INSECT ABDOMEN:IT’S SEGMENTATION AND APPENDAGES,STRUCTURE,FUNCTION AND MODIFICATION IN DIFFERENT ORDER OF INSECT.

1. INSECT ABDOMEN:IT’S SEGMENTATION AND
APPENDAGES,STRUCTURE,FUNCTION AND
MODIFICATION IN DIFFERENT ORDER OF INSECT.

2.  The abdomen is third and posterior region of the insect body. The primitive
number of abdominal segments are eleven, with a terminal non segmental
region or telson (12" segment found in Protura), but in higher orders less
than 11 segments are found due to fusion of adjacent segments e. g.
collembolla have only six abdominal segments in both embryonic and adult
stage. Proturans have differ from all other hemimetabolous insects as the
number of abdominal segments increases during post- embryonic
development, the youngest instars having only six or eight segments and a
telson.
 The number of segments increases during postembryonic development is
called as anamorphosis.
 Abdomen possess 8 pairs of spiracles on the first eight abdominal segments
 abdominal segments are telescopic in nature and are interconnected by a
membrane called conjunctiva.
 A pair of cerci found on terminal abdominal segment.
INTRODUCTION

3.  In hymenoptera, first abdominal segment fused together with metathorax
during the changes of form, larva to the pupa, and is known as the
propodeum (epinotum or median segment).
 The 11th segment has three plates i.e. an epiproct dorsal to anus and two
paraprocts, one on either side of the anus.
 Abdomen consists of 11 rings like segments known as Uromere.
 Dorsal plate (sclerites) of abdomen known as tergum and ventral plate
(sclerites) known as sternum. Lateral area is membranous (Pleuron) which
connect tergum and sternum.
 Except supra plate, all tergites are inverted 'U' shaped while sterna are slight
convex ventrally.

4.  The abdomen can be divided into 3 Region:
• The pregenital (or visceral) region - segments 1-7
• The genital region - segments 8-9
• The postgenital region - segments 10-11 (or more if present).
 On 8thand 9th segment of female and 9th segment of male, the appendages
are modified as external organs of reproduction or genetalia.
 The insect's genital opening lies just below the anus: it is surrounded by
specialized sclerites that form the external genitalia.
 In females, paired appendages of the eighth and ninth abdominal segment
fit together to form an egg-laying mechanism called the ovipositor. These
appendages consist of four valvifers (basal sclerites with muscle
attachments) and six valvulae (apical sclerites which guide the egg as it
emerges from the female's body).
 In males, the genital opening is usually enclosed in a tube-like aedeagus
which enters the female's body during copulation (like a penis).

5.  The structure of these genital sclerites differs from species to species to the
extent that it usually prevents inter-species hybridization and also serves as a
valuable identification tool for insect taxonomists. In general, the 11th segment
is the last true somite of the adult insect. In all insects the 11th segment is
reduced. In the grasshopper, the 11th segment is reduced to a tergal plate called
the epiproct, and 2 later ventral plates called paraprocts. It can also be united
with the 10th segment (as in some Homoptera) to form an anal tube.
Sometimes the 11th segment is suppressed or completely absent forming a 10th
segmented abdomen (in all holometabolous insects). The 11th segment is the
only postgenital segment with any indication of having true appendages called
cerci.
 Cerci are often implanted in the intersegmental membrane between the 10th
and 11th segments or between the epiproct and paraprocts. They are not present
in all insects.

6. Abdominal Structure
 Spiracles: Respiration
 Cercus: hind sensor
 Anus: paraproct + epiproct
 Claspers: female egg laying can be modified into
stinger in some wasps and bees.
 Most adult insects have the same number of abdominal
segments as the immature forms this type of
development is called epimorphic.this is not true in the
proturans.they start with 8 abdominal segments and
increase to 11 segments and a telson by the 4th instart.
this type of development is called anamorphic

7. Abdominal appendages:
 Pregenital abdominal appendages in wingless
insects:
1) Styli : Varying number of paired tube like outgrowths are
found on the ventral side of the abdomen of silverfish. These
are reduced abdominal legs which help in locomation.
2) Collophore or ventral tube or glue peg: It is located on the
ventral side of the first abdominal segment of spring tail. It is
cylindrical. It is protruded out by the hydrostatic pressure of
haemolymph. It might serve as an organ of adhesion. It aids in
water absorption from the substratum and also in respiration.
3) Retinaculum or tenaculum or catch: It is present on the
ventral side of the third abdominal segment. It is useful to hold the
springing organ which not in use.
4) Furcula or Furca: This is a 'Y' shaped organ. It is present on
the venter of fourth abdominal segment. When it is released from
the catch, it exerts a force against the substratum and the insect is
propelled in the air.

