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Insect Morphology - Full Course for Undergaduate Students.pptx
Insects are characterized by a three-part body—head, thorax, and abdomen—protected by a chitinous exoskeleton that provides support and minimizes water loss. The head features sensory organs (antennae, compound eyes, and sometimes ocelli) and diverse mouthparts (like mandibles, maxillae, labium) adapted for feeding. The thorax comprises three segments (pro-, meso-, meta-) that support three pairs of legs and, if present, one or two pairs of wings. The abdomen contains most of the internal systems—digestive, respiratory (spiracles and tracheae), excretory, and reproductive structures—all segmented and often adorned with specialized appendages like cerci or ovipositors.
Insect Morphology - Full Course for Undergaduate Students.pptx
- 1. Insect Morphology Undergraduate Department ofPlant Protection
- 2. 2 Learning Objectives Students willbe able to identify and describe the external body regions of insects: Including head, thorax and abdomen along with their major Appendages Students will understand the structure of insect mouthparts: wings, antennae and legs along with explanation of how these related to insect habits and habitats Students will classify different types of insect morphology: comparing modifications found across various insect orders Students will analyse morphological adaptations in insect that support survival, feeding, locomotion and reproduction in diverse environment
- 3. 3 Chapter 1 Introduction &Body Wall of Insect
- 4. 4 Insect Morphology • Definition •Insect morphology is the study of the structure and form of insects, encompassing both their external features and internal anatomy. • Scope • Covers the vast diversity of insect forms and adaptations. • Body regions, • Appendages, and • Sensory structures.
- 5. 5 Origin and Meaningof "Insect Morphology" • Etymology of "Insect" • Derived from Latin "insectum," meaning "cut into" or "segmented." • Refers to the segmented body structure of insects. • Etymology of "Morphology" • Comes from Greek "morphē," meaning "form" or "shape," and "logia," meaning "study of." • Morphology is the study of the form and structure of organisms. • Combined Meaning • "Insect Morphology" refers to the study of the form, structure, and segmentation of insects. • Focuses on understanding their external and internal anatomical features.
- 6. 6 Arthropoda • Introduction • Arthropodais the largest phylum in the animal kingdom, encompassing a diverse range of invertebrate animals. • Etymology • The term "Arthropoda" is derived from Greek words: • "Arthron" meaning "joint" • "Pous" (pod-) meaning "foot" or "leg" • Literal Translation • "Arthropoda" translates to "jointed foot," highlighting the defining characteristic of jointed appendages in these animals.
- 7. 7 Key Characteristics • Exoskeleton: •A hard, chitinous outer shell that provides protection and support. • Segmented Body: • Divided into regions such as the head, thorax, and abdomen. • Jointed Appendages: • Legs, antennae, and other structures that facilitate movement and interaction with the environment.
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- 9. 9 Classes of PhylumArthropoda • Overview • Phylum Arthropoda is divided into several smaller groups known as classes. • There are a total of 18 classes, excluding the extinct trilobites. • Major Classes • Insecta: Includes insects like beetles, butterflies, and ants. • Arachnida: Includes spiders, scorpions, and ticks. • Crustacea: Includes crabs, lobsters, and shrimp. • Myriapoda: Includes centipedes and millipedes. • Hexapoda: Often synonymous with Insecta but can include other six-legged arthropods.
- 10. 10 Arthropoda Phylum of Animal Kingdom Arachnida Spiders,Scorpions, Mites, Ticks. Crustacea Lobster, Crabs, Shrimps, Barnacles Myriapoda Centipedes & Millipedes Hexapoda Insects and Springtails
- 11. 11 Class Arachnida • Characteristics •2 body segments - cephalothorax and abdomen • 8 legs • 1 pair of chelicerae • no antennae • Examples • Spiders • Scorpions • Ticks • Mites
- 12. 12 Class Crustacea • Characteristics •Several body segments - head, thorax and abdomen • Segments may be fused • Varied number of legs • 2 pairs of antennae • Examples • Crabs • Shrimp • Barnacles • Sowbugs
- 13. 13 Class Myriapoda • Characteristics •many body segments • 1 pair or 2 pair of legs per body segment • 1 pair of antennae • 1st pair of legs modified into venomous fangs • Examples • Centipedes • Millipedes
- 14. 14 Class Insecta • Characteristics •3 body segments • 6 legs • 1 pair of antennae • Diverse modifications to appendages • Examples • Beetles • Bugs • Wasps • Moths • Flies
- 15. 15 The Integument: Definitionand Meaning • Definition • The integument is the outermost covering of an organism, serving as a protective layer. • In arthropods, it includes the epidermis (hypodermis) and the cuticle. • Meaning • Etymology: Derived from Latin "integumentum," meaning "a covering." • Significance • Essential for the success and adaptation of insects and other arthropods to diverse habitats.
- 16. 16 Structure of ArthropodIntegument • Exoskeleton Overview • All arthropods possess an exoskeleton composed of chitin and proteins. • Provides structural support and protection. • External Growth • Unlike internal skeletal systems in humans, arthropods grow their exoskeleton externally. • Components of the Integument • Cuticle (Exoskeleton) • Epidermis (Hypodermis) • Basement Membrane
- 17. 17 The Cuticle • Natureof the Cuticle • Complex, non-cellular, and non-living structure. • Secreted by the epidermis. • Coverage • Envelops the entire external body surface. • Lines ectodermal invaginations such as the foregut, hindgut, and tracheae. • Composition • Accounts for 50% of the dry weight of insects. • Formed by polymerization of chemicals like chitin, protein, and lipid secreted by epidermal cells.
- 18. 18 Structure of theCuticle • Primary Divisions of the Cuticle • Epicuticle • Non-chitinous layer. • Functions as a protective barrier against environmental factors. • Procuticle • Comprised of a chitin-protein complex. • Provides structural strength and flexibility.
- 19. 19 Structure and Coverageof the Epicuticle • Non-Chitinous Layer • The epicuticle is a non-chitinous component of the insect cuticle. • Thickness and Coverage • Typically 1-4µ in thickness. • Envelops the entire external surface of an insect, excluding some chemoreceptive sensillae, the midgut, and ends of gland cells. • Primary Function • Prevents water loss from the insect body, crucial for maintaining hydration.
- 20. 20 Functional Roles ofthe Epicuticle • Water Uptake and Regulation • Helps maintain water content by facilitating water uptake in both terrestrial (e.g., flea Xenopsylla brasiliensis) and aquatic (e.g., alderfly Sialis lutaria) insects. • Growth and Expansion Control • Restricts exoskeleton dimensions during intra-stadial growth in holometabolous larvae. • Regulates expansion of newly ecdysed cuticle and distension during feeding in sap- sucking or blood-sucking insects. • Selective Permeability and Reservoir Functions • Thought to be selectively permeable to moulting fluid, aiding in digestion and recycling of the cuticle. • Acts as a reservoir for metabolic waste products, defensive secretions, and the juvenile hormone.
- 21. 21 Layers of Epicuticle •Overview • The epicuticle is composed of four layers, all secreted by the epidermis. • The Cement Layer • The Wax Layer • The Outer Epicuticle (Cuticulin) • The Inner Epicuticular Layer • Functions in protection, water conservation, and structural integrity.
- 22. 22 The Cement Layer •Structure and Composition • Also known as the tectocuticle, it protects the wax layer. • Formed by specialized dermal glands (Verson glands). • Composed of carbohydrates (lactose), proteins, lipids, and polyphenolic substances. • Thickness and Distribution • Typically not more than 0.1µ thick; may vary within or between insects. • Sometimes absent, as in honeybees. • Functions • Protects the wax layer from abrasions. • Acts as a reservoir for mobile lipids to replace lost waxes.
- 23. 23 The Wax Layer •Structure and Function • Known as the lipoid layer, it provides waterproofing and conserves water. • Lies below the cement layer; secreted by the epidermis before ecdysis. • Composition and Variability • Composed of hydrocarbons (12-31 carbon chains), esters of fatty acids and alcohols. • Composition varies between individuals and development stages. • Forms and Layers • Exists as a monolayer, combined with cement, or extends as wax blooms. • Composed of three layers: oriented monolayer, thick layer, and outer "bloom" layer.
- 24. 24 The Outer Epicuticle(Cuticulin) • Structure • Trilaminar layer, 12-18nm thick. • Present universally except over sensory endings; lines the trachea. • Composition and Resistance • Consists of protein and polyphenols; resistant to acids and solvents. • Derived from plasma membrane plaques. • Functions • Serves as the insertion point for muscle tonofibrillae. • Facilitates movement of apolysial droplets for cuticle digestion during moulting.
- 25. 25 The Inner EpicuticularLayer • Composition • Consists of polymerized lipoproteins stabilized by quinones. • Produced by epidermal secretions. • Functions • Acts as a reservoir for extracellular enzymes for wound repair. • Formed before apolysis alongside the outer epicuticle.
- 26. 26 Formation Timing • Definition •Apolysis refers to the separation of the new cuticle from the old cuticle. • Formation Sequence • Outer and inner epicuticular layers form before apolysis. • Cement and wax layers form after apolysis, playing crucial roles in insect physiology and development.
- 27. 27 The Procuticle • Overview •The procuticle is a comparatively much thicker layer of the cuticle. • Composed primarily of chitin and proteins, along with other substances. • Main Component: Chitin • Chitin is the chief constituent, forming 20-50% of the dry weight. • It is a polysaccharide made up of N-acetyl glucosamine and glucosamine.
- 28. 28 Composition of theProcuticle • Non-Chitinized Substances • Contains 25-37% non-chitinized materials, including proteins like arthropodin and resilin. • Includes lipids, pigments, and salts. • Thickness and Appearance • Thickness ranges from 0.2µ to 200µ. • Primary endocuticle is in contact with the epidermis (hypodermis). • Colourless in living insects.
- 29. 29 Outer Exocuticle • Characteristics •Tanned (sclerotized) layer, hard and dark in color. • Contains rigid areas called sclerites. • Function • Contributes to the rigidity and toughness of the cuticle. • Exocuticle is absent or reduced in more flexible regions of the integument.
- 30. 30 Inner Endocuticle • Characteristics •Untanned, soft, and flexible. • Contains chitin and protein fibers. • Structure • Composed of fine horizontal lamellae and vertical pore canals. • Largest section of the integument.
- 31. 31 Chemical Similarity andFusion • Chemical Composition • Layers are chemically similar, differing in the relative amounts of chitin and protein. • Intimately fused in most insects, despite physical differences. • Conclusion • The procuticle's structure and composition are crucial for providing both flexibility and strength to the insect cuticle.
- 32. 32 Cuticle Composition • MainComponents • The cuticle is primarily composed of chitin and cuticular proteins. • Variability in Composition • Proportions of these components determine the type of cuticle. • Low levels of chitin result in a highly elastic cuticle. • Elastic, rubber-like cuticles, containing the protein resilin, are found in articulatory sites of wings and mouthparts, aiding in movement.
- 33. 33 Chitin: Structure andRole • Chemical Composition • Chitin is a nitrogenous polysaccharide made of long chains of N- acetylglucosamine interspersed with glucosamine molecules. • Role in Procuticle • Main constituent of the procuticle, chemically linked with the protein arthropodin. • Undergoes tanning to form hard, inflexible, dark sclerotin. • Distribution and Solubility • Accounts for 25-60% of the dry weight of cuticles, the rest being protein. • Absent in epicuticle, less in exocuticle, more in endocuticle. • Insoluble in water, dilute acids, alkalies, and organic solvents; dissolves in concentrated mineral acids.
- 34. 34 History and Distributionof Chitin • Historical Discovery • First described by Henri Braconnot in 1811 from mushrooms as "fungine." • Named "chitin" by Odier in 1823, derived from Greek for "belted coat" or "gown." • Biological Distribution • Widely distributed in invertebrates, absent in protozoa and vertebrates. • In plants, restricted to fungi.
- 35. 35 Arthropodin • Proteins inCuticle • The cuticle contains a mixture of several proteins, with arthropodin and resilin being the most important. • Arthropodin Characteristics • Present in the upper layers of the procuticle. • Initially water-soluble but becomes insoluble through tanning reactions. • Tanning Process • Quinones, derived from tyrosine, tan arthropodin. • Tanned arthropodin forms the hard exocuticle, known as sclerotin. • The process is called "scleretisation" or "tanning."
