The second axillary sclerite (2Ax) is more variable in form than the first axillary, but its mechanical relations are no less definite. In females there are three types of genitalia based on the relating taxa: monotrysian, exoporian, and dytresian. The postcubitus, however, has the status of an independent wing vein and should be recognized as such. Large numbers of cross-veins are present in some insects, and they may form a reticulum as in the wings of Odonata (dragonflies and damselflies) and at the base of the forewings of Tettigonioidea and Acridoidea (katydids and grasshoppers, respectively). It can be divided into three sections the foregut, midgut and hindgut each of which performs a different process of digestion. These three groups form segments by using a "growth zone" to direct and define the segments. [14][15] Compound eyes grow at their margins with the addition of new ommatidia. Flies come in great populations due to their ability to mate effectively and in a short period of time especially during the mating season.[71]. The more advanced groups making up the Neoptera have foldable wings, and their muscles act on the thorax wall and power the wings indirectly. The bubble usually covers one or more spiracles so the insect can breathe air from the bubble while submerged. The lateral pleural sclerites are believed to be derived from the subcoxal segment of the ancestral insect leg. Humans have a head, torso (similar to thorax) and abdomen. The tarsus is occasionally fused with the tibia in larval insects, forming a tibiotarsal segment; in some cases, it appears to be eliminated or reduced to a rudiment between the tibia and the pretarsus. The posterior lobe is usually the larger and is termed the meron. Salivary secretions from the labella assist in dissolving and collecting food particles so they can be more easily taken up by the pseudotracheae or laid their egg on the suitable media; this is thought to occur by capillary action. The pleural articular surface of the coxa is borne on a mesal inflection of the coxal wall. In aquatic beetles (Coleoptera) and bugs (Hemiptera), the tibiae and/or tarsi of one or more pairs of legs usually are modified for swimming (natatorial) with fringes of long, slender hairs. A coxa with an enlarged meron has an appearance similar to one divided by a coxal suture falling in line with the pleural suture, but the two conditions are fundamentally quite different and should not be confused. When movable on the femur the trochantero femoral hinge is usually vertical or oblique in a vertical plane, giving a slight movement of production and reduction at the joint, though only a reductor muscle is present. The mandibles cut and crush food, and may be used for defense; generally, they have an apical cutting edge, and the more basal molar area grinds the food. [7] Each such pair occupies one segment, though not all segments in modern insects bear any visible appendages. The insect circulatory system has no veins or arteries, and instead consists of little more than a single, perforated dorsal tube that pulses peristaltically. Many insects, however, are beneficial from a human viewpoint; they pollinate plants, produce useful substances, control pest insects, act as scavengers, and serve as food for other animals (see below Importance). In the Jugatae group of Lepidoptera, it bears a long finger-like lobe. [8][1]:2224, Because the mesothorax and metathorax hold the wings, they have a combined name called the pterothorax (pteron = wing). In pterygotes, the postocciput forms the extreme posterior, often U-shaped, which forms the rim of the head extending to the postoccipital suture. Please refer to the appropriate style manual or other sources if you have any questions. In Elateridae species, the predatory larvae defecate enzymes on their prey, with digestion being extraorally. In addition, in Orthoptera and Blattodea, the anal area is folded like a fan along the veins, the anal veins being convex, at the crests of the folds, and the accessory veins concave. The mandibles are positioned between the labrum and maxillae. Conversely, an increase in venation may occur by the branching of existing veins to produce accessory veins or by the development of additional, intercalary veins between the original ones, as in the wings of Orthoptera (grasshoppers and crickets). A palp arises from each side of the prementum, often being three-segmented. Most phylogenetically advanced insects have two pairs of wings located on the second and third thoracic segments. Long, slender (extratory) malpighian tubules can be found between the junction of the mid- and hind gut. Furthermore, insects are valuable objects of study in elucidating many aspects of biology and ecology. Insects, like all arthropods, have no interior skeleton; instead, they have an exoskeleton, a hard outer layer made mostly of chitin that protects and supports the body. Insect respiration is accomplished without lungs. They can produce glue and protective substances for coating eggs or tough coverings for a batch of eggs called oothecae. The labrum is a broad lobe forming the roof of the preoral cavity, suspended from the clypeus in front of the mouth and forming the upper lip. Winged aphids invade New York City. [13], Because the individual lenses are so small, the effects of diffraction impose a limit on the possible resolution that can be obtained (assuming they do not function as phased arrays). One or both pairs of lobes may be absent or they may be fused to form a single median process. Let us know if you