scale insect

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scale insect,

common name for members of a highly modified group of insects belonging to several families of the superfamily Coccoidea. Scales possess antennae and are characterized by reduced legs. Only the males have wings; females are always wingless. Scales are popularly subdivided into three groups; the armored scales, the unarmored scales, and the mealybugsmealybug,
common name for certain unarmored scale insects that exude a granular white secretion, giving them a mealy appearance. Many are common greenhouse and crop pests. Adult females are wingless, with oval, segmented bodies and well-developed legs.
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. The armored scales secrete a wax covering, the shape of which is characteristic for any given species. Under this coat, the insects develop and feed, sucking the sap of plants with their thin tubular mouthparts. The females never leave the protection of the scale after once forming it, but the adult males, which do not feed, develop a single pair of wings, leave the scale, and seek out the females, fertilizing them after the females are under the shell. Among the important armored scale pests of citrus, other fruits, and ornamentals are the San Jose scaleSan Jose scale,
common name for a scale insect, Aspidiotus perniciosus, introduced from China into San Jose, Calif., c.1870 on nursery stock. The insect has since spread throughout much of the United States and Canada.
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, the oyster scale, the purple scale, and the California and Florida red scales. The unarmored scales (or soft scales) are similar to the armored scales except that only a small amount of wax is secreted, which adheres to the insect. Unarmored scale pests of citrus fruits include the black scale and citricola scale. Mealybugs appear as white cottony clusters on citrus, ornamentals, and greenhouse plants. Like other scale insects, newly hatched nymphs, called crawlers, have legs and actively seek out food. When they find a suitable spot, they settle down to feed. Some scales secrete a resinous covering, which is used in the commercial production of shellac, varnish, and paints (see laclac,
resinous exudation from the bodies of females of a species of scale insect (Tachardia lacca), from which shellac is prepared. India is the chief source of shellac, although some is obtained from other areas in Southeast Asia.
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). Control of scale insects has been largely by use of natural enemies, especially ladybird beetles and small parasitic wasps, which are natural predators of these pests. Scale insects have proved difficult to control by chemical means. Scale insects are classified in the phylum ArthropodaArthropoda
[Gr.,=jointed feet], largest and most diverse animal phylum. The arthropods include crustaceans, insects, centipedes, millipedes, spiders, scorpions, and the extinct trilobites.
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, class Insecta, order Homoptera, superfamily Coccoidea.

Scale Insect

 

the common name for any one of numerous homopterous insects of the suborder Coccoidea, which unites representatives of the families Ortheziidae, Margarodidae, As-terolecaniidae, Pseudococcidae, and Eriococcidae.

Scale insects are tiny sucking insects with marked sexual dimorphism. The males have wings, usually the first pair; the extremities are normally developed, and there are two setae or a tuft of setae at the caudal end of the abdomen. There is no mouth apparatus (the males do not feed in the adult stage). The females are wingless and larva-like and are covered with a waxy coating secreted by numerous glands. The head is fused with the prothorax. The mouth apparatus is a sucking one. In a number of species the legs are reduced or absent. Segmentation of the abdomen is not always marked. Most species lay eggs; some species are viviparous. Fertility is very high; many forms produce two, sometimes as many as four, generations in a year. First-stage larvae (wanderers) actively move over the host plant and may be carried by wind. Upon attaching themselves to a plant, the larvae lose their mobility; after molting, the next-stage larvae again seek a feeding ground. Females have three stages (instars) of larval growth. Males have two additional nonmotile, nonfeeding, nymphal stages. Adult females of some species can actively crawl over the host plant. Prior to egg laying, many forms abandon their feeding ground and disappear from view.

There are more than 1,600 species of scale insects distributed throughout the world; there are about 250 species in the USSR. Scale insects are most numerous in warm climates. Many are pests of fruit, industrial and ornamental crops, and greenhouse plants. Best known are the greenhouse scale (Orthezia insignis), the cottony-cushion scale (Icerya purchasi; a pest of citrus plants, infestation with which necessitates quarantine), the bamboo scale (Antonina crawi), the citrus mealybug (Planoccocus citri), the grape mealybug (Pseudococcus maritimas), the grape scale (Aspidiotus uvae or Eulecanium persicae), the Comstock mealybug (a pest of mulberry), and the olive scale (Parlatoria oleae). Some species secrete beneficial substances that are used in the paint and varnish industry; they include the lac insect and the cochineal insect, which yields the red dye carmine.

REFERENCES

Borkhsenius, N. S. Podotriad chervetsy i shchitovki (Coccoidea). Moscow-Leningrad, 1960. (Fauna SSSR: Nasekomye khobotnye, vol. 8.)
Zhizn’ zhivotnykh, vol. 3. Moscow, 1969.

B. R. STRIGANOVA

scale insect

[′skāl ′in‚sekt]
(invertebrate zoology)
Any of various small, structurally degenerate homopteran insects in the superfamily Coccoidea which resemble scales on the surface of a host plant.
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