Silk moth and silk production

The basic knowledge about silk production for industrial purpose

1. SILK MOTH AND SILK PRODUCTION Subham Preetam Master in Biotechnology Email Id: [email protected] Linked in :- www.linkedin.com/in/subham-preetam-97b2b0148 Reserchgate ID:- https://www.researchgate.net/profile/Subham_Preetam2

2. I/ NTRODUCTION Silk fire is protein produced from the silk glands of silkworms. The technique of silk production is known as sericulture. It is an agro industry and is playing an important role in the economic development of silk rearing pockets of rural India providing gainful occupation to 64 lakh persons. One hectare of Mulberry generates employment of about 12 man years and family members ranging in age between 18 to 60 years can engage themselves in various sericulture activities, such as, cultivation of food plants (Mulberry, castor etc., silkworm rearing, egg production, silk reeling, weaving etc. India is the second largest producer of silk in the world after China and has the distinction of producing all the four types of silk i.e. (a) Mulberry silk (91.7%); (b) Tasar silk (1.4%); (c) Eri silk (6.4%); and (d) Muga silk (.5%) which are produced by different species of silkworms

3. TYPES OF SILKWORMS A large number of wild and semi-domesticated silk-moths belong to the family satumiidae . Many of them have been partly cultivated for centuries to produce usable silk in oriental Asia. Muga silkworm :- ( Antheraea assamentsis ). It is a wild and semidomesticated species in Assam, W.Bengal , Bihar and Orisa . Cocoons are amber or white and the caterpillars feed on Machilus , cinnamon, etc. 2. Tussore or Tassah Silkworm ( Antheraea mylitta or A. paphia ). It is found in China , India, and Shri lanka , etc. its caterpillars feed on leaves of fig, oak, ber , sal , etc. cocoons are brown, red or yellow and collected from forestes , as the moths do not breed easily in captivity

4. Oaksilkworm :- a. pernyi of china nand japan, a . roylei of the Himalaya and a. yamamai of japan have been collected and reared for centuries. They produce silk of a fine quality. Giant silkworm :- Attacus atias of India and Malaysia, is nearly the largest of all living insects reaching up to 28 cm in wing span. Eri silkworm :- Attacus rechinii or phlosamia ricinii of S.E. Asia, feeds on castor and produces a rough and strong silk locally known as “ Arandi silk ”.

5. Chinese of mulberry silkworm :- The commonest of all, which produces most of the raw silk we use, is Bombyx mori . It belongs to ithe family Bombycidae . It is found on mulberry leaves in india . Although a native of china, it is almost universally domesticated. It has been reared for so many centuries that it no langer exists in a wild state. By careful selextion and hybridization many races have been developed to meet the various nees of climate, quality and quantity of the silk obtained. The silk obtained from this silkworm is white or yellow in colour.

6. Habits and Habitat Silkworm has been domesticated for so long that it can no longer survive in nature without human care. The original stock probably no longer exists. As a result of domestication for centuries and continued selection for certain qualities, the present day silk moth is far from resembling its ancient ancestors. The adult silk moths con no longer fly due to heavy body and feeble wings. The larvae have lost the capacity to search food, and will starve unless the food is placed right near them. They are reared in domestication on a diet of mulberry leaves. But, the adult moth does not feed during its short span of 4 to 5 days only. Commercial silk is secreted by the silk glands of larvae.

7. External Features Adult silk moth is a medium-sized insect, about 25 mm long and with a wing span of 40-50 mm. body is robust, creamy-white or yellow in colour, and divided into usual 3 regions: head, thorax and abdomen. Head is small and bears a pair of compound eyes, a pair of branched or plumed antennae, and degenerate siphoning mouth parts. Thorax bears 3 pairs of small legs and 2 pairs of large but feeble wings marked by several faint or brown lines. Entire body is covered by minute coloured scales. Abdomen of female is larger and much distended due to great number of eggs it contains.

8. Life History Silkworm is dioecious, i.e., the sexes are separate. Fertilization is internal, preceded by copulation. Development includes a complicated metamorphosis.  

