Epidermis is formed by a single layer of epithelial cells followed by a thick layer of procuticlepicuticle and wax are known to constitute the outermost covering of the cuticle.
This not only serves as a protective barrier against pathogenic organisms but also prevents water loss and acting as an interface between insect and its environment.
Out of all these components, chitin which is a kind of heteropolysaccharide made with the polymerization of N-acetyl glucosamine through 1–4 β-linkage constitutes an important structural component of insect’s integument.
Pathogen has to invade this tough integument covering to gain entry into the host.