Sericulture is an agro-based industry. It involves rearing of silkworms for the production of raw silk, which is the yarn obtained out of cocoons spun by certain species of insects. The major activities of sericulture comprises of food-plant cultivation to feed the silkworms which spin silk cocoons and reeling the cocoons for unwinding the silk filament for value added benefits such as processing and weaving.
India is the second largest producer of silk in the world. Among the four varieties of silk produced in 2015-16, Mulberry accounts for 71.8% (20,434 MT), Tasar 9.9% (2,818 MT), Eri 17.8% (5,054 MT) and Muga 0.6% (166 MT) of the total raw silk production of 28,472 MT.
There is no authentic information regarding the origin and use of silk. The ancient literature gives two views. According to one view, silk industry originated for the first time in India at the foot of the Himalayas, and from there it spread to other countries of the world.
Second view, which has greater acceptance, says that this industry originated in China about 3000 B.C. According to this, a Chinese Princess Siling Chi was the first to discover the art of reeling an unbroken filament from a cocoon. This art was kept a close secret for nearly 3000 years. This art later on spread to the rest of the world through several agencies like civil war refugees, war prisoners’ marriage of royal families etc.
Types of Silk(Sericulture):
Moths belonging to families Satumidae and Bombycidae of order lepidoptera and class Insecta produce silk of commerce. There are many species of silk-moth which can produce the silk of commerce, but only few have been exploited by man for the purpose. Mainly four types of silk have been recognised which are secreted by different species of silk worms.
(i) Mulberry Silk(Sericulture):
This silk is supposed to be superior in quality to the other types due to its shining and creamy white colour. It is secreted by the caterpillar of Bombyx mori which feeds on mulberry leaves.
(ii) Tasar Silk (Sericulture):
It is secreted by caterpillars of Antheraea mylitta, A. paphia, A. royeli, A. pernyi, A. proyeli etc. This silk is of coppery colour. They feed on the leaves of Arjun, Asan, Sal, Oak and various other secondary food plants.
(iii) Eri Silk(Sericulture):
It is produced by caterpillars of Attacus ricini which feed on castor leaves. Its colour is also creamy white like mulberry silk, but is less shining than the latter.
(iv) Munga Silk(Sericulture):
It is obtained from caterpillars of Antheraea assama which feeds on Som, Champa and Moyankuri.
Different types of silk and their insects along with their particular food plants are given in the table below:
Out of the four different silk types the two i.e., mulberry and Eri are manufactured from domesticated silkworms, whereas Tasar and Munga silkworms are wild in nature, although attempts are in progress to domesticate them too. The life-cycle of these four types of silk moths are much in common, as they lay eggs, from which caterpillars hatches. They eat, grow and produces cocoon for their protection, then pupate inside cocoon. After sometime moths emerge from the cocoon, male and female mate, lay eggs, and repeat their lifecycles.
The characteristic feature of these silk-producing moths is that they spin a cocoon of silk for the protection of their pupae. The man with his mental superiority has discovered the technique of robbing the silk threads from these cocoons for his own use.
Hatching the Eggs(Sericulture)
The first stage of silk production is the laying of silkworm eggs, in a controlled environment such as an aluminum box, which are then examined to ensure they are free from disease. The female deposits 300 to 400 eggs at a time.
In an area the size of your monitor screen, 100 moths would deposit some 40,000 eggs, each about the size of a pinhead. The female dies almost immediately after depositing the eggs and the male lives only a short time after. The adult possesses rudimentary mouth parts and does not eat during the short period of its mature existence.
The tiny eggs of the silkworm moth are incubated (about 10 days) until they hatch into larvae (caterpillars). At this point, the larva is about a quarter of an inch long.
The Feeding Period(Sericulture)
Once hatched, the larvae are placed under a fine layer of gauze and fed huge amounts of chopped mulberry leaves during which time they shed their skin four times. The larvae may also feed on Osage orange or lettuce. Larvae fed on mulberry leaves produce the very finest silk. The larva will eat 50,000 times its initial weight in plant material.
For about six weeks the silkworm eats almost continually. After growing to its maximum size of about 3 inches at around 6 weeks, it stops eating, changes color, and is about 10,000 times heavier than when it hatched.
The silkworm is now ready to spin a silk cocoon.
spinning the Cocoon(Sericulture)
The silkworm attaches itself to a compartmented frame, twig, tree or shrub in a rearing house to spin a silk cocoon over a 3 to 8 day period. This period is termed pupating.
Silkworms possess a pair of specially modified salivary glands called sericteries, which are used for the production of fibroin – a clear, viscous, proteinaceous fluid that is forced through openings called spinnerets on the mouthpart of the larva.
Liquid secretions from the two large glands in the insect emerge from the spinneret, a single exit tube in the head. The diameter of the spinneret determines the thickness of the silk thread, which is produced as a long, continuous filament. The secretions harden on exposure to the air and form twin filaments composed of fibroin, a protein material. A second pair of glands secretes a gummy binding fluid called sericin which bonds the two filaments together.
Steadily over the next four days, the silkworm rotates its body in a figure-8 movement some 300,000 times, constructing a cocoon and producing about a kilometer of silk filament.
Reeling the Filament(Sericulture)
At this stage, the cocoon is treated with hot air, steam, or boiling water. The silk is then unbound from the cocoon by softening the sericin and then delicately and carefully unwinding, or ‘reeling’ the filaments from 4 – 8 cocoons at once, sometimes with a slight twist, to create a single strand.
As the sericin protects the silk fiber during processing, this is often left in until the yarn or even woven fabric stage. Raw silk is silk that still contains sericin. Once this is washed out (in soap and boiling water), the fabric is left soft, lustrous, and up to 30% lighter. The amount of usable silk in each cocoon is small, and about 2500 silkworms are required to produce a pound of raw silk.
Uses of Silk(Sericulture)
Silk is used for clothing such as shirts, ties, blouses, formal dresses, high fashion clothes, lingerie, pajamas, robes, dress suits, sun dresses and Eastern folk costumes,plain silk, deluxe, satin, chiffon, chinnons, crepe, broacades are made from mulberry silk.
Cosy and soft sky jackets, comforters, sleeping bags, Knitted materials i.e. socks, stocking are made from hand-spun silk.