids, waxes, and hydrocarbons, and it is less rigid than the deeper layers. Its surface often bears a waxy coating that helps reduce water loss and provides a barrier to chemical penetration.

Composition and structure of the epicuticle can vary by species and developmental stage. It generally contains lipids and hydrocarbons rather than chitin, which characterizes the inner layers. In many insects, a cement or wax layer atop the epicuticle enhances waterproofing and external adhesion, while the underlying epicuticle remains comparatively flexible.

Formation and functions are tied to the molt cycle. The epicuticle is secreted by epidermal cells before the procuticle during molting and often remains relatively unsclerotized, contributing to the flexible surface of the new cuticle. Its primary roles include preventing desiccation, acting as a chemical barrier to external substances, and participating in chemical communication through cuticular hydrocarbons that influence social interactions and mate recognition. Environmental factors such as humidity and temperature can influence the lipid composition of the epicuticle, affecting desiccation resistance.

Overall, the epicuticle is a key protective and ecological interface of the arthropod exoskeleton, balancing water retention, chemical defense, and communication.