This document discusses the classification of insects. It divides the class Insecta into two subclasses: Apterygota and Pterygota. Apterygota includes primarily wingless insects with no metamorphosis. Pterygota is further divided into Exopterygota and Endopterygota. Exopterygota undergo incomplete metamorphosis and include orders like mayflies, dragonflies, and grasshoppers. Endopterygota undergo complete metamorphosis through distinct larval, pupal and adult stages, and include orders such as butterflies, flies, beetles and ants. Examples are provided for most orders.

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

6. 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.

7. 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.

8. 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.

9. 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.

10. 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)

11. 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

12. 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.

13. 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.

14. 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

15. 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.

16. 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).

17. 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

18. 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.

19. 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

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

21. 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.

22. 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

23. 1.Ephemeroptera, Ex: May flies

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

25. 3.Plecoptera Ex: Stone flies

26. 4.Grylloblattoidea Ex: Ice crawellers

27. 5.Orthoptera Ex: Grass hoppers

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

29. 7.Dermptera Ex: Ear wigs

30. 8.Embioptera Ex: Web spinners

31. 9.Dictyoptera Ex: Cockroach

32. 10. Isoptera Ex: White ants

33. 11. Zoraptera Ex: Zorapterans

34. 12. Psocoptera Ex: Book lice

35. 13. Mallophaga Ex: Bird lice

36. 14. Siphunculata Ex: Head louse

37. 15. Hemiptera Ex: Bugs

38. 16. Thysanoptera Ex: Thrips

39. ENDOPTERYGOTA

40. 1.Neuroptera Ex: Ant lions

41. 2.Mecoptera Ex: Scorpion flies

42. 3.Lepidoptera Ex: Butter flies

43. 4.Trichoptera Ex: Caddish flies

44. 5.Diptera Ex: House fly

45. 6.Siphonoptera Ex: Fleas

46. 7.Hymenoptera Ex: Ants

47. 8.Coleoptera Ex: Beetles

48. 9. Strepsiptera Ex: Strepsipterans,stylopids