external genetalia and reproductive system, endocrine glands.pptx

insect external genetalia and type of reproduction

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

2. 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-insect an hexapods. Aquatic larvae often have segmental gills , while many holometabolous larvae, especially among the Diptera and Lepidoptera, have lobe-like abdominal legs called prolegs.

3. 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 carrying 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.

4. 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.

5. Typically there are 3 valves of the ovipositor- 1. Coming off the venteral of segment 8 is the first pair of valves - the basal portions are called the valvifers 1 and coming off each basal valvifer is the valvula 1 . 2. Coming off the venteral of segment 9 is the basal pair of valvifers 2 and off each basal lobe are born the pair of valvulae 2 and 3 . [In most of the Thysanura there are only 2 pairs of valvulae ]. Valvulae 1 and 2 form the shaft down which the egg travels when it is oviposited . So the 1st valvifer is associated with the 8th abdominal segment and the 2nd valvifer is associated with the 9th abdominal segment.

6. There is often in the grasshoppers a median process of the subgenital plate behind the genital opening called the egg guide (the subgenital plate is usually the 8th sternum). In most of the Heteroptera the ovipositor is reduced or absent, but it is usually well developed in the Homoptera . The 8th abdominal sternum is reduced in all Hemiptera , and the subgenital plate is the 7th sternum. In the Hymenoptera the first gonocoxae ( valifers 1) are absent, although they may be present in a few species, and the second gonapophyses are united. In the Symphyta and the parasitic groups the ovipositor retains its original function, but in the bees and wasps it forms the sting. But even here the structure of the sting is basically the same as the ovipositor. The genital opening is now at the base of the sting. In the honey bee, the 1st gonapophysis is known as the lancet, and the fused second gonapophyses as the stylet . This forms an inverted trough which is enlarged into a basal bulb into which the reservoir of the poison gland discharges.

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 - organ of male on which the male gonopore is located - terminal portion of the ejaculatory duct. Aedeagus distal part of phallus (tip). Ectophallus - outer wall of aedeagus. Endophallus - inner wall of aedeagus. Gonopore - opening of ejaculatory duct. Phallotreme - opening of aedeagus. Phallomeres - accessory lobes at side of gonopore - in some insects these actually form phallus.

8. 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. REPRODUCTIVE SYSTEM IN INSECTS Insects are bisexual. But also occurs by Parthenogenesis and hermaphroditism The reproductive system is divided in to internal and external genitalia Internal genitalia serve to the development of germ cells External genitalia accomplish the mating and enable female to deposit eggs Female reproductive system: Ovaries : • Present on the either side of alimentary canal • Connected to body wall by suspensory ligaments • Covered with fat body and trachea • Consists of a no of ovarioles or egg tubes Ovarioles : • Enveloped by a double layered cellular wall • Outer ovarial sheath with supply of tracheae • The inner layer is elastic tunica propria • Terminal filaments unites to form suspensary ligament

10. Ligament is attached to body wall or dorsal diaphragm The eggs are discharged in to the lateral oviducts Number of ovarioles in an ovary varies, usually 4 to 8. In Isoptera more than 2000 Typical ovariole or egg tube consists of 3 parts namely- 1.Terminal filament 2.Egg tube 3.Supporting stalk or pedicel The Egg tube is divided in to two parts 1. Germarium /egg chamber contain the primordial germ cells These cells give rise to three types of cells- 1.Germ cells developing in to oogonia and finally oocytes 2.Nutritive cells or nurse cells or trophocytes 3.Follicle cells

11. 2. Vitellarium or Zone of growth- Contains large number of oocytes and eggs in different stages of development In the anterior, the nurse cells and oocytes remain mixed at centre , follicle at periphery In posterior end oocytes are enclosed by follicle cells to form follicular layer Nurse cells absorb nutrients from haemolymph through follicular cells and transmit to oocytes In some case follicle cells provide nutrients to the oocytes where nurse cells are absent Types of ovarioles : 1. Panoistic : nutritive cells are absent and oocytes develop by follicular cells e.g.: Odonata , Dictyoptera , Orthoptera and Ephemeroptera 2. Meriostic : They contain trophocytes / nutritive cells Based on the position of trophocytes - ( i ) Polytrophic: oocyte and trophocytes arranged alternatively in vitellarium e.g.: Mecoptera , Dermaptera , Psocoptera (ii) Acrotrophic / teletrophic : trophocytes are present in the germarium (apex) and connected with developing oocytes by cytoplasmic strands e.g.: Hemiptera and Coleoptera

12. Types of ovarioles

13. Lateral oviducts: Proximal end of all ovarioles join forms lateral oviduct The wall of oviduct is glandular and muscular Median Oviduct: • Two lateral oviducts combine to form a median oviduct Vagina: • median oviduct opens in to a tubular vagina • formed by invagination of bodywall from VIII segment • opens outside and the opening is called vulva • receive the sperms and discharge the eggs Bursa Copulatrix : • vagina develops a separate pouch called Bursa Copulatrix • It has two reproductive openings, vulva for receiving the sperms open on VIII sternum ovipore or gonopore on IX segment for egg discharge Eg : Lepidoptera and water beetles

