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HEMIPTERA (Gr. 77µi-, half and IrTep6...

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Originally appearing in Volume V13, Page 262 of the 1911 Encyclopedia Britannica.
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HEMIPTERA (Gr. 77µi-, half and IrTep6P, a wing), the name applied in zoological classification to that order of the class Hexapoda (q.v.) which includes bugs, cicads, aphids and scale-insects. The name was first used by Linnaeus (I735), who derived it from the half-coriaceous and half-membranous condition of the forewing in many members of the order. But the wings vary considerably in different families, and the most distinctive feature is the structure of the jaws, which form a beak-like organ with stylets adapted for piercing and sucking. Hence the name Rhyngota (or Rhynchota), proposed by J. C. Fabricius (1775), is used by many writers in preference to Hemiptera. Structure.— The head varies greatly in shape, and the feelers have usually but few segments—often only four or five. The arrangement of the jaws is remarkably constant throughout the order, if we exclude from it the lice (Anoplura). Taking as our type the head of a cicad, we find a jointed rostrum or beak (figs. 1 and 2, IV. b, c) with a deep groove on its anterior face; this organ is formed by the second pair of maxillae and corresponds therefore to the labium or " lower lip '' of biting insects. Within the groove of the rostrum two pairs of slender piercers — often barbed at the tip—work to and fro. One of these pairs (fig. 2, II. a, b, c) represents the mandibles, the other (fig. 2, III. a, b, c) the first maxillae. The piercing portions of the latter—representing their After Martau, Bull. r4 (N.S.) Div. Ent. U.S. inner lobes or laciniae— Dept. Agr. lie median to the man- FIG. 1.-Head and Prothorax of Cicad dibular piercers in the from side. natural position of the IL' Frons. , Base of mandible. organs. These homologies III., Base of first maxillae. of the hemipterous jaws IV., Second maxillaeformingrostruin, were determined by J. C. V., Pronotum. Savigny in 1816, and though disputed by various subsequent writers, they have been lately confirmed by the embryological researches of R. Heymons (1899). Vestigial palps have been described in various species of Hemiptera, but the true nature of these structures is doubtful. In front of the rostrum and the piercers lies the pointed flexible labrum and within its base a small hypopharynx (fig. 2, IV. d) consisting of paired conical processes which lie dorsal to the " syringe " of the salivary glands. This latter organ injects a secretion into the plant or animal tissue from which the insect is sucking. The point of the f rostrum is pressed against the surface to be pierced; then the stylets come into play and the fluid food is believed to pass into the mouth by capillary attraction. The prothorax (figs. r and 2, V.) in Hemiptera is large and free, and the mesothoracic scutellum is usually extensive. The number of tarsal segments is reduced; often three, two or only one may be present instead of the typical insectan number five. The wings will be described in connexion with the various After Marian, Bull. re (N. S.) Div. Ent. U.S. Dept. Agr. I., a, frons; b, clypeus; c, labrum; d, epipharynx. 1'., Same from behind. II., Mandible. IV., and maxillae, a, sub-mentum; b, mentum; c, ligula, forming beak; d, hypopharynx (shown also from front d', and behind d'). V., Prothorax, b, haunch; a, trochanter. sub-orders, but an interesting peculiarity of the Hemiptera is the occasional presence of winged and wingless races of the same species. Eleven abdominal segments can be recognized, at least in the early stages; as the adult condition is reached, the hinder segments become reduced or modified in connexion with the external reproductive organs, and show, in some male Hemiptera, a marked asymmetry. The typical insectan ovipositor with its three pairs of processes, one pair belonging to the eighth and two pairs to the ninth abdominal segment, can be distinguished in the female. In the nervous system the concentration of the trunk gangliain many Hemiptera. Tn the adult there is apa.ir of such glands opening ventrally on the hifidmost thoracic segment, or at the base of the abdomen; but in the young insect the glands are situated dorsally and open to the exterior on a variable number of the abdominal terga. Development.