THRIPS


Meaning of THRIPS in English

plural thrips, any member of the order Thysanoptera, among the smallest of the winged insects. They are abundant in the tropical and temperate regions of the world. Approximately 5,000 species have been described. Thrips have an economic importance, for some species transmit plant viruses, and by their feeding they reduce seed production, disfigure flowers and fruits, and damage plant leaves. In warm areas a number of them cause plant galls and leaf rolls. On the other hand, a few species prey on destructive mites and scale insects, and a number may aid in the pollination of flowers and, indirectly, in the formation of leaf mold. Most thrips are 1.5 to 3 millimetres in size, with the smallest being about 0.6 millimetre and the largest about 15 millimetres. Because of their minute size they can enter the smallest flowers or tiniest cracks in stems and bark. Their wings, when present, are narrow and fringed, hence the name Thysanoptera (Latin, fringed wings). Despite their Lilliputian size, thrips are often elaborately ornamented with hexagonal designs, spines, or body flanges. The bristles (setae) of some are expanded at the tips or elongated, or the body wall may be expanded into prongs or forks. The larvae of thrips tend toward bright colours (red, orange, or yellow); the adults range from whitish to browns or black. Adults have extensible bladders on the tarsi of the legs, as suggested by the common name bladder feet. ( (singular), ) plural Thrips, a member of one of some 5,000 species of tiny winged insects, of the order Thysanoptera, that feed chiefly on plants. Thrips are well known to the gardener as pests, for grasshopper thrips, pear thrips, orange thrips, and onion thrips are destructive to cultivated plants, while other types of thrips are transmitters of viral diseases to tomatoes, pineapples, beans, sugar cane, and other plants. Thysanoptera are among the smallest of all insects; most range from 0.5 to 3 millimetres (0.02 to 0.12 inch) in length, although a few are as much as 15 millimetres (0.6 inch) long. They are distinguished by their long and narrow wings (although not all species possess them), which have fringes of tiny hairs. Thrips are distributed throughout the tropical and temperate zones of the world. They are often found on the leaves and blossoms of plants and flowers. Most feed on the sap of plants and ferns, sucking the sap out with the aid of their specialized mouth structures. A few are predators; one species ingests spores instead of sap, and another has been reported to ingest human blood on occasion. Some feed on only one type of plant, while others feed on many types. The evolution of thrips is poorly recorded. Specimens have been found preserved in amber dating from the Oligocene Epoch (12,000,000 to 38,000,000 years ago) and for one family from the Cretaceous Period (71,000,000 to 136,000,000 years ago). The bodies of thrips are slender and elongated and often exhibit elaborate designs, spines, or bristles. The body is composed of head, thorax, and abdomen. The head is quadrangular and contains the eyes, antennae, and mouth. The compound eyes are small but prominent, while the antennae are usually longer than the head and have four to nine segments. The mouth is asymmetrical, lacking a right mandible. It is midway in structure between the biting and piercing mouth of a predator and a sucking mouth. The two pairs of wings and three pairs of legs are borne on the thorax. Some species, and particularly the male of some species, have lost their wings entirely. The legs are equipped with protrusible bladders that aid in climbing. The abdomen has 10 segments and is elongated and tapered. The females of some species have a sawlike ovipositor (an egg-laying organ) with which they cut into the outer tissues of plants to deposit their eggs. In other species the females lack an ovipositor and lay their eggs in secluded places. In a few species the eggs hatch inside the body of the female. Parthenogenesis, reproduction without fertilization by males, is occasionally observed. After the bean-shaped eggs are laid, they hatch in 3 to 16 days. The young resemble the adults in general form, although their heads are disproportionately large and their bodies are more richly coloured. The young pass through two larval stages, when they are pale and soft-skinned. The pupal forms shelter themselves in the soil or in decaying matter before molting into adults. Thrips are of economic interest primarily because they are often destructive to commercially grown plants. The damage inflicted by thrips infestation may range from disfigurement to the spread of disease. Thrips may help in the control of certain insects and in pollinating certain types of flowers, but how large a role they play is not known. Other insects, reptiles, and birds prey on Thysanoptera, but the largest toll is probably taken by wind, dust, and rainstorms. Additional reading The literature on Thysanoptera is widely scattered throughout numerous entomological journals with occasional summaries given in monographs or lists. The monographs are predominantly faunal studies, though they often include regional revisions of some of the taxa. Only a few complete generic revisions have been published. Some of the latest, though not necessarily recent, faunal monographs are S.F. Bailey, The Thrips of California, Part 1: Suborder Terebrantia, Bull. Calif. Insect Surv., vol. 4, no. 5, pp. 143220 (1957); H.E. Cott, Systematics of the Suborder Tubulifera (Thysanoptera) in California (1956); L.J. Stannard, The Thrips, or Thysanoptera, of Illinois, Bull. Ill. Nat. Hist. Surv., vol. 29, no. 4, pp. 215552 (1968); G.D. Morison, Thysanoptera of the London Area, Lond. Nat., reprint no. 59 (194749). Two comprehensive catalogs and annotated synopses are C.F. Jacot-Guillarmod, Catalogue of the Thysanoptera of the World (Part 1), Ann. Cape Provincial Museums (Nat. Hist.) (1970); and L.J. Stannard, The Phylogeny and Classification of the North American Genera of the Suborder Tubulifera (Thysanoptera) (1957). Proposals for the classification of the thrips that have received general acceptance are those by H. Priesner, Zur Vergleichender Morphologie des Endothorax der Thysanoptera, Zool. Anz., vol. 159, no. 78, pp. 159167 (1957), and Das System der Tubulifera (Thysanoptera), Anz. st. Akad. Wiss., 13:283296 (1960). Morphological treatments of the Thysanoptera are found in R.G. Davies, Observations on the Morphology of the Head and Mouthparts in the Thysanoptera, Proc. R. Ent. Soc. Lond. (A), vol. 33, no. 79, pp. 97106 (1958); and P. Pesson, Ordre des Thysanoptera, in P. Grasse, Trait de zoologie, vol. 10, no. 2, pp. 18051869 (1951). A source of ecological information on thrips is that by L. Cederholm, Ecological Studies on Thysanoptera (1963). Lewis Judson Stannard, Jr.

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