- 36. 36 Resilin • Resilin Characteristics •A rubber-like, elastic protein found in movable joints, such as wing joints and mouthparts. • Functionality • Provides elasticity and flexibility, allowing structures to stretch under tension. • Returns to its original shape immediately upon release, facilitating efficient movement. • Importance in Arthropods • Critical for movement and flexibility, enhancing the mechanical properties of joints.
- 37. 37 Structural and SupportFunctions of the Cuticle • Exoskeleton Role • Acts as an exoskeleton, providing essential support to the body. • Contributes to the shape and form of the arthropod. • Muscle Attachment and Movement • Muscles are attached to the cuticle, facilitating various types of movement. • Invaginations in the cuticle provide internal support and additional sites for muscle attachment. • Wing Movement • Hard cuticular flight sclerites in the thoracic region enable wing movement.
- 38. 38 Protective and SensoryFunctions of the Cuticle • Water Conservation • Epicuticular wax layer provides a mechanism to conserve water, crucial for terrestrial insects. • Protection from Infection • Secretions over the cuticular layer in some insects have bactericidal properties, offering protection from infection. • Sensory Functions • Various parts of the cuticle are modified to form sense organs, enabling the reception of environmental stimuli.
- 39. 39 The Epidermis • Locationand Structure • The epidermis is a single cellular layer situated between the basement membrane and the endocuticle. • Between moults, epidermal cells are flattened with no distinct boundaries. • Role in Molting • During and after a moult, cells develop long cytoplasmic processes extending into the pore glands, which retract as the cuticle matures. • Epidermal cells secrete the moulting fluid during apolysis, dissolving the old cuticle. • Cuticle Formation and Repair • Secretes the greater part of the cuticle. • Absorbs digestion products of the old cuticle and repairs wounds.
- 40. 40 Specialized Functions ofEpidermal Cells • Specialization • Some epidermal cells specialize to form sense organs (mechanoreceptors or chemoreceptors) or glands (e.g., dermal or peristigmatic), neurons, or glial cells. • Dermal and Peristigmatic Glands • Dermal glands secrete and deposit the cement layer over the newly formed outer epicuticle during cuticle formation. • Peristigmatic glands, present in dipterous larvae around the spiracle, secrete substances that provide hydrofuge properties to the cuticle, preventing water entry into the tracheal system.
- 41. 41 Oenocytes • Description andLocation • Oenocytes are large, round or oval cells of epidermal origin. • Typically found in groups on either side of each abdominal segment or between the bases of epidermal cells and the basement membrane (e.g., Ephemeroptera, Odonata, Hemiptera). • In Homoptera, Hymenoptera, and Diptera, oenocytes are embedded in the fat body. • In Lepidoptera and Orthoptera, they form clusters in the body cavity. • Functions • Secrete the lipoprotein components of the procuticle and epicuticle. • Likely involved in the synthesis of waxes.
- 42. 42 Pore Canals • Structureand Function • Pore canals are extracellular extensions of the cytoplasm extending from the surface of epidermal cells to the inner layer of the epicuticle, possibly penetrating the outer epicuticle. • Filled with cuticular material; absent in old endocuticle due to new layers forming underneath. • Contain a filament for maintaining a hole in the new cuticle and transferring materials. • Characteristics and Variability • Pore canals become helical due to compressive forces during tanning. • Number of pore canals per cell varies by species: cockroaches have about 200 per cell (1,200,000/mm²), while Sarcophaga has 50-70 per cell.
- 43. 43 Basement Membrane • Description •The basement membrane is an amorphous, granular layer composed of neutral mucopolysaccharides. • Typically up to 0.5µ thick. • Location and Function • Lies just below the epidermis, forming a continuous sheet. • Similar in structure to the neural lamella, providing support and separation between the epidermis and underlying tissues.
- 44. 44 Cuticular Appendages • Definition: •Cuticular appendages are outgrowths of the cuticle connected by membranous joints. • Origin: • Arise from modified epidermal cells. • Include structures such as setae and spurs. • Types: • Setae (or Macrotichia): Hollow structures extending from the exocuticle. • Spurs: Differ from setae by having a multicellular origin.
- 45. 45 Setae (Macrotichia) • Structure: •Each seta arises from a cup-like pit called an alveolus. • Known as hairs or hair-like projections, originating from a trichogen cell (sensillum forming) penetrating through a tormogen cell (socket forming). • Function: • In some insects, setae innervate sense organs connected to the sensory nervous system.
- 46. 46 Types of Setae •Main Types of Setae: • Clothing Hairs: Cover the body or appendages (e.g., plumose hairs in Apoidea, bristles in Tachinidae). • Scales: Highly modified clothing hairs, characteristic of lepidopteran wings. • Glandular Setae: Serve as outlets for epidermal gland secretions; rigid ones are glandular bristles (e.g., certain lepidopteran larvae). • Sensory Setae: Modified for sensory functions, connected to the nervous system.
- 47. 47 Spurs • Structure andOrigin: • Spurs differ from setae by being of multicellular origin. • Location and Examples: • Commonly occur on insect legs. • Examples: End of the tibia in Orthoptera, lateral claws on insect legs. • Function: • Provide structural support and aid in movement or attachment.
- 48. 48 Cuticular Processes • Definition: •These outgrowths have no membranous articulation. • Types: • Microtrichia/Fixed Hairs/Aculei: • Minute hair-like structures found on wings of Mecoptera and certain Diptera. • Spines: • Outgrowths of the cuticle that are thorn-like in form.
- 49. 49 Sr. No. SpursSpines 1. Cuticular appendages Cuticular processes 2. Movable, multicellular structures and thick walled These are immovable outgrowths of cuticle 3. E.g.: present on tibia of plant hoppers and honey bees E.g.: hind tibia of grasshopper and leaf hoppers
- 50. 50 Cuticular Invagination • Overview: •The body wall or cuticle invaginates internally, forming definite structures. • Types of Invaginations: • Apodemes: • Hollow cuticular invaginations. • Provide areas for muscle attachment. • Apophyses: • Solid invaginations of the cuticle. • Offer mechanical support to various organs by forming distinct skeletal structures.
- 51. 51 Arthropod Exoskeleton • Exoskeleton: •A defining characteristic of the phylum Arthropoda (insects, spiders, crustaceans). • Hard, protective outer layer with muscles adhering inside. • Growth Limitation: • Growth occurs in steps, not continuously, due to the rigid exoskeleton. • Molting is necessary for growth, with stages called instars.
- 52. 52 Molting Process • Molting: •Involves changes for forming a new cuticle, allowing growth. • Triggered by hormones when growth reaches exoskeleton limits. • Instars: • Each molt marks the transition to a new growth stage. • Number of instars can vary based on environmental factors.
- 53. 53 Moulting, Ecdysis, andApolysis • Moulting: • Series of changes for new cuticle formation. • Ecdysis: • Shedding of the old cuticle to liberate the new instar. • Apolysis: • Separation of the epidermis from the cuticle, creating space for growth.
- 54. 54 Sclerotization and Tanning •Sclerotization: • Hardening of the cuticle with substances other than chitin. • Tanning: • Darkening of the cuticle, completing its texture and appearance. • Pharate Condition: • Stage during new exoskeleton construction, prior to ecdysis.
- 55. 55 Hormonal Control andGrowth Factors • Hormonal Triggers: • Molting initiated by hormonal changes. • Growth Factors: • Instar duration and growth extent influenced by temperature, food, and water. • Imago Stage: • When insects reach adulthood, molting stops, and energy shifts to reproduction.
- 56. 56 Mechanism of ExoskeletonRenewal • Epidermal Activity: • Epidermal cells increase protein synthesis, leading to apolysis. • Cuticulin Layer: • Forms to protect against molting fluid digestion. • Exoskeleton Recycling: • Old endocuticle digested, components recycled for new procuticle.
- 57. 57 Finalizing the NewExoskeleton • Ecdysial Sutures: • Lines of weakness where the old exoskeleton splits. • Teneral Condition: • Newly molted insects are soft and unpigmented until tanning is complete. • Sclerotization Process: • Sclerites harden and darken, giving the exoskeleton its final form.
- 58. 58 Hormonal Trigger andApolysis • Step 1: Hormonal Control • Molting is triggered by hormonal control. • Ecdysone is secreted from prothoracic glands behind the brain, initiating the molting process. • Step 2: Apolysis • Separation of the old exoskeleton from the epidermis. • A narrow space forms between the epidermis and the cuticle.
- 59. 59 Secretion and Activationof Molting Fluid • Step 3: Secretion of Molting Fluid • Epidermis secretes molting fluid, filling the space created by apolysis. • Contains enzymes like proteinase and chitinase to digest the endocuticle. • Step 4: Formation of Cuticulin Layer • First layer secreted is the protein epicuticle or cuticulin. • New cuticle is secreted underneath the old cuticle.
- 60. 60 Activation and Digestion •Step 5: Activation of Molting Fluid • Enzymes activate after the epicuticular layer is complete. • Molting fluid does not affect the exocuticle or nerve/muscle connections. • Step 6: Digestion and Absorption • Old endocuticle is digested and absorbed. • Wax layer is laid on the surface of the new cuticle.
- 61. 61 Formation and Secretionof New Cuticle • Step 7: Secretion of New Procuticle • Epidermis secretes new procuticle beneath the epicuticle. • Differentiates into exo- and endo-cuticle after tanning. • Step 8: Wax Layer Formation • Waxy material is produced and transported through pore canals. • Deposited over the protein epicuticle as lipid-epicuticle.
- 62. 62 Ecdysis and Sclerotization •Step 9: Ecdysis • Shedding of the old exo- and epicuticle through muscular activity. • The insect emerges, expanding as the new cuticle is soft. • Step 10: Tanning/Sclerotization • New exocuticle hardens and becomes brittle. • Arthropodin becomes water- insoluble sclerotin, completing sclerotization.
- 63. 63 Chapter 2 Body Segmentationin Insects
- 64. 64 Insect Body Segmentation •Characteristics: • Insects are small invertebrates with a hard exoskeleton protecting soft interiors. • Body segmented into three main parts: • Head, • Thorax, • Abdomen. • Features include three pairs of jointed legs and usually two pairs of wings. • Part of the Arthropods group, distributed worldwide.
- 65. 65 Detailed Body Segmentation •Head: • Contains a pair of feelers or antennae for smell, eyes and mouthpart. • Thorax: • Middle segment where legs (for walking or running) and wings (for flying) are attached. • Abdomen: • End segment where digestion, excretion, and reproduction occur. • Terminology: • Each segment in Insecta is referred to as a somite or metamere.
- 66. 66 Tagmosis and Tagmata •Tagmosis: • Grouping of segments into distinct body regions or tagmata. • Tagmata: • In adult arthropods, some segments unite to form distinct trunk sections. • This organization is crucial for the specialization of body regions.
- 67. 67 Structure of theInsect Head • Formation: • The head is a nearly completely sclerotized capsule. • Formed by the fusion of six segments. • Composition: • Mainly composed of rigid sclerites or sclerotized segments. • Contains: • Compound Eyes: For broad vision. • Simple Eyes (Ocelli): Additional visual input. • Mouthparts and Antennae. • Antennae: • Various types, sometimes exhibiting sexual dimorphism.
- 68. 68 Head Appendages andRegions • Appendages: • Antennae: Sensory organs. • Mandibles: Principal jaws. • Maxillae: Accessory jaws. • Labium: Lower lip. • Regions: • Procephalon: Anterior to the mandibles. • Gnathocephalon: Behind the procephalon; bears maxillae and mandibles.
- 69. 69 Types of Head Orientation HypognathousPrognathous Opisthognathous
- 70. 70 Hypognathous Mouthpart • Hypognathous: •Mouthparts directed downward. • Primitive type, common in vegetarian species in open habitats.
- 71. 71 Prognathous Mouthpart • Prognathous: •Mouthparts directed forward. • Found in carnivorous species and burrowing larvae.
- 72. 72 Opisthognathous Mouthpart • Opisthognathous: •Elongated proboscis slopes backward between front legs. • Common in Hemiptera and Homoptera.
- 73. 73 The Head Capsule •Structure: • The head is a nearly completely sclerotized capsule. • Formed by the fusion of six segments. • Composition: • Mainly composed of rigid sclerites or sclerotized segments. • Provides protection and structural support to sensory and feeding appendages.