have suggestions to improve this article (requires login). Whats the Difference Between a Grasshopper and a Cricket? In some of the Hymenoptera, a basal subdivision of the femur simulates a second trochanter, but the insertion of the reductor muscle on its base attests that it belongs to the femoral segment, since as shown in the odonate leg, the reductor has its origin in the true second trochanter. It can be described as the floor of the mouth. Muscles arising on the frons are inserted into these sclerites, which distally are hinged to a pair of lingual sclerites. The uric acid is formed using hemolymph waste products diffused from the Malpighian tubules (element 20). Thus cockroaches, like all insects, are not dependent on the mouth and windpipe to breathe. Omissions? Many species of insects have reduced numbers of ganglia due to fusion or reduction. [26], Mouthparts can have multiple functions. [72] This hormone is produced by corpora allata and corpora cardiaca, where it is also stored. The remainder of the male reproductive system is derived from embryonic mesoderm, except for the germ cells, or spermatogonia, which descend from the primordial pole cells very early during embryogenesis. The rectum absorbs 90% of the water in these fecal pellets, and the dry pellet is then eliminated through the anus (element 17), completing the process of digestion. The basal shafts of the veins are convex, but each vein forks distally into an anterior convex branch and a posterior concave branch. Updates? [46], An insect uses its digestive system for all steps in food processing: digestion, absorption, and feces delivery and elimination. The sclerite anterior to the pleural suture is called the episternum (serially, the mesepisternum and metepisternum). Please refer to the appropriate style manual or other sources if you have any questions. A more formal definition is that it is the sclerite from which the pharyngeal dilator muscles arise, but in many contexts that too, is not helpful. [27] Most of the hypopharynx is membranous, but the adoral face is sclerotized distally, and proximally contains a pair of suspensory sclerites extending upwards to end in the lateral wall of the stomodeum. As larvae, many insects have gills that can extract oxygen dissolved in water, while others need to rise to the water surface to replenish air supplies, which may be held or trapped in special structures. If there is a median ocellus, it generally is on the frons, though in some insects such as many Hymenoptera, all three ocelli appear on the vertex. This bubble may be held under the elytra, or it may be trapped against the body using specialized hairs. The Greek word entomon, meaning "notched," refers to the segmented body plan of the insect. [8]:880, The main component of the male reproductive system is the testis, suspended in the body cavity by tracheae and the fat body. The meron reaches the extreme of its departure from the usual condition in the Diptera. The zoological categories of genetics, taxonomy, morphology, physiology, behaviour, and ecology are included in this field of study. The distal plate (m') is less constantly present as a distinct sclerite and may be represented by a general sclerotization of the base of the mediocubital field of the wing. They dominate the present-day land fauna with about 1 million described species. What is an insect? [4] The difference between the unmodified and modified forms is evident when comparing the body wall of a caterpillar (unmodified) to a beetle (modified). Omissions? Also included are the applied aspects of economic entomology, which encompasses the harmful and beneficial impact of insects on humans and their activities. Spermathecae are tubes or sacs in which sperm can be stored between the time of mating and the time an egg is fertilized. [8]:279, In the circulatory system, hemolymph, or insect blood, is used to circulate heat in a form of thermoregulation, where muscles contraction produces heat, which is transferred to the rest of the body when conditions are unfavorable. This strategy allows insects to extract a significant proportion of the available nutrients from the food source. The tracheae of insects are attached to the spiracles, excluding the head. This break-down process is known as digestion. [8] The shape and dimensions of the proboscis have evolved to give different species wider and therefore more advantageous diets. Each tube is inwardly concave, thus forming a central tube through which moisture is sucked. Some insects bear a sclerite in the pleural area called a laterotergite. In the Odonata, both nymphs and adults, there are two trochanteral segments, but they are not movable on each other; the second contains the reductor muscle of the femur. The insect body is divided into three main parts, the head, thorax and abdomen. Hairs of two types may occur on the wings: microtrichia, which are small and irregularly scattered, and macrotrichia, which are larger, socketed, and may be restricted to veins. This article was most recently revised and updated by, https://www.britannica.com/science/entomology, entomology - Student Encyclopedia (Ages 11 and up). The tarsus of adult pterygote insects having fewer than five subsegments is probably specialized by the loss of one or more subsegments or by a fusion of adjoining subsegments. The frons is that part of the head capsule that lies ventrad or anteriad of the vertex. Benefits from insect studies include improvements in pest-management practices and advances in genetics research. The male external genitalia