The science that deals with the culture of silkworm - both under indoor and outdoor conditions and till the production of silk yarns - is designated as Sericulture. It is an emerging discipline of Applied Biology. Sericulture is a cottage and/ or agro-forestry and forestry based industry that provides sustainable livelihoods to rural communities and earning foreign exchange worth about Rs.1600 crores per annum. The global production of raw silk is approximately 70,000 tonnes per year , of which 16,500 tonnes per year is produced by India. Silk industry has a lot of socio-cultural and traditional linkages in the country. In developing countries such as India, agriculture and agro-based industries play a vital role in the improvement of rural economy. Limited availability of land, limited cash returns and agriculture being confined to one or two seasons in the year have made villages to look for supporting rural industries such as sericulture. The agriculturists in regions where the ecological conditions are favorable adopt agriculture and sericulture simultaneously. In India, over three million people are employed in various fields of sericulture. Though India is the second largest silk producer in the World after China, it accounts for just 5% of the global silk market, since the bulk of Indian silk thread and silk cloth are consumed domestically. Germany is the largest consumer of Indian silk. The present market context for silk in India is one of vigorously growing internal demand for silk fabrics, with growth rates of above 10% per year. It is mostly for traditional (sari type) design and does not impose sophisticated quality requirements upon the industry. The bulk of today’s world export demand is almost exclusively based on high graded quality bivoltine raw silk. If Indian sericulture is unable to generate a substantial production of bivoltine raw silk, these important market segments will continue to be lost to outside competitors.
Silk is a proteinaceous fibre derived from cocoon (pupal nest) spun by a large variety of moth caterpillars belonging to families Bombycidae and Saturniidae of the order Lepidoptera. The family Bombycidae includes 7 domesticated and 2 wild species of the genus Bombyx and all these species feed on Morus alba and hence are called as mulberry silkworms. Of the different species of Bombyx, the most widely used in sericulture is B. mori. The other wild silkworms, Philosamia ricini (Eri silkworm), Antheraea assama (muga silkworm) and Antheraea mylitta (tasar silkworm), belong to the family Saturniidae.
India has unique distinction of producing all the four varieties of silk i.e. mulberry, eri, tasar and muga. Nearly 90% of our silk is mori silk or mulberry silk produced by the silkworm Bombyx mori. Further India has merit of producing two different kinds of tasar silk. Temperate tasar (oak tasar) is finer variety of tasar produced by the silkworm, Antheraea proylei, which feed on natural food plants of oak, found in abundance in the sub-Himalayan belt of India covering the states of Jammu & Kashmir, Himachal Pradesh, Uttar Pradesh, Assam, Meghalaya and Manipur. China is the major producer of oak tasar in the world.
Unlike mulberry silk production, non-mulberry silk production is unsteady and fluctuates from year to year. The central silk board has not given enough attention to their R & D and extension activities in the area of non-mulberry sericulture in spite of its potential to directly help the poor. Presently, muga and eri silks are produced mostly for self-consumption. But with their uniqueness to India, they have great potential for value-added exports.
Tasar (Tropical tasar) silk largely found in the tribal habitats of the Gondwana region is peculiarity of India not being found any where else in the world. This silkworm is reared in the jungles of central and north-eastern parts of India. In India, tasar silk is mainly produced in the states of Jharkhand, Chattisgarh and Orissa, besides Maharashtra, West Bengal and Andhra Pradesh. Tasar culture is the main source of income for many tribal communities in India. Around 3,000 tasar rearers, mostly tribals, are dependent on the industry.
It is mainly used for furnishings, dress materials and saris. The porous texture and thermal properties makes these silks user friendly and healthy. The large number of women engaged in the activity, cultivation taking place in tribal and economically under developed regions, conservation of naturally grown food plants for the silkworms contributing to the bio-diversity conservation are some of the other features that gives it an unique identity.
Fig. 1A - 5th Instar larva of tasar silkworm, Antheraea mylitta on twig of Host Plant, Terminalia arjuna
The food plants for most of the silkworms are tree/shrubby species of open habitat/ or found along margins of forests/ or of the forest community. Tasar silkworm, A. mylitta feeds on foliage of many plant species belonging to different families, but it prefers the foliage of Terminalia arjuna, T. tomentosa and Shorea robusta and these are designated as primary food plants. The other food plants of A. mylitta are T. bellerica, T. chebula, T. catapa and T. paniculata of Combretaceae, Bauhinia variegata, Dalbergia sissoo and Hardwickia binata of leguminosae, Careya arborea of Myrtaceae, Madhuca latifolia of Sapotaceae, Zizyphus mauritiana and Zizyphus jujuba of Rhamnaceae and Ficus religiosa of Moraceae.
Fig. 1B - Garlands of tasar silkworm cocoons tied on Terminalia arjuna branches for drying
All these plant species are designated as secondary food plants. As the result of adoption of a species to variable eco factors and interaction of a genetic constitution to changed environment, A. mylitta also shows diversity in respect of morphological, physiological and economic characters. The species of A. mylitta has been distributed in varied eco-climatic conditions of central India. About 44 eco races of A. mylitta are recognized from India. Depending on number of times they are being reared in a year, various eco races of A. mylitta can be distributed into three different categories i.e. univoltine, bivoltine and trivoltine. Bivoltine races of A. mylitta which are reared twice in a year are most commonly being used for practicing tasar sericulture in our country. The first crop usually called the seed crop is raised during July-August, whereas the commercial crop is raised during October-November.
The tasar sericulture is an important discipline of applied biology that needs to be given special attention to promote conservation and sustainable utilization of natural resources. They contribute to our socio-economic and cultural heritage. There are factors that contribute to the low tasar silk productivity in India. The tasar silkworms are yet to be domesticated and their host plants are forest species. Sericulture is practiced by tribal communities for a short period of the year (July-August and October-November) as one of the alternative livelihood. Thus a detail research works on various ecological and biochemical aspect of host plant-tasar silkworm interactions is critical for enhancement of yield and quality of tasar silk either through domestication or by improving the genotypes of host plants and insect species. The government now must give importance to these non-mulberry silk and facilitate focused R & D, targeted extension and innovative product development for value-added exports.
 Ministry of Textile (2006) Annual Report.
Sohn, Kee-Wook (2003). Conservation Status of Sericulture Germplasm Resources in the World - II. Conservation Status of Silkworm (Bombyx Mori) Genetic Resources in the World, Food and Agriculture Organization of the United Nations, Rome.
Mohanty, P. K. (2003). Tropical wild silk cocoons of India. Daya Publishing house, Delhi.
Suryanarayana, N. and Srivastava, A.K. (2005). Monograph on Tropical tasar Silkworm. Aggarwal Press, Ranchi (India).
Thangavelu, K. (2000). Lessons on Tropical Tasar. Speed-O-Print, S.N.Ganguly Road, Ranchi (India).