Introductory logy

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<p>INTRODUCTORY ENTOMOLOGY A. THE PHYLUM ARTHROPODA 1. General Characteristic The Phylum Arthropoda is the largest phylum in the animal kingdom. With almost a million species there are more arthropods than all kinds of plants and animals combined. Not only are there great numbers of species in the phylum but many species are represented by countless numbers of individuals. Members of the Arthropoda are segmented animals; that is, their body parts are serially repeated along a longitudinal axis. Collections segments may be grouped into discernible body region such as well-developed head which usually bears compound eyes, thorax, or cephalothorax and abdomen. Another distinguishing characteristic of arthropods is their chitinous exoskeleton. The exoskeletons serve as a protective coat of armor without sacrificing mobility. In addition to serving as protective coat and as a surface for the attachment of muscles it has made possible for the arthropods to live on land. Land life for any kind of organism requires a relatively impermeable outer covering to prevent desiccation and the arthropods exoskeleton certainly does this. Another most conspicuous feature of arthropods are the jointed appendage and it is this characteristic which give the phylum its name. the success of arthropods is in large measure due to the wide variety of adaptive uses of the appendages. Not only did they serve as waking legs, they became modified for swimming, breathing and reproductive activity. They also produced specialized structures which are used in defense, food procurement, chewing and sensory perception. Unlike some lower form of animals, which are radially symmetrical., arthropods are bilaterally symmetrical. Their body, if cut along a o Longitudinal axis, will be divided into two equal halves causing each half to be a mirror image of the other. Also, the coelom in the adult is much reduced and replaced as a perivisceral space by the enlargement of the haemocoele. 2. The Classes of Arthropods There are 4 existing groups of arthropods; the myriapods, the crustaceans, the arachnoideans and the insectants.</p> <p>a. The Myriapod Group The myriapod group includes arthropods which exhibit many differences in basic structure but share many superficial resemblances. They have centipedelike shapes, a distinct formed the original prostomium and several body segment whose appendages became the mouth parts, an elongate trunk region bearing segmented walking legs, and a well-developed antennae.a</p> <p>1 Class Chilopoda (Centipedes)</p> <p>Body elongates dorso-ventrally, head with one pair of jaws; one pair of antennae; two pairs of maxillae, the first pair forming a lower lip; eyes simple, compound or absent. The first pair of body appendages is modified with a sharp poison claw at the tip. The rest of the body segments numbering from 14 to over 10, each with a single pair of legs.a</p> <p>2 Class Symphyla</p> <p>Head posses long antennae and the mouth parts consists of mandibles, maxillae and labium. They are about inch long and centipede like in form. The 15 segments composing the trunk are not fused in pairs of which 11 or 12 bear legs.a</p> <p>3 Class Diplopoda (Millipedes)</p> <p>Body segment, except a few at each and of body, fused into pairs so that each apparent segment has two pairs of legs. Body long and usually cylindrical with a distinct head and trunk. Head with many small simple eyes; one pair of antennae, mandible and maxillae. The maxillae are usually fused to form a plate like guathochilarium. Thorax of four segment the first of which is legless while each of the other thre have a single pair of legs. The abdomen makes up most of the body with up to100 or more segments, each of which bears two pairs of legs.a</p> <p>4 Class Pauropoda</p> <p>The body consist of 11 to 12 segments, of which the dorsal portions are fused in pairs; eight or nine segments each bear a pair of legs, each pair evenly spared from the next. Head with a pair of eyes represented only by a small spot; antennae biramons. The mouth parts consist of a pair of mandibles and lower lip believed to be the same as the guathochilarium in the Diplopoda.</p> <p>b. Class Arachnida The typical arachnoid have the body divided into two regions, the cephalothorax and the abdomen. The cephalothorax of the adult morph usually bears six pairs of appendages, the anterior chelicerae, the pedipals which are often chelicerae, and four pairs of walking legs, the segmentation of the abdomen may or may not be apparent external and bears no jointed appendages. c. Class Crustacea This class includes a varied assortment of forms which are mostly aquatic in habit and made respiration. Majority of the members have the following characteristics; body usually divided into three regions; head and thorax often closely joined and referred to as the cyphalothorax ; two pairs of antennae; and in some forms, four pairs of accessory feeding appendages which includes two pairs