The document summarizes the structure of the thorax and appendages of insects. It discusses that the thorax is comprised of three segments - prothorax, mesothorax, and metathorax. Each segment contains a pair of legs and the mesothorax and metathorax together form the pterothorax which contains the fore and hind wings. It also describes the different types of wing coupling mechanisms seen in insects like hamulate, amplexiform, frenate and jugate.

1. STRUCTURE OF THORAX
AND APPENDAGES
PRESENTED BY:
N.AKASH
2021031008

2. THORAX
Pterothorax
3 Segmented
Mesothorax Metathorax
Prothorax

3. Prothorax
Mesothorax Metathorax
Leg I Leg II Leg III
Pterothorax
Thorax
Fore wing
Hind wing

4. THORAX
 Middle tagma
 Three segmented - pro, meso and meta
 Meso and meta thorax with wing are called as
Pterothorax
 Thorax is made of three scleritic plates
1. dorsal body plate - Tergum or Nota
2. ventral body plate (Sterna)
3. lateral plate (Pleura)

5. THORACIC NOTA
 3 segments - pronotum, mesonotum & metanotum
respectively
 Pronotum - undivided & Saddle shaped in grass hopper,
Shield like in cockroach
 Pterothoracic notum - have 3 transverse sutures
(Antecostal, Pre scutal and Scuto-scutellar)
&5 tergites(Acrotergite, Prescutum, Scutum, Scutellum
and Post-scutellum)

6. THORACIC STERNA
 Vental body plate - prosternum,
mesosternum and metasternum
 Made up of a segmental plate called
 Eusternun and a intersternite called Spinasternum
 Eusternum - made of three sclerites - presternum,
basisternum and sternellum

7. THORACIC PLEURA
 Lateral body wall between notum & sternum
 Selerites of pleuron is called as pleurites
 fuse to form Pleural plate
 Pleural plate is divided into anterior episternum
and posterior epimeron by Pleural suture
 Pterothoracic pleuron provides space for articulation of wing
and
 Two pairs of spiracles are also present in the mesopleuron and
metapleuron.

8. ABDOMEN
 Third and posterior tagma
 This tagma is made up of 9-11 Uromeres
(segments) and is highly flexible
 abdominal segments are interconnected by a
membrane called conjunctiva
 Each abdominal segment is made up of only two
sclerite
1. Tergum 2. Sternum

9. ABDOMEN
 Eight pairs of spiracles in - first eight
abdominal segments
 in addition to a pair of tympanum in the first
abdominal segment
 Eight and ninth segments - female genital
structure
 Ninth segment - male genital structure.
 Cerci

10. THORAX APPENDAGES
Legs Wings

11. • Insects have three pairs of legs, One pair each in
pro-, meso- and metathorax - ‘Hexapods’
• Each leg consists of six segments, articulating with
each other by mono-or-dicondylic articulations set
in a membrane, the corium.
LEGS

12. Structure and Types of Insect Legs

13. • Leg pads - walking on smooth surface
• Claws give needed grip - walking on rough surface
• When one structure is used, the other is bent
upwards.

14. Reduction of legs (Adult stage)
(i) Nymphalid butterflies:
In males the tarsus and pretarsus of foreleg are lacking
In females the fore tarsus consists of very short tarsomeres
(ii) Female coccids:
Sedentary - held in position by the stylets. The legs are
reduced.
(iii) Female stylopids:
Legs absent and are parasitic

15. (i) Leaf miners of Lepidoptera, Coleoptera and Sawflies
(ii) Parasitic larvae of Hymenoptera and Strepsiptera
(iii) Grubs of blister beetles
(iv) In Hymenoptera - larvae fed by the adults are apodous
Reduction in leg (Larval stage)

16. Based on the habitat and food habit
1. Walking/ Ambulatorial leg
2. Running / Cursorial leg
3. Jumping / Saltatorial leg
4. Grasping / Raptorial leg
5. Digging / Burrowing / Fossorial leg
6. Swimming / Natatorial leg
7. Clinging / Scansorial leg
8. Honey bee’s legs/ Foragial leg
Types or modifications of legs

17. Wings and its Modifications

18. • Each wing is a hollow extension of the body wall
• It arises dorsolaterally between the pleura and
nota of meso and metathoracic segments.
• The pleural plates of the thoracic segments -
support the bases of the paranotal lobes
Wing development in modern insects
• Adult insects - fully developed wings
• In holometabolus larvae - develop internally
• In hemimetabolous larvae - visible as external pads
• Mayflies have two winged stages viz., subimago and
imago

19. Areas of the wing
• The flexion and fold-lines divide the wing into
different areas.
• The region containing the bulk of the veins in front of
the claval furrow is called remigium.
• The area behind the claval furrow is called clavus
• In hind wings in which this area is greatly expanded
and known as vannus & the fold – vannal fold / plica
vannalis.
• The jugum is cut off by the jugal fold / plica jugalis if
it is present

20. Margins and angles
• triangular in shape – 3 sides & 3 angles
• anterior margin strengthened by the costa - coastal
margin
• lateral margin - apical margin
• posterior margin - anal margin
• angle of attachment to the thorax - humeral angle.
• angle between the coastal and apical margins - apical
angle
• angle between apical and anal margins - anal angle.
Humeral
angle
Costal
Margin
Apical
angle
Apical
margin
Anal angle
Anal
margin
Claval
furrow
Juga
fold

21. Pterostigma
• Pigmented spot on the anterior margin of the wing
• Present on both pairs of wings in Odonata
• In the forewings of many Hymenoptera, Psocoptera, Mecoptera an
Neuroptera.
• In Odonata, - it reduce the wing flutter during gliding and thereb
increases the gliding speed.

22. Wing membrane
• The wing membrane is semitransparent and exhibits
iridescence
• Sometimes wings are patterned by pigments in the
epidermal cells eg. mecoptera and tephritidae
• In insects with hardened forewings such as
Orthoptera and Coleoptera, the whole wing is
pigmented

23.  higher pterygote insects, fore & hind wings -
coupled together as a unit
 both pairs move synchronously
Types of wing coupling
1. Hamulate :
• A row of small hooks - on the
coastal margin of the hind
wing - hamuli.
• engage the folded posterior
edge of fore wing.
• e.g. bees.
WING COUPLING

24. 2. Amplexiform :
• the simplest form of wing coupling
• A linking structure is absent.
• Coupling is achieved by broad overlapping of adjacent
margins.
• e.g. butterflies.

25. 3. Frenate :
There are two sub types. e.g. Fruit sucking moth.
i Male frenate :
• Hindwing bears near the base of the coastal margin
a stout bristle called frenulum
• held by a curved process, retinaculum arising from
the subcostal vein found on the surface of the
forewing

26. ii. Female frenate :
Hindwing bears near the base of the costal margin
a group of stout bristle (frenulum)
engages there in a retinaculum formed by a patch
of hairs near cubitus.

27. 4. Jugate :
Jugam of the forewings are lobe like and it is locked
to the coastal margin of the hind wings.
e.g. Hepialid moths.