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The book “A Colour Handbook on Fundamentals of Entomology" was conceived during the lockdown period of COVID-19. Although, there are a large number of standard and good books on the subject but they are either too exhaustive or too brief or mainly research oriented, and they deal, only one aspect of the subject, hence they do not fulfill the basic need of the under-graduate students of Entomology. Entomology is a biological science dealing with a specific group of organism, the insects. Insect constitute the largest class of the whole living organism. The general understanding of the subject of entomology is must for its practical application in the field. The book required by UG students strictly as per syllabus required by the under graduate students of Entomology is hardly available. The book embodies a fairly comprehensive treatment of the Basic Entomology. This book provides a balanced and up to date account on morphology, anatomy, physiology of various organs and systematics as well as systematics of class Insecta. A good number of illustrations and photographs have been introduced for better understanding of the students. The book would have useful to students preparation for various competitive examinations conducted by Indian Council of Agricultural Research-JRF, Agricultural Scientific Recruitment Board-ARS/ NET, National Academy of Agricultural Research Management-SRF, Indian Agricultural Research Institute-PG/Ph.D. Entrance, Union Public Service Commission, SAUs Entrance and Allied Agricultural Examinations. We hope the Entomology students will find the book extremely useful and welcome this edition. We wish to thank all near and dears offering useful suggestions during the preparation of this study material.

Human beings came into existence 1 million years ago. Insects which constitute 70-90% of all animals present in this world came into existence 250- 500 million years ago.Insects are highly specialized group of invertebrates belonging to phyla arthropoda characterized by having a bilateral symmetrical body covered by Exoskeleton chitin; with jointed appendages provided with independently movable muscle and inserted in to special pockets of exoskeleton; with a haemocoelic body cavity containing the circulating blood in which are bathed the internal organs; with a dorsal heart and decentralized ventral nerve cord; and with tracheal system for respiration; metamorphosis direct or indirect. The insects are bilaterally symmetrical tracheate Arthopods is which the body is divided into head, thorax and abdomen. A single pair of antennae is present and head also bears a pair of mandibles, a pair of maxillae,. The thorax possess three pairs of legs and usually two pairs of wings. The abdomen is devoid of any ambulatory appendages and the genital opening is situated near the posterior end of the body. Post embryonic development is rarely direct and metamorphosis usually occurs. Insect definition Insects (from Latin insectum, a calque of Greek ?ντομον [éntomon], “cut into sections”) are a class of invertebrates within the arthropod phylum that have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of jointed legs, compound eyes and one pair of antennae.

American Ecologist Whittaker (1969) proposed the five kingdom system of classification. In his ‘Five Kingdom System’, he added three more kingdoms in to Linnean model of two kingdom system. These were: Monera, Protista and Fungi. Whittaker succeeded to overcome the difficulties as well as demerits of two, three and four kingdom systems and to represent the living organisms according to the evolutionary relationships among themselves. He also defined the kingdoms by a number of special characteristics such as whether the organisms possessed a true nucleus or not. Whittaker’s five kingdom system of classification is based on (a) mode of nutrition (b) cell structure and complexity (c) phylogenetic relationship (d) body organization and (e) reproduction. The large branches within the Animal Kingdom evolutionary tree are ‘phyla’ (the singular being ‘phylum’). ‘Animal phyla’ outlines thirty three phyla, although there are still disputes and disagreements concerning how many phyla are needed to classify the less well-known species. The most easily recognised are Porifera, Cnidaria, Arthropoda, Nematoda, Annelida, Mollusca, Platyhelminthes, Echinodermata, and Chordata. Animal phyla each comprise a branch of the evolutionary tree and these branches are always connected to other branches.

