SILKWORMS I) Silk is a valuable natural protein fibre produced by certain insects. Various insects, like Lepidoptera in their larval stages and wasps in their adult stages, produce silk as secretion from their salivary glands, Embioptera from tarsal glands, certain Coleopteran and Neuropteran from Malpighian tubules, and spiders and certain mites from their anal glands for making webs. The silk is used for construction of cocoons over the pupae, for making webs or silken tunnels for protected living under their cover, or for making nests by binding leaves and earth particles. Among insects, caterpillars of Bombycidae and Saturnidae are the important silk producers. However, silk is commercially produced employing the mulberry silkworm and the Eri silkworm. The silkworms of lesser importance are the Tasar silkworm and the Muga silkworm. The Chinese started sericulture, or the science of raising silkworms. Though the discovery of the usefulness of silk is credited to Lotzu, the Empress of K wang- Ti as early as about 2687 B.C. It is being produced by the Chinese. India has the unique distinction of producing all the four commercial varieties of natural silk viz. mulberry, tasar, eri and muga. Even now Asia holds the monopoly in silk production, producing about 95 per cent of the world's total output; of this 60 per cent is produced by Japan, 15 per cent by China, 5 per cent by Manichiura and only 1.5 per cent by India. Pure silk is produced by Bombyx mori on mulberry leaves, while the other varieties of silk are produced Antheraea mylilta Drury, A. assamensis Helfer and Samia cynthia Drury, yielding Tasar, Muga and Eri silks respectively. Besides these the hybrid strain evolved as a result of cross-breeding of a Chinese species Antheraea pernyi with A. proylei, produces Oak Tasar silk II) MULBERRY SILKWORM, Bombyx mori It belongs to the family Bombycid. It is a totally domesticated insect and is never found in a wild state. It is the most important of all the silkworms and is extensively reared in many countries. In India it is cultivated on mulberry in Assam, Bihar, Jammu & Kashmir, Punjab, West Bengal, Orissa, Madhya Pradesh, Maharashtra, Karnataka and Tamil Nadu. Depending upon the number of generations per year, these silkworms are classified as univoltine, bivoltine and poly or multivotine races. The univoltine race has a single generation a year spending the remaining period of the year under hibernation as eggs, and the others have two or more generations a year. Univoltine race is found in Europe, Kashmir and Punjab and the silk produced is of superior quality and the multivoltine race is found in South India, Assam and Bengal producing an inferior quality of silk. Biology : Adult moth is cream in colour, about 2.5 cm long and sluggish. It lives for two or three days only. Mating takes place immediately after emergence. Each female moth lays about 300 to 400 brownish white seed-like eggs in masses. Hatching takes place in 8- 12 days. The caterpillars on hatching are about 3 mm long and dark in colour; they moult four times. The full grown caterpillar is elongate, about 5 ern long, cylindrical, yellowish white in colour with a small anal horn. Larval period extends from 28 to 30 days. It produces a long continous strand of silk to form an oval cocoon and takes about one or two days for constructing the same. Pupation takes place inside the cocoon and adult emerges in 10-12 days. Life cycle is completed in six to eight weeks. Silkworm Races: The Central Silk Board (CSB) has brought out a system of 'authorisation of silkworm races’. Test rearings are done twice a year at 14 centres in the country and silkworm hybrids authorised by CSB are exploited commercially in sericulture. Mulberry silkworm hybrids for different states such as Andhra Pradesh, Assam, Bihar, Madhya Pradesh, Orissa, West Bengal, Jammu & Kashmir and Uttar Pradesh have been identified. In India, over 95% of commercial silk being produced is from multivoltine female x bivoltine male parent (cross breed). The hybrid BL23 x NB4D2 is meant for rainfed areas in Karnataka and BL24 x NB4D2 is for irrigated areas in all seasons. Rearing package for the above has been developed by Central Sericultural Research & Training Institute, Mysore (CSR & TI) initiated breeding work for production of quality silk utilising two Japanese commercial hybrids, which resulted in the evolution of highly productive CSR breeds. THE ERI SILKWORM, Samia cynthia ricini Boisduval This belongs to the family Saturniidae. The adult moth is stout and dark and the wings darkish brown and white. It lays 120-200 eggs in clusters which hatch in 7-10 days. The caterpillar has a green body with a brown head and the body has small tubercles bearing short