Insect Genitalia: It’s Structure, functions and modification in different orders of insect.

Insect Genitalia: It’s Structure, functions and modification in different orders of insect.

1. Insect Genitalia: It’s Structure, functions and modification in different orders of insect.

2. Insect Genitalia: It’s Structure, functions and modification in different orders of insect s .

3. INTRODUCTION: The insect abdomen is more obviously segmental in origin than either the head or the thorax, consisting of a series of similar segments, but with the posterior segments modified for mating and oviposition. In general, the abdominal segments of adult insects are without appendages except for those concerned with reproduction and a pair of terminal, usually sensory, cerci. Pregenital appendages are, however, present in Apterygota and in many larval insects, as well as in non- insectan hexapods. Aquatic larvae often have segmental gills, while many holometabolous larvae, especially among the Diptera and Lepidoptera, have lobe-like abdominal legs called prolegs.

4. Definition: The organs concerned specifically with mating and the deposition of eggs are known collectively as the external genitalia, although they may be largely internal. Insect genitalia, especially male genitalia, is often directionally asymmetrical, and this trait has evolved multiple times in various orders. Abdomen in insects is divided into three main areas: Pregenital segments: Which include the first seven segments and be free from appendages in adult phase. Genital segments: Include the ninth segment in male and carting genital appendages. In females, paired appendages of the eighth and ninth abdominal segment fit together to form an egg-laying mechanism called the ovipositor. Post genital segments: Include the tenth and eleventh segment. Carrying the two appendages anal cerci.

5. Female genitalia: Structure and Function . In some insects the female has no special structures associated with egg-laying, but in others the posterior part of the abdomen or some posterior abdominal appendages are modified to form an ovipositor. The ovipositor: In the female most of the differentiation of the genital segments is due to the development of an ovipositor. The ovipositor is nearly always rudimentary or suppressed in those insects in which the genital openings are on the 9th segment, and often it is reduced or absent in those with the openings on the 8th segment.

6. Typically there are 3 valves of the ovipositor

7. Male genitalia: Structure and Function The external male genitalia are primarily concerned with coupling with the female genitalia and the intromission of the sperm. Structure of male genitalia: Phallic organs Genital chamber (pocket) - may conceal external genitalia - invagination in body wall where phallus can be protected - usually a ventral invagination between segments 9 and 10. Phallus (penis) - organ of male on which the male gonopore is located - terminal portion of the ejaculatory duct. (1) Aedeagus distal part of phallus (tip). (2) Ectophallus - outer wall of aedeagus. (3) Endophallus - inner wall of aedeagus. (4) Gonopore - opening of ejaculatory duct. (5) Phallotreme - opening of aedeagus. (6)

8. Phallomeres - accessory lobes at side of gonopore - in some insects these actually form phallus. Periphallic organs - most are on the 9th segment; some are on the 7th and 8th segments. These are accessory structures which can be classified by whether they are movable or immovable. These are often called claspers , and they may be derived from parameres , cerci, or paraprocts . Movable - harpagones - occur in Ephemeroptera, Lepidoptera, Diptera , Hemiptera, and a few others (in most holometabolous insects). They are movable clasping hooks. They are called a number of different names depending upon what insect they are present in - eg. hamulus , parameres , etc. Immovable - different accessory processes (a number of them) which are immovable extensions of the tergum and/or sternum Male genitalia structure:

9. Modification of genitalia in different insect orders:  

10. THYSANURA(Bristle tails, silverfish) : Female genitalia: In the female, panoistic ovarioles number 5 on each side in lepismatidae and 7 in machilidae . In the machilidae the ovarioles join a lateral oviduct one behind the other so as to present a metameric appearance. The two oviducts join to form short vagina which, opens behind the 7 th abdominal segment in Lepisma and Neomachilis and behind the 8 th in Nicoletia . In the Lepismatidae a spermatheca and a pair of accessory glands are present, but the Machilidae do not possess them. Male genitalia: In the male the testes comprise a group of lobes, each apparently made up of several follicles. The vasa deferentia are more or less convoluted. According to Gustafson in Lepisma and ctenolepisma the vasa deferentia of opposite sides do not join but extend separately into the penis on which they open by a pair of gonopores. In other cases there is a short median ejaculatory duct.