- 74. 74 Segments of theHead Capsule • Pre antennary bears compound eyes and no other appendages • Antennary a pair of antennae is present. • Intercalary segment inserts in between without any appendages. • Mandibular a pair of mandibles is present. • Maxillary a pair of maxillae is present (with 1st maxilla). • Labial a pair of second maxillae or labium is present.
- 75. 75 Head Capsule Sclerites •Vertex (Epicranium): • The top or dorsal side of the head. • Situated between the eyes, behind the frons. • Contains ocelli and antennae. • Frons: • Located on the anterior face, between or below the epicranial arms. • Houses the median ocellus. • Bounded by the frontoclypeal suture ventrally. • Clypeus: • Tip-like structure between frontoclypeal suture and labrum. • Attached to the frons. • Labrum hangs below, articulated by a membranous connection.
- 76. 76 Lateral and PosteriorSclerites • Labrum: • Functions as the lower lip. • Gena (Lateral Sides): • Lower part beneath the eyes, posterior to the frons. • Separated from the frons by a general suture. • Post Gena: Located directly posterior to the eyes. • Post Gena: • Sclerites below the genae, above the mandibles.
- 77. 77 Occipital and ConnectiveStructures • Occiput: • Comprises most of the back of the head. • Divided from vertex and genae by the occipital suture. • Post-Occiput: • Forms the margin of the occipital foramen, narrow ring-like shape. • Separated from occiput by the post-occipital suture. • Occipital Foramen: • Connects the back of the head with the body.
- 78. 78 Sclerites and Sutures •Sclerites and Sutures: • Sclerites are the areas of the head enclosed between sutures. • Sutures or sulci are lines or grooves that separate these segments. • Key Features: • The head capsule contains seven distinct sutures. • Sutures define the boundaries of different sclerites, providing structural divisions.
- 79. 79 Detailed Description ofSutures (Part 1) • Epicranial Suture (Ecdysial Suture): • Inverted 'Y' shaped suture separating vertex and frons. • Stem is the coronal suture; arms are frontal sutures. • Present in some grasshoppers. • Fronto-clypeal Suture (Epistomal Suture): Line between frons and clypeus. • Clypeo-labral Suture: • Line between clypeus and labrum.
- 80. 80 Detailed Description ofSutures (Part 2) • Genal Suture: • Located on either side of the head below the compound eyes. • Separates the facial part from the gena. • Sub-genal Suture: • Line below the gena on either side of the head. • Occipital Suture: • Line between occiput and post occiput. • Post-occipital Suture: • The only real suture, separating maxillary and labial segments. • Other sutures do not represent real divisions.
- 81. 81 Thorax- Definition • Position: •The thorax is the middle section of the insect body, located between the head and abdomen. • Function: • It is the center for locomotion, containing all the muscles for the wings and legs. • Features: • Wings are attached to the mesothorax and metathorax. • Each segment typically bears one pair of legs.
- 82. 82 Insect Thorax –Segments • Division: • The thorax is divided into three parts: • Prothorax (Pro = First) • Mesothorax (Meso = Middle) • Metathorax (Meta = Last)
- 83. 83 Thorax Structure • Sclerites: •Each segment consists of hardened plates, or sclerites. • Dorsal Sclerites: • Called Nota (singular: Notum) • Lateral Sclerites: • Called Pleura (singular: Pleuron) • Ventral Sclerites: • Called Sterna (singular: Sternum)
- 84. 84 Thoracic Segments andAppendages • Terga: • Thoracic terga are called Notum. • Pronotum, • Mesonotum, • Metanotum • Dorsal sclerites of pro-, meso-, and metathoracic segments. • Legs: Each thoracic segment contains one pair of legs.
- 85. 85 Wings and Pterothorax •Wings: • Found only on meso- and metathoracic segments. • Together called the Pterothorax. • Prothorax • Never bears wings and varies in size.
- 86. 86 Pronotum Variations • Pronotum: •Grasshopper • Saddle-shaped with four subdivisions (prescutum, scutellum, post scutellum). • Cockroaches • Pronotums extend forward over the head. • Beetles and Treehoppers • May have unusual or bizarre pronotums.
- 87. 87 Insect Abdomen • Segments: •Typically consists of eleven segments. • Function: • Contains reproductive organs and the majority of the organ systems. • Terminology: • Terga: Dorsal abdominal segments. • Sterna: Ventral abdominal segments.
- 88. 88 Abdomen Features andStructures • Spiracles: • Usually found in the conjunctive tissue between the terga and sterna of abdominal segments 1-8. • Hymenoptera Specialization: • In wasps, bees, and ants: • The first abdominal segment is transferred to the thorax, forming the Mesosoma. • The 1st abdominal segment is called Propodaeum. • The 2nd abdominal segment is long and called Petiole or Pedicel. • Remaining segments are enlarged, collectively called Gastor.
- 89. 89 Reproductive Structures • Males: •Located on the 9th segment. • Includes the Aedeagus (or penis) and often a pair of claspers. • Females: • Located on the 8th and 9th segments. • Includes female external genitalia, copulatory openings, and Ovipositor.
- 90. 90 Ovipositor in Insects •Definition: • The ovipositor is the egg-laying device found only in female insects. • Variations: • Highly Modified and Conspicuous: In some insects. • Needle or Blade-like: In others. • Examples: • Parasitic Wasps (Hymenoptera): Use ovipositors to insert eggs or larvae into/onto a host. • Bees and Wasps: Stingers are modified ovipositors without egg-laying ability. • Crickets and Katydids (Orthoptera): Have needle-like and blade-like ovipositors, respectively. Blade-like ovipositor Needle-like ovipositor Needle-like ovipositor
- 91. 91 Abdominal Segmentation • Collembola: •Abdomen consists of six segments. • General Abdominal Segmentation: • Pre-Genital Segments: • Segments 01-07 • Genital Segments: • Segments 08-09 • Post-Genital Segments: • Segments 10-11
- 92. 92 Abdominal Appendages • Types: •Filaments: Thread-like processes at the end of the abdomen. • Cerci: Shorter, usually scleritized appendages of the last segment. • Anal Cerci: Attach to the 11th segment; post-genital appendages. • Special Cases: • Dermoptera (Earwigs): Cerci transformed into forceps-like structures (Furca). • Ephemeroptera (Mayflies): Immature stages possess tracheal gills on the abdomen.
- 93. 93 Abdominal Features andVariations • Spiracles: • 8 pairs located from the 1st to 8th segments on the margin of the tergite. • Additional Structures: • Caterpillars (Lepidoptera) & Sawflies: Possess abdominal prolegs. • Diptera (House Flies): Terminal segments form a pseudo-ovipositor during oviposition. • Homoptera (Aphids): Have "cornicles" on the 5th and 6th abdominal terga.
- 94. 94 Development Types • EpimorphicDevelopment: • Young ones hatch with a definite number of segments that remain constant. • Example: • Majority of insects. • Anamorphic Development: • Young ones hatch with only 8 segments; additional segments added post- embryonically. • Example: • Protura.
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- 96. 96 Insect Antennae • Overview •Antennae are mobile, sensory segmented appendages located on the head. • They articulate with the head in front of or between the eyes and arise from the antennal socket. • Position and Variation • First pair of appendages on the head; in some larvae and adults, they arise from the base of the mandibles. • Size and shape vary among different insects, often larger in males (sexual dimorphism), aiding in sex identification. • Development and Taxonomy • Well-developed in almost all adults and nymphs; absent in Protura and reduced in endopterygota larvae. • Antennal characteristics are useful for taxonomic classification.
- 97. 97 Structure of Antennae •Overview • Insect antennae are segmented appendages important for sensory functions. • Three Main Parts • Scape • The base segment that connects the antenna to the head. • Pedicel • The second segment, often containing sensory structures such as Johnston's organ, which helps detect movement and sound. • Flagellum • Comprises the remaining antennal segments, known as flagellomeres. • The flagellum is typically the most variable part among different insect species and is crucial for sensory perception.
- 98. 98 Serrate (saw like) •Description • The segments of the flagellum in these antennae are triangular with projecting points on one side, giving them a saw- like appearance. • Examples • Pulse Beetle • Jewel Beetle (Order Coleoptera) Order of Coleoptera: Click Beetle Serrate (saw like)
- 99. 99 Clavate (clubbed) • Description •These antennae have segments that gradually increase in diameter from the base to the tip. • They end in a club-like apical part, hence the name "clavate" or clubbed antennae. • Examples • Carrion Beetles (Order Coleoptera) • Adult carrion beetles feed on decaying animal matter or maggots. • Butterflies Order Coleoptera: Red-breasted carrion beetle Clavate (clubbed)
- 100. 100 Clavate with hook(clubbed antennae with hook) • Description • These antennae have segments that gradually increase in diameter from the base to the tip. • The terminal segment ends with a small hook-like structure. • Examples • Skipper Butterflies Clavate with hook Order of Lepidoptera: Skipper Butterflies
- 101. 101 Capitate (clubbed withknob) • Description • These antennae have segments that gradually increase in diameter from base to apex. • The terminal 3 to 5 segments suddenly enlarge to form a knob-like structure, resulting in an abruptly clubbed appearance at the end. • Examples • Red Flour Beetle • Blister Beetles • Butterflies (Order Lepidoptera) Order of Lepidoptera: Red-banded hairstreak Capitate (clubbed with knob)
- 102. 102 Geniculate (elbowed) • Description •In these antennae, the first segment, known as the scape, is greatly elongated. • The flagellum forms an angle with the elongated scape, creating a distinctive structure. • Examples • Ants • Honey Bees (Order Hymenoptera) Geniculate (elbowed) Order Hymenoptera: Carpenter ant
- 103. 103 Lamellate • Description • Theterminal segments of these antennae expand into lateral oval lobes, giving them a leaf-like appearance. • Known as lamellate or clubbed antennae, they end in nested plates. • Examples • Rhinoceros Beetle • Dung Rollers • Chaffer Beetle • Order • These examples belong to the order Coleoptera. Lamellate Order Coleoptera: Japanese beetle Order Coleoptera: Conifer scarab
- 104. 104 Flabellate (Plate like) •Description • The terminal segments of these antennae expand on one side into lateral lobes. • The sides of the lobes are parallel, creating a symmetrical appearance. • Examples • Stylopids Flabellate (Plate like) Order of Strepsiptera: Stylops
- 105. 105 Plumose (brush likewith dense hairs) • Description • Plumose antennae are characterized by whorls of hairs arising from each joint of the segment. • Each whorl contains multiple hairs, giving the antennae a feather-like appearance. • Examples • Moths (Order Lepidoptera) • Mosquitoes (Order Diptera) Plumose (brush like with dense hairs) Order of Diptera: Mosquito male Order of Lepidoptera: Luna moth
- 106. 106 Pilose (brush likewith sparse hairs) • Description • These antennae resemble plumose antennae but have fewer hairs in each whorl, resulting in a more sparse appearance. • Examples • Female Mosquito Pilose (brush like with sparse hairs) Order of Diptera: Female mosquito
- 107. 107 Aristate (antennae witharista) • Description • These antennae are small and microscopic, consisting of three segments. • The third segment is enlarged and bears a bristle called an arista on its dorsal side. • Examples • House Flies (Order Diptera) • Shore Flies (Order Diptera) Aristate (antennae with arista) Order of Diptera: House fly
- 108. 108 Stylate (antennae withstyle) • Description • These antennae are small and consist of 3 to 4 segments. • The terminal segment elongates into a bristle-like structure called a style. • Example • Robber fly Stylate (antennae with style) Order of Diptera: Robber fly
- 109. 109 Functions of Antennae •Sense Organs • Antennae primarily function as sense organs with a large number of sensilla, most found in the middle of the flagellum. • Olfactory Receptors • Odor receptors on antennae bind to odor molecules, particularly useful in males for detecting pheromones. • Sound Perception and Air Speed Measurement • Antennae are involved in sound perception in male mosquitoes and other insects, with movements monitored by Johnston’s organ in the pedicel. • Mating Functions • In fleas and collembolan, antennae are used in mating; male fleas use them to clasp females.