—In most Hemiptera the young insect (fig. 3) resembles its parents except for the absence of wings, and is active through all stages of its growth. In all Hemiptera the wing-rudiments develop externally on the nymphal cuticle, but in some families—the cicads for example—the young insect (fig. so) is a larva differing markedly in form from its parent, and adapted for a different mode of life, while the nymph before the final moult is sluggish and inactive. In the male Coccidae (Scale-insects) the nymph (fig. 4) remains passive and takes no food. The order of the Hemiptera affords, therefore, some interesting transition stages towards the complete metamorphosis of the higher insects. Distribution and Habits.—Hemiptera are widely distributed, and are plentiful in most quarters of the globe, though they probably have not penetrated as far into remote and inhospitable regions as have the Coleoptera, Diptera and Aptera. They feed entirely by suction, and the majority of the species pierce plant tissues and suck sap. The leaves of plants are for the most part the objects of attack, but many aphids and scale-insects pierce stems, and some go underground and feed on roots. The enormous rate at which aphids multiply under favourable conditions makes them of the greatest economic importance, since the growth of immense numbers of the same kind of plant in close proximity —as in ordinary farm-crops—is especially advantageous to the insects that feed on them. Several families of bugs are predaceous in habit, attacking other insects —often members of their own order—and sucking their juices. Others are scavengers feeding on decaying organic matter; the pond skaters, for example, live mostly on the juices of dead floating insects. And some, like the bed-bugs, are parasites of vertebrate animals, on whose bodies they live temporarily or permanently, and whose blood they suck. The Hemiptera are especially interesting as an order from the variety of aquatic insects included therein. Some of these—the Hydrometridae or pond-skaters, for example—move over the surface-film, on which they are supported by their elongated, slender legs, the body of the insect being raised clear of the water. They are covered with short hairs which form a velvet-like pile, so dense that water cannot penetrate. Consequently when the insect dives, an air-bubble forms around it, a supply of oxygen is thus secured for breathing and the water is kept away from the spiracles. In many of these insects, while most individuals of the species are wingless, winged specimens are now and then met with. The occasional development of wings is probably of service to the species in enabling the insects to reach new fresh-water breeding-grounds. This family of Iemiptera (the Hydrometridae) and the Saldidae contain several insects that are marine, haunting the tidal margin. One genus of Hydrometridae (Halobates) is even oceanic in its habit, the species being met with skimming over the surface of the sea hundreds of miles from land. Probably they dive when the surface becomes ruffled. In these marine genera the abdomen often undergoes excessive reduction (fig. 5). Other families of Hemiptera—such as the " Boatmen " (Notonectldae) and the " Water-scorpions " (fig. 6) and their allies (Nepidae) dive and swim through the water. They obtain their supply of air from the surface. The Nepidae breathe by means of a pair of long, grooved tail processes (really out-growths MER21 After Jfarlatt, Ball. 4 (N.S.) Dr'. Ent. U.S. Dept. Agr. into a single nerve-centre situated in the thorax is remarkable. The digestive system has a slender gullet, a large crop and no gizzard; in some Hemiptera the hinder region of the mid-gut forms a twisted loop with the gullet. Usually there are four excretory (Malpighian) tubes; but there are only two in the Coccidae and none in the Aphidae. " Stink glands," which secrete a nauseous fluid with a defensive function, are present After Riley and Insect Life, vol. Dept. Agr.). Howard i. (U.S. of the abdominal pleura) which when pressed together form a tube whose point can pierce the surface film and convey air to the hindmost spiracles which are alone functional in the adult. The Notonectidae breathe mostly through the thoracic spiracles; the air is conveyed to these from the tail-end, which is brought to the surface, along a kind of tunnel formed by overlapping hairs. Sound-producing Organs.—The Hemiptera are remarkable for the variety of their stridulating organs. In many genera of the Pentatomidae, bristle-bearing tubercles on the legs are scraped across a set of fine striations on the abdominal sterna. In Halobates a comb-like series of sharp spines on the fore-shin can be drawn across a set of blunt.processes on the shin of the opposite leg. Males of the little water-bugs of the genus Corixa make a shrill chirping note by drawing a row of teeth on the flattened fore-foot across a group of spines on the haunch of the opposite leg. But the loudest and most remarkable vocal organs of all insects are those of the male cicads, which " sing " d e From Marlatt, Bull. 14 (N.S.) Div. Ent. U.S. Dept. Agr. FIG. 7. a, Body of male Cicad from c, Section showing muscles which below, showing cover-plates vibrate drum (magnified) ; of musical organs; d, A drum at rest; b, From above showing drums, e, Thrown into vibration, more natural size; highly magnified. ' by the rapid vibration of a pair of " drums " or membranes within the metathorax. These drums are worked by special muscles, and the cavities in which they lie are protected by conspicuous plates visible beneath the base of the abdomen (see fig. 7). Fossil History.