of maxillae, and a pair of maxillipeds; thorax usually consist of four to twenty distinct segments, each with a pair of segments, with short appendages or none. Some of the parasitic and sedentary form exhibit extreme reduction in both body segments and appendages. Several forms have a carapace covering a large portion of the body, others have shell and look like bivalves. d. Class Insecta The body has three distinct regions; head, thorax and abdomen; head bears eyes, both simple and compound, and one pair of antennae (except Protura); three pairs of legs borne by three-segmented thorax (a few are legless, and some large posses additional leglike appendages, such as prolegs, on the abdominal segments; often one or 2 pairs of wings, borne by the second and/or the third the thoraxic segments. The postoral appendages of the head typically consisting of a pair of mndibles, a pair of maxillae, a Hypopharynx, and a labium). THE GENERAL STRUCTURE OF AN INSECT THE BODY WALL The insect body wall or exoskeleton consists of three principal layers; an outer cuticle containing a nitrogenous polysaccharide, chitin, proteins and usually pigments; the outer cell layer of the insect, the epidermis, that lies beneath and secrete the cuticle, and the basement membrane a non cellular layer up to 0.5 thick beneath the epidermal cells. The cuticle covers the whole of the outside of the body as well as the inner walls of the foregut and hindgut and the tracheae. It is differentiated into two principal parts,</p> <p>the epicuticle, a thin layer containing no chitin and is only 1-4 thick; and an inner region which contains chitin and forms the greater part of the cuticle. This chitinous cuticle is known as procuticle as it is first secreted, but subsequently the outer part becomes harder than the rest to form the exo-cuticle while the inner portion remains undifferentiated and is now called endocuticle. The exocuticle and edocuticle are traversed by minute pore canals which extend up to the epicuticle during its early formation to allow various substances including waxes to pass through. In this way the epicuticle is coated and waterproofed. The hardened surface of the insect body form plates called sclerites, which are separated by membranous areas known as sutures. Sutures permit movement of the various parts of the body and its appendages. The principal sclerite on the dorsum of an abdominal segment is called the tergum (pl. terga) and on the thoracic segment, and on the thoracic segment, notum (pl. nota). The main sclerite on the center of a body segment is the sternum (pl., sterna) and that of the lateral area, the pleuron (pl., pleura). The external and internal processes are found on the body wall. The external processes sucs as scales, spines and setae, may be of solid cuticle, some contain all three body layers, while still others are outgrowth of individual or several epidermal cells. The internal processes are infoldings of the body wall which strengthen it and serve as muscle attachment; some are ridge-like whileothers are spines like. THE INSECT HEAD This is the anterior heavily scleritized capsule-like body region that bears the antennae, eyes and mouth parts. It can be likened to a mammalian skull that protects the vital parts of the nervous system and the sense organs. Most insects have both simple and compound eyes. The relatively large compound eyes are located dorsolaterally on the head and between them on the upper part are the three simple eyes or ecelli. THE ANTENNAE the antennae are usually situated between or below the compound eyes. The vary greatly in size and form and are frequently used in classification. Typical antennae consist of a basal segment called the scape; the second segment, the pedicel; and the flagellum or remaining segments. The antennae are sensory in function and act as organs of smell, hearing or touch. THE MOUTH PARTS The insect mouth parts are variously modified in different insect groups and are much used in classification and identification. Typically, the insect mouth parts, consist of a labium or upper lip; a pair of heavily scleritized jaws lying behind the labium; a pair maxillae; and a hypotharynx, a short tongue-like structure located between the maxillae and above the labium. There are two general types of insect mouth parts, the mandibulate or chewing and haustellate or insects with mandibulate mouth parts, the mandibles can</p> <p>move sideways and the food is bitten off chewed. Insects with haustellate mouth parts have these in the form of elongated proboscis or break through which liquid food is sucked. These two general types of mouth parts vary considerably in different insects; these variations are given subsequently. THE MANDIBULATE MOUTH PARTS This is considered the more primitive and is found in the adult of the following orders; Thysanura, Diplora, Collembola, Orthoptera, Dermaptera, Psocoptera, Mallophaga, Odonata, Plecoptera, Isoptera, Neuroptera, Mecoptera, Tricoptera, Coleoptera and Hymenoptera. It also occurs in