9. Eggs :- Soon after fertilization, each female lays about 300-500 eggs in clusters upon the leaves of mulberry tree. Female covers the eggs bya gelatinous secretion which sticks them to the leaves. Small, smooth and spherical eggs are first yellowish white and become darker later on. After laying, the female does not take food and dies within 4-5 days.

10. Caterpillar larva :- The larva which hatches from egg in about 10 days, is known as the caterpillar. The 1 st instar larva is a tiny creature,about 6 mm long, and moves about in a characteristic looping manner. It has a rough and wrinkled whitish or grayish body, which is made of 12 segments. Its head bears mandibulate mouth parts with which it at-once starts feeding on mulberry leaves and grown very quickly. It can also be fed on lettuce and osage orange ( maclura ) leaves. After 4 or 5 days, it stops feeding and becomes inactive. Moulting or ecdysis then takes place. Its older skin bursts and a new caterpillar emerges out with a new skin and slightly bigger in size than the older caterpillar. It resumes eating voraciously and growing until the skin is again cast off after a week. The larva repeats this process four times.

11. Pupa :- Mature caterpillar stops feeding and returns to a corner among the leaves. Its salivary glands now secrete a sticky fluid through a narrow pore of its spinning apparatus, called spinneret, situated on hypopharynx . The sticky substance urns into a fine, long and solid thread of silk in contact with air. Silk thread is made of 5 filaments stuck t ogether by a gummy substance or sericin , which is secreted by two other glands. It becomes wrapped around the body of caterpillar forming a pulal case or covering known as cocoon. This process goes on for about 3-4 days, at the end of which the silkworm is enclosed within a thick, oval, white or yellow silken cocoon. A single caterpillar is said to produce nearly 1000-1500 meters of silk thread in this manner. Within a fortnight the silkworm transforms inside, cocoon info a tubular brownish organism, the pupa or chrysalis.

12. Imago :- A active metamorphic changes take place during pupation. Unregimented abdominal prologs disappear, while thorax develops two pairs of wings. The pupa finally metamorphoses into the baby insect or imago. It secretes an alkaline fluid to moisten one end of cocoon and then escapes by forcing its way out of the softened silk. Soon after emergence the male and female moths mate, lay eggs and die within 3 to 4 days.  

13. SILK PRODUCTION Commercial silk is secreted by the silk glands (salivary glands) of larval silkworms. The rearing of silkworms for the production of raw silk is known as sericulture. It is an industry in a few countries including I ndia .   Historical:- Silk was manufactured for the first time probably in China, about 3500 B.C It was introduced in Europe in 552 A.D. today, sericulture is an important industry of several Asian and European countries, but China and Japan are the only great producers of raw silk .

14. Sericulture industry (Management) The major steps and requirements of sericulture industry are briefly as follows :- Requirements and appliances :- The prime requirement for commercial production of good silk, are genetically improved races of Bombyx mori , keeping in view the climatic conditions of the region. Another need of the industry is the plantation of good nutritive varieties of mulberry for a continuous supply of their leaves for feeding the larvae.

15. Grainage management : - Maintenance of good quality races of silkworms and the supply of good quality seeds to readers is known as grain age management. Soon after emergence, the males and females are segregated before they can mate . Females of one lot are later kept with males of another lot for mating and they die soon after laying eggs. The eggs, now known as “seeds” are kept in sterilized trays at 4 c and moved periodically with feather to ensure 100 per cent hatching. The seeds are kept in diapauses and their hatching time is artificially coincided with the best season of mulberry. The readers are provided with either seeds or the 2 nd instars larvae, depending on their knowledge and managing capacity for obtaining good quality cocoons.

16. Stiffing.:- For obtaining the commercial silk the cocoons are treated with hot water or placed in a hot oven to kill the pupae inside. If allowed to hatch, they would cut the silk threads in emerging. This process of killing the cocoons is called stifling in the industry.

