The Insect Chest

Entomology

1. Entomology 353 Bio T. Amani Alsharidah 1441 – 2019

2. Lecture 5 The chest and its composition

3. The Thorax The thorax is composed of three segments: The first or prothorax. The second or mesothorax The third or metathorax. In most winged insects the mesothorax and metathorax are enlarged relative to the prothorax and form a pterothorax . bearing the wings and associated musculature. Wings occur only on the second and third segments. Almost all nymphal and adult insects have three pairs of thoracic legs : one pair per segment. Typically the legs are used for walking, although various other functions and associated modifications occur.

4. The thorax

5. The thorax Openings spiracles of the gas-exchange, or tracheal system are present laterally on the second and third thoracic segments at most with one pair per segment.

6. The Thorax Thoracic terga are called nota (singular: notum ), to distinguish them from the abdominal terga. The pronotum of the prothorax may be simple in structure and small in comparison with the other nota . In cockroaches the pronotum forms a shield that covers part of the head and mesothorax .

7. The Thorax The insect thorax is a box like structure. It is made up of four sclerites (cuticular plates): 1. notum ( tergum) : the dorsal plate. 2. sternum ( ventral plate) 3. pleuron ( lateral) 1 in each side. The sclerites play important role in locomotion.

8. Legs In most adult and nymphal insects, segmented fore, mid, and hind legs occur on the prothorax, mesothorax, and metathorax. Typically, each leg has six segments , and these are, from proximal to distal: coxa, trochanter, femur, tibia, tarsus, and pretarsus (or more correctly post-tarsus) with claws. The tarsus is subdivided into five or fewer components, giving the impression of segmentation. Generally the femur and tibia are the longest leg segments but variations in the lengths and robustness of each segment relate to their functions.

9. Leg segments The coxa is most often cone like, and is the point of articulation with the thorax, and has varying degrees of mobility depending on the insect group. Trochanter articulate the coxa to the femur, usually small and triangular. Femur is generally small in larval insects, but in most adult insects is the most robust segment of the leg. Tibia is the long shank of the leg and it moves in the vertical plane. Tarsus the tarsus is divided into 1-5sub-segments, which are called tarsomeres. The tarsomeres can move independently. Pretarsus is the apical most segment, and the smallest. It is the point of contact between the insect and its environment. It is most often composed of 1-2 claws, and there may be a lobe-like structure between the claws, called the arolium, which has a supporting or attaching function.

10. The hind leg of cockroach

11. Legs modification 1-walking leg Femur normal not thickened. Femur and tibia are long. Legs are well developed. Example: cockroach

12. Legs modification 2- jumping leg Insects such as grasshoppers have disproportionately developed hind femora and tibiae. Femur with powerful muscles and thick. Example: hind leg of grasshoppers.

13. Leg modification 3- Swimming (natatorial) legs In aquatic beetles (Coleoptera) and bugs (Hemiptera) The tibiae and/or tarsi of one or more pairs of legs usually are modified for swimming with fringes of long slender hairs.

14. Leg modification 4- Digging (fossorial) leg Many ground-dwelling insects, such as mole crickets, nymphal cicadas (Hemiptera: Cicadidae), and scarab beetles ( Scarabaeidae ), Have the tibiae of the fore legs enlarged and modified for digging (fossorial).

15. Leg modification 5- raptorial leg The fore legs of some predatory insects, such as mantispid lacewings ( Neuroptera ) and mantids ( Mantodea ), Specialized for seizing prey. Coxa is very long, femur long and thick with spines. Tibia is shorter.

16. Leg modification 6- collecting pollen and cleaning There are three pairs of legs which are densely covered with hairs , which besides walking, help in collecting pollen and are variously modified

17. A. Prothoracic leg of honeybee Each prothoracic (Fore) leg has: Arow of stiff bristles on tibia forming an eye brush for cleaning the compound eyes . At the distal end of tibia is a movable spine, the velum which can close over a notch on the tarsus to form an antena comb through which the antenna is drawn for cleaning. Long bristles on the tarsus form a pollen brush for removing pollen from the front part of the body. In some references it called antenna cleaner.

18. b. Mesothoracic leg in honeybees Each mesothoracic (middle) leg has a pollen brush on the tarsus. The end of the tibia has a spur like a spine for removing pollen from the pollen basket and wax from abdomen.

19. C. metathoracic leg in honeybees Each metathoracic (hind) leg has a large tibia with a cavity with bristles forming a pollen basket used for storing pollen during collection, At the distal end the tibia has a row of stiff bristles called pecten below which is a flat plate, the auricle. The pecten and auricle form a wax pincher for removing wax from the abdomen of workers . The outer surface of the tarsus has a pollen brush and the inner surface has a pollen comb having rows of stiff spines the pollen comb removes pollen from the body and fills it in the pollen basket.

20. Wings Insects were the first animals to evolve flight and are the only invertebrates that have the ability to fly. Wings are developed fully only in the adult. functional wings are flap-like cuticular projections supported by tubular, sclerotized veins. The venation network allows for fluid and nutrient transport across the structure while providing a mechanical skeleton that stiffens the wing. wings show a range of hierarchies of complexity, varying greatly in size and venation, stiffness and flexibility, pigmentation and flight behaviors.

21. Type of insect wings 1-Membranous wings Example: Dragons Fly, Honeybees. Wings are thin and transparent. They are supported by a system of tubular veins. They are useful in flight.

22. Type of insect wings 2-Fringed wings Example: Thrips Wing lamina is usually reduced in size. Wing margins fringed with long setae .

23. Type of wings 3- Haltere wing Example: Hind Wings of Housefly, flies Wings are modified into small knobbed vibrating organ called halters Which act as balancing organs and provided the needed stability during flight.

24. Type of wings 4-Scaly wings Example: Moths and Butterflies Wings are covered with scales which are unicellular, flattened outgrowths of the body wall. Scales are responsible for color. They are important in smoothening the airflow over wings and body. They also insulate the insect against cold.

25. Type of wings 5- Tegmina wing Forewings of Grasshopper and Cockroach Wings are leathery or parchment-like. They are protective in function. They are not useful for flight.

26. Type of wings Elytra wings Example: Forewings of Beetles and Weevils Wing is heavily sclerotized and thick. Wing venation is lost. Wing is tough and protective in function. It protects the hindwings and the abdomen. It is not used for flight. In flight they are kept at an angle to allow free movement of the hindwings.

27. Type of wings 7- Hemelytra wings Example Red Cotton Bug The basal half of the wing is thick and leathery. The distal half is membranous. They are protective in function and not involved in flight.