have been used widely to aid in distinguishing species, whereas the female external genitalia may be simpler and less varied. In insects, the goblet cells excrete positive potassium ions, which are absorbed from leaves ingested by the larvae. The first insect hormone PTTH (Prothoracicotropic hormone) operates the species life cycle and diapause (see the relates section). Paternity testing of insects has revealed that some, and probably many, female insects use the spermatheca and various ducts to control or bias sperm used in favor of some males over others. The anterior branch may break up into several secondary branches, but commonly it forks into two distal branches. [26], As a result, the distal arm of the third axillary sclerite rotates upwards and inwards, so that finally its position is completely reversed. Segmentation in biology is the division of some animal and plant body plans into a series of repetitive segments. Then, through the hypopharynx, the mosquito injects saliva, which contains anticoagulants to stop the blood from clotting. Insects have six segmented legs, which take many different forms depending on their function. Activity of the same muscle in flight affects the power output of the wing and so it is also important in flight control. The meron may be greatly enlarged by an extension distally in the posterior wall of the coxa; in the Neuroptera, Mecoptera, Trichoptera, and Lepidoptera, the meron is so large that the coxa appears to be divided into an anterior piece, the so-called "coxa genuina," and the meron, but the meron never includes the region of the posterior trochanteral articulation, and the groove delimiting it is always a part of the basicostal suture. The great fan-like expansions of the hindwings of Acrididae are clearly the vannal regions, since their veins are all supported on the third axillary sclerites on the wing bases, though Martynov (1925) ascribes most of the fan areas in Acrididae to the jugal regions of the wings. The stylets are needle-like projections used to penetrate plant and animal tissues. The true jugum of the acridid wing is represented only by the small membrane (Ju) mesad of the last vannal vein. In turn, the notum of the prothorax is called the pronotum, the notum for the mesothorax is called the mesonotum and the notum for the metathorax is called the metanotum. In the forewing of Blattidae, however, the only fold in this part of the wing lies immediately before the postcubitus. Strong neuron connections connect the neurohemal corpora cardiaca to the brain and frontal ganglion, where the closely related median corpus allatum produces juvenile hormone III in close proximity to the neurohemal dorsal aorta. In some cases the adult insects make elaborate preparations for the young, in others the mother alone defends or feeds her young, and in still others the young are supported by complex insect societies. [38]:165, The femur is the third segment of the insect leg, is usually the longest and strongest part of the limb, but it varies in size from the huge hind femur of leaping Orthoptera to a very small segment such as is present in many larval forms. The anterior segment, closest to the head, is the prothorax; its major features are the first pair of legs and the pronotum. They can be extremely hard (around 3 on Mohs, or an indentation hardness of about 30kg/mm2); thus, many termites and beetles have no physical difficulty in boring through foils made from such common metals as copper, lead, tin, and zinc. These small variations in the actual position of the vannal fold, however, do not affect the unity of action of the vannal veins, controlled by the flexor sclerite (3Ax), in the flexion of the wing. [43] Some cockroaches have just six ganglia in the abdomen, whereas the wasp Vespa crabro has only two in the thorax and three in the abdomen. [30] There is an allometric scaling relationship between the body mass of Lepidoptera and length of the proboscis[33] from which an interesting adaptive departure is the unusually long-tongued hawk moth Xanthopan morganii praedicta. The light produce is highly efficient, as it is produced by oxidation of luciferin by the enzymes luciferase in the presence of ATP (adenosine triphosphate) and oxygen, producing oxyluciferin, carbon dioxide, and light. Some species are in close association with human dwellings and widely found around garbage or in the kitchen. Hardened plates in the exoskeleton are called sclerites, which are subdivisions of the major regions tergites, sternites, and pleurites, for respective regions tergum, sternum, and pleuron.[6]. These chemicals mix and result in an explosive ejection, forming temperatures of around 100 C, with the breakdown of hydroquinone to H2 + O2 + quinone, with the O2 propelling the excretion. [1]:57. [69] Ancestors of lepidopteran species, stemming from Hymenoptera, had midgut ceca, although this is lost in current butterflies and moths. The jugal vein (J) of the jugal lobe of the wing is often occupied by a network of irregular veins, or it may be entirely membranous; sometimes it contains one or two distinct, small veins, the first jugal vein, or vena arcuata, and the second jugal vein, or vena cardinalis (2J). In Orthoptera, it usually has this position. [1]:2224 On its inner side, it is membranous and may be produced into a median lobe, the epipharynx, bearing some sensilla. [52], In the hindgut (element 16 in numbered diagram), or proctodaeum, undigested food particles are joined by uric acid to form fecal pellets. It contains all the muscles for the legs