Silk is obtained from which stage of silkworm?

Insects such as the silkworm (Bombyx mori) develop through complete metamorphosis in a fixed sequence of four life stages: egg, larva (caterpillar), pupa, and adult (moth). Before entering the pupal stage, the larva spins a protective covering called a cocoon out of a single continuous protein thread (fibroin bound with sericin); this cocoon is what sericulture harvests to produce raw silk.

In this question, the insect is still enclosed inside that cocoon while it is transforming from larva to adult -- that enclosed, transitional stage is the pupa. Silk is reeled from the cocoon at this point, and the pupa inside is stifled with heat or steam so the moth cannot cut the thread by breaking out. So the stage from which silk is obtained is the pupa.

This matches the UPTET 2016 Paper 2 official answer key for this exact question. It is also the standard convention in exam GK material: although the larva is the one that spins the cocoon, the cocoon -- and the silk drawn from it -- belongs to the pupal stage that follows, which is why 'pupa' rather than 'larva' is keyed here.

• Egg -- the starting stage of the life cycle, before the larva even hatches; no cocoon or thread exists yet.

• Larva -- the caterpillar stage that spins the cocoon thread by thread, but the finished, sealed cocoon is complete only once the larva has withdrawn inside it; the raw silk is not drawn off during the spinning itself.

• Adult -- the moth that has already broken out of the cocoon; by this point the continuous silk filament has been cut, so this stage yields no usable silk.