the larval stages in many insects. In a few insects such as bees and larvae of Nyeuroptera their mouth parts are described as chewing-sucking; the labium, maxillae and mandibles are modified into tongue like structures through which liquid food is sucked. THE HAUSTELLATE MOUTH PARTS This type of mouth parts has eight principal variations and occurs in the following groups of insects: 1 ) Thysanoptera, 2 ) Hemiptera and Homoptera, 3 ) lower Diptera, 4 ) the Asilidae, 5 ) Higher Diptera, 6 ) Siphonapteram, 7 ) Anoplura, 8 ) Lepidoptera. THE THYSANOPTERAN MOUTH PARTS the mouth parts of thrips is asymmetrical and have been called rasping-sucking. Some of the parts have become rudimentary leaving only three functional stylets: two maxillary and the left mandibles. THE HEMIPTERAN MOUTH PARTS In the heteroptera, the proboscis arises infront while the labium which forms a sheath, enclosing two mandibulan and two maxillary stylets. The maxillae fit together forming two channels: a food and salivary channel. The other structures of the mouth parts are either reduced or wanting. THE MOUTH PARTS OF LOWER DIPTERA The lower Diptera include the mosquitoes, black flies and house flies and are otherwise also called listing flies. In these insects, the labium, mandibles, maxillae, and hypopharynx. The mandibles as wanting and the principal piercing organ is the hypopharynx are stylet-like. They encloses these six stylets and do no piercing. THE MOUTH PARTS OF ASILIDAE these insects have four stylets, the labium, maxillae, and hypopharynx. The mandibles as wanting and the principal piercing organ is the hypopharynx. THE MOUTH PARTS OF THE HIGHER DIPTERA there are two modifications of the mouth parts of higher Diptera namely; the piercing type and the sponging or the lapping type.</p> <p>The piercing type occurs in tsetse flies, horn flies, stable flies and house flies. The labium and hypopharynx are slender and stylet-like lying in a dorsal groove of the labium is the labella, a pair of small hard plates armed with teeth. Between the labrum and hypopharynx is the food channel and salivary channel is in the hypopharynx. The sponging or the lapping type occurs in houseflies, blow flies and house flies. The proboscis is made up of the lower part of the head called the rostrum and the haustellium which is formed by the labium. The structures of the mouth part hang from the rostum and the maxillary palpus arise at its distal end. The groove of the labium receives the slender hypopharynx, which bear the salivary channel, and the labium between which the hypopharynx lies the food channel. The labium terminates in a pair of large, oval lobes, the labella. The lower surface of the labella bears numerous transverse grooves, which serve as food channels. This type of mouth parts lap up food which may be already in liquid form or still solid but first liquefied by salivary secretions. THE SIPHONAPTERAN MOUTH PARTS the mouth parts of adult fleas consists of three piercing stylets, namely; the epipharynx and the laciniae of the maxillae. Adult fleas are blood suckers but their larvae feed on organic debris and have mandibulate type of mouth parts. THE ANOPLURAN MOUTH PARTS the mouth parts of sucking lice has an eversible rostum from which produces three piercing stylets; the dorsal stylet, which probably represents the fused maxillae, had its edges curved upward and inward forming a food tube; the slender intermediate stylets containing the salivary channel which probably represents the hypopharynx; and the ventral stylet or principal piercing organ which probably is the labium. THE LEPIDOPTERAN MOUTH PARTS Insects having this type of mouth part do not piercing but merely suck or siphon liquid up through the proboscis. This structure is uncoiled by blood pressure and recoils by its own elasticity. It is made up of two galeae of maxillae which come together to form the food channel. The labium is a mere transverse sclerite across the lower margin of the face. The labial palps are well developed but the maxillary palps are either reduced or wanting. The mandibles and hypopharynx are lacking. THE THORAX this is the region of the body after the head to which it is connected by a membranous neck region called the cervix. In most adult insects it is usually bears three pairs of legs and two pairs of wings. The thorax is divided into three segments: the prothorax, mesothorax, and metathorax, the last two are usually known as the ringbearing segments. Each thoracic segment is like a box composed of four groups of sclerites: the norsal notum, the two lateral pleura and the ventral sternum. THE LEGS Fully developed and functional wings may be present in immature stages. The wings appear as thin, rigid flaps arising dorsolaterally from between the pleura and</p> <p>nota of the wing-bearing thoraxix segments. Each wing consists of thin membrane supported by tubular veins. The wing membrane is formed by two layers of integument closely apposed an...</p>


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