17. Reeling and spinning. :- Removal of silk thread from cocoons is termed reeling. After boiling, the cocoons become soft and their fibre become loose so that they can be easily unwoven or reeled off. Each cocoon is made of a single fibre . A single cocoon yields 1,000 to 1,500 meters of unbroken silk fibre . 454 gm of silk is obtained from about 25,000 cocoons. A few alive cocoons are kept as “seeds” for the next crop. 4 or 5 silk fibers are passed through eyelets of wooden guides and twisted into one thread. It is wound round a large wheel and later transferred to spools. This is called raw silk or reeled silk. For achieving its characteristic luster, raw silk is again boiled, purified by acid or by fermentation, and thoroughly washed. Several such silk threads are twisted to get fibre silk, through the process known as spinning. The damaged cocoons and waste treads are also teased and spun into threads, called spun silk.

18. Diseases of silkworm :- The caterpillars of silkworm are subject to a severe hereditary disease, known as pebrine . It is caused by a protozoan parasite ( Nosema bombycis ) which is transmitted through the eggs. The examination of the blood of females and avoiding the eggs containing the parasite. Caterpillars are also subject to parasitism by certain tachina flies, which lay their eggs upon mulberry leaves and thus get inside the body of caterpillars through their alimentary canal.    

19. Sericulture in india Sericulture is unique and profitable in many ways, in india . It provides larger opportunities to unskilled labor at the minimum cost.l Even the old and handicapped members of a family can be employed gainfully. It requires a small capital investment of a few hundred rupees and the returns are quick and adequate.

20. Besides I ndia , other natural silk producing countries are japan, china, south korea and U.S.S.R.india is the onlycountry producing all the four commercial varieties of natural silk . Production of mulberrysilk is confined to karnatak , west Bengal, jammu and Kashmir, Andhra Pradesh and tamil nadu . India is fifth in the world production of mulberry silk. The major tasar silk producing centres are in B ihar , Madhya Pradesh, Orissa and west Bengal. India is second in the world production of tasar silk . The bulk of e ri silk is produced in Assam which also holds the virtual monopoly over the world muga silk production . The states of Manipur, assam , Nagaland, uttar Pradesh, arunachal Pradesh, Meghalaya and Mizoram are producing a new variety of tassar known as oak tassar

21. Problems :- At present, the Indian silk industry faces many problems of productivity, marketing and finance. Per hectare yield and quality of raw silk are poor in comparison to other major silk producing countries. The central silk research institute, Mysore is dealing with these problems,. The Karnataka Government has also taken various steps to improve silk production and quality.

22. Silk has following peculiar properties: - Natural colour of Mulberry silk is white , yellow or yellowish green; that of Tasar brown; of Muga , light brown or golden; and of Eri , brick red or creamy white or light brown. Silk has all desirable qualities of textile fibres , viz. strength, elasticity, softness, coolness, and affinity to dyes. The silk fibre is exceptionally strong having a breaking strength of 65,000-lbs/sq. inch. Silk fibre can elongate 20% of original length before breaking. Density is 1.3-1.37g/cm 3 . Natural silk is hygroscopic and gains moisture up to 11%. Silk is poor conductor of heat and electricity. However, under friction, it produces static electricity. Silk is sensitive to light and UV- rays

23. . Use of silk : Silk is used in the manufacture of following articles: Garments in various weaves like plain, crepe, georgette and velvet. Knitted goods such as vests, gloves, socks, stockings. Silk is dyed and printed to prepare ornamented fabrics for saries , ghagras , lehengas and dupattas . Jackets , shawls and wrappers. Caps , handkerchiefs, scarves, dhotis, turbans. Quilts , bedcovers, cushions, table-cloths and curtains generally from Eri -silk or spun silk. Parachutes and parachute cords. Fishing lines. Sieve for flour mills. insulation coil for electric and telephone wire. Tyres of racing cars. Artillery gunpowder. Surgical sutures.

24. THANKS AND REGARDS SUBHAM PREETAM BIOTECHNOLOGIST, ITER, SOA UNIVERSITY