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fine, horny, translucent, yellowish fiber produced by the silkworm in making its cocoon and covered with sericin, a protein. Many varieties of silk-spinning worms and insects are known, but the silkworm of commerce is the larva of the Bombyx mori,
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name for the larva of various species of moths, indigenous to Asia and Africa but now domesticated and raised for silk production throughout most of the temperate zone. The culture of silkworms is called sericulture.
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a branch of agriculture, the raising of silkworms for their cocoons, which are the raw materials used in the manufacture of silk. In the USSR the domesticated Asiatic silkworm moth Bombyx mori is cultivated; other countries also use the cocoons of some wild silkworms (Antheraea pernyi, Philosamia cynthia, and Philosamia ricini). The raising of Asiatic silkworm moths to obtain silk began about 5,000 years ago in China. In the territory of what is now the USSR, sericulture developed in Middle Asia and Transcaucasia between the fifth and seventh centuries. In Russia silkworm raising was mainly concentrated in the households of peasants; the facilities were usually not large, producing 10–15 g of silkworm eggs.
The first large-scale specialized sericultural sovkhozes were established in the USSR. State silkworm egg farms, centers for the primary processing of cocoons, and silk-reeling factories have also been built, and state and kolkhoz silkworm farms have been organized. A unified state system has been created for breeding and pedigree work and for the procurement and primary processing of cocoons. Soviet scientists have developed highly productive white-cocoon breeds and hybrids of silkworms and highly productive varieties of mulberry trees; more effective methods for cultivating the trees have also been developed. Such efforts have resulted in an average yield of 56–57 kg of cocoons per box of silkworm eggs containing 29 g of eggs. Cocoon production was 34,800 tons in 1965 and 45,000 tons in 1976. The production of raw silk totaled 2,600 tons in 1965 and 3,400 tons in 1976.
Production processes in sericulture include cultivation of mulberries, the leaves of which are the only food for the larvae of the silkworm moth (seeMULBERRY CULTIVATION); production of silkworm eggs (seeSILKWORM EGG FARMING); incubation and hatching of the eggs; rearing of the silkworms; and primary processing of cocoons, including killing and drying.
Incubation takes place in incubators having a capacity of 150–200 boxes of silkworm eggs. It is timed to coincide with the appearance of the first five-six leaves on the mulberry trees. The hardiest larvae obtained in the course of the first three days of hatching are kept for rearing. The silkworms are reared in special breeding houses, where a constant temperature and humidity are maintained according to the age of the silkworms. Larvae in the first three stages of growth are fed chopped leaves and young shoots. An average of 17–18 kg of leaves is needed to produce a 1 kg cocoon; 11–12 kg of leaves suffices on the best-run farms. Feeding is halted during the periods of sleep and molting, and the temperature is raised somewhat. Rearing is completed in approximately 35 days; the best-run farms complete rearing in 22–25 days. The majority of the cocoons are obtained from the spring generation. On some farms in the Ukraine, Moldavia, and the Northern Caucasus, several generations are reared by using the silkworm eggs of the hardiest varieties and hybrids and by planting the mulberries so that they produce young leaves during the period from summer to fall.
The aim of selective breeding in sericulture is the development of new, highly productive varieties. A notable achievement in the selective breeding of silkworms has been the genetic development of varieties that, when crossed, lay viable eggs of only the male sex. The males produce cocoons with more silk, and such an advance eliminates the labor-intensive operation of sorting out female eggs. Of crucial importance in the development of sericultural selective breeding were the works of B. L. Astaurov on the regulation of sex and the development of polyploid strains of silkworms, the introduction of commercial hybridization, and the use of the biological effects of thermal shock to disinfect live silkworm eggs infected with the pathogenic organism of pébrine (Nosema bombycis). Research in selective breeding is conducted at the Middle Asia Scientific Research Institute of Sericulture in Tashkent, the Azerbaijan Scientific Research Institute of Sericulture in Kirovabad, the Georgian Agricultural Institute, various institutes of the academies of sciences of the USSR and of the Union republics, and test stations. Sericultural stations or the corresponding shops on silkworm egg farms are responsible for increasing the number of silkworm varieties and improving their economic characteristics.
World production of silkworm cocoons totaled 438,700 tons in 1938 and 270,000 tons in 1974. Other major producers include Japan (106,000 tons in 1974), China (90,000 tons), and India (30,000 tons). Sericulture is also developed in Korea, Indochina, southern Europe, and Brazil.
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Miliaev, A. P. Spravochnik po shelkovodstvu, Moscow, 1960.
Astaurov, B. L. Tsitogenetika razvitiia tutovogo shelkopriada i ee eksperimental’nyi kontrol’. Moscow, 1968.
Uchebnaia kniga shelkovoda, 2nd ed. Moscow, 1973.
S. D. LAVRENTEV