—The Heteroptera can be traced back farther than any other winged insects if the fossil Protocimex silurica Moberg, from the Ordovician slates of Sweden is rightly regarded as the wing of a bug. But according to the recent researches of A. Handlirsch it is not insectan at all. Both Heteropterous and Homopterous genera have been described from the Carboniferous, but the true nature of some of these is doubtful. Eugereon is a remarkable Permian fossil, with jaws that are typically hemipterous except that the second maxillae are not fused and with cockroach-like wings. In the Jurassic period many of the existing families, such as the Cicadidae, Fulgoridae, Aphidae, Nepidae, Reduviidae, Hydrometridae, Lygaeidae and Coreidae, had already become differentiated. Classification.--The number of described species of Hemiptera must now be nearly 20,000. The order is divided into two sub-orders, the Heteroptera and the Homoptera. The Anoplura or lice should not be included among the Hemiptera, but it has been thought convenient to refer briefly to them at the close of this article. HETEROPTERA In this sub-order are included the various families of bugs and their aquatic relations. The front of the head is not in contact with the haunches of the fore-legs. There is usually a marked difference between the wings of the two pairs. The fore-wing is generally divided into a firm coriaceous basal region, occupying most of the area, and a membranous terminal portion, while the hind-wing is delicate and entirely membranous (see fig. 6). In the firm portion of the fore-wing two T£RZI. After Marlatt, Bull. 4 (N.S.) Div. Ent. U.S. Dept. Age. a, Female from above; d, Jaws, very highly magnified b, From beneath; (tips of mandibles and 1st c, Vestigial wing; maxillae still more highly magnified). distinct regions can usually be distinguished; most of the area is formed by the corium (fig. 6, co), which is separated by a longitudinal suture from the clavus (fig. 6, cl) on its hinder edge, and in some families there is also a cuneus (fig. 9 cu) external to and an embolium in front of the corium. Most Heteroptera are flattened in form, and the wings lie flat, or nearly so, when closed. The young Heteropteron is hatched from the egg in a form not markedly different from that of its parent; it is active and takes food through all the stages of its growth. It is usual to divide the Heteroptera into two tribes—the Gymnocerata and the Cryptocerata. Gymnocerata.—This tribe includes some eighteen families of terrestrial, arboreal and marsh-haunting bugs, as well as those aquatic Heteroptera that live on the surface-film of water. The feelers are elongate and conspicuous. The Pentatomidae (shield-bugs), some of which are metallic or otherwise brightly coloured., are easily recognized by the great development of the scutellum, which reaches at least half-way back towards the tip of the abdomen, and in some genera covers the whole of the hind body, and also the wings when these are closed. The Coreidae have a smaller scutellum, and the feelers are inserted high on the head, while in the Lygaeidae they are inserted lower down. These three families have the foot with three segments. In the curious little Tingidae, whose integuments exhibit a pattern of network-like ridges, the feet are two-segmented and the scutellum is 'hidden by the pronotum. The Aradidae have two segmented feet, and a large visible scutellum. The Hydrometridae are a large family including the pond-skaters and other dwellers on the surface-film of fresh water, as well as the remarkable oceanic genus Halobates already referred to. The Reduviidae are .reRa After Carpenter, Proc. R. Dublin Sot., vol. viii. a family of predaceous bugs that attack other insects and suck their juices; the beak is short, and carried under the head in a hook-like curve, not—as in the preceding families—lying close against the breast. The Cimicidae have the feet three-segmented and the fore-wings greatly reduced; most of the species are parasites on birds and bats, but one—Cimex lectularius (figs. 3, 8)—is the well-known " bed-bug " which abounds in unclean dwellings and sucks human blood (see BUG). The Anthocoridae are nearly related to the Cimicidae, but the wings are usually well developed and the forewing possesses cuneus and embolium as well as corium and clavus. The Capsidae are a large family of rather soft-skinned bugs mostly elongate in form with the two basal segments of the feelers stouter than the two terminal. The forewing in this family has a cuneus (fig. 9 cu), but not an emboli um. These insects are often found in large numbers on plants whose juices they suck. Cryptocerala.