Insect body wall: It’s structure,cuticular outgrowth, colouration and special integumentary structures in insects with their functions and modification in different orders of insects.�

Insect body wall: It’s structure,cuticular outgrowth, colouration and special integumentary structures in insects with their functions and modification in different orders of insects.�

1. Insect body wall: It’s structure,cuticular outgrowth, colouration and special integumentary structures in insects with their functions and modification in different orders of insects.

2. Introduction The body wall of an animal is that part of the ectoderm which remains at the surface in the fully developed stage and serves to maintain anatomical integrity in the rest of the organism. Though primarily an integument, because of its position numerous responsibilities devolve upon the body wall: it must bear the brunt of all external things and forms of energy that touch upon the animal; it must be able to receive impressions of changes in the environment to which it is advantageous or necessary that the creature should respond; and in the arthropods it is the principal agent of the motor mechanism. The integument is the external layer of tissue that covers the outer surface of insects and the surfaces of the foregut and hindgut. It consists of a single layer of ectodermal cells (epidermis, hypodermis), which is covered by the cuticle, a chitinous apical extracellular matrix secreted by the epidermis. Epidermal cells are also involved in the formation of a basal extracellular matrix, the basement membrane, which effectively separates the integument from the hemocoel. The integument largely determines the outer shape of an insect and functions as exoskeleton, to which the muscles are attached. It forms a sensory interface with the environment and protects the insect from various harms, including mechanical damage, radiation, desiccation and invasion of pathogenic microorganisms. For this purpose almost all outer surfaces of the insect body are covered by the integument, including ectodermal invaginations like the oral cavity, the fore- and hindgut, the lower genital ducts and many glands.

3. Structure, Composition and Functions The integument consists of the following layers: the cuticle the epidermis basement membrane

4. ( I) Cuticle: It is a outermost thick non – cellular layer of chitin secreted by epidermis / hypodermal cells. It is non – living. It is composed of sclerites, membranes and semi-membranous areas. The cuticle is a biological composite material containing chitin, proteins, lipids and catecholamines (e.g., N-acetyl-dopamine), cross-link proteins and chitin filaments, which results in specific mechanical properties. The cuticle does not only cover the surface. Internal organs such as the tracheae and fore- and hindgut are also covered by a very thin cuticle, the intima. Cuticle comprises up to one-half the dry weight in certain species. It is divided into two parts a). Epicuticle (Non-chitinous) An outer layer of cuticle with 0.03 to 4µ in thickness. Thin and non-chitinous and unpigmented in nature. b). Procuticle (Chitinous)

5. [ A] Epicuticle The outermost layer of a cuticle is called epicuticle. It forms a continuous layer covering the complete cuticular surface. Seldom more than 2 µm thick, it is responsible for the waterproofing properties of the cuticle. It is outermost layer without chitin. It contains sulphur & fatty substances. Electron microscopy shows that the epicuticle can be subdivided into several layers, which have been differently named by different authors. It consists of the 4 layers. 1. Cement layer/ tectocuticle / roofcuticle Upper most thin layer, not always present.(It is absent in many adult insects that possess cuticular scales. Some insects like cockroaches may form a spongy meshwork in which wax molecules can move about.)Bears spine or microtrichia. Secreted by epidermal cells or dermal glands and is composed of lipoprotein. It protects the body from external damage. It is give the size and shape of insect body. Protect the underlying wax layer and Contain anti-fungal components. In many insects ( Homoptera ), a waxy bloom appears on the surface of the cement layer.

6. 2. Wax / Lipid layer Thin layer of wax beneath cement layer. It is secreted by epidermal glands and transported through pore canals. It is prominent layer, 0.25μ in thickness. Impermeable to water so conserve the water. Made up of long chain hydrocarbons, esters of fatty acids and alcohols(wax). 3. Polyphenol layer Beneath the wax layer. It contains various types of phenols which are mainly used in the formation of the proteins and transported from the pore canals and accumulates on outer surface of the cuticulin. Resistant to acids and organic solvents. 4. Cuticulin layer It is thin membrane over the surface of epidermal cells, which is strengthened by outer polyphenol layer. Rich in polyphenol Highly resistant to acids & organic solvents. Elaborated by oenocytes . It serves the purpose of permeability and also acts as growth barrier.    