- 110. 110 Chapter 4 Mouth Parts(Feeding Organs)
- 111. 111 Main Parts ofa Typical Insect Mouth • Upper Lip (Labrum) • Anterior Jaws (Mandibles) • Accessory Jaws (Maxillae) • Lower Lip (Labium) • Tongue-like Structure (Hypopharynx)
- 112. 112 Insect Mouthparts –Labrum & Mandibles • Labrum (Upper Lip) • Description: Simple fused sclerite, often called the upper lip. • Movement: Moves longitudinally. • Connection: Hinged to the clypeus. • Mandibles (Anterior Jaws) • Description: Highly sclerotized paired structures. • Movement: Move at right angles to the body. • Function: Used for biting, chewing, and severing/cutting food.
- 113. 113 Insect Mouthparts –Maxillae & Labium • Maxillae (Accessory Jaws) • Description: Paired structures with segmented palps. • Movement: Move at right angles to the body. • Function: Used for holding and sending food into the mouth. • Labium (Lower Lip) • Description: A fused structure with segmented palps. • Movement: Moves longitudinally.
- 114. 114 Types of InsectMouthparts • Overview: • Mouthparts vary greatly among insects of different orders. • They can be divided into two basic groups: • Chewing and Biting Type (Mandibulate) • Description: Considered primitive. • Function: Used for biting and chewing. • Sucking Type (Haustellate) • Description: Adapted for sucking. • Function: Used for feeding on liquids.
- 115. 115 Types of MouthParts Mandibulate Haustellate Other types Chewing & Biting Chewing & Lapping With Stylets Without Stylets Mask Type Degenerate Type Piercing & Sucking Sponging & Sucking Rasping & Sucking Siphoning
- 116. 116 Different types ofMouthpart with examples Chewing and Biting Type Grasshoppers, Cockroaches Chewing and Lapping Type Honey Bee Piercing and Sucking Type Aphids, Bugs, Mosquitoes, Lice Rasping and Sucking Type or Lacerating and Sucking Type Thrips Sponging or Lapping and Sucking Type House fly Siphoning Type Butter Flies, Moths Mask Type Young ones (Naiads) of Dragon Fly Degenerate Type Maggots
- 117. 117 Chewing & BitingType Mouthparts • Description: • The generalized biting type of mouthparts is found in nymphs and adults of various insects. • Examples of Insects with Chewing & Biting Mouthparts: • Dragonflies and Damselflies (Order: Odonata) • Termites (Order: Isoptera) • Adult Lacewings (Order: Neuroptera) • Beetles (Order: Coleoptera) • Ants (Order: Hymenoptera) • Cockroaches (Order: Blattaria) • Grasshoppers, Crickets, and Katydids (Order: Orthoptera) • Caterpillars (Order: Lepidoptera)
- 118. 118 Labrum in chewingmouthpart • Structure: • A simple, plate-like structure located below the clypeus on the anterior side of the head. • Function: • Overlaps the bases of the mandibles. • Features: • Inner surface equipped with chemoreceptors. • In Hymenoptera, it extends into a small lobe-like epipharynx.
- 119. 119 Mandibles in chewingmouthpart • Structure: • Paired, heavily sclerotized, un-segmented jaws located immediately behind the labrum. • Articulation: • Connect to the head capsule via two joints: • Ginglymus: A groove or cavity articulating with a convex process on the clypeus. • Condyle: A rounded head fitting into a socket at the lower end of the gena or postgena. • Teeth Types: • Incisors: Used for cutting. • Molars: Used for grinding. • Functions: • Adapted for cutting or crushing food. • Frequently used for defense.
- 120. 120 Maxillae in chewingmouthpart • Location: • Paired structures positioned behind the mandibles. • Structure: • Segmented with each maxilla bearing a feeler-like organ called the palpus, which helps determine the quality and taste of food. • Segments: • Cardo: Basal segment. • Stipes: Second segment. • Palpifer (Maxillary Palpi): The palpus is borne on the lobe of the stipes. • Lacinia: An elongate, jaw-like structure, spined or toothed on its inner border. • Galea: A lobe-like structure. • In some insects, the stipes bears a single lobe called male. • Function: • Serve as accessory jaws. • Lacinia aids mandibles in holding and masticating food.
- 121. 121 Labium in chewingmouthpart • Location: • Lower lip situated behind the maxillae. • Structure: • Divided by a transverse suture (labial suture) into: • Basal Post-Mentum • Further divided into basal sub-mentum and distal mentum. • Distal Pre-Mentum • Bears a pair of palpi and apical lobes forming the ligula. • Components: • Labial Palpi: Located on lateral lobes of the prementum, known as palpiger. • Ligula: Consists of: • Glossae: Pair of small central lobes. • Paraglossae: Pair of larger lateral lobes. • Function: • Labial palpi serve as sense organs.
- 122. 122 Hypopharynx in chewingmouthpart • Structure: • A short, tongue-like structure located above the labium and between the maxillae. • Function: • In most insects, the ducts from the salivary glands open on or near the hypopharynx.
- 123. 123 Chewing & LappingType Mouthparts- Overview • Example: • Honey Bees • Purpose: • Mouthparts are modified for collecting nectar and pollen. • Components: • Labrum, Mandibles, Maxillae, Labium, Epipharynx • Details: • Epipharynx: Located below the labrum; serves as an organ of taste. • Mandibles: Smooth and situated on either side of the labrum. • Used for molding wax and making honeycombs.
- 124. 124 Chewing & LappingType Mouthparts- Detailed Structure • Labium Structure: • Consists of sub-mentum, mentum, paraglossa, and glossa (tongue). • Glossa: Long, with a small "Flabellum or Labellum" at the tip; serves for gathering honey and as an organ of taste and smell. • Labial Palps: Long, located on each side. • Tube Formation: • Maxillae and labial palps form a tube enclosing the glossa, which moves up and down to collect nectar. • Functionality: • Labrum and mandibles are for biting. • Maxillae, labium, and hypopharynx combine to form a sucking proboscis.
- 125. 125 Haustellate Mouthparts • Definition: •Haustellate mouthparts are specialized for sucking liquids. • Subgroups: • With Stylets: • Needle-like projections for penetrating plant and animal tissue. • Modified mandibles, maxilla, and hypopharynx form stylets and feeding tube. • Insects use these to pierce tissue and suck liquids from the host. • Examples: • Insects with stylets can access fluids from within plant or animal tissues.
- 126. 126 Haustellate Mouthparts WithoutStylets • Characteristics: • Lack stylets, unable to pierce tissues. • Rely on accessible food sources such as nectar. • Examples: • Lepidoptera (Butterflies and Moths): • Possess a long siphoning proboscis for accessing nectar. • Rasping-Sucking Rostrum of Some Flies: • Considered haustellate without stylets. • Method of liquid transport differs from Lepidopteran proboscis. • Key Point: • Haustellate mouthparts, whether with or without stylets, are adapted for specific feeding strategies.
- 127. 127 Piercing & SuckingMouthparts • Examples: • Cicadas, aphids, and other plant bugs (order Hemiptera). • Sucking lice (order Phthiraptera-Anoplura). • Stable flies and mosquitoes (order Diptera). • Structure: • Mandibles and Maxillae: • Modified into slender, bristle-like stylets. • Rest in a grooved labium. • Stylet Pairs: • Mandibular Stylets: Anterior/outer pair, serrated for piercing. • Maxillary Stylets: Posterior/inner pair, tapered and grooved for feeding.
- 128. 128 Function and Mechanism •Mechanism: • Stylets are hollow and can protrude/retract via muscular action. • The groove in maxillary stylets divides into two channels for feeding. • Feeding Process: • Saliva: Pumped down one tube to liquefy food. • Suction: Liquefied food is sucked up the other tube. • Sheath and Support: • Stylets enclosed in a sheath formed by the labium. • Labrum covers the grooved labium. • Hypopharynx forms the floor of the cibarial sucking pump or mandibular plates. • Feeding Strategy: • Stylets pierce plant tissues to suck sap from phloem vessels.
- 129. 129 Rasping & SuckingMouthparts • Example: • Thrips • Mouth Cone: • Formed by the labrum, labium, and bases of maxillae. • Small tubular structure used for feeding. • Stylets: • Maxillae: Modified into stylets. • Mandibles: • Right mandible is absent. • Left mandible is modified into a stylet.
- 130. 130 Feeding Mechanism andHypopharynx • Feeding Mechanism: • Three stylets are inserted into plant tissues. • Cell sap oozes out and is sucked up using the mouth cone. • Hypopharynx: • Reduced and small, assisting in the feeding process.
- 131. 131 Sponging/Lapping & SuckingMouthparts • Purpose: • Used to sponge and suck liquids. • Examples: • House flies and blow flies (order Diptera). • Structure Overview: • Comprises a fleshy and retractile proboscis (modified labium) under the head. • Proboscis is divided into three parts: • Basal Rostrum • Middle Haustellum • Distal Labella Basal Rostrum Middle Haustellum
- 132. 132 Detailed Structure ofMouthparts • Rostrum (Modified Labium): • Cone-shaped with a clypeus in front. • Bears a pair of maxillary palps. • Contains a chitinous fulcrum enclosing the pharynx. • Haustellum: • Highly modified labium hinged to the fulcrum. • Contains two triangular plates: labrum-epipharynx and hypopharynx. • Posterior part has a chitinous mentum. • Front side features a deep oral groove with a salivary duct. • Labella: • Fleshy distal end of the labium. • Acts as a sponge-like organ to absorb liquids.
- 133. 133 Feeding Mechanism • FeedingProcess: • Proboscis is lowered to release salivary secretions onto food. • Dissolved or suspended food is absorbed via capillary action into pseudotracheae. • Pseudotracheae have channels for moving liquid and may have sharp teeth for rasping. • Additional Features: • Mandibles and maxillae are absent. • Labella's outer surface has pseudotracheae, which open externally. • Near the mouth, small prestomal teeth aid in rasping solid food.
- 134. 134 Siphoning Type Mouthparts •Examples: • Butterflies and moths are known for simple sucking. • Key Characteristics: • Mandibles: • Completely absent in this type. • Mouthparts Structure: • All mouth organs are highly reduced except for the galea of maxillae. • Each galea is elongated into a hollow, semicircular structure. • Sucking Proboscis: • Formed when both galea come together, enclosing the proboscis. • The proboscis is coiled and kept below the head when not feeding.
- 135. 135 Mask Type Mouthparts •Examples: • Naiad (young stage) of Dragonflies • Key Characteristics: • Modified for Biting and Chewing: • Specialized for catching and consuming prey. • Structure: • Labium: Modified into a mask. • Components: • Prementum and postmentum form a hinge at the suture. • Labial palps assist in catching prey. • Function: • When prey is sighted, the labium extends rapidly to capture it. • At rest, the labium covers a portion of the head, resembling a mask.
- 136. 136 Degenerate Type Mouthparts •Example: • Maggots • Key Characteristics: • Head Structure: • Maggots lack a definite head. • Mouthparts: • Highly reduced in form. • Represented by one or two mouth hooks. Hook
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- 138. 138 Structure of InsectLegs • Location: • Fore-legs: Located on the prothorax. • Mid-legs: Located on the mesothorax. • Hind-legs: Located on the metathorax. • Components: • Six major parts from proximal to distal: • Coxa • Trochanter • Femur • Tibia • Tarsus • Pretarsus • Tarsus: • Divided into one to five "pseudosegments" called tarsomeres.
- 139. 139 Modifications and Adaptations •Functional Diversity: • Like mouthparts and antennae, insect legs are modified for various functions based on environment and lifestyle. • Setae: • Unicellular hair-like outgrowths that act as sensory organs. • May appear as pegs, hooks, or scales. • Femur and Tibia: • May have spines (immovable, multi-cellular outgrowths) or spurs (movable, articulated).
- 140. 140 Structural Details • Sutures: •Impressed lines or internal ridges between sclerites. • Conjunctivae: • Flexible areas in the body wall for folding. • Articulation: • Definite joints between segments of legs. • Conjunctive and Articular Membrane: • Flexible portion of the cuticle connecting hard segments.
- 141. 141 Basal Segments • Overviewof Insect Leg Structure: • A typical insect leg consists of multiple segments, each with specific functions and characteristics. • Coxa: • Basal thick short segment. • Functional base of the leg. • Articulates with the body between pleura and sterna. • Trochanter: • Second segment, triangular in structure. • Articulates with the coxa, rigidly fixed to the femur. • Divided into sub-segments in Odonata and parasitic Hymenoptera.