11. Diplura (Japygids) Female genitalia: In the Female of Campodea has single pair of large polytrophic ovarioles but in other members of the order they are panoistic . Japyx has 7 metamerically arranged ovarioles on each side ( 1 st to 7 th abdominal segments). In all cases the vagina is extremely short and the two oviducts combine immediately before opening by the gonopore behind the 8 th abdominal sternum. Male genitala : In the male, Campodea has a single pair of large testes with a very short vas deferens on each side. Japyx has 1 pair of testes with long, convoluted vas deferentia .

12. Odonata:( dragon fly) Female genitalia: Each ovary composed of a large number of longitudinally arranged panoistic ovarioles. The two oviducts are very short and open into a large pouch like spermatheca in the 8 th segment. A pair of accessory glands communicates by a common duct with the dorsal side of the spermatheca. Male genitalia : The vasa deferentia are rather short narrow tubes which enter a common duct just above the genital aperture. The common passage is dilated to form a conspicuous sperm sac. The spermatophore are somewhat mucilaginous externally and are adopted for transfer from the 9 th to the 2 nd segment before copulation.  

13. Ephemeroptera(May flies): There are no accessory glands, and the gonoducts are paired in both sexes, each duct opening to the exterior separately. Female genitalia: Each ovary is composed of a large number of samll panoistic ovarioles, disposed along a common tube which is continued posteriorly as the oviduct. Male genitalia: In the male the testes are ovoid sacs, and the two vasa deferentia each communicate separate penis of its side.

14. Grylloblattodea (Rock crawlers): Female genitalia: In the female the 8 th sternite is somewhat reduced and bears the anterior pair of ovipositor valves. The 9 th sternite is greatly reduced but bears the remaining two pairs of ovipositor valves; a gonangulum is also present. Male genitalia: In the male the 9 th sternite is large and bears an asymmetrical pair of coxites , each with a small terminal style. Immediately behind the coxites is the male copulatory organ, composed of pair of lobes; the right one bears irregular sclerotization while the left is membranous and carries an eversible sac of unkown function. The gonopore lies on the inner side of right lobe.

15. PHASMIDA (Stick and leaf insects): Female genitalia: The ovipositor is composed of 3 pairs of small valves, the first pair being appendages of the 8 th abdominal segment while the two posterior pairs are derived from the 9 th segment. The gonangulum is fused with the first valvifer . The whole ovipositor is concealed within the enlarged 8 th sternum. Male genitalia: In the male the terminal abdominal segments and aedeagus are rather variable in form. The latter is asymmetrical and made up of a number of lobes, which are sometimes more or less completely united into a single structure. The 9 th abdominal sternum is prolonged beneath the genitalia.

16. Coleoptera (Beetles, weevils): Female genitalia: In some coleoptera ( Dytiscus ) a colleterial glands is present in association with each oviduct. A spermatheca is generally present and opens, by a slender and often exceedingly long duct, either into vagina or the bursa copulatrix. An accessory gland of variable character, is generally found in connection with the spermatheca. Male genitalia: Male reproductive system consists of testes, the vas deferentia , one or more pairs of accesssory glands and median ejaculatory duct. Vesiculae seminales are often present as dialations of the vas deferentia . Male reproductive organs of: left, Adephaga ; right, Polyphaga . The right testis in the Adephaga is represented uncoiled A, aedeagus; E, ejaculatory duct; G, accessory gland ( ectadenes ); Gl > accessory gland ( mesadenes ); T, testis; VD, vas deferens; VS, vesicula seminalis . Adapted from Bordas .

17. Orthoptera (Grasshoppers): Female genitalia: The external genitalia of female grass hopper consists of a copulatory pouch and a special egg laying organ known as ovipositor. These organ are considered to be the appendages of 8 th and 9 th abdominal segments. The ovipositor helps the female in depositing her eggs in the soil by digging the hole in the ground. There are three pairs of valve which collectively from the ovipositor. The first pair originates from the ninth sternum is triangular pointed and hard in structure known as dorsal valve, second pair of ventral valves originating from the 8 th sternum is similar to dorsal and ventral valves known is inner valves. The inner valves are considered to be vestigial and non-functional whereas the dorsal and the ventral valves fit together to form the functional ovipositor. Besides, an egg guide is also found originating from the base of 8 th sternum and extending as a slender appendage through the ventral valves to the genital chamber.