Body Segmentation In general, insect body is divided in to a series of segments, which in primitive arthropods are known as “somites” or “metameres”. During the process of evolution, these somites gets fused with each other in different ways forming the body parts of the existing arthropods. The type of arrangement of these body segments in embryonic stage is known as primary segmentation while in adult insects is known as the secondary segmentation which differ from primary in having a sclerotized membranous intersegmental region. In adult and nymphal insects, and hexapods in general, one of the most striking external features is the amalgamation of segments into functional units. This process of tagmosis has given rise to the familiar tagmata (regions) of head, thorax, and abdomen. In this process the 20 original segments have been divided into an embryologically detectable six-segmented head, three-segmented thorax, and 11-segmented abdomen (plus primitively the telson), although varying degrees of fusion mean that the full complement is never visible. Types of body segmentation. (a) Primary segmentation, as seen in soft-bodied larvae of some insects. (b) Simple secondary segmentation. (c) More derived secondary segmentation. (d) Longitudinal section of dorsum of the thorax of winged insects, in which the acrotergites of the second and third segments have enlarged to become the postnota. (After Snodgrass 1935)

Endoskeleton of the Head (Tentorium) • The tentorium forms during development when 2-4 pairs of apophysis/ apodemes (finger-like invaginations of exoskeleton) fuse internally to create a “bridge”. • The major components of the tentorium are the anterior tentorial arms, the posterior tentorial arms, the dorsal tentorial arms, and the tentorial bridge. • The anterior tentorial arms originate as invaginations at the lateral limits of the frontoclypeal suture. The coalescence of the anterior tentorial arms forms a more or less solid structure, the tentorial bridge. • The posterior tentorial arms arise from pits at the ventral ends of the post occipital suture and they unite to form a bridge running across the head from one side to the other. • In many insects, e.g. Orhtoptera, the central part of the composite tentorium enlarged to form a broad plate referred to as the Corporotentorium. • The tentorium serves as an internal “truss” that reinforces the head capsule, cradles the brain, provides attachment for muscles and provides a rigid origin for muscles of the mandibles and other mouthparts. The antennal muscles also arise from the tentorium.

Antennae are paired, highly mobile, segmented appendages present between or below or behind the compound eyes. The antennae arise from the 2nd or antennal segment of the head possessing nerves coming from deutocerebrum of the brain. Antennae are absent in order protura and class Arachnida whereas 2 pairs of antenna (antennules) are present in class Crustacea. Antennae are set in a socket of the cranium called antennal socket (anetnnifer) and connected by an articulatory membrane which allows free movement of antenna. Antennal socket is provided with an antennal suture. Although antennae vary widely in shape and function, all of them can be divided into three basic parts: • Scape • Basal segment, larger than other segments and articulates with the head capsule. It is provided with intrinsic muscles. • Pedicel • Second segment of antennae. In this, mass of cells called Johnston organ (auditory) is present (eg. houseflies). The above two segments have intrinsic muscles ie., their own muscles. In honey bee, wasps pedicel forms the pivot between scape and flagellum. • Flagellum/Clavola • The remaining segments or annuli or flagellomeres are called flagellum which lack individual muscles. Flagellum is supplied with many sensory receptors that are connected by nerves to brain. Flagellum is further divided into three parts

Light spectrum holds rich information about the world. The spectrum of natural illumination changes with daily cycle and objects differ in spectral reflection or emission properties. Like many other animals, insects use chromatic information to f ind favorable habitat, to efficiently locate food sources and to identify conspecific mates using the spectral information. Pollinating insects such as many species of bees and butterflies use their color vision to maximize success in foraging. They detect flowers, memorize the colors and patterns of rewarding flowers, and preferentially collect nectars from the flowers in their later visits. Visual guidance of behaviour is challenging when photons, the elementary particles of light, are scarce. To produce a reliable representation of the surroundings, the visual system must (i) ensure absorption of a sufficient number of photons into a photoreceptor, (ii) house photoreceptors that efficiently convert each photon absorption into a neural signal, and (iii) process these signals appropriately. Insects are a numerous and diverse class of arthropods that have evolved to occupy ecological niches from the brightest to the darkest.