7. [ B ] Procuticle The region of the cuticle, located between epicuticle and the epidermal cell layer, is called procuticle. It constitutes the main part of the total cuticle. Secreted by epidermal cells Makes the bulk of integument. It is differentiated into exo and endocuticle after sclerotization process. Histologically, the sclerotized regions (sclerites) are often subdivided into layers with different staining properties: (1) the outermost layer, the exocuticle , may be dark coloured because of sclerotization, but is refractory to staining (2) the innermost, uncoloured layer, the endocuticle , stains blue. (3) in between these two layers one often observes a layer of mesocuticle , staining red with Mallory triple stain. The flexible cuticle (arthrodial membranes), which connects the sclerites, stains blue with Mallory throughout most of its thickness. Exocuticle may correspond to the part of the procuticle deposited before ecdysis, stabilized by sclerotization. Mesocuticle plus endocuticle often correspond to the post- ecdysially deposited procuticle, and if these layers are sclerotized at all, it is only slightly. The procuticle consists mainly of chitin and proteins; water is an essential component, and other materials, such as lipids, phenolic compounds, salts, pigments, and uric acid may be present.

8. 1. Exocuticle Provides rigidity & toughness to the cuticle. Consists of chitin & hard proteins called sclerotin. It is darkly pigmented by hard, brown material and referred to as “Tanned”. Shaded off at the time of moulting . 2. Endocuticle It contains more chitin but lacks hard protein sclerotin so it is more soft & flexible layer. It is light coloured and unsclerotized. Pore canals passes through endocuticle. 3. Mesocuticle Lies between exocuticle and endocuticle. It is a region, which hardens but not fully darkens. Pore canals In the procuticle, there are large no of ducts running perpendicularly from epidermis to inner epicuticular layer is known as pore canals. These are numerous fine vertical channels traversing both exo and endocuticle measuring < 1μ (0.1 – 0.15μ) in diameter. In adult beetles and hemipteran bugs, the pore canals are more abundant in the outer procuticle and some 30 pore canals per cell in the outer region may join to a single canal lower down. In Rhodnius (Hemiptera) the pore canals are circular in cross-section, but in many species they have a flattened, ribbon-like form, the plane of flattening being parallel with the microfibers in each layer of the cuticle. Functions of Pore canal Act as transport the cuticular material and enzymes to the outer pro and epicuticle parts during formation stage of cuticle. Carry oxidizing enzymes used in sclerotization to exocuticle. Transport the materials used in healing of wounds and They carry moulting fluid, protein, polyphenols and wax’.

9. [C] Subcuticle / Schmidt’s layer A narrow, histochemically distinct layer, called subcuticle , is situated between the procuticle and the epidermal cells. It stains positively for muco- and glycoproteins. It has been suggested that it serves to bind cuticle and epidermis together and that this layer is the deposition zone, where new cuticular material is assembled and added to the already existing cuticle It is an amorphous layer without any fibers. Composition of cuticle   1) Chitin: It is a nitrogenous polysaccharide. (C8H13O6N)x . It accounts for 25-60 per cent of the dry weight of the cuticle. It is named by Odier in 1834. It consists of high molecular weight polymer of anhydro-N-acetyl glucosamine residues joined by β-glycosidic linkages. It is embedded with proteins in the procuticle to form glycoproteins. It is colourless, amorphous substance, insoluble in water, alcohol, organic solvents, dilute acids and concentrated alkalis. It is soluble only in concentrated mineral acids and sodium hypochlorite. Chitin is not affected by digestion enzymes of mammals. 2) Arthropodin: It is soft water soluble protein present in endocuticle. The conversion of arthopodin in to sclerotin is known as sclerotization or tanning. 3) Sclerotin: It is also called tanned protein which is amber coloured and present only in exocuticle. 4) Resilin : It is a rubber like elastic protein which is colourless and present in joints such as wing hinge ligaments, leg joints, clypeolabral joints or suture and tergosternal joints.