and wings, which are attached to this part of the body. The valves open when the CO2 level in the insect rises to a high level; then the CO2 diffuses out of the tracheae to the outside and fresh O2 diffuses in. Distally on the stipes are two lobes, an inner lacinea, and an outer galea, one or both of which may be absent. The maxillae occupy a lateral position, one on each side of the head behind the mandibles. The most common coupling mechanism (e.g., Hymenoptera and Trichoptera) is a row of small hooks on the forward margin of the hindwing, or "hamuli", which lock onto the forewing, keeping them held together (hamulate coupling). Each wing is attached to the body by a membranous basal area, but the articular membrane contain several small articular sclerites, collectively known as the pteralia. The basicosta strengthens the base of the coxa and is commonly enlarged on the outer wall to give insertion to muscles; on the mesal half of the coxa, however, it is usually weak and often confluent with the coxal margin. They lie in the median area of the wing base distal to the second and third axillaries and are separated from each other by an oblique line (bf), which forms a prominent convex fold during flexion of the wing. [1]:4142 The vannal veins (lV to nV) are the anal veins immediately associated with the third axillary, and are directly affected by the movement of this sclerite that brings about the flexion of the wings. With the aid of the newly developed microscope, the Dutch naturalist Jan Swammerdam was able to observe the minute structures of many insect species. Insect orders use different flight mechanisms; for example, the flight of a butterfly can be explained using steady-state, nontransitory aerodynamics, and thin airfoil theory. In its unmodified form, chitin is translucent, pliable, and resilient. Each alinotum (sometimes confusingly referred to as a "notum") may be traversed by sutures that mark the position of internal strengthening ridges and commonly divide the plate into three areas: the anterior prescutum, the scutum, and the smaller posterior scutellum. In Hemiptera and many Diptera, which feed on fluids within plants or animals, some components of the mouthparts are modified for piercing, and the elongated structures are called stylets. As digestion slowly occurs, lipids are synthesized and accumulate in the fat body, mainly as triacylglycerol, in . Each segment is delineated by an intersegmental suture. Though fold lines may be transverse, as in the hindwings of beetles and earwigs, they are normally radial to the base of the wing, allowing adjacent sections of a wing to be folded over or under each other. Segmentation And Tagmosis - Natural Enemies - Insectomania Insects represent about 90 percent of all life forms on earth. [24], The mouthparts and rest of the head can be articulated in at least three different positions: prognathous, opisthognathous, and hypognathous. Entomology also plays an important role in studies of biodiversity and assessment of environmental quality. The terminalia of adult female insects include internal structures for receiving the male copulatory organ and his spermatozoa and external structures used for oviposition (egg-laying; section 5.8). [10], On the posterior aspect of the head are the occiput, postgena, occipital foramen, posterior tentorial pit, gula, postgenal bridge, hypostomal suture and bridge, and the mandibles, labium, and maxilla. The body of knowledge gleaned from the study of insects has enabled modern economic entomologists to develop a wide range of methods for controlling insect pests. [1]:65,75 While the corpora cardiaca produce PTTH, the corpora allata also produces juvenile hormones, and the prothorocic glands produce moulting hormones. In many species the difference in body structure between the sexes is pronounced, and knowledge of one sex may give few clues to the appearance of the other sex. These glands are part of the endocrine system: Female insects are able make eggs, receive and store sperm, manipulate sperm from different males, and lay eggs. [50]:3031, The salivary glands (element 30 in numbered diagram) in an insect's mouth produce saliva. What is an insect? | Science Literacy and Outreach | Nebraska This forces the male to lie on its back in order for its genitalia to remain engaged with those of the female, or the torsion of the male genitals allows the male to mate while remaining upright. Aquatic larvae and nymphs may have gills laterally on some to most abdominal segments. [38]:163164, The inflection of the coxal wall bearing the pleural articular surface divides the lateral wall of the basicoxite into a prearticular part and a postarticular part, and the two areas often appear as two marginal lobes on the base of the coxa. [65] All species studied so far carry the obligate mutualistic endosymbiont bacterium Blattabacterium, with the exception of Nocticola australiensis, an Australian cave dwelling species without eyes, pigment or wings, and which recent genetic studies indicates are very primitive cockroaches. [62][63], Cockroaches are most common in tropical and subtropical climates. [12] The main exception is in those species whose larvae are not fully sclerotized, mainly some holometabola; but even most unsclerotized or weakly sclerotized larvae tend to have well-sclerotized head capsules, for example, the larvae of Coleoptera and Hymenoptera. However, most adult Lepidoptera have siphoning mouthparts, while their larvae (commonly called caterpillars) have mandibles. The first section of the alimentary