• The thorax is the organ of locomotion due to articulation of wings and legs and is connected with the by neck or cervix. • Thoracic segments are made up of three sclerites namely, dorsal body plate tergum or nota, ventral body plate sternum and lateral plate pleuron. • Second and middle tagma which is three segmented, namely prothorax, mesothorax and metathorax. Meso and metathorax which bear wings are called as Pterothorax. • In the apterygote insects the three thoracic segments are similar in size and structure. In the pterygote insects the thorax is highly modified. • The prothorax is quite large and is somewhat independent of the other segments. The large shield that covers the dorsal and lateral sides of the prothorax is the pronotum. • The pronotum is the dorsal sclerite of the prothorax, which can be highly modified in various orders such as the Hemiptera, Blattaria, and Coleoptera. E.g undivided and Saddle shaped in grass hopper, Shield like in cockroach. • Cockroaches have pronotums that extend forward over the head. • Scarab beetles and other beetles may also have unusual pronotums. • Treehoppers have some of the most bizarre pronotums of all insects.

• It is the posterior most and largest region of the insect-body. It is The abdomen is the metabolic and reproductive centre, where digestion, excretion, and the sexual functions take place. • All the definitive number of segments differentiate in embryo (Epimorphic condition) except protura (Anamorphosis) • In general more segments are visible in more generalised hemimetabolus insects than in more specialised holometabolus insects. For example in Acridids all 11 segments are visible whereas in muscidae only 2-5 segments are visible • The basic number of abdominal segments in insect is eleven plus a telson/ tail (Protura) which bears anus. Abdominal segments are called uromeres. • The undivided tergel plates overlap the sternal ones and the membranous pleura are enclosed in between them. • The posterior part of each segment overlaps the anterior part of the segment behind it and the two segments are joined by the inter-segmental membrane. • There are eight pairs of abdominal spiracles. The first pair lies just in front of each tympanum and the other lie dorso-laterally on each of the tergites of the segment to eighth abdominal segments. • The terga and sterna bear antecostal ridges. The internal dorsal and ventral longitudinal muscles run one antecostal ridge to the other and act as retractors. The contraction of these muscles helps the segments to be retracted. The external muscles originate from the posterior part of the segment and attach to the anterior part of the acrotergite of the next segment. Thus, protraction of these muscles help in the extension of abdomen. Hence, musculature running longitudinally between helps in the contraction and extension of the abdomen. • The abdominal segments are conveniently divided into three subregions i.e. pregenital, genital and postgenital segments.

Insects development Once an insect hatches from the egg it is usually able to survive on its own, but it is small, wingless, and sexually immature. Its primary role in life is to eat and grow. If it survives, it will periodically outgrow and replace its exoskeleton (a process known as molting). In many species, there are other physical changes that also occur as the insect gets older (growth of wings and development of external genitalia, for example). Collectively, all changes that involve growth, molting, and maturation are known as morphogenesis. Metamorphosis • Metamorphosis actually means change in form Metamorphosis is derived from Greek word ‘Meta’ = Change, ‘morph’ = form or structure. • The changes in the development from egg to adult, collectively called Metamorphosis (life cycle). • Post-embryonic changes in form are collectively called as metamorphosis. • Metamorphosis refers to the way that insects develop, grow, and change form. Metamorphosis include three developmental processes namely growth, differentiation and reproduction which takes place in larval, pupal and adult stages, respectively. • Majority of insects pass through profound metamorphosis. The growth of an immature insect is accompanied by a series of molts or ecdysis, in which the cuticle is shed off and renewed. The number of molts varies in most insects from 4-8. However some undergo as many as 20 or more molts. A few insects like Bristle tail silver fish (apterygota) may continue molting even after reaching the adult stage. But most of the insects neither molt nor increase in size once then adult stage is reached. The intervals between the ecdysis are called Stadia. The term instar is applied to form of an insect during stadium. In numbering the instar, the form assumed by the insect between hatching from the egg and the first post embryonic molt is termed “First Instar”.

