Rearing Techniques of Mulberry Silk Worm
The silkworm can be reared in places where the temperature ranges from 25 ̊ to 30 ̊ C and humidity from 70 to 80 percent.
1. The fertilized moth is covered with an inverted funnel and eggs are allowed to be laid over a cardboard.
2. The egg masses are brushed with a fine brush to remove any parasites and to obtain an uniform hatch.
3. In a bamboo tray paddy husk is spread and very tender chopped mulberry leaves are added to tray and the hatched out larvae are transferred to the leaves.
4. The leaves are changed every two or three hours during the first two or three days.
5. From fourth day, the caterpillars are given clean full leaves.
6. A net of small mesh is placed over the tray and the leaves are placed over this. The caterpillars crawl through the net to the fresh leaves. After one or two hours the net is taken and placed in another tray.
7. The unused leaves and the voids in the former trays are thrown out.
8. The feeding trays are cleaned at frequent intervals.
9. Full grown caterpillars are spread in a regular order about 8 cm apart in the Chandrika and are allowed to pupate.
10. The cocoon is constructed of a single reel able thread of silk. If the moths are allowed to emerge from the cocoons the silk thread is cut into pieces during the process. Therefore, the pupae are killed two or three days before the emergence of moths by exposing them to sun for two or three days, by passing steam or hot air over them or by fumigating with a chemical. This is known as stifling.
11. The stifled cocoons are dried and the loose outer floss is removed by brushing.
12. They are then soaked in warm water to soften the gum that binds the silk threads.
13. Threads from four to five cocoons are put in a spool of reeling machine and made to a single thread of sufficient thickness to form the raw silk. About 50 to 60 percent of the silk of the cocoon is reel able and it forms the raw silk and the rest is formed into waste silk.
14. Raw silk is boiled, steamed, stretched, purified by acid and washed twice or thrice to remove the gum and to bring out the characteristic and much cherish luster.
15. The cocoons required for further rearing are kept separately and moths are slowed to emerge from them.
The consumption of leaves by the caterpillars increases with their age from about 0.1 gram per day per caterpillar during the first stage to 5 gram during the last stage and the total consumption during the entire larval life of a caterpillar is about 90 grams.
A dry cocoon weighs of about the gram and is about two-third weight of a green cocoon. The chrysalides form 60 percent and the silk matter 40 percent of the weight of the cocoon. It has been estimated that about 60,000 cocoons yield a kilogram of raw silk and they require about a ton of mulberry leaves.
A good cocoon should be round, firm and silvery white in colour. It should have a comparatively large proportion of reel able silk and it should have been spun by a caterpillar, which does not consume very large quantities of leaves.