Colours of Domesticated Silkworm Cocoons

• 14 Nov 2023

For Prelims: Silk, Carotenoids and Flavonoids, Silk Samagra, Central Silk Board

For Mains: Sericulture in India, Economics of Animal-Rearing

Source: TH

Why in News?

Silk, often referred to as the “queen of fibres,” has been valued for its beauty and luxury for ages. Researchers have revealed the genetic factors behind the cocoon colors and adaptations of silk-producing insects, and how they have transformed the silk industry.

What is Cocoon in Silk?

• A cocoon in silk is a protective layer of silk thread that is spun by a silkworm around itself.
  • The silk thread is very fine, strong, and lustrous. The cocoon usually has an oval or round shape.
• The cocoon can be used to make silk fabric by unwinding the thread and weaving it.

What Genetic Insights Does Silk Moth Domestication Uncover?

• Evolution of Silk Moth Domestication:
  • It is produced by the cocoons of the domesticated silk moth (Bombyx mori), which was derived from the wild silk moth (Bombyx mandarina) more than 5,000 years ago in China.
    • While the domesticated silk moth thrives worldwide, the ancestral moth still roams in regions like China, Korea, Japan, and far-eastern Russia.
• Types of Silk:
  • Wild Silk (Non-mulberry Silks):
    • Wild’ silks, which include the muga, tasar, and eri silks are obtained from other moth species: namely, Antheraea assama, Antheraea mylitta, and Samia cynthia ricini.
    • These moths survive relatively independently of human care, and their caterpillars forage on a wider variety of trees.
    • Non-mulberry silks comprise about 30% of all silk produced in India.
      • These silks have shorter, coarser, and harder threads compared to the long, fine, and smooth threads of the mulberry silks.
  • Mulberry Silk:
    • The most common and widely produced type of silk, accounting for about 90% of global silk production.
      • Derived from the cocoons of the domesticated mulberry silkworm (Bombyx mori), which feeds exclusively on mulberry leaves.
    • Has long, smooth, and lustrous fibers that can be woven or knitted into various fabrics with different textures and finishes.
    • Suitable for a wide range of applications, such as clothing, bedding, curtains, upholstery, and accessories.
• Cocoon Colours:
  • The ancestral mulberry moth makes (uniform) brown-yellow cocoons.
    • In contrast, domesticated silk moth cocoons come in an eye-catching palette of yellow-red, gold, flesh, pink, pale green, deep green or white.
  • The pigments that colour the silkworm cocoons are derived from chemical compounds called carotenoids and flavonoids, which are made by the mulberry leaves that the silkworms feed on.
    • The silkworms absorb the carotenoids and flavonoids and transport them to the silk glands, where they are taken up and bound to the silk protein.
    • The amount and type of pigments in the silk glands determine the colour and intensity of the silk threads, which are then extruded by the silkworms to form the cocoons.
  • The pigments that coloured the cocoons are water-soluble, so they gradually fade away.
    • The coloured silks we see in the market are instead produced by using acid dyes.
  • Mutations in genes responsible for carotenoids and flavonoids cause differently colored cocoons, providing insight into the molecular basis of silk diversity.

What is the Status of India’s Silk Industry?

• Silk Production:
  • India stands as the world's second-largest producer of raw silk after China.
  • In the fiscal year 2020-21, the country produced a substantial 33,739 MT of raw silk.
    • India boasts a diverse range of silk types, including Mulberry, Tasar, Muga, and Eri. The variations arise from the distinct feeding habits of the silkworms.
  • The silk industry stands as one of India's largest foreign exchange earners, contributing significantly to the country's economic landscape.
• Leading States:
  • In the fiscal year 2021-22, Karnataka emerged as the leading state in India's silk production, making a substantial contribution of 32%.
    • Other significant contributors include Andhra Pradesh (25%), along with states like Assam, Bihar, Gujarat, and West Bengal, all playing pivotal roles in the thriving silk industry.
• Top Importers:
  • The country exports to more than 30 countries in the world. Some of the top importers are the USA, UAE, China, UK, Australia, and Germany.
• Workforce:
  • The country's sericulture industry employs around 9.76 million people in rural and semi-urban areas. The sericulture activities in India are spread across 52,360 villages.
• Central Silk Board (CSB):
  • It is a statutory body, established in 1948 by an Act of Parliament, under the administrative control of the Ministry of Textiles, Government of India.
    • Its headquarters is located in Bangalore.
  • The CSB is responsible for the overall development and promotion of the sericulture and silk industry in India, through retesearch, extension, training, quality control, and marketing support.
• Initiative:
  • Silk Samagra.
  • North East Region Textile Promotion Scheme (NERTPS):
    • The objective of this scheme is the revival, expansion, and diversification of sericulture in the North Eastern States with a special focus on Eri and Muga silks.