Cuticular hydrocarbon trafficking in insects: Transport, deposition, and barrier assembly

Cuticular hydrocarbons (CHCs) contribute to water retention, cuticle barrier integrity, protection against xenobiotic penetration, and chemical communication in insects. Classical physiological and biochemical studies established that hydrocarbons are synthesized mainly in oenocytes, transported through the hemolymph by lipophorin, and, in several insect systems, selectively accumulated at the cuticle and other target tissues. Building on this framework, recent genetic, cellular, and structural studies have begun to characterize molecular components associated with tissue accumulation, epidermal export, and pore-canal organization, including lipophorin receptors, ATP-binding cassette transporters, and extracellular pore-canal factors. However, the evidence remains limited, taxonomically concentrated, and derived largely from a small number of experimental systems, while many reported phenotypes do not distinguish direct hydrocarbon transport from broader effects on lipid allocation, membrane organization, or cuticle development. This review integrates classical physiological evidence with recent molecular studies of hydrocarbon production, systemic carriage, tissue accumulation, epidermal export, and surface deposition. It evaluates the comparative distribution and evidential strength of current findings and identifies unresolved questions concerning hydrocarbon loading and unloading, substrate specificity, extracellular passage through pore canals, and regional deposition. By separating established processes from functional associations and untested hypotheses, this synthesis clarifies the present limits of the field and defines the evidence required to determine how chemically distinct hydrocarbons reach specific functional destinations.