PESTS
Insects
INSECTS
Anatomy continued
Exoskeleton
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Knowledge about the structure and function of the insect exoskeleton has proven critical in developing insecticide formulations that are able to penetrate this multi-layered protective covering. |
The amazing success of insects must in part lie with the incredible mixture of flexibility and strength of the integument (exoskeleton) that allows insects their freedom of movement without loss of defence and protection. Exoskeleton is like natural fiberglass, inelastic, and must be shed for the insect to grow. It is made up of layers for waterproofing, the most visible of which is the outer 'cuticle' and its attendant bristles and hairs, below this are the 'epidermis' and the 'basement membrane'.
The cuticle
The cuticle is a relatively thin layer of non-cellular material which lines the external surface of the body as well as lining the tracheae the anterior and posterior sections of the alimentary canal and parts of the reproductive system. The most common ingredient of the cuticle is chitin (N-acetyl-D-glucosamine), which is a polysaccharide similar to cellulose, resilin (a protein) and arthropodin (proteins). The cuticle is flexible, elastic and white when first formed and stays this way in many larval forms, however in most adults it undergoes chemical processes which result in hardening and darkening and which are referred to as sclerotization.
The cuticle can be divided into two layers, a very thin outer layer called the epicuticle which contains no chitin and is highly resistant to water and other solvents. Beneath this is the much thicker procuticle which can again be divided into two distinct layers, an outer exocuticle which lies immediately below the epicuticle and an inner endocuticle which consists of a large number of layers of protein and chitin fibres laid down in a laminated pattern such that the individual strands in each layer cross each other thus creating an extremely tough and flexible substance.
Below the cuticle lie the other two components of the integument, the hypodermis which is a single layer of secretary cells and various glands and the basement membrane which is an amorphous layer of tissue about 0.5 micrometres thick and serves for the attachment of muscles.
