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forces of insect flight. Biological flight is highly complex and still remains to be

elucidated fully; hence, the research is being carried out in different laboratories [1].

Structure of Thorax and Wing Morphology

The insect body is differentiated into three distinct regions such as head, thorax and

abdomen as shown in Fig. 4.1. The thorax is considered as a locomotory apparatus

having three pairs of legs ventrally and two pairs of wings laterally for flight. A

detailed description of the morphology of insect thorax has been documented after

[2] and others [1].

Thorax has three segments: prothorax (pro is first), mesothorax (meso is second)

and metathorax (meta is third). Prothorax has no wings. However, meso and

metathorax have a pair of lateral flying wings which are known as the first and

second pair of flying wings. The dorsal portion of the thorax is covered by a sclerite

which is known as tergum. While the V-shaped ventral portion covered by a plate

is known as the sternum and the lateral portion (where tergum and sternum meet)

is called as pleuron. The pleuron forms the semi-elastic lateral wall of the thorax

and surrounds the base of the leg. Each of the thoracic segments has a pair of legs

ventrally. Insects are also named as hexapoda since they possess six legs as compared

to spiders, millipedes, centipedes and crabs.

The wings are thin chitinous membranes attached to the sides of the thorax by

an elastic membrane (resilin). Each wing has a geometric structure and is traversed

by longitudinal veins, which support the membrane and contribute to the flapping

flexible behaviour of the wing resulting in the lift, thrust and drag due to aeroelasticity

and structural deformation of the wing.

Each segment of pterothorax (flying segments) has a pair of parallel muscles

running longitudinally below the tergum. They also have a pair of vertical muscles

connecting the sternum to the tergum, which help in up and down movements of the

wings indirectly. Thorax also has other muscles attached to the base of the wings for

effective turning/rotation of the wings when the insect is flying. During the rest time,

Fig. 4.1 Outline features of

Grasshopper (a typical

insect)