8. Abdominal appendages in immature insects:
1) Tracheal gills: Gills are lateral outgrowths of
body wall which are richly supplied with
tracheae to obtain oxygen from water in naiads
(aquatic immature stages of hemimetabolous
insects). Seven pairs of filamentous gills are
present in the first seven abdominal segments of
naiads of mayfly and are called as lateral gills.
Three or two leaf like gills (lamellate) are found
at the end of abdomen of naiad of damselfly and
are called as caudal gills. In dragonfly the gills
are retained within the abdomen in a pouch like
rectum are called as rectal gills.
2) Anal papillae: A group of four papillae
surrounds the anus in mosquito larvae. These
papillae are concerned with salt regulation.

9. 3) Dolichasters: These structures are
found on the abdomen of antlion grub.
Each dolichaster is a segmental
protuberance fringed with setae.
4) Prolegs: These are present in the larvae
of moth, butterfly and sawfly. Two to five
pairs are normally present. They are
unsegmented, thick and fleshy. The tip of
the proleg is called planta upon which are
borne heavily sclerotised hooks called
crochets. They aid in crawling and
clinging to surface.

10. Abdominal appendages in winged adults:
1) Cornicles: Aphids have a pair of short tubes
known as cornicles or siphonculi projecting
from dorsum of fifth or sixth abdominal
segment. They permit the escape of waxy fluid
which perhaps serves for protection against
predators.
2) Caudal breathing tube: It consists of two
grooved filaments closely applied to each other
forming a hollow tube at the apex of
abdomen.e.g.waters scorpion.

11. 3) Cerci : (Cercus - Singular) They are the
most conspicuous appendages associated
normally with the eleventh abdominal
segment. They are sensory in function. They
exhibit wide diversity and form.
• long and many segmented:e.g.may fly
• long and unsegnmented: e.g.cricekt
• short and many segmented:e.g.cockroach
• short and unsegmented:e.g.grasshopper
• Sclerotised and forceps like : e.g. Earwig.
Cerci are useful in defense, prey capture,
unfolding wings and courtship.
4) Asymmetrical cerci : Male embiid. Left
cercus is longer than right and functions as
clasping organ during copulation.

12. 5) Median caudal filament: In mayfly (and
also in a wingless insect silverfish) the
epiproct is elongated into cercus like median
caudal filament.
6) Pygostyles: A pair of unsegmented cerci
like structures are found in the last abdominal
segment of scoliid wasp.
7) Anal styli: A pair of short unsegmented
structure found at the end of the abdomen of
male cockroach. They are used to hold the
female during copulation.
8) Ovipositor: The egg laying organ found in
female insect is called ovipositor. It is suited
to lay eggs in precise microhabitats. It
exhibits wide diversity and form.
 Short and horny :e.g. Short horned
grasshopper.
 Long and sword like: katydid

13. Abdominal Function
 The abdomen is the final and largest body region. It holds
most of the insect's guts and reproductive organs. Some insects
breathe directly through skin or gills, but most breathe through
small holes on the sides of the body, called spiracles.

14. Modification in different order of insect
 COLLEMBOLA (Spring-tails):
• The abdomen is composed of six segments only.
• collophore or ventral tube: on ventral surface
of 1st abdominal segment; fleshy,may function as
either an adhesive organ for waking or for water
uptake.
• Furcula : the "springtail" jumping organ found
in Collembola on the ventral side of the fourth
abdominal segment.
• Tenaculum; is used for jumping. Tenaculum - a
catch on the ventral surface of the 3rd abdominal
segment; is a catch to hold the furcula.
THYSANURA: The abdomen is composed of
11 segments. The 10th segment is reduced and
bears no appendages while the 11th is also small
but carries the cerci and its tergum is prolonged
into the median cerciform appendage. The 8th
and 9th abdominal segments are modified
through the development of external genitalia.
These have styli that arise from flattened plates
called the coxopodites.

15.  ODONATA (DRAGONFLIES) :
 The Abdomen is always greatly elongate
in proportion to its breadth, and in
extreme cases it is so attenuated as to be
scarcely thicker than a stout bristle.
 Ten complete segments are evident and
parts of the 11th segment and the telson
are also recognizable. In males of the
Anisoptera and a few Zygoptera the
second abdominal tergite bears lateral,
spinose processes, the auricles or
oreillets, which apparently act as guides,
enabling the end of the female abdomen
to make effective contact with the
secondary copulatory organ of the male.

