- Cuticle:
- The cuticle is an outer layer which contains a characteristic chemical compounds called chitin, proteins and pigments.
- The cuticle is made up of three principal layers: epicuticle, exocuticle and endocuticle.
- The exo- and endo- cuticle together referred as procuticle.
Principle Layers of the Cuticle
a) Epicuticle :Epicuticle is the outer, thin, delicate layer without any chitin and may have four sub- layers. They are:
I. Inner epicuticle: it is the thickest layer of 0.5 to 2.0 µm immediately outside the procuticle and chemically consists of tanned lipoproteins.
ii. Outer epicuticle: This is very thin trilaminar layer only of about 15 nm.The material forming the outer epicuticle is highly polymerized lipid is often referred to as cuticulin.
iii. Epicuticular wax layer: Wax comprises over 90% and is important in water proofing the cuticle.
iv. Cuticular cement layer: It consists of mucopolysaccharide. It protects underlying wax and no produced by all insects.
b. Exocuticle:
- It is a thicker layer below epicuticle and is often darker and harder than the rest.
- It contributes rigidity and toughness to the cuticle.
- The exocuticle structurally consists mainly of chitin and protein.
- Other constituents of cuticle include quinones which polymerized to form dark brown or black pigment known as melanin and in others quinones are utilized in forming sclerotin.
c. Endocuticle:
- The inner undifferentiated part below the exocuticle is endocuticle and is characterized by the presence of chitin.
- It provides space for attachment of muscles of antenna and mouthparts, called as Tentorium.
- Epidermis:
- It is below endocuticle and are glandular and secrete cuticle and the enzymes for the cuticle formation and digestion at the time of molting.
- Basement membrane:
- Also called basal lamila and is a noncellular layer beneath epidermis and serves as stable platform where epidermal cells are anchored and muscles are attached.