LOCOMOTION IN INSECTS Thorax The body section after

LOCOMOTION IN INSECTS

Thorax The body section after the head, with the legs and wings attached. The: the prothorax, the mesothorax, and the metathorax.

Insect leg attachment and structure • Each leg pair is attached to a segment of the thorax. • The front pair to the prothorax, • the second pair to the mesothorax and • the third to the metathorax. • Most insect legs consist of six segments, and they are as follows in order, from the thorax to the tip of the leg:

• Each segment bears a pair of walking legs, • the first pair of wings arise from the meso thorax while the second pair from the metathorax • The exoskeleton of each thoracic segment is formed by four chitinous sclerites

Four Chitinous sclerites • A dorsal tergite or tergum • Lateral pleurite or pleuron • ventral sternite or sternum • Arthrodial membranes ( which join the sclerites from adjacent segments)

Walking legs • Each leg consists of five segments • Coxa: articulating between the pleuron and sternum • Trochanter : freely movable on the coxa but fixed to the femur • Femur : usually broad and long • Tibia : long and uniformly thick • Tarsus : last segment having five tarsomeres or podomeres or metatarsals with last tarsus having 2 claws

Coxa Trochanter Femur Tibia, 1 2 3 4 5 Tarsus (tarsomeres 1 -5 claws

Cursorial : Periplaneta americana

Saltatorial Grasshopper hind leg

Raptorial Stagmomantis sp (Praying mantis)

natatorial leg (predaceous diving beetle hind leg)

fossorial leg Grylotalpa africana )

WINGS • The wings are actually two layers of epidermis covered by a thin layer of cuticle. • Most of the orders of Pterygota have four wings. • Some, like the Diptera have only two wings. • Each wing pair is attached to a segment of the thorax, more specifically the last two pairs, the mesothorax and the metathorax

Wings • The wings are jointed to the second and third thoracic segments and are moved up and down by the action of muscles. As in the case of limbs, the muscles are attached to the inside of the exoskeleton. There are two types of attachment for either direct or indirect flight muscles

Section through the thorax to show direct muscle attachment when this muscle contracts it pulls the wing down when this muscle contracts it pulls the wing up

Direct flight muscles • One end of each muscle is attached to the inside of the thoracic segment; the other end is attached to the wing near the joint. The muscles act directly on the wing

Attachment of indirect flight muscles these muscles deepen the thorax and flip the wing down these muscles slightly flatten the thorax and flip the wing up

• Indirect flight muscles These act on the thorax and distort it, so flipping the wings up and down. This produces a rapid wing beat. There also muscles which adjust the angle of the wings

Abdomen • Spiracles • Genitalia

Diagram of insect tracheal system main trachea spiracles

• The breathing system in insects consists of a series of tubes called tracheae. • The tracheae connect to the atmosphere by openings called spiracles. • Air diffuses through the spiracles and tracheae to all parts of the body supplying the organs directly with air.

Muscle fibre finely branched tracheae (tracheoles) supplying muscle fibres with air spiracle Body cuticle spiracle main trachae

Insect Genitalia The insect's genital opening lies just below the anus: it is surrounded by specialized sclerites that form the external genitalia. In females, paired

• In females, paired appendages of the eighth and ninth abdominal segment fit together to form an egg-laying mechanism called the ovipositor. • ). In males, the genital opening is usually enclosed in a tube-like aedeagus which enters the female's body during copulation (like a penis). •

• The external genitalia may also include other sclerites (e. g. subgenital plate, claspers, styli, etc. ) that facilitate mating or egg-laying. The structure of these genital sclerites differs from species to the extent that it usually prevents inter-species hybridization and also serves as a valuable identification tool for insect taxonomists.