16.  ISOPTERA(TERMITES & WHITE ANTS):
• The abdomen has 10 visible terga, the
11th tergum probably being fused with
the 10 th while the 11th sternum is
represented by a pair of paraprocts.
• The terminal segment of the abdomen
carries a pair of short cerci which are
present in all castes
• In queen termite after mating the
abdomen becomes gradually swollen
due to enlargement of overies.
• Obesity of abdomen of queen termite is
called physogastry.

17.  ORTHOPTERA:
 The hind region of the grasshopper's body, the
abdomen, consists of 11 segments. 1 segment is
firmly fused with the metathorax and contains
the auditory organ with its eardrum cover, the
tympanum.
 Eleven segments are recognizable in the
abdomen, though the first sternum is reduced and
the terminal segments modified in connexion
with the genitalia In the female there is usually a
well-developed ovipositor which, in its most
complete form (Tettigonioidea), consists of three
pairs of long valves held together by tongue and
groove joints. The anterior (ventral) valves are
derived from the 8th abdominal segment, a basal
sclerite representing the coxite while the large
valve corresponds with the gonapophysis. The
inner and posterior (dorsal) valves originate from
the reduced 9th abdominal sternum, the former
pair being gonapophyses while the latter are
modified coxites. A discrete gonangulum is
present, with the normal articulation

18.  HEMIPTERA ( PLANT BUGS) :
 Its least modified condition, as in many Homoptera 11
segments are present though the first two may be
modified in connection with sound-producing organs.
 the 8th and 9th undergo changes due to the development
of external genitalia and the 10th and 11th are small
annuli at the end of which the anus opens.
 Cornicles are tubes that project from the abdomen of
an aphid. There are usually a single pair of cornicles
with one on each side of the abdomen. The cornicles
are used to emit pheromones or defensive secretions. It
is often incorrectly believed that honeydew is secreted
from the cornicles.

19.  COLEOPTERA (BEETLES):
 The Abdomen - The number of segments
comprising this region of the body is difficult to
determine. As a rule the 1st tergum is membranous
and one or more of the sterna from the 1st to the 3rd
are aborted. The 1st sternite is never visible
externally and is at most traceable in vestigial form
at the back of the hind coxal cavities. Eight tergites
are commonly visible externally, the 9th and 10th
plates being invaginated
 The Adephagid type -The hind coxae are
immovably fused with the metathorax and
completely divide the 1st visible abdominal sternite
which is more or less fused with the next two, the
sulci between them being partly obliterated
 The haplogastrous type - The 2nd abdominal
segment exhibits a pleurite and a small lateral plate
representing the sternite. Exceptionally, in some
Staphylinidae, the 2nd sternite is complete
 The symphiogastrous type - The pleurite of the 2nd
abdominal segment is fused to that of the 3rd and the
sternite is membranous and nowhere visible
externally
 The hologastrous type - In some Cantharoidea,
the 2nd abdominal sternite is, perhaps secondarily,
fully sclerotized and distinct from the 3rd
Fig:Three types of
abdomen in Coleoptera.
A.Haplogastrous type
B.Symphiogastrous type
C.Hologastrous type

20.  DIPTERA:
 In the Abdomen the first segment is usually
much reduced. Of the segments that follow
the 2nd - 11th are present in Tipula, but
among the Cyclorrhapha the number is
difficult to ascertain, and rarely more than 4
or 5 are evident without dissection.
 There are two spiracles in the thorax and
may be eight in the abdomen. Their position
in the latter and the number which remain
functional is modified in higher groups.
Their regulatory mechanism is discussed by
Hassan. Fig. Abdomen of Calliphora

21.  LEPIDOPTERA :
 Ten abdominal segments are present and a
certain number are always fixed and
immovable. The only free segments are
the 4th , 5th and 6th in both sexes, while
among certain of the butterflies all the
segments are immovable. Spiracles are
present on the first eight segments. The
anus is carried on the caudal margin of the
10th segment, and this somite is produced
to form the cremaster, which is the
homologue of the suranal plate of the larva
 HYMENOPTERA:
 The Abdomen is restricted physiologically
to the region which commences with the
2nd segment, the 1st abdominal segment
being the propodeum already referred to.
The region behind the propodeum may be
called the gaster or metasoma
 The number of segments that can be
identified in the gaster varies very greatly:
the maximum number of nine are present
in the Tenthredinidae. As a rule, in the
higher groups, there are six exposed
segments in the females and seven or eight
in the males.