10. (II) Epidermis / Hypodermis It is a middle layer of body wall. Continuous single / unicellular layer of living cells formed from polygonal cells which modifies in to cuboidal or columnar during the process of moulting. These cells consists of well developed nucleus and other cytoplasmic contents. All the epidermal cells are glandular and secrete cuticle and the enzymes involved in production and digestion of old cuticle during moulting. The cells forming cuticular sensilla are also found in this layer. During postembryonic development, the epidermal cells are well defined. Scattered among the normal epidermal cells are specialized gland cells and those concerned in the formation of cuticular sensilla. Muscle attachments penetrate the epidermis, the myofibrillae usually being associated with tonofibrillae that run through the epidermis and into the procuticle, while the oenocytes which originate from epidermal cells sometimes remain closely associated with this layer. Not only does the epidermis secrete the greater part of the cuticle but it also produces the moulting fluid (Bade and Wyatt, 1962; Jeuniaux , 1963), which dissolves the old endocuticle before the immature insect moults, it absorbs the digestion products of the old cuticle, repairs wounds and differentiates in such a way as to determine the surface patterns of the insect (Wigglesworth, 1959; Lawrence, 1967).  

11. The epidermal cells get differentiated in to following types based on the function they perform and may modify in to Dermal glands producing cement layer Trichogen cell producing hair like seta or trichome. Moulting glands secreting moulting fluid which digests the old cuticle. Peristigmatic glands around the spiracles in case of Dipteran larvae. Function of Epidermis Secrete major part of cuticle & moulting fluid. Absorb the digested old culticle ( endocuticle ). Responsible for repairing of wounds. Determine the surface pattern of insects. Produces setae/ macrotrichia viz., hairs, bristles, scales, glandular and sensory setae. Forms the epidermal glands . It also secretes the basement membrane/ basal lamina

12. Oenocytes These large cells (IS-ISO fLm or more across) have been recorded from most orders of insects (Richards, A. G., 1951). They arise from the ectoderm or epidermis, usually near the abdominal spiracles (Figs. 129 and 130) and sometimes remain closely associated with the bases of the epidermal cells. In other cases they project into the haemocoele or become separated from the epidermis to form segmentally arranged clusters or are even dispersed among the fat-body. They are usually amber- coloured but may be brown, red, green or colourless and either arise repeatedly during postembryonic development or, in some Endopterygotes , are composed of a larval and an imaginal generation (e.g. Kaiser, 1950; Schmidt, 1961). Develops in epidermal cells around the spiracles. Found either in epidermis or between epidermis & Basement membrane. It may present in fat body. Play important role in process of metabolism & moulting .

13. ( III) Basement Membrance It is the basal part of the body wall formed from degenerated epidermal cells Continuous layer, adjacent to internal organ below the epidermis. Epidermal cells are attached to the basement membrane by hemidesmosomes. It is amorphous (shapeless) granulated layer. It is about 0.5 μ in thickness beneath the epidermis and consists of connective tissue made up of fibrous protein, collogen, mucopolysaccharide and glycosaminoglycans which are polymers of disaccharides. Providing attachment to muscles, oenocytes , chordotonal organs, tympanal organs, tracheoles & nerves passed through basement membrane Apparently composed of mucopolysaccharide secreted by blood cells ( Haemocytes ). The basement membrane forms a continuous sheet beneath the epidermis, where muscles are attached and become continuous with sarcolemma of the muscles .  

14. Cuticular/ Integumental modifications   Cuticular out growths

15. ( A) Cuticular appendages (Presence of membranous articulations ) These structures include all outgrowths of the cuticle that are connected with it by means of a membranous joint. They arise from modified epidermal cells and may be classified into setae and spurs. Insects are well endowed with cuticular extensions, varying from fine and hair-like to robust and spine-like. Four basic types of protuberance, all with sclerotized cuticle, can be recognized: 1. spines are multicellular with undifferentiated epidermal cells; 2. setae, also called hairs, macrotrichia or trichoid sensilla, are multicellular with specialized cells; 3. acanthae are unicellular in origin; 4. microtrichia are subcellular, with several to many extensions per cell.

