Why in News
Silk is an acme of domestication, comparable in its success to basmati rice, alphonso mangoes, and the golden retriever.
Today, the tools are at hand for scientists to make and compare genetically identical hybrid silk moths that differ only in which of a gene’s two parental versions is inactivated
Queen of Fibres
Silk, the queen of fibres, is drawn or reeled from cocoons of thesilk moth (Bombyx mori).
Humans domesticated it more than 5,000 years ago in China.
The ancestral moth is today found in China, the Korean Peninsula, Japan, and far eastern Russia, whereas the domesticated moth is reared all over the world, including in India.
In fact, India is the world’s second largest producer of raw silk after China.
Caterpillars, also known as silkworms, of both these species feed exclusively on leaves of mulberry plants (genus Morus).
The domesticated mothis much larger thanits wild progenitor, and thus extrudes a longer silk fibre to build its larger cocoon, up to 900 metres long.
It depends wholly on human care for its survival and reproduction.
Since having been domesticated, it has lost the ability to fly, .
Its need for camouflage no longer exists, it has also lost its caterpillar and adult-stage pigmentation.
What are muga, tasar, and eri?
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.
The ancestral mulberry moth makes (boringly 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.
Human handlers selected the differently coloured cocoons whenever they emerged, possibly in the hope of breeding for coloured silks.
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.
Importance of carotenoids and flavonoids in cocoons
Carotenoids and flavonoids are two types of plant pigments that play important roles in the development and survival of cocoons.
Carotenoids are responsible for the yellow, orange, and red colors of many fruits and vegetables.
They also act as antioxidants, which help to protect cells from damage caused by free radicals.
In cocoons, carotenoids are thought to help to protect the pupae from harmful sunlight and to provide them with camouflage.
Flavonoids are a group of plant pigments that are found in a wide variety of fruits, vegetables, and flowers.
They are known for their antioxidant and anti-inflammatory properties.
In cocoons, flavonoids are thought to help to protect the pupae from infection and to promote their development.
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