—In this tribe are included five or six families of aquatic Heteroptera which spend the greater part of their lives submerged, diving and swimming through the water. The feelers are very small and are often hidden in cavities beneath the head. The Naucoridae and Belostomatidae are flattened in-sects, with four-segmented feelers and fore-legs inserted at the front of the prosternum. Two species of the former family inhabit our islands, but the Belostomatidae are found only in the warmer regions of the globe; some of them, attaining a length of 4 to 5 in., are giants among insects. The Nepidae (fig. 6) or water-scorpions (q.v.)—two British species—are distinguished by their three-segmented feelers, their raptorial fore-legs (in which the shin and foot, fused together, work like a sharp knife-blade on the grooved thigh), and their elongate tail-processes formed of the abdominal pleura and used for respiration. The Notenectidae, or " water-boatmen " (q.v.) have convex ovoid bodies admirably adapted for aquatic life. By means of the oar-like hind-legs they swim actively through the water with the ventral surface upwards; the fore-legs are inserted at the hinder edge of the pro-sternum. The Corixidae are small flattened water-bugs, with very short unjointed beak, the labrum being enclosed within the second HOMOPTERA This sub-order includes the cicads, lantern-flies, frog-hoppers, aphids and scale-insects. The face has such a marked backward slope (see fig. I) as to bring the beak into close contact with the haunches of the fore-legs. The feelers have one or more thickened basal segments, while the remaining segments are slender and thread-like. The fore-wings are sometimes membranous like the hind-wings, usually they are firmer in texture, but they never show the distinct areas that characterize the wings of Heteroptera. When at rest the wings of Homoptera slope roofwise across the back of the insect. In their life-history the Homoptera are more specialized than the Heteroptera; the young insect often differs markedly from its After Weed, Riley and Howard, Insect Life, vol. iii. parent and does not live in the same situations; while in some families there is a passive stage before the last moult. The Cicadidae are for the most part large insects with ample wings; they are distinguished from other Homoptera by the front thighs being thickened and toothed beneath. The broad head carries, in addition to the prominent compound eyes, three simple eyes (ocelli) on the crown, while the feeler consists of a stout basal segment, followed by five slender segments. The female, by means of her serrated ovipositor, lays her eggs in slits cut in the twigs of plants. The young have simple feelers and stout fore-legs (fig. so) adapted for digging; they live underground and feed on the roots of plants- After M. V. Slingerland, Cornell Univ. Ent. Bull. O. From Marlatt, Bult. 14 (N. S.), Div. Ent. U. S. Dept. Agr. maxillae, and the foot in the fore and intermediate leg having but a single segment. The hinder abdominal segments in the male show a curious asymmetrical arrangement, the sixth segment bearing on its upper side a small stalked plate (strigil) of unknown function, furnished with rows of teeth. On account of the reduction and modification of the ,of in the Corixidae, C. Borner has Lately suggested that they should form a special sub-order of Ilemiptera the Sandaliorrhvncha. After Howard, Year Book U. S. Dept. Age., 1894. In the case of a North American species it is known that this larval life lasts for seventeen years. The " song " of the male cicads is notorious and the structures by which it is produced have already been described (see also CICADA). There are about 900 known species, but the family is mostly confined to warm countries; only a single cicad is found in England, and that is restricted to the south. The Fulgoridae and Membracidae are two allied families most of whose members are also natives of hot regions. The Fulgoridas have the head with two ocelli and three segmented feelers; frequently as in the tropical " lantern-flies " (q.v.) the head is prolonged into a conspicuous bladder, or trunk-like process. The Membracidae arc remarkable on account of the backward prolongation of the pronotum
End of Article: HEMIPTERA (Gr. 77µi-, half and IrTep6P, a wing)
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