16. Setae or Microtrichia are commonly known as hairs and each arises from a cup-like pit or alveolus. At its base the seta is attached by a ring of articular membrane. Setae are hollow structures developed as extensions of the exocuticle and each is produced by a single, usually enlarged, trichogen cell. The articular membrane is usually produced by a separate tormogen cell. The arrangement of the more constantly located setae (chaetotaxy) is important in the systematics of some insect groups, e.g. the Diplura , Thysanoptera, Cyclorrhaphan Diptera and larval Lepidoptera. Chaetotaxy: - Study of arrangement of seta is known as Chaetotaxy. Unicellular structures- a. Clothing hairs , plumose hair – eg. honeybee These invest the general surface of the body or its appendages and frequently exhibit various degrees of specialization. When furnished with thread-like branches as in the Apoidea they are termed plumose hairs. Setae which are particularly stout and rigid are known as bristles and are well exhibited for example in the Tachinidae . b. Scales – eg. Moths and butterflies These are highly modified clothing hairs and are characteristic of all Lepidoptera and many Collembola: they are also present in some Thysanura , Coleoptera, Diptera and Hymenoptera. Transitional forms between ordinary clothing hairs and scales are frequent.

17. c. Glandular setae – eg. Caterpillar Grouped under this heading are those setae which function as the outlet for the secretion of epidermal glands. If they are especially stout and rigid they are then termed glandular bristles as in the urticating hairs of certain lepidopterous larvae. d. Sensory Setae – Very frequently the setae of certain parts of the body, particularly the appendages, are modified in special ways and become sensory in function. Sensory setae are in all cases connected with the nervous system. e. Bristles- e.g., Flies Multicellular Structure- Spurs- movable; Spine- immovable O ccur on the legs of many insects and differ from setae in being of multicellular origin.

18. INTEGUMENTAL GLANDS Epidermal glands are present in many types of integument; they often consist of a single cell surrounding a cavity, which functions as a product reservoir and is connected to the cuticular surface by a small duct. Glands of this type are assumed to be responsible for forming and maintaining the cement layer, which after ecdysis is spread as a protective layer on top of the epicuticular wax layer. Other integumental glands produce various chemical defense secretions, which may be forcibly ejected when the insect is disturbed. Integumental glands may also consist of epidermal cells without a cavity and duct, but with direct contact to the inner surface of the cuticle, through which the secretion passes. Often the secretions of such glands function as pheromones, playing a part in communication between individuals. The glands of the ectoderm discharging their secretion externally are too numerous to be described here in detail. They arise from all parts of the body wall, from the stomodaeal and proctodaeal sections of the alimentary canal, and from the ectodermal ducts of the reproductive organs. Classified according to their function they include salivary glands, silk glands, wax glands, lac glands, food glands, trophallactic glands, scent glands, adhesive glands, excretory glands, poison glands, stinging glands, defensive glands, repellent glands, moulting Glands, colleterial or egg-covering glands, mucous glands, and others. Examples i . Wax gland - e.g. Honey bee and mealy bug ii. Lac gland - e.g. Lac insects iii. Moulting gland secreting moulting fluid. iv. Androconia or scent scale - e.g. moth v. Poison gland - e.g. slug caterpillar

19. Unicellular Glands : A one-celled gland is usually of greater size than the cells surrounding it and, in its simplest form (Fig. 32 A), discharges its products directly through the covering cuticula. A larger glandular area may include a group of secretory cells (B). Some writers have claimed that the cuticular covering of such glands is penetrated by fine pores, but in most insect glands the secretion escapes by diffusion through the very thin cuticula covering the surface of the cells. In many glands, however, a minute cuticular ductule extends from the exterior into the body of each cell (C, H, a), thus allowing the secretion to passout through an extremely thin layer of cuticula. Unicellular glands of this kind often have the distal end of the cell drawn out into a slender neck, or duct (C, Dct ). Multicellular Glands: The many-celled glands may be, as we have just noted, merely a group of cells situated at the surface of the body (Fig. 32 B); but most of them are invaginations of the body wall. A simple multicellular gland is a mere tube of secretory cells lined with a delicate cuticular intima (D). Such glands are sometimes eversible. By a specialization in function between its outer and inner parts a tubular gland may become differentiated into a duct (E, Dct ) and a true glandular part ( Gl ), while a widening of the duct may constitute a reservoir (F, Res) for the storage of the secretion products. Glands are frequently branched, the branches in some cases being long and tubular and in others sacculated at the ends, giving the gland a racemous structure (G). In all forms of multicellular glands the intima is continuous over the inner surfaces of the cells, but in some it gives off minute capillary ductules into the individual cells (H), as in some of the unicellular glands (C).