canal is the foregut (element 27 in numbered diagram), or stomodaeum. The cuticle surrounding the veins becomes thickened and more heavily sclerotized to provide strength and rigidity to the wing. Updates? Instead, all the digestive enzymes other than initial digestion, are immobilized at the surface of the midgut cells. Such an organ is generally a membrane (tympanum) stretched across a frame backed by an air sac and associated sensory neurons. [38], In many insect species, the forewing and hindwing are coupled together, which improves the aerodynamic efficiency of flight. Different glands specialize for different pheromones produced for finding mates. Unlike other insects, the gonopore, or genital opening is behind the seventh abdominal segment. [38], The vannus is bordered by the vannal fold, which typically occurs between the postcubitus and the first vannal vein. The combined tubular structures are referred to as the proboscis, although specialized terminology is used in some groups. There is a brain, a subesophageal ganglion, three thoracic ganglia, and six abdominal ganglia. Often an ability to detect the E-vector of polarized light exists in polarization of light. [57][58] An additional role of the haemolymph in some orders, can be that of predatory defence. [17]:811. The coxa in its more symmetrical form, has the shape of a short cylinder or truncate cone, though commonly it is ovate and may be almost spherical. The proximal part of the maxilla consists of a basal cardo, which has a single articulation with the head, and a flat plate, the stipes, hinged to the cardo. It is then emptied directly into the alimentary canal, at the junction between the midgut and hindgut. In the Ephemerida, according to present interpretations of the wing venation, both branches of the media are retained, while in Odonata, the persisting media is the primitive anterior branch. Microscopic projections from the midgut wall, called microvilli, increase the surface area of the wall and allow more nutrients to be absorbed; they tend to be close to the origin of the midgut. Insects that inhabit streams and other freshwater habitats such as mayflies, caddisflies, and stoneflies are used as biotic indicators of water quality. [1]:69 Air is taken in through spiracles along the sides of the abdomen and thorax supplying the trachea with oxygen as it goes through the lepidopteran's respiratory system. This is because the primary axis of the head is rotated 90 to become parallel to the primary axis of the body. Insect flight can be rapid, maneuverable, and versatile, possibly due to the changing shape, extraordinary control, and variable motion of the insect wing. The main structure of an insect's digestive system is a long-enclosed tube called the alimentary canal (or gut), which runs lengthwise through the body. Please select which sections you would like to print: Professor of Biology, University of Cambridge, 195266; Director, Agricultural Research Council Unit of Insect Physiology, 194367. [20], The number of segments in an antenna varies amongst insects, with higher flies having 3-6 segments,[21] while adult cockroaches can have over 140. insect, (class Insecta or Hexapoda), any member of the largest class of the phylum Arthropoda, which is itself the largest of the animal phyla. [9], The clypeus is a sclerite between the face and labrum, which is dorsally separated from the frons by the frontoclypeal suture in primitive insects. The basal part of the labium, equivalent to the maxillary cardines and possibly including a part of the sternum of the labial segment, is called the postmentum. The palp has levator and depressor muscles arising in the stipes, and each segment of the palp has a single muscle causing flexion of the next segment. [1]:7077. Ventral sclerites are sometimes called laterosternites. The second branch of the cubitus (Cu2) in Hymenoptera, Trichoptera, and Lepidoptera, was mistaken by Comstock and Needham for the first anal. In many Diptera, a deep incision of the anal area of the wing membrane behind the single vannal vein sets off a proximal alar lobe distal to the outer squama of the alula. Adult insects have segmented bodies divided into a head, a thorax and an abdomen. Insects are also used by forensic entomologists in a wide variety of legal situations that include both civil and criminal cases. [2] The head is specialized for sensory input and food intake; the thorax, which is the anchor point for the legs and wings (if present), is specialized for locomotion; and the abdomen is for digestion, respiration, excretion, and reproduction. The radius is generally the strongest vein of the wing. Three physical features separate insects from other arthropods: they have a body divided into three regions (called tagmata) (head, thorax, and abdomen), three pairs of legs, and mouthparts located outside of the head capsule. Three physical features separate insects from other arthropods: they have a body divided into three regions (called tagmata) (head, thorax, and abdomen), three pairs of legs, and mouthparts located outside of the head capsule. In number, the vannal veins vary from one to 12, according to the expansion of the vannal area of the wing. Cockroaches are generally omnivorous with the exception of the wood-eating species such as Cryptocercus; these roaches are incapable of digesting cellulose themselves but have symbiotic relationships with various protozoans and bacteria that digest the cellulose, allowing them to extract the nutrients.
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