- 142. 142 Middle Segments andTarsus • Femur: • Largest and strongest part of the leg. • Conspicuous in insects with leaping ability. • Tibia: • Fourth segment, slender, often equal to or longer than the femur. • Carries one or more tibial spurs near its distal extremity. • Tarsus: • Last segment, divided into five sub-segments (tarsomeres). • Variation in number of segments: • Single joint: Human louse • Two joints: Aphid • Three joints: Mole cricket, Gryllidae (grasshopper) • Four joints: Tettigonidae (grasshopper), Leaf beetle.
- 143. 143 Pre-tarsus and SpecialStructures • Pre-tarsus: • Located at the apex of the tarsus, with various structures: • Single claw: Collembola, Protura. • Paired claws with "Arolium" between: Housefly. • Two lobes or "Pulvilli" with an Arolium between: Housefly (Diptera). • Medium bristle "Empodium" instead of arolium.
- 144. 144 Ambulatory or WalkingType Insect Legs • Definition: • Ambulatory legs are adapted for walking. • Examples of Insects: • Bugs (Order Hemiptera) • Leaf beetles (Order Coleoptera) • Characteristics: • All legs are of normal structure, used for walking. • Similar Structure: • Resemble cursorial (running) legs in form. • Designed for steady and efficient movement on various surfaces.
- 145. 145 Cursorial Type (RunningType) Insect Legs • Definition: • Cursorial legs are adapted for running. • Examples of Insects: • Cockroaches (Order Blattaria) • Ground and tiger beetles (Order Coleoptera) • Wasps • Characteristics: • All legs are of normal structure but specifically modified for running. • Leg Segments: • Long and thin, providing speed and agility. • Designed for efficient and rapid movement.
- 146. 146 Saltatorial Type (JumpingType) Insect Legs • Definition: • Saltatorial legs are adapted for jumping. • Examples of Insects: • Grasshoppers • Crickets • Katydids (Order Orthoptera) • Characteristics: • Hind Legs: • Specifically adapted for jumping. • Femur and Tibia: • Elongated to provide leverage and power. • Essential for effective leaping and jumping.
- 147. 147 Fossorial Type (DiggingType) Insect Legs • Definition: • Fossorial or digging legs are adapted for ground dwelling insects that require specialized limbs for digging. • Examples of Insects: • Dung rollers • Mole crickets (Order Orthoptera) • Cicada nymphs (Order Hemiptera) • Rhinoceros beetle • Characteristics: • Front legs are modified specifically for digging. • Tibia and tarsus are adapted with teeth-like or rake-like projections. • These modifications are useful for digging out tender roots of plants. • A slit-like oar is present beneath the tarsus, aiding in the digging process.
- 148. 148 Raptorial Type (GraspingType) Insect Legs • Definition: • Raptorial or grasping legs are adapted for seizing and holding onto prey. • Examples of Insects: • Mantids (Order Mantodea) • Ambush bugs • Giant water bugs • Water scorpions (Order Hemiptera) • Characteristics: • Raptorial forelegs are specifically modified for grasping prey. • Front legs are adapted for catching prey. • Coxa: Very long, providing reach and leverage. • Femur: Spiny with a central longitudinal groove for holding prey. • Tibia: Narrow, blade-like, and spinose, fitting into the groove of the femur for a secure grip.
- 149. 149 Natatorial Type (SwimmingType) Insect Legs • Definition: • Natatorial or swimming legs are adapted for aquatic locomotion. • Examples of Insects: • Water beetles • Water bugs • Characteristics: • Natatorial legs are specifically modified for swimming. • Hind Legs: Modified for effective swimming. • Tarsi: Equipped with long setae, aiding in propulsion through water. • Tibia and Tarsus: • Short and broad • Provided with dense, long marginal hairs for increased surface area and efficiency in water. • Coxa: Flattens out on the body wall, providing stability. • Tibia and Tarsus: Flat to facilitate smooth movement through water.
- 150. 150 Scansorial Type (ClingingType) Insect Legs • Definition: • Scansorial or clinging legs are adapted for climbing and holding onto surfaces like hair or fur. • Example of Insect: • Head louse • Characteristics: • All legs are specifically modified for clinging. • Tarsus: • Without a joint. • Equipped with a single curved claw. • These adaptations are particularly useful for catching and clinging to hairs.
- 151. 151 Prehensile or BasketForming Legs • Definition: • Prehensile legs are adapted to form a basket-like structure for catching prey. • Example of Insect: • Dragonflies • Characteristics: • Thoracic Segments: • Obliquely arranged. • Tergal plates pushed backward. • Sternal plates pulled forward. • Leg Positioning: • All legs are attached to the sternal plates, coming forward and positioned below the head. • Legs together form a basket-like structure, enhancing the ability to catch prey.
- 152. 152 Antennal Cleaning Legsin Honey Bees • Function: • Adapted for cleaning antennae and compound eyes. • Characteristics: • First Pair of Legs: • Tibia: Possesses a process for cleaning. • 1st Tarsal Segment: Features a semicircular notch. • Eye Cleaning: • Each thoracic leg has a row of stiff bristles on the tibia, forming an eye brush for cleaning compound eyes. • Antenna Cleaning: • Distal end of the tibia has a movable spine called yelum. • Yelum can close over the notch on the tarsus to form an antenna comb. • Antennae are drawn through this comb for cleaning.
- 153. 153 Wax Picking TypeLegs in Honey Bees • Function: • Adapted for collecting and cleaning pollen and wax. • Characteristics: • Second Pair of Legs: • Long Bristles: On the mesothoracic leg tarsus form a pollen brush. • Pollen Brush: Used for removing pollen from the front part of the body. • Pollen and Wax Handling: • Each mesothoracic leg has a pollen brush on the tarsus. • End of the tibia features a spur-like spine. • The spine is used for removing pollen from the pollen basket and wax from the abdomen. • The tibial spine is referred to as a wax pick.
- 154. 154 Pollen Collecting TypeLegs in Honey Bees • Function: • Adapted for collecting and storing pollen. • Characteristics: • Hind Legs (Metathoracic Legs): • Large Tibia: Features a cavity with bristles forming a pollen basket, also known as the corbicula, for storing pollen during collection. • Pectin and Auricle: • Tibia has a row of stiff bristles called pectin. • Below the pectin is a flat plate known as the auricle. • Together, they form a wax pincher for removing wax from the abdomen of worker bees. • Tarsus: • Outer surface has a pollen brush. • Inner surface has a pollen comb, with a row of stiff spines. • The pollen comb removes pollen from the body and helps fill the pollen basket.
- 155. 155 Leg Structure inCaterpillars • Thoracic Legs (True Legs): • Three pairs located on the thorax. • Jointed and sclerotized. • Abdominal Legs (Prolegs): • Typically five pairs located on the 3rd, 4th, 5th, 6th, and last abdominal segments. • Unjointed, short, fleshy with a flat surface called the planta. • Crochets: Hook-like structures arranged in circular or semi-circular patterns on the planta. • Variations in Larvae: • Semi-loopers: • Prolegs absent on the 3rd and 4th abdominal segments. • Movement resembles a semi-loop. • Loopers: • Prolegs present only on the 6th and last segments. • Movement resembles a loop.
- 156. 156 Leg Structure inSawfly Larvae • Thoracic Legs: • Three pairs of true legs located on the thorax. • Prolegs: • Six or more pairs on the abdomen. • Unique feature: These prolegs do not bear crochets, unlike lepidopteran larvae. • Comparison with Caterpillar Larvae: • Sawfly larvae have more prolegs. • Lack of crochets distinguishes them from caterpillar larvae.
- 157. 157 Chapter 6 Wings (FlightOrgans)
- 158. 158 Importance and Structureof Insect Wings • Significance: • Flight contributes to the success of insects as terrestrial animals. • Wings and their characteristics are vital for taxonomic studies and identification. • Structure: • Adult insects typically have two pairs of wings connected to the thorax, supported by hollow veins. • Wings are located on the mesothorax and metathorax (forming the pterothorax). • Exceptions: • Silverfish and springtails (Apterygota) lack wings. • Some insects, like Diptera, have only one pair of functional wings.
- 159. 159 Wing Structure andShape • Triangular Shape: • Wings often have a somewhat triangular outline. • Margins of the Triangle: • Remegium (Costal Margin): The front or anterior side. • Apical Margin: The outer side. • Anal Margin: The inner side. • Angles of the Wing: • Humeral Angle: Near the wing base. • Apical Angle: At the wingtip. • Anal Angle (Tornus): Near the anal margin. • Significance: • The triangular shape and defined margins aid in aerodynamic efficiency and flight control.
- 160. 160 Veins, Cells, andStructural Support • Cells: • Areas enclosed between veins. • Closed Cells: Entirely surrounded by veins. • Open Cells: Extend to the wing margin without intervening veins. • Veins and Cross Veins: • Veins: Run from the wing base toward the apex, providing structural support. • Cross Veins: Run crosswise, connecting the main veins. • Structural Considerations: • Veins are heavier or closely placed towards the costal margin due to the greatest stress during flight. • Functionality: • The arrangement of veins and cells contributes to the wing’s strength, flexibility, and ability to withstand aerodynamic forces.
- 161. 161 Wing Venation • Definition: •Venation refers to the pattern of veins and cross veins in insect wings. • Archedictyon: • A hypothetical scheme of wing venation proposed for the earliest winged insects. • Represents a "template" modified over 200 million years. • Consisted of 6-8 longitudinal veins. • Comstock-Needham System: • Developed by John Comstock and George Needham in 1898. • Provides a naming system for insect wing veins, highlighting their homology.
- 162. 162 Major Longitudinal Veins •Costa ("C"): • Forms the thickened anterior margin, always unbranched. • Sub Costa ("Sc"): • Runs below the costa, divided into Sc1 and Sc2. • Radius ("R"): • Stout vein branching into R1 and radial sector Rs, which forks into R2, R3, R4, R5. • Media ("M"): • Divided into M1, M2, M3, M4; sometimes further into MA and MP.
- 163. 163 Additional Longitudinal Veins •Cubitus ("Cu"): • Forks into Cu1 and Cu2; Cu1 may further divide into Cu1a and Cu1b (or CuA and CuP). • Anal Veins ("A"): • Located posteriorly, associated with the 3rd axillary sclerites. • Several anal veins labelled A1, A2, etc. • Cross Veins: • Link longitudinal veins, named according to their location (e.g., m-cu for medio- cubital cross vein). • Some have unique names, like the humeral cross vein (h) and the sectoral cross vein (s).
- 164. 164 Significance of WingVenation • Functional Importance: • Provides structural support and reinforcement. • Veins filled with hemolymph, tracheal tubes, and nerves. • Taxonomic Relevance: • Wing venation patterns are crucial for identifying insect families and species. • Distinctive venation patterns aid in classifying and studying insect evolution. • Evolutionary Insight: • Paleoptera (e.g., Ephemeroptera and Odonata) lack wing-flexing mechanisms, contrasting with Neoptera.