20. Cuticular sensilla Sensilla are the basal functional and structural units of cuticular mechanoreceptors and chemoreceptors. They include the cuticular component (e.g., the cuticle of a seta), the sensory neuron (or neurons), the associated sheath cells with the cavities they enclose and the structures they produce. (Chapman 1998). • The cells involved in the formation of a sensillum are derived from the same hypodermal cell (sense organ precursor cell, sense organ mother cell). In addition to the tormogen and trichogen cells, a small thecogen cell is present between the latter and the neuron. It secretes a cuticular layer around the distal dendrite, the dendrite sheath, which usually ends at the base of the hair. Modified types of cuticular sensilla are the apically rounded sensillum basiconicum , and the sensillum campaniformium , which scarcely protrudes beyond the basal ring enclosing it. The sensillum placodeum is entirely flat and the sensilla coeloconica and ampullacea are sunk below the external cuticular surface to different degrees.

21. Coloration The colours of adult and immature insects may be grouped into three classes: (I) pigmentary or chemical colours, (2) structural or physical colours, and (3) combination or chemico -physical colours. I. Pigmentary Colours - These are due to chemical substances that absorb some wavelengths of the incident light and reflect others. They may be present in the cuticle, epidermis or subepidermal tissues (usually fat-body or blood). A colour pattern often consists of an epidermal or subepidermal ground colour (which may fade rapidly after death) and overlying areas of more permanent cuticular pigmentation. Eye pigments occurring in the ommatidial cells of some insects may be of special interest since studies of their metabolism reveal something of the mode of action of genes controlling eye colour. The substances concerned may be classified as follows. ( a) Melanins . These are amorphous, highly stable, dark brown or black cuticular pigments which are generally non- granular and are insoluble in the usual solvents though they are rapidly decolorized by oxidizing agents. Their chemical nature has not been satisfactorily elucidated and it is, in fact; difficult to distinguish between cuticular darkening due to sclerotization and that caused by the presence of true melanins (Richards, A. G., 1967). (b ) Carotenoids . These are polyene pigments usually containing 40 carbon atoms in the molecule; they are readily soluble in fat-solvents and are characteristically synthesized by plants (Lederer, 1938; Feltwell and Rothschild, 1974). When ingested by animals they accumulate in the blood and tissues unchanged or after minor oxidative alterations and in some cases they form the prosthetic group of a chromoprotein. carotene, derived from the tissues of the potato plant, occurs in the blood of the Colorado Potato-beetle Leptinotarsa decemlineata and is responsible for the red and yellow coloration of the Pentatomid Perillus bioculatus which preys on larvae of the beetle (Palmer and Knight, 1924).

