Integument Modifications: Sclerotization
Image Richard Bartz: Wikimedia Commons.
Tanning
Tanning, or sclerotization as it is called, is an irreversible process involving proteins that darkens the cuticle. Protein chains become linked by phenolic bridges (quinone tanning). Water is excluded and the cuticle dries. The proteins in the cuticle become water-insoluble.
Only exocuticle becomes sclerotized.
The black pigment, melanin is also often formed during sclerotization since it is made from excess dopamine involved in the chemical process. Melanin, as well as contributing to sclerotization and blackening of the cuticle is useful in photon-shielding (UV light protection) and as an antibiotic for insects
Unseclerotized or poorly sclerotized cuticle is found in some larval insects and in intersegmental regions in adults where it can allow for bending and stretching. This is seen, for example, in honey pot ants; scale insects; abdomens of mosquitoes and other blood feeders; and in grub-like larvae that feed on plants. In honey pot ants the intersegmental membranes stretch while the sclerites maintain the same shape and size as their “unexpanded” sisters.
Soft cuticle has about 50% each of chitin and protein whereas stiffer cuticles have about 30% chitin and 70% protein.