hairs. The full-grown caterpillar is 8 cm long and the larval stage lasts for 17-25 days. The caterpillars feed on castor leaves. It can pupate anywhere so no chandraki is necessary. The cocoon is not compact but loosely spun. Silk is white or brick- red in colour and not as glossy as the mulberry silk. It is not in one single strand, therefore, not reelable and has to be carded and spur like cotton. Since the thread is not a continuous one, the moths can be allowed to emerge from the cocoon~ and after emergence the cocoons are reversed to remove the pupal cases. The cocoons are then soaked In cold water for 18 hours, in warm water for 45 minutes, washed in washing soda solution, dried and spun into silk. Twenty eight grams of eggs will give about 1600 larvae which can yield 4 kg of silk after consuming leaves from about 0.5 hectare of castor crop. These silkworms are commonly reared in Assam and West Bengal and can be successful in all places with good rainfall and warm climate like Kerala and where castor is grown. They cannot withstand severe summer. c. THE TROPICALTASAR SILKWORM, Antheraea mylitta Drury At present 0.56 million hectares of forest is covered with tasar silk production while an estimated 11.16 million hectares of forest land has been identified as eligible for cultivating tasar silkworm. Madhya Pradesh, Orissa, Andhra Pradesh, Maharashtra, Bihar, Karnataka and West Bengal have the food plants capable of breeding tasar silkworm. This is also a saturniid moth usually found in forest areas feeding on Dalbergia, Shorea, Terminalia, Zizyphus, Ficus, etc., but the more important hosts are Shorea and Zizyphus mauritiana. Eggs are laid on tender leaves of the host trees and a moth lays about 200 eggs; egg stage lasts for 8 to 10 days. The caterpillars are stout, green with red spiracles, and the larval period is 35 - 70 days. Pupal period is 25-50 days. The moths do not mate in captivity and so the caterpillars cannot be domesticated. The silk is reelable unlike that of the eri silkworm and, therefore, the pupae have to be killed before emergence of the moth, to prevent cutting of the silk thread into pieces. THE MUGA SILKWORM, Antheraea assamensis Helfer The Muga silk moth, restricted to the north eastern states, particularly Assam, is semi domesticated and multivoltine, producing a many as five to six broods in a year. The period of the life cycle may prolong from nearly 1 to 2 months in summer to about 3 months in winter. The larvae on hatching are yellowish, but as they grow they turn to translucent green. On maturity the larvae come to the tree trunk early morning for cocoon formation, and thus can be easily collected unlike the Antheraea mylitta. The cocoons are light to deep brown, but white is not uncommon. Males are reddish pink, females lighter. The oak tasar silkworm is the temperate tasar silkworm represented by Antheraea yamamai, A. roylei and A. pernyi respectively, in Japan, India and China. III) Silkworms as food This silkworm (Bombyx mori) is food to reptiles and amphibians. Silkworms are a nutritious part of any reptile’s diet. Silkworms make tasty treats for any reptile because it is slow moving and comes in all different sizes. The worms in their second instar, are large enough to be fed to reptiles and amphibians. Silkworms contain less fat then most feeders, and they contain much more calcium which is good for reptiles. IV) Cultivation of mulberry plants: Mulberry plants come up in any soil and in any climate. It is propagated by cuttings. The land is ploughed well six or seven times in April-May and manured with cattle manure at the rate of 20-25 tonnes per hectare. Furrows are opened a metre apart either way and at the junctions small pits are scooped out and 2 or 3 cuttings are planted in each pit. Each cutting should be 20 to 22 cm long with three nodes. When the plants grow too high, they are cut back and this will also help in the production of new flush or leaves. The plants can yield well for 12 years after which they are pulled out and fresh planting taken up. From the plants each year six to eight crops of leaves are taken and the average yield per hectare is 25 to 30 metric tonnes of green leaves. Accessories required for successful rearing of silkworm are: i) A bamboo rack to keep the trays containing the various stages of the insect; the racks should have ant pans at the base of the stands; ii) Many circular trays made of split bamboo for leaving the worms; iii) Many bamboo baskets for fetching mulberry leaves; iv) Chopping knife for cutting leaves; and v) Chandraki or cocoonage which is a circular basket with a spiral wall about five cm width to facilitate the worms to attach their cocoons to them, and vi) paraffin paper, brushes and foam pads.