14. Spermathea : • opens in to vagina through spermathecal duct • used for storing the sperms • also produces some fluids responsible for longevity of cells Accessory glands: • a pair of collateral glands which open in to the distal portion of vagina • secrete the substance responsible for the formation of ootheca of cockroach, preying mantids • poisonous secretions in case of Hymenoptera • This sticky substances are useful for attachment of egg to the substrate

15. Male reproductive system 1. Testis : • lie above the gut and connected to the body wall through translucent ducts • consists of number of oval shaped follicles covered by a peritoneal membrane • testis is completely enveloped within a scrotum Structure of follicle divided into a series of zones by the presence of the sperms in different stages of development ( i ) Germarium : contains spermatogonia which undergo multiplication (ii) Zone of growth : spermatogonia increase in size with mitosis and form spermatocytes ( iii) Zone of division : spermatocytes undergo meiosis and give rise to spermatids (iv) Zone of transformation : spermatids get transformed in to spermatozoa Spermatozoa enclosed in testicular cyst cells from which they are released in to vasa efferens 2. Vasa deferens : formed by the union of vasa efferens receives the sperms from testis and allow their transport to the ejaculatory duct 3. Seminal vesicles: vasa deferens enlarge posteriorly into a sac for storage of spermatozoa

16. 4. Ejaculatory duct: formed by the union of both the vasa deferens posteriorly terminal section of ejaculatory duct is enclosed in a male copulatory organ or aedeagus or penis 5. Accessory glands: 1-3 pairs of glands open in to the ejaculatory duct Their secretion facilitates sperm transmission from male to female Mushroom glands in cockroaches and mantids as appear mushrooms

17. Types of Reproduction 1. Oviparity : reproduce by laying eggs by the female which later hatch and produce young ones e.g.: moths and butterflies 2. Viviparity : female gives birth to the young ones instead of laying eggs It is of 4 types based on the source of nourishment 3. Ovo - viviparity : retain the eggs within the genital track and immediately after hatching , the young ones will be released outside e.g.: Thysanoptera 4. Adenoparous : eggs have sufficient yolk, and young ones nourished from milk glands young ones after release pupates immediately without feeding e.g.: Glossina pupipara of Diptera 5. Pseudoplacental : eggs with little (or) no yolk and nourishment is through pseudoplacenta e.g.: Psocoptera , Dermaptera , aphids etc. 6. Haemocoelous : nourishment of young one takes place from the haemolymph of mother young one comes out either through genital canal or by the rupture in the walls of the parent Eggs have a trophic membrane through which nutrients are supplied from the maternal tissues e.g : strepsipterans & some larvae of cecidomyids ( Diptera )

18. 3. Parthenogenesis : ability of the females to reproduce without fertilization / copulation with males occurs due to the genetic characters, heredity, failure in finding a mate, hormonal changes within the body and weather factors This parthenogenesis is classified as – Sporadic : occurs occasionally e.g.: silkworm Constant : occurs regularly e.g.: thrips Cyclic : it is nothing but the alternation of generations e.g.: aphids II. Based on the sexes of the off springs produced, parthenogenesis can be Arrhenotoky : only males are produced e.g.: Hymenoptera Thelytoky : only females are produced e.g.: acridids Amphytoky : both females and males are produced e.g.: hymenopterans 4. Paedogenesis (or) Neoteny : the immature insects or stages give birth to young ones This usually occurs due to the hormonal imbalance insects reproduce by paedogenesis also reproduce by parthenogenesis e.g.: cecidomyids

19. 5. Polyembryony : Insects reproduce by giving birth to two or more young ones instead of a single one, as two or more embryos are produced from a single egg e.g.: endo parasitic Hymenoptera like platygaster 6. Hermaphroditism : both male and female gonads are present in the same individual may be functional as in Icerya purchasi (or) non functional as in of stonefly, Perla marginata 7. Castration : The separation of the individuals occurs mainly due to the development of the reproductive organs The insects with well developed ovaries develop in to females (queens) the insects with well developed testis develop in to males (drones) insects with underdeveloped ovaries develop in to workers e.g.: honey bees 8. Alternation of generation : Insects reproduce by parthenogenesis and bisexual reproduction e.g.: aphids reproduce by parthenogenesis in summer and sexual reproduction in winter

20. Endocrine Organs in Insects A- Neurosecretory cells (NSC) B - E ndocrine g lands

21. A-Neurosecretory cells (NSC) Origin-Nervous Produce small neuropeptides – neurohormones They can be found in brain (major source) and all the ganglia. Protocerebrum A Med i an NS C s / inter ce r ebra l is B Lateral NSCs C Tritocerebral Suboesophageat ganglion 3.All Other ganglion

22. A Neurosecretory cells (NSC) 1 . D o r sal pa r t of hormone called p r otoc e r eb r u m p r oduce a P r o t ho r a c ico t r o p ic Ho r m o ne ( P T T H ) o r BRAIN HORM O N E w hi c h act i v ates prothoracic glands. NSC i n b rain sec r et e s B UR S IC O N w h i c h is involved in hardening and darkening of cuticle. Ne u r o sec r eto r y ce l ls scatte r ed i n the v entral nerve cord produce Diuretic Hormone .

