At which stage in its life cycle does the silk worm yield the fibre of commerce ?

The silk worm yields silk fiber during the pupa stage when it spins a cocoon around itself. The cocoon is made of a continuous silk filament that can be 300-900 meters long. This filament is unwound to obtain commercial silk. The egg and larva stages precede cocoon formation, while imago is the adult moth that emerges after mating.