Correct Option (C)
The silkworm yields the fibre of commerce during its pupa stage. After hatching from the egg, the silkworm larva feeds extensively and grows. It then enters the pupa stage, during which it spins a cocoon around itself using a continuous silk filament. This cocoon is the source of commercial silk.
Incorrect Options:
A) Egg: The egg is the initial stage of the silkworm life cycle. It is a dormant stage and does not produce silk fibre.
B) Larva: The larva, also known as the caterpillar, is the feeding and growth stage. While it prepares for silk production by accumulating nutrients, it does not produce the commercial fibre during this stage itself.
D) Imago: The imago is the adult moth stage. After emerging from the cocoon, the moth's primary function is reproduction. It does not produce silk fibre.