• In most insects, life begins as an independent egg (ovipary). • Majority of insects are oviparous. Egg stage is inconspicuous, inexpensive and inactive. Yolk contained in the egg supports the embryonic development. • Eggs are laid under conditions where the food is available for feeding of the future young ones. • Production of eggs by the female’s body is called oogenesis and the egg laying process is known as oviposition. • The outer protective shell of the egg is called chorion. Near the anterior end of the egg, there is a small opening called micropyle which allows the sperm entry for fertilization. Chorion may have a variety of textures. • Size and shape of the insect eggs vary widely.

Alimentary canal of an insect is a tubular structure passing through the body that provides the special internal environment for the food to be mechanically and chemically disintegrated and brought to the vicinity of absorbent cells. Hence, it is involved in the transport of nutrients to the individual cells. It is concerned with ingestion, trituration (chewing), digestion, absorption of nutrient material into haemolymph and egestion of unused food materials. It is tubular structure, which extends from mouth to the anus. It is divided into three distinct regions, namely fore-gut (stomodaeum), mid-gut (mesenteron) and hind-gut (proctodaeum). The fore- and hind-guts are ectodermal in origin and the mid-gut is endodermal. Longitudinal and circular (intrinsic) muscles are usually associated with each of these three regions and by means peristaltic contractions move the food along the alimentary canal. The functional stomach is the mesenteron usually a circular valve-like fold separates the cavities between stomodaeum and mesenteron is known as stomodael or cardiac valve, and the one closing the entrance to the proctodaeum as the proctodaeum or pyloric valve. Fore-gut An insect’s mouth, located centrally at the base of the mouthparts, is a muscular valve (sphincter) that marks the “front” of the foregut. Food in the buccal cavity is sucked through the mouth opening and into the pharynx by contractile action of cibarial muscles. These muscles, located between the head capsule and the anterior wall of the pharynx, create suction by enlarging the volume of the pharynx (like opening a bellows). This “suction pump” mechanism is called the cibarial pump. It is especially well-developed in insects with piercing/sucking mouthparts.

The sense organs in an insect body are distributed on different parts and respond to a given stimulus such as light, sound, touch, chemicals etc. The sense organs may be classified as • Visual organs (or) photoreceptors • Auditory organs (or) organs of hearing • Chemoreceptors which respond to chemicals • Tacticle receptors which respond to touch • Gustatory receptors which respond to taste. Photoreceptors Light is perceived by insects through a number of different sense organs and these are the organs that react with light and useful for vision. These are of different types, but most important are the compound eyes. Compound eyes

History • Aristotle (384-322 BC): A good beginning of taxonomy was made by Aristotle (Historia Animalium). He erected entomon. He could distinguish mandibulates and haustellates; winged and wingless forms. The insect orders like coleopteran, dipteral, psyche (Lepidoptera) were created by him. Hence, he was called as Father of Biological Classification. • Linnaeus (1707-1778): Father of Taxonomy and Binomial Nomenclature. He coined the term Insecta. He used the term Systematics. His greatest contribution is Systema Naturae. • Brawer (1885): Laid foundations for modern system of classification and responsible to divide class Insecta into Apterygota and Pterygota. • Michael Anderson (1727-1806): Contemporary and rival of Linnaeus. Introduced Numerical Taxonomy and hence is called Father of Numerical Taxonomy.  • Johan Christian Fabricius (1745–1808), the first systematist considered to specialize on insects, published in 1778 his Philosophia Entomologica (40), the first textbook of entomology. • Fabricius had already set forth his system of insects in 1775 (Systema Entomologiae), his system of genera in 1776 (Genera Insectorum), and then numerous works on species, culminating in individual accounts of the species of each order

Apterygotes The Apterygota, which formerly included the other primitively wingless insects currently placed in the class Entognatha, are now restricted to the two orders Archaeognatha and Zygentoma, which in turn were formerly united as the Thysanura. Despite the superficial similarity of the two groups, it is now clear that they are not closely related, mainly because of fundamental differences in the mouthparts. The Archaeognathous mandibles are monocondylic, having a single articulating point with the head so that the mandible can rotate. The Zygentomous mandibles are dicondylic, with two articulating points that restrict the motion to a single plane yet enable the development of a much stronger biting action; this is the type found in all the higher insects, and the Zygentoma may well be the sister group of the Pterygota, or winged insects. Clearly the ‘Apterygota’ is not a monophyletic group and is simply retained for convenience in grouping these two orders that superficially resemble each other and have similar life histories.  