22. Again, in Coccinella , the red colour is due to the presence of the plant carotenoids lycopene and a- and {3-carotene (Lederer, 1938). Astaxanthin (3:3-dihydroxY-4:4-diketo-{3-carotene) and {3-carotene both occur as chromoproteins in the integument of locusts and the green chromoprotein pigment of many insects (known as insectoverdin ) is a complex, the yellow-orange component of which may have as its prosthetic group {3-carotene Carausius ), lutein (Sphinx, Tettigonia ) or astaxanthin. ( c) Pteridines . These pigments are derived from a heterocyclic pyrimidinepyrazine ring structure and are found more often in insects than in other organisms (Ziegler and Harmsen , 1969). The majority belong to the class of pterines (2-amino4-hydroxy-pteridines) and the natural pigment is often a mixture of two or more of these. Thus the conspicuous colours of the Heteroptera , Dysdercus , Pyrrhocoris , Oncopeltus and Phonoctonus are due to the red and yellow pterines erythropterin and xanthopterin, along with the white leucopterin . Xanthopterin and leucopterin are also found in the integument of the Vespidae, while the body- and wing-scales of many Pierid butterflies contain leucopterin , xanthopterin, isoxanthopterin and erythropterin . Some pterines occur characteristically as eye pigments, e.g. a group of so-called drosopterins contribute to the red eye colour of the wild-type Drosophila melanogaster. In addition to their role as pigments some hydrogenated pterines can act metabolically as co-factors in hydroxylation reactions; in the Pieridae they are not only pigments but also represent the insoluble end products that accumulate in 'storage excretion' of nitrogenous metabolites. (d) Ommochromes ( Linzen , 1974). These are best known as eye pigments and comprise two groups of substances, the sulphur -free om matins of low molecular weight and the sulphur -containing ommins of high molecular weight. The latter are the main pigments occurring in the eye of insects from many orders. Xanthommatin is an eye pigment in Drosophila; its biosynthesis from tryptophane via kynurenine and 3-hy~roxykynurenine is under genetic control. Like other ommochromes it is a redox pigment, yellow when oxidized and red when reduced. In the dragonfly Sympetrum striolatum the scarlet male contains ommatins and the yellow female their reduced equivalents.

23. (e) Anthraquinones . These are confined to the Coccoidea , where the best known is carminic acid, the colouring principle of cochineal, found in the eggs and fat body of the female Dactylopius coccus and accounting for half its body weight. Kermesic acid is the pigment in the dyestuff kermes, from females of Kermococcus ilicis , and laccaic acid is the water-soluble red pigment of lac. (f) Aphins . These are polycyclic quinones which decompose immediately after the death of the insect containing them, giving rise to the erythroaphin reported from Aphis labae , Eriosoma lanigerum and other aphids. ( g) Miscellaneous pigments . Many other substances playa minor role as insect pigments, occurring either in small amounts or only in a few species. Among such are haemoglobin , derivatives of chlorophyll, anthoxanthins , anthocyanins, riboflavin (which accumulates as the greenish-yellow 'entomo-urochrome' of the Malpighian tubules) and purines. The bile pigment mesobiliverdin is perhaps more important since it is the prosthetic group of the blue component of the insectoverdins (complex green pigments) mentioned above in connection with the carotenoids. Colour Causes of colour Insect Black Melanin Aphins Coleoptera Aphidiae Red Ommochrons Carotenoids Odonata Coccinellidae Green Insectoverdin Orthoptera Blue Tyndall effect Odonata

24. 2 . Structural Colours - Structural colours differ from those due to in that they are changed or destroyed by physical changes in the cuticle such as result from shrinkage, swelling, distortion or permeation with liquids of the same refractive index as the cuticle. They may also be duplicated by physical models, are not destroyed by bleaching and all the component wavelengths of the incident light are to be found in either the reflected, scattered or transmitted fractions. Four types of structural coloration may be distinguished: ( i ) Structural white is caused by the scattering, reflection and refraction of light by microscopic particles large in comparison with the wavelength of light and which, in themselves, are usually transparent. Probably most insect whites have a structural basis. (ii) Tyndall blue , though uncommon, occurs in some Odonata and is due to the scattering of the shorter wavelengths by particles with dimenSIons of about the same size as the wavelengths of light. (iii) Interference colours are produced by optical interference between reflections from a series of superimposed laminae or ribs. This is one of the commonest types of physical coloration and the iridescent appearance is well seen, for example, in the wing-scales of Morpho butterflies, in the Diamond beetles Entimus and Cyphus and in the Chrysididae . (iv) Diffraction colours , resulting from the presence of closely spaced striae, occur in the Mutillidae and various beetles such as Serica , several Carabidae and Gyrinidae , Nicrophorus and others (Hinton and Gibbs, 1969, 1971). It is possible that variations in the colour and intensity of light reflected from these structures help to confuse predators as to the size and distance of the insect. The beetle Dynastes hercules can change colour quite quickly from yellow to black and vice versa. This process has a structural basis elucidated by Hinton and Jarman (1973). Below the transparent epicuticle of the elytra is a very thin spongy layer; when its interstices are filled with air this appears yellow, but when they fill with water the black colour of the underlying cuticle becomes apparent. 3. Combination Colours - These are produced by a structural modification in conjunction with a layer of pigment and are much commoner than purely structural colours . In the butterfly Teracolus phlegyas a red pigment in the scale wall (but not in the striae) combines with a structural violet to produce magenta: in Ornithoptera poseidon the emerald green is due to a structural blue combined with a yellow pigment in the walls and striae of the scales.