23. NEU R OS E C R E T O R Y CELLS In insects, the a r e r es p o n sible f or production of hormones, except Ecdysone & Juvenile hormones , which are produced from Non-neural Tissues like Prothoracic Glands and Corpora Allata. Insect NSCs shows Excitatory and Inhibitory post- synaptic potentials. The release of hormone is mediated through the influx of Ca 2+ ions .

24. B-Conventional endocrine glands (hormone synthesis and secretion) 1.Corpora cardiaca(CCStores & releases brain /neuropeptide hormones , Adipokinetic Hormones. 2 Corp o ra a l l a ta ( C A ) - P r o d uces-j u ven i le h o rmones (JH). 3 P r o t h o racic / E c d y si c -g l a n d s (PGs ) --P r o d uce- E c d y s o ne 4Midgut endocrine cells---Produce-various peptides . 5Gonadal/Epitracheal glands------Produce Ovaries: ecdysteroid Testes: androgen

25. Insect endocrine system. 2 4 1 3 6 5

26. paired/fused (cardiacum-Singular) Origin-ectodermal / epithelial origin (neurohemal organ-Stores & releases brain /neuropeptidehormones Found in most of insects except COLLEMBOLA Lies on each side of Aorta behind brain Connected to protocerbrum and hypocerbral ganglion It acts as a Conventional Storage and release organ for neurosecretory cells 1 . Corpora cardiaca(CC)

27. Contain 4 cellular element 1.Bulbous ending of NS axones whose perikarya are located in the dorsum of the brain 2 . The peri k arya o f NSC t h e send axo n s i n t o ner v e that supply various peripheral organs 3.Glia like cells 4.Intrinsic corpus cardiacum cells Function- Growth & differenciation It cont r ols heart beat & regu l ate trehalose level in haemolymph Corpora cardiaca(CC )

28. 2 . C orpo r a all a ta(C A ) Discovered- JANET 1899 Origin –ectodermal/epithelail origin Paired/fused gland present in between mandible & I-Maxillary Secretes - JUVENILE HORMONE (JH) OR NEOTININ Function- T here by inhibit metamorphosis (adult characteristics) C A ho r m o nes are r espons i ble for the inhib iti o n of metamorphosis. 3. The CA hormones i s there f ore s o m et i m es also c al led as ‘ Inhibi tory or Stat us Quo’ Ho r mone 4. In a d ult ser ve as an endocrine g l an d - r ep r o d uct i on & other body function

29. 3 . Prothoracic (PG)/ thorasic/ventral/ ecdysial glands I experimental proof -Fukuda 1940 in silkworm. Paired gland prese n t i n ventro later a l part of prothorax of larva Also called as Pericardial or Ecdysial Gland Degenerated in adults Secretes the moulting hormone ECDYSONE Neurosecretory cells (NSC) activate prothoracic glands to secrete ECDYSONE

30. 4. Gonadal/Epitracheal glands- Ovaries : ecdysteroid Testes : androgen 5. Midgut endocrine cells Source ---various peptides- proctodone hormone. Found in 2 species of lepidoptera Function : Play role in photoperiodism & diapause

31. 6. Weismann's ring/ Ring gland Weismann's ring Present in Cyclorrophous Diptera Formed by the fusion of Carpora cardiaca , Carpora allata , Prothoracic glands and Hypocerebral ganglion Occur as small ring like tissue supported by trachea around aorta Secrete puparium hardening hormone Controls metamorphosis in flies A special type with both CC and CA fused and connected by the fused PG to form a single structure is represented by the RING GLAND in CYCLORRHAPHOUS DIPTERA Weismann's ring

32. Ring Gland Hypocerebral Ganglion

33. Functions of the Endocrine Glands Regulation of Molting Determination of form at Metamorphosis Polymorphism Regulation of Diapause Involvement in Reproduction Regulation of Metabolic Acti v iti e s a nd general body functions Regulation of Behavior

34. Types of Hormones in Insects  Steroid hormone - ecdysteroids  Sesquiterpenes -Juvenile hormones  Peptide hormones - Prothoracicotropic hormone (PTTH) -many others  Biogenic amines - Octopamine - Serotonin