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

The silk worm yields silk fiber at the pupa stage of its life cycle. When the silk worm (larva) is ready to pupate, it spins a cocoon using silk fibers produced from its silk glands. This cocoon is then harvested to extract commercial silk. The egg and larva stages precede silk production, while imago is the adult moth stage.