Q.(a) Explain the life cycle of Bombyx Mori. OR

Bombyx mori, the mulberry silk moth, undergoes complete (holometabolous) metamorphosis through egg, larva, pupa, and adult stages, and its silk cocoon is the commercial source of natural silk.

Answering part (a): Life cycle of Bombyx mori.

1. Egg: The adult female moth lays hundreds of tiny eggs, usually on mulberry leaves. Under suitable temperature and humidity, the eggs hatch into larvae.

2. Larva (caterpillar/silkworm): The larva is the actively feeding stage — it feeds voraciously on mulberry leaves and grows rapidly, moulting (shedding its exoskeleton) several times as it increases in size through successive instars. Towards the end of the larval stage, the larva stops feeding and prepares to pupate.

3. Pupa: The mature larva spins a protective covering called a cocoon around itself, using a continuous thread of silk secreted by a pair of modified salivary (labial) glands, known as silk glands. The silk thread itself is made of a protein core called fibroin, coated and held together by a gummy protein called sericin. Inside this cocoon, the larva transforms (metamorphoses) into a pupa, and then into an adult moth.

4. Adult: Eventually, the adult moth emerges from the cocoon (usually by secreting a fluid that dissolves an opening) to mate and lay eggs, restarting the cycle.

   …