UPSC Prelims 2000 · General Studies

Question 116: Science and Technology

At which stage in its life-cycle does the silkworm yield the fibre of commerce?

aEgg

bLarva

cPupa

dImago

AnswerThe answer is (c).

The silkworm larva spins a cocoon of a single long silk fibre and then turns into a pupa inside it. Silk is reeled from the cocoon while the insect is at the pupal stage, usually before the moth emerges, as the moth would cut the fibre. So the fibre of commerce is obtained from the pupa stage, the cocoon.

Why each option is right or wrong

(a) The egg stage yields no fibre.
(b) The larva spins the fibre, but the commercial fibre is reeled from the cocoon at the pupal stage.
(c) Right: the cocoon is reeled at the pupal stage.
(d) The adult moth cuts its way out and spoils the fibre.

Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2000, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.