Silkworm Moth

silkworm moth

Silkworm larvae (genus Bombyx) feeding on mulberry leaves.

(credit: UPI)

Any moth in the genus Bombyx (family Bombycidae). The Chinese silkworm (B. mori) has been used in commercial silk production for centuries. The adult, which has a wingspan of about 2 in. (50 mm) and a thick, hairy body, lives only two or three days. The female lays 300–500 eggs. The pale, naked larvae are fed mulberry leaves until pupation begins, when they are about 3 in. (75 mm) long. They spin a cocoon of one continuous white or yellow silken thread, about 1,000 yards (900 m) long. The pupa is killed with hot air or steam to preserve the thread intact. See also saturniid moth.

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Silkworm Moth 

(Bombyx morí), a moth of the family Bombycidae. The silkworm moth has a wingspread of 4–6 cm. It has underdeveloped mouth organs and does not feed. The larva feeds on leaves of the mulberry bush or tree; less satisfactory substitutes for mulberry include viper’s-grass, dandelion, Osage orange, and paper mulberry. Various strains of the silkworm moth are univoltine, producing one generation a year, bivoltine (two generations), or polyvoltine (several generations). Incubation lasts ten to 12 days. A diapause occurs during the egg stage. Eggs that enter diapause develop in the spring of the following year, while those that do not undergo diapause develop in the same year. The hatched larva, dark in color and covered with thick hairs, measures approximately 3 mm in length and weighs approximately 0.0004 g. The silkworm passes through five instars divided by four molts. Under normal feeding conditions, at a temperature of 23°–25°C, the larval stage lasts 25–28 days. During that time the silkworm eats 20–25 g of mulberry leaves, 75 percent of them in the fifth instar, by the end of which it weighs approximately 4 g. The silk glands comprise approximately 40 percent of the silkworm’s weight. Mature silkworms do not feed; in the course of three days they spin their cocoons, which are enveloped by a continuous silken strand 1,000–1,500 m in length. On the fourth day of spinning the silkworm is transformed into a pupa. The cocoon weighs 1.7–2.3 g, and the silk covering constitutes 20 to 25 percent of its weight. The cocoons of males contain 20 percent more silk than those of the females. On the tenth day the pupae are transformed into moths, which mate immediately after emerging from the cocoon. The fertilized females deposit 500–700 eggs in two to three days, and ten to 20 days later they die.

The silkworm was domesticated in China circa 3000 B.C. By artificial selection, many strains have been developed; they differ in regard to silk productivity, as well as morphology and physiology. Modern sericulture uses hybrids that are preferred over pure strains, as they yield a higher number of cocoons with a higher quantity of silk and cocoon strands of superior quality. More than 400 hereditary strains of the silkworm have been described. Methods have been devised for eliminating the diapause of the eggs, obtaining polyploid forms, regulating sex, and facilitating reproduction by parthenogenesis and androgenesis. The most serious diseases of the silkworm moth are pébrine, polyhedrosis, flacherie, streptococcosis, and septicemia.

REFERENCES

Poiarkov, E. F. Tutovyi shelkopriad Bombyx mori L. Tashkent, 1929.
Mikhailov, E. N. Shelkovodstvo. Moscow, 1950.
Astaurov, B. L. Tsitogenetika razvitiia tutovogo shelkopriada i ee eksperimental’nyi kontrol’. Moscow, 1968.

V. A. STRUNNIKOV