25. COLOURATIONAL DEFENSE 1. Cryptic colouration (I am not there): By the deceptive look, the insect gains protection. The insect looks like a particular object that forms a common component of the environment or the colour of the insect blends with the background. There are three types. Homochromism : Colour is similar e.g., Praying mantis. Homomorphism: From is similar e.g., cowbug . Homotypism : Both colour and form are similar e.g., stick insect. 2. Revealing colouration ( I am dangerous) e.g., Giant silkworm.Forewings are cryptically colured . Hind wings are attractively coloured.If once the bird locates the insect, the prey insect exposes the bright hind wings with eye spots to startle the predator. 3. Warning colouration (I am not tasty): Butterflies are usually attractively coloured . The bright colour serves as a warning to the predator. Larva of monarch butterfly while feeding on the milkweedplant , ingests cardiac glycosides. As a result, both the larva and adult become unpalatable. 4. Mimicry (I am someone else): One species of animal imitates the appearance of another better-protected animal species, thereby sharing immunity against destruction. The former is called mimic and the latter is known as model. There are two types of mimicry. Batesian mimicry : Mimic is restricted to palatable species. Mimic alone gets protection because the predators are apparently misled. e.g., i . Viceroy butterfly: Liminitis archippus - Mimic Monarch butterfly: Danaus plexippus - Model ii. Hypolimnas bolina – Mimic, Euploea core - Model iii. A fly-mimicking wasp. Mullerian mimicry : Both model and mimic are unpalatable and the ingestion of either by a predator result in the avoidance of both the species. This form of mimicry is advantageous to both the mimic and model. e.g., Danaus chrysippus , D. genetua .

26. MOULTING The whole process of casting off old cuticle and deposition of new cuticle at certain time interval is known as moulting or ecdysis. OR Periodical process of shedding the old cuticle accompanied by the formation of new cuticle is known as moulting or ecdysis. Why moulting is necessary ? ✓ To Insect body is covered by hard & nonelastic cuticle layer so body cannot grow in size continuously. ✓ To accommodate the growing internal parts, insect has to cast off its cuticle periodically. ✓ New cuticle is soft & elastic which allows for expansion of internal organs & resulting in increasing size of body. ✓ Later on, new cuticle undergoes seclerotization which makes it hard & dark.

27. Steps of process of ecdysis 1. Behaviroual changes: Before moulting , insect stops feeding & become quiescent for a short time. 2. First, the old cuticle is loosened to from a small space between cuticle & epidermal cells. 3. Change in epidermis: The epidermal cells became active & undergoes mitosis under influence of brain hormones & change in size & shape. 4. Apolysis: Due to this process they generate tension & pushing the cuticle off ( apolysis ). 5. Formation of Sub cuticular space: The old cuticle is detached & epidermal cells secretes a 6. Secretion of moulting gel: The space between old & new cuticle is filled with moulting fluid which contains 2 enzymes i.e. Protenase & chitinase. 7. These enzymes dissolve endocuticle & dissolved fluids is absorbed by epidermis. 8. New epicuticle formation: The epidermal cells begin to secrete new cuticle. 9. Procuticle formation: Procuticle is formed below the epicuticle 10. Activation of moulting gel: Moulting gel is converted into moulting fluid rich in enzymes. This activates endocuticle digestion and absorption.The Epidermal cells absorb the digested old cuticle. 11. Wax layer formation: When formation of new cuticle is completed the dermal glands discharge their contents over out side of new cuticle whichforms the final waxy layer of Cuticle. 12. Cement layer formation : Dermal glands secretes cement layer( Tectocuticlenew cuticle). How Ecdysis occur? The ecdysis starts immediately after completion of digestion. The old cuticle burst at the ecdysial cleavage line. The rupture is caused by pressure of blood. Insect contract the abdomen & forcing the blood into thorax until the cuticle breaks. Insect may swallow air ( water if aquatic ) for this process.

