Principle Layers of the Cuticle

a) Epicuticle: The 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 a very thin trilaminar layer only of about 15 nm. The material forming the outer epicuticle is highly polymerized lipid and is often referred to as cuticulin.

iii. Epicuticular wax layer: Wax comprises over 90% and is important in waterproofing the cuticle.

iv. Cuticular cement layer: It consists of mucopolysaccharide. It protects underlying wax and is not produced by all insects.

b. Exocuticle:

• It is a thicker layer below the 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 are 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 the endocuticle and is characterized by the presence of chitin.
• It provides space for the attachment of muscles of the antenna and mouthparts, called as Tentorium.