Sericulture industry and its potential in India [Part 3]

July 6, 2012
By Krishiworld

MULBERRY SILK

The systematic cultivation of mulberry, the food plant of Bombyx mori, is the first step in the production of mulberry silk. The total area under mulberry in India is 1,20,567 hectares, of which only 28,781 hectares is irrigated Whereas, mulberry is raised as a bush plantation in Karnataka & West Bengal, it is grown as trees in Jammu & Kashmir. Four Indian species of Morus, namely Morus alba, M.indica, M. serrata & M. laevigata, are raised as main food plants of silkworms.

The propagation of mulberry in Karnataka & west Bengal is through vegetative propagation, whereas root-grafting & bud-grafting are practised in the hilly areas of Jammu & Kashmir & Uttar Pradesh. Considering the ecological conditions, such as rainfall & the nature of soil, different systems of plantations for raising mulberry are practised in India.In the rain-fed areas,mulberry is planted at a distance of 7.6*7.6 cm whereas under irrigation the spacing of 5 cm* 5cm & the row system ( 4 cm between rows & 15 cm between plants) are followed. In West Bengal, a modified system of row plantation, popularly called ‘Malda System‘ is practised even under rainfed conditions, because of the rich soil & heavy rainfall.Recently, tree plantation have ben introduced into Jammu & Kashmir.

The cost of producing mulberry has a direct impact on the cost of producing cocoons, as nearly 605 of the total cost of production of cocoons goes to the production of mulberry leaves.

Experiments conducted in the moriculture divisions of the research institutions to evolve new varieties of mulberry & improved methods of cultivation have shown that over 30,000 kg of quality leaf can be produced per annum at competitive costs against 15,000 kg by adopting the traditional methods under irrigation. Many high-yielding varieties have been introduced into the country, & they not only double the leaf yield, but also maintain the succulence of the leaves, a factor which is very important under tropical conditions.

SILKWORM-REARING

In India(Karnataka state), where the temperature ranges from 16-31 degree centigrade, enjoys favourable climatic conditions for rearing the silkworm Bombyx mori throughout the year, whereas in West Bengal, the multivoltine silk-worm rearing is practised even under adverse conditions of temperature. In Jammu & Kashmir, the rearing of silkworms is practised once a year during May-June.

Of a life span of 50 days of B.mori, the egg stage lasts 10 days, the larval stage lasts longest-25-30 days. The pupa stage takes 10 days. The silkworm pass 4 moults during growth. The total quality of leaf required to raise a unit of 40,000 larvae(100 dfls) is 500-600 kg by using the traditional methods. The silkworms consume as much as 95% of the food after the third & fourth moults. At the end of the larval duration, the silkworm emits silk from its mouth & constructs a cocoon on a scaffolding. The cocoons produced by hybrids are used for extracting the silk fibre. For preparing the hybrid silkworm eggs, pure races of silkworms are raised in seperate areas. The cocoons are preserved properly in the egg-producing factories, popularly called silkworm grainages. the moths are allowed to emerge. The selected combination of moths are allowed to copulate for 4 hrs. The male after the first copulation is either rejected or used for copulating with another female. Later, the female is consigned to a dark plastic ‘cellule‘. She lays about 400 eggs in 24 hours. At the end of 24 hours, the female is crushed & examined for hereditary diseases. Only certified disease-free hybrid eggs are reared for industrial silk production.

Considering the various factors, such as the place of origin,voltinism, the colour of the cocoons, the larval markings, the colour ,shape & size of cocoons,the silkworms are classified into different breeds. The multivoltine races & their hybrids are reared in West Bengal & Karnataka. Owing to the non-diapausing of the eggs & the copious growth of the mulberry, these breeds can be reared six times & the cocoons are harvested after 2 months. These multivoltine hybrids have a short larval duration & are generally poor yielders of cocoons. Bivoltines, because of the interruption of diapause, can have only 2 life-cycles a year. However, its possible to break the diapause artificially by treating 1-day old eggs in Hydrochloric acid of 1.064 specific gravity at 46.1 degree centigrade. By adopting this technique, it is possible to take more than 4 crops in a year. Univoltines & bivoltines require more leaves than multivoltines. However, the yield & quality of the cocoons are superior to those of multivoltines. The multivoltine silkworms yield about 25 kg of cocoons per 40,000 eggs reared, whereas the bivoltines yield 40 kgs. The average annual yield of cocoons in India is as low as 150 kg under rainfed conditions, & under irrigated conditions, it is about 400 kg.

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