18. Male genitalia: Unlike female genitalia, the genital organs of male grass hopper are located only in 9 th segment. As already the 9 th and 10 th abdominal tergites are partly fused to form a large cuticular supra anal plate besides a pair of podical plates and a pair of anal cerci, as seen in the female sex, are also present in the male grass hopper. The ninth sternum of male grass hopper forms the genital apparatus which is distinctly differentiated in to two parts, first the proximal or the true normal sternite and the second distal, which works as the subgenital plate and is formed by the union of the coxites of this segment. Only because of this fact the subgenital plate is also known as gonocoxite . The posterior region of the abdomen is thus enclosed directly by surpa anal plate, laterally by podical plates and ventrally by the subgenital plates. These plates and the aedeagus which are the proximal and distal ends, respectively. All this structures constitute a sperm ejection pump in which opens the ejaculatory duct on the dorsal side of the phallobase , a large complex sclerite is found known as pseudo sternite which parameres are found. In normal condition (at rest), the subgenital plate presses against the surpa anal plate and thus closing the end of the abdomen. In this situation the penis remains folded in the genital atrium.

19. Lepidoptera(Butterflies): Female genitalia: Each ovary consists typically of four polytrophic ovarioles but a certain number of exceptions to this rule are known among the lower members of the order. The structure of the female genital apparatus is of fundamental importance in the classification of the order.A pair of ramified or filiform colleterial glands open into bladder-like ducts which communicate with the common oviduct just behind the aperture of the receptaculum seminis . Male genitalia: The genital complex of male Lepidoptera includes the eighth, ninth, and tenth abdominal segments. The eighth segment forms at least a protractile base for the copulatory apparatus, and in some cases it bears accessory genital lobes. The 9th segment or tegumen is a narrow ring encircling the apex of the body and its sternal region or vinculum is usually invaginated to form a median saccus which extends into the preceding segment. A pair of claspers or valves ( harpes of Pierce) are hinged to the vinculum and form the most prominent organs of the external genitalia. The harpes are spine- likestructures often present in the inner aspect of the claspers. Attached to the hind margin of the 9th tergum is a median process or uncus which is usually hook-like or bifid.  

20. Hymenoptera(bees, wasps):   Female genitalia: The ovaries are composed of polytrophic ovarioles; in Apis the latter are very numerous but their number is in constant. In Blastophaga the ovarioles are very attentuated and closely packed together; according to Grandi there are r30-r82 to each ovary. In Aphelinus there are five, while in other Chalcids and in the Ichneumonoidea there are commonly four.The two oviducts unite to form the vagina and, in Apis , the latter is dilated posteriorly as the bursa copulatrix. A median spermatheca is generally present together with a pair of colleterial glands. Male genitalia: In the male, the 9th abdominal sternite is always developed though concealed and the genitalia lie above it. The testes are separate in the Symphyta and also in Apis and Bombus. According to Bordas (1894) they are in close contact in Vespula and fused together in other Hymenoptera studied by him. Each testis is enclosed in a double membrane and may consist of 250-300 follicles as in Vespula, Bombus and Apis ; these follicles are much less numerous in ants, and are usually reduced to three in other Hymenoptera. The vasa deferentia enlarge to form vesiculae seminales which are usually cylindrical or sac-like in form. In Vespula and Apis they are particularly voluminous, while they are tubular and convoluted in Athalia , Cimbex and Bombus. The two ejaculatory canals, which leave the vesiculae , receive the ducts of a pair of accessory glands. The latter are large and sac-like in almost all members of the order. In Apis the ejaculatory canals are rudimentary, and the accessory glands open into the common ejaculatory duct.

21. Reproductive organs, etc., of queen bee I, acid gland and 2, its duct; 3, alkaline gland ; 4,bursa copulatrix; 5, ovary; 6, oviduct ; 7, poison sac ; 8, spermatheca and 9, its gland; 10, terebra ; II, sting palp; 12, vagina; 13 , 9th sternum. Adapted from Snodgrass, IDe . cit.

22. Conclusion: Genitalia play an important role in the life histories of insects, as in other animals. These sexually dimorphic structures evolve rapidly and derive from multiple body segments. Insect genitalia are complex structures, with elements derived from the internal reproductive organs, posterior abdominal segments, and appendages, which may be elaborated or reduced in different groups. Male genitalia consists of the copulatory organ, and in some groups males possess external clasper’s. In different insects these genitalia modified in different ways according to their mode of living and behavior.

23. REFERENCE: The Insects: Structure and function by R.F. Chapman IMMS’ general textbook of entomology ( volumeII ) http://blog-rkp.kellerperez.com/wcontent/uploads/2009/11/lab22_23.pdf (24/01/2023) Taxonomic characters Komal (2021)