in thorax of insect which sclerites is seeing

1. SCLERITES OF THORACIC SEGMENT
Assignment on
PREPARED BY:
Rudani Gaurang K.
M.Sc.(Agri.)Entomology
Semester: 1st
C. P. College of Agriculture,
S. D. Agricultural University,
Sardarkrushinagar
SUBMITTED TO:
Dr. P. S. Patel
Associate Professor
Dept. of Agril. Ento
C. P. College of Agriculture,
S. D. Agricultural University,
Sardarkrushinagar

2.  INTRODUCTION
 Thorax is the body region situated between head and the abdomen.
 The insect thorax is divided into three parts:
a) Prothorax (pro=first)
b) Mesothorax (meso=middle)
c) Metathorax (meta=last)
 The insect thorax is a box-like structure and is composed of a number of sclerites which play
an important role in insect locomotion.
 Each segment consists of hardened plates, or sclerites.
1. Dorsal sclerites- notum
2. Lateral sclerites- pleuron
3. Ventral sclerites- sternum
 Each of the three thoracic segments contains one pair of legs arise from pleura. Wings
articulated between notal and pleural regions.

3. Fig. Three regions of the insect body

4. Legs articulated on ventro lateral position
one pair on prothorax
one pair on mesothorax
one pair on metathorax
Wing articulated on dorso-lateral position
one pair on mesothorax
one pair on metathorax
Two slit like opening present on thorax known as spiracles
one pair between prothorax and mesothorax
one pair between mesothorax and metathoax

5. Prothorax never beras wings and it may vary in size. Sometime, the
dorsal regions of prothorax enlarged and from shield like structure
known as pronotum. e.g orthoptera. The pronotum is the dorsal sclerites
of the prothorax, which can be highly modified in various orders such as
the hemiptera, blattadia and coleoptera.
Sclerites of thoracic segment
Protergum is refers as the tergum of the prothorax,
Mesotergum is the tergum of mesothorax and
metatergum is the tergum of metathorax

6.  THORACIC SEGMENTATION
In larval holometabolous insects the cuticle is soft and flexible, or only partially
sclerotized, and longitudinal muscles are attached to the intersegmental folds.
This represents a primitive condition comparable with that occurring in the annelids.
When the cuticle is sclerotized, sclerites in the intersegmental folds which have
longitudinal muscles attached to them are usually fused with the segmental sclerites
behind.
Anteriorly it incorporates the intersegmental region, the original fold being marked by
the antecostal sulcus where the cuticle is inflected.

8. The narrow rim-acrotergite which never occurs at the front of the
prothorax because anterior part of this segment forms part of the neck &
the muscles from the head pass directly to the acrotergite of the
mesothorax.
An area at the back of each segment remains membranous, forming a
new intersegmental membrane.
This basic condition with a membranous area at the posterior end of each
segment occurs in the abdomen where this is sclerotized, in the meso
and meta-thoracic segments of larval insects with a sclerotized thorax.
In the Apterygota and in adult Blattodea and Isoptera where the wings
are not moved by indirect muscles

9. SUTURE OF TERGUM, STERNUM AND
PLEURON

10.  TRANSVERSE STRUCTURE OF AN INSECT THORAX:

11. 1. TERGUM
The tergum of the prothoracic segments- pronotum.
 Prothoracic tergum is an undivided skeletal plate.
Tergum is simple in wingless/immature winged insects and modified in
winged insects.
In winged insects the tergum divided into 2 parts-
a) Alinotum: anterior, wing-bearing portion,
- internally bears anterior phragma (antecosta)
a) Postnotum: posterior portion, wingless;
- bears posterior phragma -modified for wing support
Notum of wing bearing segments is divided by transverse sutures.
They are the prescutum, scutum and scutellum.

12. Fig. Tergum and there sutures

13. 2. STERNUM
The primary sclerotizations on ventral side are segmental and inter segmental
plates which often remain separate in thorax.
The prosternum resembles with sterna of the pterothorax.
The sternum of any thoracic segment is composed of a segmental plate, the
eusternum and the frontal intersegmental sclerite, spinasternum.
Eusternum: Large anterior plate, divided into 3 sclerites, the presternum, the
basisternum and the sternellum.
Sternocostal suture which seperates basisternum from the sternellum.
Spinasternum called as poststernellum, smaller posterior plate
 Spina and furca provide areas for attachment to ventral longitudinal muscles.

14. Fig. Sternum region of insect thorax.

15. Fig. Sternum and there suture

16.  Basisternum is bigger, providing for attachment of the large
dorso ventral flight muscles.
Sternum is attached to pleuron by pre and post-coxal bridges.
Arising of eusternum are a pair of apophyses called as sternal
apophyses.
The origins of these on sternum are marked externally by pits
joined by a sulcus.

17. In higher insects, two apophyses arise together in midline and
only separate internally, forming a Y-shaped furca.

18. 3. PLEURON
Pleural regions are membranous in many larval insects, but typically
become sclerotized in adult.
Consists of three sclerites; one ventral, the sternopleurite and two dorsal,
the anapleurite and coxopleurite which may originally have been derived
from coxa.
Sternopleurite articulates with coxa. It is fused with sternum and becomes
its integral part.

19. The anapleurite and coxopleurite are separated from one another in the
Apterygota and larvae of Plecoptera.
 In the adult pterygote insects, they fuse to form a common pleuron. The
coxopleurite or its anterior remnants remain partially separated in lower
pterygote insects.
 In these insects they form a distinct sclerite, trochantin as an additional
ventral articular sclerite for articulation with coxa.
Stonefly

20. Fig. Pleuron and there suture

21. In higher insects, trochantin may reduce or fuse with lower margin of
episternum.
Trochantin and coxal articulation is used as in many cases, important for
leg movements.
Pleuron of the pterothoracic segments is divided by a pleural suture which
extends from pleural ring process onward to pleural coxal process into two
pleurites;
a)Anterior episternum
b)Posterior epimeron.

22.  Pleural suture: internally forms Pleural ridge
-Gives strength to pleuron
-Bears Pleural apophyses in winged segments
-Arm like projection directed ventrally, associated with a Sternal
apophyses
 In some insects, episterna and epimera are divided into two parts by a
transverse suture.