Character of insecta

Entomology Insect characters

1. 2. Characters of class Insecta – Division of class Insecta into subclasses – pterygota , Apterygota , their characters, classifications and examples

2. Character of Insecta Insects have segmented bodies, jointed legs, and external skeletons (exoskeletons). Insects are distinguished from other arthropods by their body, which is divided into three major regions: 1 . The head, which bears the mouthparts, eyes, and a pair of antennae, 2 . The three-segmented thorax, which usually has three pairs of legs (hence “ Hexapoda ”) in adults and usually one or two pairs of wings. 3 . The many-segmented abdomen, which contains the digestive, excretory, and reproductive organs

3. The Insect Head The insect's head is sometimes referred to as the head-capsule, and is the insect's feeding and sensory centre . It supports the eyes, antennae and and jaws of the insect. (Note -: insects do not breath through their mouths but through their thoracic and abdominal spiracles ) The upper-mid portion of an insects face is called the 'frons' below this is the 'clypeus' and below this the 'labrum' to either side of which may be seen the edges of the 'mandibles' in some insects various aspects of the ' maxilliary ' palps may extend beyond and or below these even when viewed from front on.

4. Sclerites and sutures of head The head capsule is formed by the union of number of sclerites or cuticular plates or areas which are joined together by means of cuticular lines or ridges known as sutures . These sutures provide mechanical support to the cranial wall. A general insect posses the following sclerites .

5. 1. Labrum : It is small sclerite that forms the upper lip of the mouth cavity. It is freely attached or suspended from the lower margin of the clypeus 2. Clypeus: It is situated above the labrum and is divided in to anterior ante-clypeus and posterior post-clypeus. 3. Frons : It is the facial part of the insect consisting of median ocellus. 4. Vertex : It is the top portion of the head behind the frons or the area between the two compound eyes.

6. 5. Epicraniun : It is the upper part of the head extending from vertex to occipital suture. 6. Occiput : It is an inverted “U” shaped structure representing the area between the epicranium and post occiput (Fig. 6). 7. Post occiput : It is the extreme posterior part of the insect head that remains before the neck region.

7. 8. Gena : It is the area extending from below the compound eyes to just above the mandibles 9. Occular sclerites : These are cuticular ring like structures present around each compound eye 10. Antennal sclerites : These form the basis for the antennae and present around the scape which are well developed in Plecoptera (stone flies)

8. All the above sclerites gets attached through cuticular ridges or sutures to provide the attachment for the muscles inside. The common sutures present in head are 1 ) Clypeolabral suture : It is the suture present between clypeus and labrum. It remains in the lower margin of the clypeus from which the labrum hangs down. 2 ) Clypeofrontal suture or epistomal suture: The suture present between clypeus and frons

9. 3) Epicranial suture: It is an inverted ‘Y’ shaped suture distributed above the facial region extending up to the epicranial part of the head. It consists of two arms called frontal suture occupying the frons and stem called as coronal suture. This epicranial suture is also known as line of weakness or ecdysial suture because the exuvial membrane splits along this suture during the process of ecdysis . 4 ) Occipital suture: It is ‘U’ shaped or horseshoe shaped suture between epicranium and occiput.

10. 5) Post occipital suture: It is the only real suture in insect head. Posterior end of the head is marked by the post occipital suture to which the sclerites are attached. As this suture separates the head from the neck, hence named as real suture. 6) Genal suture: It is the sutures present on the lateral side of the head i.e. gena . 7 ) Occular suture: It is circular suture present around each compound eye. 8 ) Antennal suture: It is a marginal depressed ring around the antennal socket.

11. Neck: The Neck grease is a short slender feature that attacks to the head. The base is supported by a pair of posterior and two greiva plaques in the abdomen the muscles of the neck help the head. To rotate all the sides

12. The Thorax The thorax is the midsection (tagma) of the insect body. It holds the head, legs, wings and abdomen. It is also called mesosoma in other arthropods. It is formed by the prothorax, mesothorax and metathorax and comprises the scutellum; the cervix, a membrane that separates the head from the thorax; and the pleuron , a lateral sclerite of the thorax.

