Rearing of silkwormsSelected healthy silk moths are allowed to mate for 4 hours. Female moth is then kept in a dark plastic bed. it lays about 400 eggs in one day, the female is taken out and is crushed and examined for any disease. they select only the certified disease- free eggs are reared for industrial purpose. The eggs are been hatched in an incubator.
The hatched larvae are kept in trays inside a rearing house at a temperature of about 20°C-25°C . These are first fed on chopped mulberry leaves. After 4-5 days fresh leaves are provided. As the larvae fully grow, they are transferred to fresh leaves on clean trays, when fully grown they spin into cocoons.
The cocoon
The cocoon is formed from a secretion from two large
silk glands also called as actually the salivary glands which extend
along the inside of the its body and open through a common duct on the
lower lip of the mouthparts. The larva moves the head from one side
another side very rapidly (about 65 times per minute) throwing out the
secretion of the silk glands in the form of a thin thread. The secretion
is the clear viscous fluid, when it exposure to the air gets hardened
into the fine silk fibre.
The filament forming from a cocoon is continuos and ranges in length from 700-1100 metres.
The
cocoons from which moths have emerged are called pierced cocoons. These
are of low value because continuous thread cannot be obtained. Pieces
are removed by instruments and spun into a thread.
Reeling silk
The cocoons are cooked in hot water and the silk fibre is unwound from the cocoons. This process is called as reeling. silk consists of two proteins the inner core is fibroin and an outer cover of sericin. There are four following steps for the completion of the process of reeling:
To the reeling silk the cocoons are gathered about 8 days after spinning had begun.
•
The cocoons are first treated by steam or dry heat to kill the insect inside. This is necessary to prevent the destruction of the continuous fibre by the emergence of the moth.
•
Next, the cocoons are soaked in hot water (95° -97°C) for 10-15 minutes to soften the gum that binds the silk threads together.We called This process ascooking.
•
The "cooked" cocoons are kept in hot water and the loose ends of the thread are caught by hand.
•
Threads from several cocoons are wound together on wheels ("charakhas") to form the reels of raw silk (Fig. 35.5).
we can reed Only about one-half of the silk of each cocoon .the remainder is used as a silk waste and formed into spun silk.
Raw silk thus obtained the is processed through several treatments to give it the final shape.
Non-mulberry "silks"
1.
Tasar silk is produced by certain species of another moth Antherea royeli. Their larvae are reared on Arjun trees, chiefly in Bihar state, Madhya Pradesh and West Bengal.
2.
Muga silk is obtained from Antherea assama whose larvae are reared on " Som" and " soalu" trees in Brahmaputra Valley.
3.
Eri silk is produced by the moth Philosamia ricini whose larvae feed on castor leaves. It is mainly produced in Assam in india
Main properties of silk
1. It is lustrous, soft and strong.
2. It is made of two proteins : the inner core is fibroin and an outer cover is sericin
3. It is hard wearing.
4. It can be dyed into several colours
Silk
moth Bombyx mori is at present fully domesticated. It no longer exists
in a wild state and it cannot survive without the human care.
Silk Producing States of India
Major States in india producing mulberry silk are: Karnataka West Bengal Jammu and Kashmir