This document provides information on the structure of the thorax and abdomen in insects. It describes the key segments and sclerites that make up the thorax, including the prothorax, mesothorax, and metathorax. Each segment contains a notum, pleura, and sternum. The mesothorax and metathorax each contain a pair of wings. The abdomen is segmented and contains the respiratory and reproductive structures. Spiracles are located between abdominal segments for respiration. The reproductive structures are located on segments 8-9. Abdominal appendages include styli, collembolan appendages, cornicles, gills, prolegs, cerci, and others.

1. Lecture no. 7
Body segmentation: Structure of thorax
and abdomen
R K PANSE
Assistant Professor
Entomology

2. Insect Structure

3. Thorax
It is the middle part of the body
consisting of three segments
- prothorax
- mesothorax
- metathorax
Each segment consists of hardened plates,
or sclerites. Dorsal sclerites are called nota
(singular notum) or tergite (tergum), lateral
sclerites are called pleura (singular
pleuron), and ventral sclerites are called
sterna (singular sternum).

4. Mesonotum
Pro sternum
Pronotum Metanotum
Meso sternum
Mesopleura
Metasternum
Meatpleura
The dorsal sclerites of pro-, meso- and meta-thoracic segments
are called as pronotum, mesonotum and metanotum.
The ventral sclerites of pro-, meso- and meta-thoracic segments
are called as prosternum, mesosternum and metasternum.
The lateral sclerites of meso- and meta-thoracic segments are
called as mesopleura and metapleura and plurite in
prothorax is absent.

5. Each thoracic segment contains one pair of legs.
Wings are found only on the meso- and metathoracic
segments, and are together called as pterothorax.
Prothorax never bears wings.
 Two pair of spiracles found in meso and meta thorax on
lateral side.

6. • Main function of thorax : locomotion centre
- walking/running
- jumping
- swimming
- flying

7. Structure of abdomen
 The insects abdomen is the third region.
 longer than head and thorax.
 Insects abdomen usually consists of six (Collembolas)
to ten segments.
 its terminates in the paraproct, where the anus opens.
This paraproct may form a lobe like epiproct
above the anus and a pair of leteral
paraprocts around it.
Abdomen

8. The dorsal and ventral abdominal segments are termed
terga (singular tergum) and sterna (singular sternum),
respectively. Plural membrane found in place of Plurite in
abdomen.
Spiracles usually can be found in the conjunctive tissue
between the terga and sterna of abdominal segments 1-8.
Reproductive structures are located on the 9th segment in
males (including the aedeagus, or penis, and often a pair of
claspers) and on the 8th and 9th abdominal segments in
females (female external genitalia copulatory openings and
ovipositor).

9. Abdomen
• Functions:
- respiration
- excretion
- reproduction

10. Abdomen
• Spiracles
- openings involved in respiration
- located on each side of abdomen
• Cerci
- sensory organs
• Ovipositor
- egg-laying structure
- stingers (modified ovipositor
found in some females)

11. Abdominal Appendages
Abdominal appendages of insects can be grouped as
Pre-genital appendages,
Genital appendages and
Post genital appendages.
Pre-genital appendages: Appendages prior to eight
segments
• Styliform appendages: In primitive apterygotes or in non-
insect hexapods, there are pairs of small,
unjointed styli each inserted on a basal
sclerite called coxa along with eversible
vesicles
•Collembolan appendages: On the third abdominal
segments, a median lobe called ventral tube
projects and at its tip long and tubular
eversible vesicles are present in pair.

13. •Cornicles or siphunculi
•Gills
•Prolegs or pseudolegs
•Genital appendages: The reproductive openings and genitalia
are found on the 9th abdominal segment in male
and on eight and ninth abdominal segments in the
female are commonly called genital appendages
Post genital appendages
Cerci:
Median caudal filament:
Terminal spines: