Agriculture Entomology

faisal ameen randhawa

The often tube-like body of an insect is composed of a series of segments: six in the head, three in the thorax and up to 11 in the abdomen.  Each segment is formed from up to four more or less horny plates called sclerites a dorsal tergum, a ventral sternum and two later a pleura (pleura are absent from the insect abdomen).  These plates and the various adjacent body segments may be fused together rigidly or joined by soft, flexible membranes that allow for body movement. The body appendages, such as the legs, are formed as out growths from the pleura. Where fusion has occurred (particularly in the head) the segments, or their individual components, are not always distinguishable; in the thorax, the sclerites are themselves often subdivided in to smaller plates. The body of an insect is covered by a protective three layered skin (cuticle) formed from Chitin and protein. Depending upon its precise composition and thickness, the cuticle may be soft and flexible or hard and rigid; according to requirements, it may or may not be permeable or waterproof. Following Its d position, the cuticle becomes more or less hardened and darkened by the addition of melanin, during a process called sclerotization.