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

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 11 th 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 11 th segment is the last true somite of the adult insect. In all insects the 11 th segment is reduced. In the grasshopper, the 11 th segment is reduced to a tergal plate called the epiproct, and 2 later ventral plates called paraprocts. It can also be united with the 10 th segment (as in some Homoptera) to form an anal tube. Sometimes the 11 th segment is suppressed or completely absent forming a 10 th segmented abdomen (in all holometabolous insects). The 11 th 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 10 th and 11 th 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 4 th 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 1 st 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 3 rd abdominal segment; is a catch to hold the furcula. THYSANURA: The abdomen is composed of 11 segments. The 10 th segment is reduced and bears no appendages while the 11 th is also small but carries the cerci and its tergum is prolonged into the median cerciform appendage. The 8 th and 9 th 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 11 th 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 11 th tergum probably being fused with the 10 th while the 11 th 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 8 th 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 9 th 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 8 th and 9 th undergo changes due to the development of external genitalia and the 10 th and 11 th 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 1 st tergum is membranous and one or more of the sterna from the 1 st to the 3 rd are aborted. The 1 st 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 9 th and 10 th plates being invaginated The Adephagid type -The hind coxae are immovably fused with the metathorax and completely divide the 1 st visible abdominal sternite which is more or less fused with the next two, the sulci between them being partly obliterated The haplogastrous type - The 2 n d abdominal segment exhibits a pleurite and a small lateral plate representing the sternite. Exceptionally, in some Staphylinidae , the 2 n d sternite is complete The symphiogastrous type - The pleurite of the 2 n d abdominal segment is fused to that of the 3 rd and the sternite is membranous and nowhere visible externally The hologastrous type - In some Cantharoidea , the 2 n d abdominal sternite is, perhaps secondarily, fully sclerotized and distinct from the 3 rd 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 2 n d - 11 th 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 4 th , 5 th and 6 th 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 10 th 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 2 n d 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.

22. Thank you