Bombyx mori, commonly known as the domestic silk moth, is a domesticated moth species belonging to the family Bombycidae. It is the closest relative of Bombyx mandarina, the wild silk moth. Silkworms are the larvae of silk moths. The silkworm is of particular economic value, being a primary producer of silk. The silkworm's preferred food are the leaves of white mulberry, though they may eat other species of mulberry, and even leaves of other plants. Domestic silk moths are entirely dependent on humans for reproduction, as a result of millennia of selective breeding. Wild silk moths, which are other species of Bombyx, are not as commercially viable in the production of silk. Sericulture, the practice of breeding silk moths for the production of raw silk, has existed for at least 5,000 years in China, whence it spread to India, Korea, Nepal, Japan, and then the West. The conventional process of sericulture kills the silkworm in the pupal stage. The domestic silk moth was domesticated from the wild silk moth Bombyx mandarina, which has a range from northern India to northern China, Korea, Japan, and the far eastern regions of Russia. The domestic silk moth derives from Chinese rather than Japanese or Korean stock. Silk moths were unlikely to have been domestically bred before the Neolithic period. Before then, the tools to manufacture quantities of silk thread had not been developed. The domesticated Bombyx mori and the wild Bombyx mandarina can still breed and sometimes produce hybrids. It is unknown if B. mori can hybridize with other Bombyx species. Compared to most members in the genus Bombyx, domestic silk moths have lost their coloration as well as their ability to fly.
Types Mulberry silk moths can be divided into three major categories based on seasonal brood frequency. Univoltine silk moths produce only one brood a season, and they are generally found in and around Europe. Univoltine eggs must hibernate through the winter, ultimately cross-fertilizing in spring. Bivoltine varieties are normally found in East Asia, and their accelerated breeding process is made possible by warmer climates. In addition, there are polyvoltine silk moths found only in the tropics. Their eggs typically hatch within 9 to 12 days, meaning there can be up to eight generations of larvae throughout the year. Mulberry silkworms are highly sensitive to environmental variables, and diapause - a physiological arrest in development - can be significantly influenced by photoperiod, temperature and humidity. Recent studies have reported the occurrence of non-diapause eggs in bivoltine races, indicating a more flexible diapause expression than previously understood.
Description and life cycle
Larvae (silkworms) Eggs take about 14 days to hatch into larvae. Larvae have a preference for white mulberry, having an attraction to the mulberry odorant cis-jasmone. There are five instars before pupation. The silkworm is essentially monophagous, exclusively eating mulberry leaves (Morus spp.). By developing techniques for using artificial diets, the amino acids needed for development are known.
Pupae (cocoon) After they have molted four times, their bodies become slightly yellow, and the skin becomes tighter. The larvae then prepare to enter the pupal phase of their life cycle, and enclose themselves in a cocoon made up of raw silk produced by the salivary glands. The final molt from larva to pupa takes place within the cocoon, which provides a layer of protection during the vulnerable, almost motionless pupal state. Many other Lepidoptera produce cocoons, but only a few — the Bombycidae, in particular the genus Bombyx, and the Saturniidae, in particular the genus Antheraea — have been exploited for fabric production. The cocoon is made of a thread of raw silk from 300 to about 900 metres (1,000 to about 3,000 ft) long. The fibers are fine and lustrous, about 10 μm in diameter. The number of cocoons required to produce a final yield of silk is approximately 4,000–7,000 per kilogram (2,000–3,000/lb); at least 32 million kilograms (70 million pounds) of raw silk are produced each year, requiring nearly 10 billion cocoons. If the animal survives through the pupal phase of its life cycle, it releases proteolytic enzymes to make a hole in the cocoon so it can emerge as an adult moth. These enzymes are destructive to the silk and can cause the silk fibers to break down from over a mile in length to segments of random length, which reduces the value of the silk threads, although these damaged silk cocoons are still used as "stuffing" available in China and elsewhere in the production of duvets, jackets, and other purposes. To prevent this, silkworm cocoons are boiled in water. The heat kills the silkworms, and the water makes the cocoons easier to unravel. Often, the silkworm is eaten. As the process of harvesting the silk from the cocoon kills the pupa, sericulture has been criticized by animal welfare and rights activists. Mahatma Gandhi was critical of silk production based on the ahimsa philosophy "not to hurt any living thing". This led to Gandhi's promotion of cotton spinning machines, an example of which can be seen at the Gandhi Institute, and an extension of this principle has led to the modern production practice known as Ahimsa silk, which is wild silk (from wild and semiwild silk moths) made from the cocoons of moths that are allowed to emerge before the silk is harvested.
Moth The moth is the adult phase of the silk worm's life cycle. Silk moths have a wingspan of 3–5 cm (1–2 in) and a white, hairy body. Females are about two to three times bulkier than males (due to carrying many eggs). All adult Bombycidae moths have reduced mouthparts and do not feed. The wings of the silk moth develop from larval imaginal disks. The moth is not capable of functional flight, in contrast to the wild B. mandarina and other Bombyx species, whose males fly to meet females. Some may emerge with the ability to lift off and stay airborne, but sustained flight cannot be achieved as their bodies are too big and heavy for their small wings.
The legs of the silk moth develop from the silkworm's larval (thoracic) legs. Developmental genes like Distalless and extradenticle have been used to mark leg development. In addition, removing specific segments of the thoracic legs at different ages of the larva resulted in the adult silk moth not developing the corresponding adult leg segments.
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