- 165. 165 Membranous Wings • Characteristics: •Thin and more or less transparent, though some may be darkened. • Feature highly developed venation, providing structural support. • Functionality: • Primarily used for flight, offering flexibility and maneuverability. • Examples: • Hind wings of grasshoppers. • Dragonflies and damselflies (Order Odonata). • Lacewings (Order Neuroptera). • Flies (Order Diptera). • Bees and wasps (Order Hymenoptera). • Termites (Order Isoptera). Damsel Fly (Odonata) Dragon fly
- 166. 166 Halteres in Flies •Definition: • Halteres are an extreme modification of hind wings in the order Diptera (true flies), reduced to mere nubs. • Functionality: • Serve as gyroscopic stabilizers, aiding in balance and direction during flight. • Structure: • Divided into three regions: scabellum, pedicel, and capitalum. • Examples: • Found in all flies (Order Diptera). Crane fly Bees
- 167. 167 Elytra in Beetles •Definition: • Elytra are the hardened, heavily sclerotized forewings of beetles, acting as a protective horny sheet without venation. • Functionality: • Modified to protect the hind wings when the beetle is at rest. • Examples: • Found in all beetles (Order Coleoptera). Lady Bird Beetles Colorado Potato Beetle
- 168. 168 Hemelytra in Bugs •Definition: • Hemelytra are a variation of elytra found in Hemipterans (true bugs). • Structure: • The forewings are hardened in the proximal two-thirds and membranous in the distal portion. • Functionality: • Unlike elytra, hemelytra function primarily as flight wings. • Examples: • Found in bugs (Order Hemiptera). Red Cotton Bug
- 169. 169 Tegmina in Insects •Definition: • Tegmina (singular tegmen) are the leathery forewings found in certain insect orders. • Functionality: • Protect the delicate hind wings, similar to elytra in beetles. • Sometimes used for flight. • Examples: • Grasshoppers, crickets, and katydids (Order Orthoptera). • Cockroaches and mantids (Order Dictyoptera). Cockroach Grasshopper
- 170. 170 Scaly Wings inInsects • Definition: • Scaly wings are thin and membranous front and hind wings covered with flattened unicellular setae (scales). • Functionality: • The scales make the wings colorful and are used for taxonomic studies. • They are also useful for flight. • Examples: • Butterflies, moths, and skippers (Order Lepidoptera). • Caddisflies (Order Trichoptera). Moth Monarch Butterfly
- 171. 171 Fringed Wings inInsects • Definition: • Fringed wings are slender front and hind wings with long fringes of marginal hairs, giving a feather-like appearance. • Structure: • Highly reduced wings with reduced venation. • Functionality: • Useful for flight. • Example: • Thrips (Order Thysanoptera). Thrips
- 172. 172 Hairy Wings inInsects • Definition: • Hairy wings are front and hind wings covered with setae (hair-like structures). • Functionality: • Useful for flight. • Example: • Caddisflies (Order Trichoptera).
- 173. 173 Clefted (Fissured) Wingsin Insects • Structure: • Front wing is longitudinally divided, forming a fork-like structure. • Hind wing is divided twice, forming two forks with three arms. • All forks possess small marginal hairs. • Functionality: • Useful for flight. • Example: • Both wings of the Plume Moth.
- 174. 174 Wing Coupling • Function: •During flight, insect wings are kept together by inter-locking structures called wing coupling apparatus. • Types of Wing Coupling Apparatus: • Jugum Type: Involves a lobe-like extension of the forewing that overlaps the hindwing. • Frenulum & Retinaculum Type: A bristle (frenulum) from the hindwing interlocks with a hook or fold (retinaculum) on the forewing. • Amplexiform Type: Wings overlap without specialized structures; common in butterflies. • Humuli Type: Series of tiny hooks on the hindwing that interlock with the forewing. • Significance: • Ensures coordinated wing movement, enhancing flight stability and efficiency.
- 175. 175 Jugum in PrimitiveLepidopterous Insects • Definition: • The jugum is a small lobe found at the base of the anal margin of the forewing in certain primitive Lepidopterous insects. • Structure and Function: • Known as the jugum lobe or fibula, this lobe projects behind the hindwings. • It rests upon the surface of the hindwing, facilitating wing coupling. • Sometimes, a spine is present on the costal surface of the hindwings, enhancing interlocking. • Examples: • Found in primitive Lepidopterous insects, aiding in wing stability during flight. • Significance: • The jugum mechanism allows for coordinated wing movement, essential for effective flight.
- 176. 176 Frenulum & RetinaculumType Wing Coupling in Moths • Examples: • Commonly found in moths. • Structure and Function: • Frenulum: A bristle-like structure located at the humeral angle of the hindwing. • Retinaculum: A hook-like structure situated on the anal side of the forewing. • During flight, the frenulum passes beneath the retinaculum, interlocking the wings together. • Significance: • Ensures coordinated wing movement, providing stability and efficiency during flight.
- 177. 177 Amplexiform Type WingCoupling in Butterflies • Examples: • Commonly found in butterflies. • Structure and Function: • The anal margin of the front wing and costal margin of the hindwing enlarge to overlap each other. • This overlapping mechanism keeps both wings together during flight. • Significance: • Facilitates smooth and coordinated wing movement, enhancing flight stability and maneuverability.
- 178. 178 Hamuli Type WingCoupling in Wasps and Bees • Examples: • Commonly found in wasps and bees. • Structure and Function: • The costal margin of the hindwings possesses a row of hooks known as humuli. • The humuli catch the upward fold of the front wings, interlocking them together. • Significance: • Ensures coordinated wing movement, providing stability and efficiency during flight.
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- 180. 180 Visual Organs inInsects (Photoreceptors) • Overview: • Insects perceive light through various sense organs, which are crucial for vision. • These organs react to electromagnetic stimuli. • Key Visual Organs: • Compound Eyes: • The most important and complex visual organs in insects. • Composed of numerous small visual units called ommatidia. • Function: • Enables insects to perceive light and form images. • Essential for navigation, finding food, and avoiding predators.
- 181. 181 Compound Eyes inInsects • General Features: • Most adult insects have a pair of compound eyes, providing a wide field of vision. • Located on either side of the head, they bulge outward for panoramic views. • Exceptions: • Absent in Protura, Diplura, and larval forms of holometabolous insects. • Reduced or absent in parasitic groups like Siphunculata, Siphonoptera, and female coccids. • Vision in Larvae: • Holometabolous larvae have simple stemmata and rely on ocelli for vision.
- 182. 182 Structure and Variationsof Compound Eyes • Types of Compound Eyes: • Dioptic Eyes: Separate eyes, as seen in bees (Hymenoptera). • Holoptic Eyes: Eyes that are close together, as seen in dipteran flies. • Ommatidia: • Each eye consists of numerous units called ommatidia. • Number varies from one (e.g., worker ants in Ponera) to over 10,000 (e.g., dragonflies). • Facet Arrangement: • Few ommatidia: Loosely packed, circular facets. • Many ommatidia: Closely packed, hexagonal facets.
- 183. 183 Development and Functionof Compound Eyes • Ommatidia Size and Shape: • Varies between insect species. • Packed closely in insects with more ommatidia; hexagonal in shape. • Development: • Develop embryonically in exopterygotes. • Develop post-embryonically in endopterygotes. • Function: • Essential for navigation, detecting movement, and environmental awareness.
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- 185. 185 Structure of anOmmatidium • Overview: • Each ommatidium is a unit of the compound eye, responsible for light gathering and sensory perception. • Components: • Optical Part: • Cuticular Lens (Corneal Lens): The outermost lens that gathers light. • Crystalline Cone: Located beneath the cuticular lens, further focuses light onto the sensory part. • Sensory Part: • Perceives radiation and converts it into electrical signals. • Function: • Together, these components enable the insect to perceive light and form images.
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- 187. 187 The Cornea (Lens)of an Ommatidium • Description: • The cornea is the outermost transparent, colorless layer of the cuticle. • Forms the external facet of the ommatidium and functions as a lens. • Structure: • Biconvex Shape: Optimizes light refraction and focusing. • Formation: • Secreted by epidermal cells. • Each lens is produced by two specialized cells called corneagen cells. • Corneagen cells later move to the sides of the ommatidium and become primary pigment cells. • Function: • Focuses light onto the sensory part of the ommatidium.
- 188. 188 Crystalline Cone ofan Ommatidium • Location and Structure: • Located beneath the cornea. • Comprised of four cells known as Semper cells, named after the discoverer. • Function: • Acts as a secondary lens to further focus light. • Clear, hard intracellular structure bordered by primary pigment cells. • Eye Types: • Eucone Eyes: Contain a crystalline cone. • Exocone Eyes: In some insects like Elateridae and Lampyridae, Semper cells do not form a crystalline cone but extend as slender refractile strands to the retinula cells. • Significance: • Enhances light refraction and image formation in the compound eye.
- 189. 189 Primary Pigment Cellsin an Ommatidium • Description: • Densely pigmented cells, typically two in number. • Positioned around the crystalline cone. • Formation: • Originally corneagen cells responsible for forming the cornea. • After cornea formation, they transform into primary pigment cells. • Function: • Withdraw to the sides of the ommatidium. • Surround and support the crystalline cone. • Help isolate ommatidia to enhance image resolution by preventing light leakage between them. • Significance: • Essential for effective light management and image clarity in the compound eye.
- 190. 190 Structure and Functionof Retinular Cells • Location and Structure: • Positioned immediately behind the crystalline cone in eucone eyes. • Elongated nerve cells known as retinula cells. • Role in Vision: • Retinula cells are the sensory elements of the insect's eye. • Cytoplasm contains pigment granules, especially at the edge of the rhabdomere, but these do not contain visual pigment. • Arrangement: • Each ommatidium typically contains eight retinula cells, leaving a central core space. • Each cell projects microvilli into this space. • Microvilli and Rhabdomeres: • Microvilli are the actual light-detecting parts, collectively called rhabdomeres. • Rhabdomeres from retinula cells form the rhabdom.
- 191. 191 Connectivity and Supportof Retinular Cells • Rhabdom Formation: • Rhabdom consists of 8 (or occasionally 7 or 9) rhabdomeres. • Nerve Connectivity: • Retinula cells connect to axons at the base of the eye. • Axons transmit electrical impulses to the brain, enabling vision. • Support Structures: • Corneal lens is supported by primary pigment cells. • Retinula cells and associated rhabdoms are supported by secondary pigment cells. • Functionality: • Allows insects to perceive and process visual information efficiently.
- 192. 192 Variation in theLens System of Insect Eyes • Eucone Eyes: • Feature a crystalline cone produced by four Semper cells located beneath the cornea. • Crystalline cone acts as a secondary lens to enhance light focusing. • Exocone Eyes: • Found in certain insects such as Elateridae and Lampyridae. • Semper cells do not form a crystalline cone. • Instead, they extend to the retinula cells as slender refractile strands. • Significance: • Variations in the lens system reflect adaptations to different visual requirements and ecological niches.
- 193. 193 Variation in RetinulaCells of Insect Eyes • Arrangement of Retinula Cells: • Apposition Eyes: • Rhabdom extends directly to the crystalline cone. • Common in diurnal insects. • Clear-Zone Eyes: • Clear zone present between the cone and rhabdom. • Previously known as superposition eyes. • Function and Adaptation: • Apposition Eyes: Suited for bright, daylight environments; found in diurnal insects. • Clear-Zone Eyes: Provide greater sensitivity, ideal for crepuscular and nocturnal insects inhabiting dark environments. • Significance: • Different retinula cell arrangements reflect adaptations to varying light conditions and ecological niches.
- 194. 194 Simple Eyes (Ocelli)in Insects • Presence and Types: • Simple eyes, or ocelli, are present in most insects. • Two forms: Dorsal Ocelli and Lateral Ocelli. • Dorsal Ocelli: • Found in adult insects and larvae of hemimetabolous insects. • Typically three, forming an inverted triangle on the antero-dorsal head. • Located on the front of the face, near the frons and epicranium. • Lateral Ocelli: • Found on the sides of the insect head. • Common in larval forms. • Function and Sensitivity: • Sensitive to low light levels. • Involved in circadian rhythm regulation, such as daylight responses and diapause.
- 195. 195 Structure of DorsalOcelli • Presence and Arrangement: • Found in all adult insects and nymphs of hemi-metabola. • Typically three ocelli, forming a triangle on the vertex and frons. • Sometimes reduced to two; highly reduced in cockroaches (represented by fenestrae). • Occurrence: • Absent in Apterygota forms, present in winged insects. • Structure: • Typical Ocelli: Feature a single thickened cuticular lens. • Alternative Structures: Transparent cuticle without thickening, space beneath occupied by transparent cells.
- 196. 196 Function and Developmentof Dorsal Ocelli • Optical Capability: • Lens can form an image, but at a level far below the retina. • Functionality: • Blackening reduces response speed to light in compound eyes. • Regarded as stimulatory organs. • Development and Origin: • Develop embryonically or post- embryonically. • Derived from ectoderm (ectodermal origin).
- 197. 197 Structure of LateralOcelli (Stemmata) • Presence: • Only eyes present in insect larvae of holometabola and in apterygote adults. • Positioned on either side of the head, corresponding to compound eyes' location. • Resolution and Functionality: • Poor resolution power; not image-forming. • Sensitive to light direction. • Structure: • Number varies from 1-7 or more per side. • Innervated from the optic lobes of the brain. • Image Formation: • Can form an inverted image irrespective of object distance. • Each stemmata forms an image of one visual field, creating a coarse mosaic of intensities.
