Question

If juvenile hormone is absent when silkworm moults , it will
A. Moult into another larval stage
B. Moult into pupa
C. Moult into adult
D. None of the above

Answer 1

Hint: Silkworm moth (Bombyx mori), a lepidopteran whose caterpillar for thousands of years has been used in the production of silk (sericulture). While native to China, silkworms have been introduced globally and have been fully domesticated, with species no longer present in the wild.

Complete Answer:
- The juvenile hormone (JH) postpones insect larval metamorphosis until it has reached an adequate stage and scale. Then, a decrease in JH secretion during the final larval instar makes a metamorphic moult that transforms larvae either directly (hemimetaboly) or through a pupal stage (holometabolous) into adults.
- Juvenile Hormone represents a group of hormones that assure larval growth while preventing metamorphosis..Due to their rigid exoskeleton, insects mature in their development by successively shedding their exoskeleton (a process known as moulting).
- A pair of endocrine glands behind the brain called the corpora allata are secreted by juvenile hormones. In female insects, JHs are also important for the development of eggs.
- JH has many roles, and the primary role of JH in insect growth is to modulate the action of ecdysone.
- JH retains the tissues and cells' current engagement, while ecdysone causes the moult to induce both pre-differentiated and differentiative cellular events. Thus, a moult to a larval stage occurs when JH is present. If at the start of the moult, JH is absent, metamorphosis occurs.
- Ecdysone activates larva-to-larva moults as long as adequate JH is available. Ecdysone induces pupation with decreased levels of JH. The complete absence of JH contributes to adult development.

Thus the correct Answer is option (B) Moult into pupa.

Note: If the corpora allata is separated from an immature silkworm, the cocoon spins immediately and becomes a tiny pupa. The actual appearance of a miniature adult
Likewise, when a young silkworm corpora allata is positioned in the body of a fully mature larva, there is no metamorphosis. An extra large caterpillar is created by the next mould.