108

N. Chari et al.

Fig. 8.1 Chemical structure

of chitin poly (β-(1–4)—N-

acetyl-d-glucosamine)

is also known as the most renewable biopolymer. The chemical representation of

chitin is given by (C8H13O5N)n and is a natural polysaccharide having a linkage of

(β-(1–4)–N-acetyl-d-glucosamine) and is also represented by (GlcNAc) [2]. Chitin

was discovered and named as fungine by Henri Braconnot, a French Professor, in

1811. It has also been reported in the literature from the eggshells of nematodes,

leguminous plants, Rhizobium and even in vertebrates during the early stages of

embryogenesis.

The structure of the chitin molecule in Fig. 8.1 shows two of the N-

acetylglucosamine units that repeat to form long chains in β-1, 4 linkages.

Structure of the Insect Integument

The insect integument is made up of the following layers:

1.

A thin non-cellular basement membrane that lines the body cavity of the insects.

2.

An epithelial layer composed of small cylindrical flattened cells with a distinct

central nucleus.

3.

External to the epidermis, the adjacent layer is known as the procuticle, which

is further subdivided into endochitin and exochitin. Sometimes, there may be

an ill-defined third layer known as mesochitin; however, the mesochitin is not

found in all insects. Differentiation of exocuticle involves sclerotization, where

the chitin layer becomes relatively hard.

4.

The procuticle layer contains a matrix of proteins having many microfibres

of chitin. The chitin is layered in the form of lamellae. The endocuticle and

exocuticle are made up of microfibres.

5.

The orientation of microfibres differs in endocuticle and exocuticle.

6.

An oriented monolayer of wax exists above the epicuticle. It acts as a chief

barrier to the movement of water into and out of the insect body. The wax layer

consists of a long chain of hydrocarbons and esters of fatty acids and alcohols.