• The name Zoraptera, derived from the Greek “zor” meaning pure and “aptera” meaning wingless was given to the order before winged forms were discopvered. • Members of the order Zoraptera are small (less than 4 mm) and usually found in rotting wood, under bark or in piles of old sawdust. • They live in small aggregations (gregarious) and appear to scavenge on spores and mycelium of fungi, or occasionally, on mites and other small arthropods. • polymorphism in populations; with blind, apterous individuals dominating during colony life, but populations produce eyed alates (individuals with wings) for dispersal and founding new colonies. • males with a distinctive “mating hook” and unique mating behaviors. • unique grooming behaviors Adults • Antennae 9-segmented (moniliform). • Mouthparts mandibulate, hypognathous. • Soft bodied, small (usually less than 3 mm). • Wings often absent with reduced venation when present. • Tarsi 2-segmented • Cerci 1-segmented • ovipositor absent • incomplete development (egg, nymph, adult)

The name Lepidoptera derived from the Greek words “lepido” meaning Scale and “ptera” meaning wings refers to the flattened hairs (Scales) that cover the body and wings of most adults. Lepidoptera (Moths and Butterflies) is the second largest order (1.10 lakh sp.) in the class insecta, characterized by the body, wings and appendages being generally covered densely with pigmented scales which provide the colour pattern of the characteristic of the species and play an important role in courtship and intraspecific recognition. Adults • Head: Hypognathus and relatively small. • Compound eyes are large and set well apart. Ocelli two in number in moths or reduced to Chaetosoma in butterfly. • Mouthparts form a coiled tube (Proboscis) beneath the head. • Antennal type: • Butterflies: Clubbed, clavate, capitate. • Moths: Pectinate (Uni/Bi). • Adults have siphoning type mouthparts except in micropterygidae (Mandibulate mouthparts). Front wings large, triangular, hindwings large, fan shaped. • Body and wings covered with small, overlapping scale. • Thoracic segments are fused and metathorax is the largest and most prominent. • Wings covered with scales. Androconia (Plumules) on upper surface of wings in some males serves as outlet for odouriferous glands. are fringed distally with each tip finely divided. • Wing coupling apparatus variable (generally Frenulum and retinaculum or Amplexiform type)

Borror, Delong. J., Triple Horn, C. A. and Johnson, N.F. 1987. An introduction to the study of  insects (VI Edition). Harcourt Brace College Publishers, New York, 875p.  BV David and Ramamurthy, V.V. 2016. Elements of Economic Entomology Namrutha  Publications, 76/2, Sriramalu street Madanandapuram Chennai Chapman RF. 1998. The Insects: Structure and Function. Cambridge Univ. Press, Cambridge. David BV & Ananthkrishnan TN. 2004. General and Applied Entomology. Tata-McGraw Hill,  New Delhi. Duntson PA. 2004. The Insects: Structure, Function and Biodiversity. Kalyani Publ., New Delhi. Evans JW. 2004. Outlines of Agricultural Entomology. Asiatic Publ., New Delhi. Gullan, P. J. and Cranston, P. S. 2001. The insects- An outline of Entomology, II edition,  Chapman & Hall, Madras, 491p.  Metcalf, C.K. and W.P. Flint. Destructive and Useful Insects : Their Habits and Control. Tata  McGraw Hill Pub. Co., New Delhi  Nayar, K. K., Ananthakrishnan, T. N. and David, B. V. 1976. General and applied Entomology,  Tata McGraw Hill Publishing Company Limited, New Delhi, 589p.  Richards OW & Davies RG. 1977. Imm’s General Text Book of Entomology. 10th Ed.  Chapman  & Hall, London.