- 198. 198 Function and Developmentof Lateral Ocelli (Stemmata) • Behavioral Adaptations: • Caterpillars scan side to side using these visual organs. • Capable of orienting towards the boundary between light and dark areas. • Color Vision: • Caterpillar behaviors suggest color vision, aiding in food location and pupation. • Development: • Begins embryonically, may complete post- embryonically. • All parts derived from ectoderm (ectodermal origin).
- 199. 199 Types of Image Formation Eyesof insects Apposition Eyes Diurnal Insects Superposition Eyes Nocturnal Insects
- 200. 200 Apposition Eyes • Structureand Function: • Ommatidia are optically isolated. • Rhabdom extends or reaches the crystalline cone. • Best suited for bright light conditions. • Found in diurnal insects. • Iris Cell Pigments: • Absorb light that is not refracted, aiding in image clarity. • Significance: • Optimized for environments with abundant light, providing sharp image resolution.
- 201. 201 Superposition Eyes • Structureand Function: • Secondary iris cells have mobile pigments. • Can isolate or expose retinular layer to light from adjacent ommatidia (optically not isolated). • Clear zone exists between the cone and rhabdom (clear-zone eyes). • Suitable for dim light conditions, found in crepuscular and nocturnal insects. • Adaptation: • Adopted for environments with low light, enhancing sensitivity over resolution. • Comparison: • Apposition eyes are for bright light, while superposition eyes are for dim light conditions.
- 202. 202 Auditory Organs inInsects • Sound Production: • Many insects, such as those in the Orthoptera order, produce sounds using various mechanisms. • Sounds can result from wing vibrations during flight. • Many insects can hear sounds, including some frequencies beyond human hearing. • Hearing Mechanisms: • Insects hear through four different mechanisms, with the tympanum being the most common.
- 203. 203 Tympanal Organs Structureand Function • Characteristics: • Always occur as paired organs. • Composed of a thin cuticular membrane (the tympanum) stretched across an air space. • Connected to the nervous system. • Scoplopodium: • Forms the tympanal organ of the locust. • Functional Significance: • Allows insects to detect sound vibrations, aiding in communication and predator avoidance.
- 204. 204 Examples and Locationsof Tympanal Organs • Orthoptera: • Grasshoppers: Tympanum located on the first abdominal segment. • Crickets: Tympanum located on the front legs (base of fore tibia). • Other Insect Families: • Present in Cicadidae (Hemiptera) and some Lepidoptera families (Noctuidae, Geometridae, Pyralididae). • Adaptation and Variation: • Placement varies by species, reflecting adaptations to their ecological niches.
- 205. 205 Johnston's Organ inInsects • Location and Structure: • Found in the second segment of the antenna, known as the pedicle. • Special sensory structure acting as an auditory organ. • Absent in Diplura and Collembola. • Function: • Detects motion in the flagellum (third segment of the antenna). • Senses wind, aiding in navigation and environmental awareness. • Significance in Mating: • In male mosquitoes, it plays a crucial role in detecting the wing beat frequency of females. • Facilitates attraction and mating by allowing males to locate females.
- 206. 206 Auditory Hairs andPilifer in Insects • Auditory Hairs: • Found on some Lepidopteran larvae and certain Orthoptera species. • Serve as sensory structures to detect sound vibrations in the environment. • Pilifer: • A unique auditory organ located in the head of certain Hawk Moths (subfamily Choerocampinae). • Optimum frequency range: 30 to 70 kHz. • Allows moths to hear echolocation calls of larger insectivorous bats, aiding in predator detection and avoidance.
- 207. 207 Hygroreceptors and Osmoreceptors •Hygroreceptors: • Sensilla responsive to changes in humidity. • Crucial for insects needing to conserve water. • Sense cells for temperature and humidity present in the same sensillum. • Found on the antennae of all insects. • Osmoreceptors: • Detect changes in osmotic pressure of fluids. • Not extensively studied in insects. • Suggested presence in horseflies.
- 208. 208 Thermoreceptors • Function: • Detectheat, used by hematophagous (blood-sucking) insects to induce biting. • Examples: • Two hairs on the tarsi of the foreleg of Glossina mosquitoes. • Found on tarsi of Periplaneta americana (American cockroach). • Present in heat-seeking Melanophila beetles. • Significance: • Aid in locating warm-blooded hosts and suitable environmental conditions.
- 209. 209 Chemoreceptors • Gustation (ContactReception): • Detect chemicals by contact. • Located on labrum, maxillae, labium, antennae, tarsi, ovipositor, etc. • Olfaction (Smell): • Respond to volatile chemicals. • Found on antennae, palps, genitalia. • Pheromone-binding proteins produced by trichogen and tormogen cells on antennae. • Role: • Essential for detecting food, mates, and environmental cues.
- 210. 210 Proprioreceptors and HairSensilla • Proprioreceptors: • Found in desert locusts, specialized hairs with swollen bulbs at cerci tips. • Involved in sensing balance and gravity. • Hair Sensilla: • Important for various senses: smell, touch, gravity, pressure, taste, pheromones. • Spread all over the body: antennae, cerci, ovipositor, mouthparts, etc. • Sense of air movement detected by sensilla on antennae and cerci. • Significance: • Enable insects to navigate their environment and respond to a range of stimuli.
- 211. 211 Chapter 8 Metamorphosis andDiapause in Insects
- 212. 212 Insect Development andMorphogenesis • Initial Stage: • After hatching from the egg, insects are small, wingless, and sexually immature. • Primary role is to eat and grow. • Growth and Development: • Molting: • Insects periodically outgrow and replace their exoskeleton, a process known as molting. • Physical Changes: • Growth of wings and development of external genitalia as the insect matures. • Morphogenesis: • Collective term for all changes involving growth, molting, and maturation. • Essential process for achieving adult form and function.
- 213. 213 Metamorphosis in Insects •Definition: • Metamorphosis means change. • Refers to the developmental changes from egg to adult, collectively known as the life cycle. • Post-Embryonic Changes: • Includes all changes in form after the embryonic stage, collectively termed metamorphosis. • Describes how insects develop, grow, and change form. • Profound Metamorphosis: • Majority of insects undergo significant metamorphosis during development. • Growth accompanied by a series of molts or ecdysis, where the cuticle is shed and renewed.
- 214. 214 Details of InsectMolting and Growth • Molting (Ecdysis): • Number of molts varies; most insects molt 4-8 times, some up to 20 or more. • A few insects, like Bristle tail Thysanura (silverfish), may continue molting even after reaching adulthood. • Most insects do not molt or increase in size after reaching the adult stage. • Stadia and Instars: • Intervals between molts are called Stadia. • Instar refers to the form of an insect during a stadium. • "First Instar" is the form assumed between hatching and the first post- embryonic molt.
- 215. 215 Classification of Insectsby Metamorphosis • Insect Classification: • Insects are grouped into three types based on the presence or absence of metamorphosis and the degree of metamorphosis they undergo. • Types of Metamorphosis: • Ametabolous Insects • Hemimetabolous Insects • Holometabolous Insects
- 216. 216 Ametabola Hemimetabola Holometabola Nometamorphosis Incomplete metamorphosis Complete metamorphosis Wingless Wings develop during growth of young one (nymph) Wings develop during growth of adult inside pupae Undergo slight or no metamorphosis Undergo incomplete metamorphosis Undergo complete metamorphosis Life cycle includes 3 developmental stages: egg, larva (many) and adult Life cycle includes 3 developmental stages: egg, nymph and adult Life cycle includes 4 developmental stages: egg, larva, pupa and adult Eggs laid with no coverings Eggs are often covered by an egg case Eggs are sometimes covered by hairs/scales No changes take place during development Young one (immature stage) is called nymph. Young one (immature stage) is called as larvae. The development is direct (young one to adult) The development is direct (young one to adult) The development is indirect (youngone to pupa, then to adult) Young (immature) looks like the adult in all characters, only it may be missing sexual organs Young one (nymph) resembles the adult in all characters except in wings Young one (larva) does not resemble and differs from adult both in morphological characters & feeding habits. Larva/Nymph directly becomes adult Nymph directly becomes adult Young one undergo pupal stage before adult stage All Apterygote insects Characteristics of lower insect orders: Exopterygote insects Characteristic of higher orders: Endopterygote insects
- 217. 217 Incomplete Metamorphosis • Overview: •About 12% of all insects undergo incomplete metamorphosis. • Stages: • Eggs: • Often covered by an egg case for protection and cohesion. • Nymphs: • Resemble small adults but usually lack wings. • Eat the same food as adults. • Molt 4-8 times, shedding and replacing their exoskeleton. • Adults: • Stop molting upon reaching adulthood. • Grow wings by this stage.
- 218. 218 Complete Metamorphosis • Overview: •About 88% of all insects undergo complete metamorphosis. • Stages: • Eggs: • Sometimes covered by hairs or scales. • Larva: • Hatch from eggs and have a worm-like shape. • Molt several times to grow larger. • Pupa: • Larva encase themselves in cocoons. • Do not eat while inside cocoons. • Body undergoes transformation into adult form. • Adult: • Emerges from the cocoon with wings, legs, and fully developed organs.
- 219. 219 Hormonal Regulation ofMetamorphosis • Endocrine System in Insects: • Brain Hormone (PTTH): • Produced by Corpora Cardiaca. • Juvenile Hormone: • Produced by Corpora Allata. • Ecdysone: • Produced by Pro-Thoracic Glands. • Regulation: • Neurosecretory cells in the insect brain regulate the production, storage, and release of these hormones. • These hormones control growth, molting, and the metamorphic process.
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- 221. 221 Diapause in Insects •Definition: • Diapause is a strategy evolved by many insect species. • It involves a suspension of development at various life stages (embryonic, larval, pupal, or adult). • Characteristics: • A physiological state of dormancy with specific triggering and releasing conditions. • Neurohormonally mediated, with low metabolic activity. • A response to adverse environmental conditions. • Purpose: • Survival mechanism for unfavorable conditions like temperature extremes, drought, or reduced food availability.
- 222. 222 Types and Triggersof Diapause • Types of Diapause: • Facultative Diapause: • Occurs only when induced by environmental conditions. • Obligate Diapause: • Part of the life cycle, often seen in temperate-zone insects. • Triggers: • Changes in photoperiod (day and night lengths). • Critical Day Length: • The day length when 50% of the population enters diapause. • Long-day insects enter diapause as days get shorter. • Short-day insects enter diapause as days get longer.
- 223. 223 Diapause Mechanism andAdaptation • Mechanism: • Triggered by environmental token stimuli. • Begins before severe conditions arise. • Adaptations: • Diapause during summer is called aestivation: Active in the rainy season, dormant in drought/summer. • Diapause during winter is called hibernation: Active in summer, dormant in winter. • Genetic Determination: • Critical day length is genetically determined.
- 224. 224 Hibernation vs. Aestivation •Hibernation: • Occurs during winter. • Animals live off stored fat and food energy during deep sleep. • Aestivation: • Occurs during warm conditions. • Animals enter deep sleep to avoid heat stress. • Comparison: • Hibernation is for winter dormancy. • Aestivation is for summer dormancy.
- 225. 225 Diapause in TemperateZone Insects • Importance of Diapause: • Critical for insects that overwinter in temperate zones. • Enables survival during prolonged adverse conditions. • Diapausing Eggs: • After receiving environmental warning signals, females lay eggs that enter diapause. • The development cycle from egg to adult is halted at some point. • Examples of 'Sleepers': • Specific examples of insects with diapausing eggs can be detailed here.
- 226. 226 Common Name ScientificName Diapause Stage Silk worm Bombyx mori Early-Embryonic Stage (egg diapause) Locust Schistocerca gregaria Mid-embryonic stage (egg diapause) Gypsy Moth Lymantria dispar Post-Embryonic Stage (egg diapause) Bamboo borer Omphisa fuscidentalis Larval diapause Rice stem borer Scirpophaga incertulas Larval diapause Mosquito Aedes spp Larval diapause Cabbage White Pieris brassicae Pupal diapause Colorado potato beetle Leptinotarsa decemlineata Adult diapause
- 227. 227 Distinguishing Diapause fromOther Dormancy • Induction and Release: • Diapause is induced by specific environmental stimuli. • Only certain stimuli can release an organism from diapause. • This distinguishes diapause from other dormancy forms, such as hibernation. • Warning Signals: • Insects receive warning signals before entering diapause. • Common signals include: • Day Length: Changes in photoperiod. • Temperature: Shifts in seasonal temperatures. • Food Availability: Changes in food resources. • Unique Characteristics: • Unlike hibernation, diapause involves a complex set of triggers and releases specific to each species.