28. Insect pulls out its body from the old skin. The head comes first followed by thorax, abdomen & appendages & leaving behind the exuviae. Some insects hang themselves on some support & pull out their body. Formation of exocuticle : The upper layer of procuticle develops as exocuticle through addition of protein and tanning by phenolic substance. Important terms used for moulting 1. Exuviae :-The moulted skin is called exuvae or the old cuticle which is casted off is known as exuvae 2. Pharate instar :-In some insects the old cuticle remains on insect body is called pharate instar. 3. Instar :-Shape & size of insect between two successive moulting is known as instar. 4. Stadium :-The time interval between two mounting is known as stadium. The first stadium is the time between hatching & the first moult .

29. Control of Moulting : It is controlled by endocrine gland like prothoracic gland which secrete moulting hormone. Endocrine glands are activated by prothoracico -tropic hormones produced by neurosecretory cells of brain. What is Sclerotization ? Sclerotization or tanning is the last process of moulting which involves differentiation of the procuticle into outer hard exocuticle and inner soft endocuticle. It is the process of hardening of body wall, where the exocuticle become hard, tough and inelastic. After shedding of old cuticle the new cuticle which is soft, milky white coloured becomes dark and hard through the process known as tanning (or) sclerotization. The concentration of tyrosine increases highly in the haemolymph just before the ecdysis. Tyrosine is converted to dihydroxyphenylalanine (DOPA) dopamine to N- acetyldopamine and variety of quinones. The N- acetyldopamine (diphenol) is transported via pore canals into the outer part of the epicuticle, where it oxudized to a quinone by an enzyme, phenol oxidase. The darkening of the cuticle seems to be a result of sclerotization as well as polymerization of excess quinones into melanin. Types of hormones involved in the moulting process JH : Juvenile Hormone : Produced from corpora allata of brain that helps the insects to be in immature stage. MH : Moulting hormone: Produced from prothoracic glands of brain that induces the process of moulting Eclosion Hormone: Released from neurosecretory cells in the brain that help in the process of ecdysis or eclosion .  

30. References: Encyclopedia of INSECTS Editors Vincent H. Resh University of California, Berkeley Ring T. Carde ´ IMMS' GENERAL TEXTBOOK OF ENTOMOLOGY Volume I: Structure, Physiology and Development O. W. RICHARDS M.A., D.Sc., F.R.S. Emeritus Professor of Zoology and Applied Entomology, Imperial College, University of London and R. G. DAVIES M.Sc. Reader in Entomology, Imperial College, University of London Insect Morphology and Phylogeny by Rolf G. Beutel , Frank Friedrich, Si-Qin Ge, Xing- Ke Yang Insect Morphology and Systematics Author TNAU, Tamil Nadu Principles of Insect Morphology by R.E.Snodgrass THE INSECTS AN OUTLINE OF ENTOMOLOGY P.J. Gullan and P.S. Cranston Research School of Biology, The Australian National University, Canberra, Australia & Department of Entomology and Nematology, University of California, Davis, USA The Insects Structure and Function by R. F. CHAPMAN Formerly of the University of Arizona, USA Edited by STEPHEN J. SIMPSON The University of Sydney, Australia ANGELA E. DOUGLAS Cornell University, New York, USA INSECTA AN INTRODUCTION by K. N. Ragumoorthi , V. Balasubamani , M. R. Srinivasan, N. Natarajan THE INSECTS: STRUCTURE, FUNCTION AND BIODIVERSITY by Dunston P. Ambrose MODERN ENTOMOLOGY by D. B. Tembhare