13. Abdomen forms the posterior part of the insect body . Pre genital appendages are absent in pterygotes and present in Apterygotes . The abdomen in the embryo usually consists 12 segments, later the last segments degenerate and appear as 7- 11 segments. Last segment is known as telson or tail as in case of Protura . Abdominal Segments from 1 to 7 are pregenital segments, eighth and ninth are known as genital segments as they form genital appendages i.e. ovipositor in females and aedeagus or penis in males.Tenth and eleventh segments are known as postgenital segments. The 10th segment in general forms the supra anal plate and 11th segment is represented by a pair of anal cerci (usually known as post- genital abdominal appendages ).

14. Apterygota Primarily wingless evolved from wingless, ancestors Metamorphosis is totally absent or slight Mandibular articulation in head is monocondylic i.e., single Pleural sulcus in thorax is absent Pregenital abdominal appendages Present Pterygota Winged or secondarily wingless. Evolved from winged ancestors. E.g. Flea, headloushe, bed bug. Present Dicondylic i.e., double Present Absent

15. PTERYGOTA Pterygote has two sub classes 1. Exopterygota , 2. Endopterygota Exopterygota The Exopterygota , also known as Hemipterodea , are a superorder of insects of the subclass Pterygota in the infraclass Neoptera , in which the young resemble adults but have externally developing wings . They undergo a modest change between immature and adult, without going through a pupal stage. The nymphs develop gradually into adults through a process of moulting .

16. Exopterygota has 16 orders 1. Ephemeroptera , Ex: May flies 2. Odonata , Ex: Dragon flies 3. Plecoptera Ex: Stone flies 4. Grylloblattoidea Ex: Mole cricket 5. Orthoptera Ex: Grass hoppers 6. Phasmida Ex: Walking sticks 7. Dermptera Ex: Ear wigs 8. Embioptera Ex: Web spinners 9. Dictyoptera Ex: Cockroach 10. Isoptera Ex: White ants 11. Zoraptera Ex: Zorapterans 12. Psocoptera Ex: Book lice 13. Mallophaga Ex: Bird lice 14. Siphunculata Ex: Fleas 15. Hemiptera Ex: Bugs 16. Thysanoptera Ex: Thrips

17. 9.Strepsiptera Ex : Strepsipterans 14.Grylloblattoidea grylloblattodians 15.Phasmida Ex: Walking sticks 16. Psocoptera :Book lice

18. Endopterygota Endopterygota (from Ancient Greek endon “inner” + pterón , “wing” + New Latin - ota “having”), also known as Holometabola , is a superorder of insects within the infraclass Neoptera that go through distinctive larval, pupal, and adult stages. They undergo a radical metamorphosis, with the larval and adult stages differing considerably in their structure and behaviour . This is called holometabolism , or complete metamorphism.

19. Endopterygota has 9 orders 1. Neuroptera Ex: Ant lions 2. Mecoptera Ex: Scorpion flies 3. Lepidoptera Ex: Butter flies 4. Trichoptera Ex: Caddish flies 5. Diptera Ex: House fly 6. Siphonoptera Ex: Fleas 7. Hymenoptera Ex: Ants 8. Coleoptera Ex: Beetles 9. Strepsiptera Ex: Strepsipterans

20. 1. Ephemeroptera , Ex: May flies

21. 2. Odonata, Ex : Dragon flies,Damselflies

22. 3. Plecoptera Ex: Stone flies

23. 4. Grylloblattoidea Ex : Ice crawellers

24. 5. Orthoptera Ex: Grass hoppers

25. 6. Phasmida Ex: Walking sticks,leaf insects

26. 7. Dermptera Ex: Ear wigs

27. 8. Embioptera Ex: Web spinners

28. 9. Dictyoptera Ex: Cockroach

29. 10. Isoptera Ex: White ants

30. 11. Zoraptera Ex: Zorapterans

31. 12. Psocoptera Ex: Book lice

32. 13. Mallophaga Ex: Bird lice

33. 14. Siphunculata Ex: H ead louse

34. 15. Hemiptera Ex: Bugs

35. 16. Thysanoptera Ex: Thrips

36. ENDOPTERYGOTA

37. 1. Neuroptera Ex: Ant lions

38. 2. Mecoptera Ex: Scorpion flies

39. 3. Lepidoptera Ex: Butter flies

40. 4. Trichoptera Ex: Caddish flies

41. 5. Diptera Ex: House fly

42. 6. Siphonoptera Ex : Fleas

43. 7. Hymenoptera Ex: Ants

44. 8. Coleoptera Ex: Beetles

45. 9. Strepsiptera Ex : Strepsipterans,stylopids