- 228. 228 Regulation of Diapausein Insects • Overview: • Diapause is regulated at multiple levels, including environmental, genetic, neuronal, endocrine, metabolic, and enzymatic changes. • Environmental Regulation: • Photoperiod: Reliable cue for seasonal changes. • Temperature: Modifies response to photoperiod; insects may respond to thermoperiod. • Food Availability: Quality and availability can impact diapause. • Example: Desert locusts remain immature during dry seasons due to lack of plant hormone giberellin.
- 229. 229 Neuroendocrine Regulation ofDiapause • Key Components: • Neurosecretory cells, corpora cardiaca, corpora allata, prothoracic glands. • Key Hormones: • Juvenile Hormone (JH): Regulates reproductive and larval diapause. • Diapause Hormone (DH): Regulates embryonic diapause. • Prothoracicotropic Hormone: Stimulates ecdysteroid production for development. • Examples: • Bean Bug: Neurons inhibit JH production during reproductive diapause. • Corn Borer: JH required for storage protein accumulation during diapause.
- 230. 230 Diapause in TropicalInsects • Tropical Diapause: • Often triggered by biotic factors rather than abiotic. • May synchronize mating seasons or reduce competition. • Challenges: • Reduction of metabolism without cold temperatures. • Increased water loss due to high temperatures. • Risk from fungi, bacteria, predators, and parasites. • Adaptations: • Aggregations for protection and reduced water loss. • Example: Fungus beetle aggregations reduce evaporative water loss.
- 231. 231 Aggregations and Adaptationsin Tropical Diapause • Aggregation Benefits: • Protection against predation. • Reduced water loss through increased humidity and decreased surface area to volume ratios. • Examples: • Fungus Beetle (Stenotarsus rotundus): Forms large aggregations to reduce water loss. • Conclusion: • Diapause in tropical insects involves complex adaptations to unique environmental challenges.
- 232. 232 Chapter 9 Types ofLarvae and Pupae
- 233. 233 Immature Stage • KeyStages: • Immature Stages: Active feeding stages such as nymphs (hemimetabolous) and larvae (holometabolous). • Pupae: Non-feeding resting stage between egg and mature stages. • Hemimetabolous vs. Holometabolous: • Nymphs: Resemble adults but lack fully developed wings and reproductive organs. • Larvae: Look completely different from adults; vary greatly in form.
- 234. 234 Characteristics of Nymphs •Definition: • Immature form in gradual metamorphosis (hemimetabolism). • Features: • Resemble adults in overall form. • Do not enter a pupal stage; final molt results in adulthood. • Examples: • Found in Orthoptera, Hemiptera, mayflies, termites, cockroaches, mantids, Odonata, and some arachnids (mites and ticks).
- 235. 235 Aquatic Nymphs andNaiads • Aquatic Insect Nymphs: • Orders Odonata, Ephemeroptera, and Plecoptera. • Known as naiads, named after mythological water nymphs. • Environment: • Adult and immature stages live in different environments (terrestrial vs. aquatic). • Adaptive Features: • Tracheal gills and modified labium in Odonata, Ephemeroptera, and Plecoptera.
- 236. 236 Holometabolous Larvae andPupae • Holometabolous Larvae: • Look completely different from adults. • Vary in number of legs, size, shape, and locomotion. • Pupae: • Appear different across insect groups. • Serve as a transition to mature stage. Nymph of Termite &Thrips Aphid nymph Naiad
- 237. 237 Young Insects • Exopterygotes(Hemimetabolous): • Young ones are called Nymphs. • Endopterygotes (Holometabolous): • Young ones are called Larvae. • Key Differences: • Nymphs resemble adults; larvae look different. • Nymphs have similar food habits to adults; larvae have different food habits.
- 238. 238 Nymph Larva Young oneof exopterygote insects Young one of endopterygote insects Resemble adults and differs from the adult with regard to the wings and genitalia-that are present in an incompletely developed condition. Differs from adults in appearance. Food habits of nymph is same as adult Food habits of larva is totally different from its adult Wing rudiments may not be discernible in the first instar, but later become visible as wing-pads that increase in size with each instar. No wing rudiments Mouthparts are similar to those of adults Mouth parts are different from adults in most cases Compound eyes in nymphs are normal in form and function Compound eyes are absent in larva and stemmata are present in place of compound eyes. Growth to adult is unaccompanied by the pupal stage Growth to adult is accompanied by the pupal stage Nymph have 3 pairs of thoracic legs as in adults Number of legs in larva are variable from 0-11 pairs invarious orders, and legs are present in both thorax and abdomen Wings and genital organs are under- developed Wings and genital organs are totally absent Antenna generally well developed and visible Antenna highly reduced to 1-3 segments, always microscopic and not visible
- 239. 239 Larval Classification Protopod ApodousOligopod Polypod
- 240. 240 Protopod Larva • Characteristics: •Prematurely hatched embryo with small yolk quantity. • Absence of abdominal segmentation. • Rudimentary cephalic and abdominal appendages. • Undeveloped nervous and respiratory systems. • Internally parasitic, cannot lead a free life. • Examples: • Parasitic Hymenoptera
- 241. 241 Apodous Larva • Characteristics: •Absence of trunk appendages or legs. • Presence of 3 pairs of sensory papillas instead of thoracic legs. • Classified into 3 types based on head capsule development. • Acephalous • Hemicephalous • Eucephalous
- 242. 242 Acephalous Hemicephalous Eucephalous Nodistinct Head Capsule. Mouth parts represented by Mouth hook and are usually called as Maggots Appreciable reduction of the head capsule (head capsule partially developed) and its appendages, accompanied by marked retraction of the head into thorax. Head capsule more or less well developed (well sclerotized head capsule) with relatively little reduction of the cephalic appendages. Cyclorrhapha (Diptera)- House flies of family Muscidae Brachycera (Diptera)- Robberflies of family Asilidae Nematocera (Diptera)- Mosquito of family Culicidae
- 243. 243 Oligopod Larva • Characteristics: •More or less developed thoracic legs. • Well-developed head capsule and its appendages. • Absence of abdominal appendages. • Classification: • Divided into 2 types based on shape and other characteristics. • Campodeiform • Scarabaeiform
- 244. 244 Campodeiform Scarabaeiform Straight body(Allegator like) C shaped body Body is falt dorso-ventrally compressed Body is cylindrical or sub-cylindrical Body wall sclerotized Body wall soft & fleshy Head-Prognathous Head-Hypognathous Thoracic legs relatively well developed and long (body looks like thrips) Thoracic legs relatively reduced, short Pair of anal cerci or styles may be present Anal cerci absent Usually active Inactive Mostly predators Mostly phytophagous Neuroptera, Trichoptera, Coccinellid beetles, Ground beetles Scarabaeidae family of Coleoptera (dung rollers, root grubs, rhinoceros beetles)
- 245. 245 Polypod Larva (EruciformLarva) • Characteristics: • Well-developed segmentation in thorax and abdomen. • Presence of both thoracic and abdominal legs. • Peripneustic respiration. • Small or rudimentary antennae. • Inactive, living close to food or host plant. • Generally phytophagous. • Examples: • Some Lepidoptera and Sawflies of Hymenoptera.
- 246. 246 Classification of Polypodlarvae • Classification Based on: • Number of legs, locomotion, and structural characteristics. • Sphingid Larva (Horn worm) • Semi Looper • Lopper • Hairy Caterpillar
- 247. 247 Sphingid Larva (Hornworm) Posses well developed hook like structure on the dorsal surface of 8th abdominal segment, in addition to all polypod characters. Hence these known as Hornworms. Example: Sphinx moth (death head moth)-Acherontia spp. Semi Looper First two pairs of prologs (3rd and 4th abdominal seg) are reduced. Due to reduction of size of first prologs, during locomotion the body form a loop shape, and hence these are called semiloopers. Castor Semilooper Achaea janata Lopper Generally only two pairs of prologs (6th and last abdominal seg) are present and other prologs are absent, and hence during the locomotion, the larva gives complete loop like shape, and hence these are called loopers. Cabbage Looper, Trichoplusia ni Hairy Caterpillar Having hairs over the entire body, hence are called Hairy Caterpillars Bihar Hairy caterpillar Spilosoma obliqua, Red Hairy Caterpillar Amsacta albistriga, Castor Hairy Caterpillar Euproctis lunata, E. similis
- 248. 248 General Names ofLarva • Types: • Lepidoptera Larvae • Caterpillars • Coleopteran and Hymenoptera Larvae • Grubs • Diptera Larvae • Maggots Caterpillar Grubs Maggot
- 249. 249 Pupa • Definition: • Apupa is the life stage of some insects undergoing transformation, resembling a "doll." • Occurrence: • Found only in holometabolous insects (complete metamorphosis). • Life stages: embryo, larva, pupa, and imago. • Names for Pupae: • Chrysalis: Lepidoptera (butterflies and moths). • Tumbler: Mosquitoes.
- 250. 250 Characteristics and Functionof Pupae • Enclosure: • May be enclosed in cocoons, nests, or shells. • Role in Life Cycle: • Follows the larval stage and precedes adulthood (imago). • Adult structures form while larval structures break down. • Activity Level: • Inactive and usually sessile. • Hard protective coating with camouflage for predator evasion.
- 251. 251 Duration and Emergencefrom Pupae • Duration: • Pupation can be brief (e.g., 2 weeks in monarch butterflies) or involve dormancy. • Dormancy during unfavorable seasons (winter in temperate climates, dry season in tropics). • May last weeks, months, or years (e.g., Anise Swallowtails). • Emergence (Eclosion): • Controlled by hormones; adults emerge by splitting the pupal case. • Pharate: Adult inside pupal exoskeleton before emergence. • Exuvium: Empty pupal exoskeleton post-emergence. • Emergence timing varies (morning for butterflies, evening/night for mosquitoes).
- 252. 252 Types of Pupae •Overview: • Pupae are mainly classified into two types based on their mandibles: • Decticous Pupa • Adecticous Pupa
- 253. 253 Decticous Pupa • Characteristics: •Possesses relatively powerful, sclerotized, articulated mandibles. • Used by adults to escape from cocoons or cells. • Considered a primitive type. • Always exarate, meaning appendages are free and not adhering to the rest of the body. • Examples: • Neuroptera • Mecoptera • Trichoptera
- 254. 254 Adecticous Pupa • Characteristics: •Has non-articulated, often reduced mandibles. • Mandibles are not used for escaping from the pupal cocoon in most species. • Examples: • Lepidoptera • Diptera
- 255. 255 Classification of AdecticousPupae • Overview: • Adecticous pupae are classified into four types based on the shape and attachment of their appendages. • Types of Adecticous Pupae: • Obtect • Exarate • Coarctate • Pharate
- 256. 256 Adecticous Exarate The pupahas free appendages, not adhering to the rest of the body. All wings, legs, antenna, mouth parts are independent, not attached except at their point of origin. Examples: Most of Coleoptera, Diptera, Hymenoptera, Primitive Lepidoptera. Adecticous Obtect The appendages of pupa are firmly attached against the body. The pupal cooon is highly chitinized. Examples: All the moths belong to Lepidoptera Adecticous Obtect - Chrysalis It is an obtect type of pupa, which has prominent stalk and coloration. Examples: All butterflies belong to lepidoptera Adecticous Exarate - Coarctate The adecticous exarate pupa remain closed in a puparium which is formed from the preceeding larval cast skin and pupa looks like a capsule or a barrel. Examples: House flies (Diptera), Suborder Cyclorrapha Exarate-Coleoptera Exarate-Diptera
- 257. 257 The content taughtto students is drawn from the book Fundamentals of Entomology I (Insect Morphology & Taxonomy), written by Dr. Cherukuri Sreenivasa Rao, Professor of Entomology at Acharya N. G. Ranga Agricultural University.
- 258. 258 Do you haveany question?