Ideal avocation for semi-arid tropics
By Our Agriculture Correspondent
ERI CULTURE, rearing of eri silk worms, is quite popular in Assam and the north-eastern States. The castor and tapioca farmers of south India can successfully adopt this, and they can earn some additional income from this promising venture, according to Prof. (Dr.) S. Jayaraj, Chairman, Sustainable Farm and Rural Development Centre (SFRDC), Chennai.
A distinguished entomologist and a former Vice-Chancellor of the Tamil Nadu Agricultural University (TNAU), Coimbatore, Prof. Jayaraj conducted extensive field research with the active participation of the farmers in six districts of Tamil Nadu, and found that eri culture can be profitably integrated in the rural development programmes in the castor and tapioca belts in the State. The yearlong research project conducted by SFRDC was sponsored by the Central Silk Board (CSB), Union Ministry of Textiles, Bangalore.
Eri silkworms (Samia ricini) produce eri silk. The word `Eri' in Assamese means castor. The worms feed voraciously on castor and tapioca leaves. Cultivated castor and tapioca leaves free of insecticide residues at the time of leaf harvest can be used for feeding the worms.
About 25 to 40 per cent of the leaves from mid-stage of crop growth can be plucked in stages without affecting the castor seed or tapioca tuber yield.
Alternative food plants are papaya, Ailanthus excelsa (matchwood tree), Terminalia catapa (country almond), green type `wild castor' Jatropha and Glyricidia . The leaves from these can be used at varying levels for the last larval stage, according to Prof. Jayaraj.
"This silkworm is multi-voltine (many generations in a year), and it is reared indoors. In Tamil Nadu, four to five rearings are possible per year.
The eggs are white and they hatch in 7 to 10 days. The emerging young larvae are fed tender castor leaves in the rearing-house for the first five days, and thereafter allowed to grow by periodical feeding (3 to 5 times a day) with medium-matured and matured leaves.
The worms pass four moults during the larval period of 18 to 20 days. Tray method, shelf (made of casuarina poles) method and bunch method of rearing are possible," said Prof. Jayaraj. Eri silkworm is generally hardy and not easily susceptible to diseases. At the end of the larval period, the larvae crawl in search of a suitable place to spin the cocoons. Dried leaves of banana, coconut and palmyra are used as mountage material on the rearing bed.
Cheap plastic mountages are also available. The cocoons are usually white. However, eri silkworm strains producing brick red cocoons are also available, according to him.
The cocoons of the eri silkworm cannot be reeled as in the case of mulberry silkworm, as they are made up of uneven and discontinuous fibres.
Usually after the emergence of the moths, the cocoons are used for producing spun yarn.
The pupae are used as poultry and livestock feed. The silk is poor man's wool. It is porous and hence cool in summer and warm in winter. Simple and inexpensive spinning machines are supplied by CSB. Field studies conducted in Tamil Nadu recorded yields ranging from 51 kg to 66 kg a 100 disease free laying in two types of rearing. The income from eri culture varied from Rs.1047 to Rs. 1320 per 0.4 hectares of crop (tapioca). The price of heavier green cocoon is Rs.50 a kg, and the lighter ones fetched Rs.40 a kg. The shell containing silk without pupae will fetch Rs. 400 a kg. "Eri culture is an eco-friendly enterprise using locally available resources, and it promises year-round employment to rural youth, women and landless farmers," said Prof. Jayaraj.
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