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Difficulty: MediumGrowth, Development, and Metamorphosis

During insect development, the transition between developmental stages is regulated by the interaction of ecdysone (moulting hormone) and juvenile hormone. A high concentration of juvenile hormone paired with ecdysone promotes larval-to-larval moulting. Which of the following developmental outcomes occurs when the secretion of juvenile hormone declines significantly while ecdysone remains active?

  1. The larva undergoes metamorphosis to form a pupaAnswer
  2. B
    The larva continues to grow into a larger larval instars
  3. C
    The insect immediately undergoes continuous ecdysis as an adult
  4. D
    Development halts and the organism reverts into an embryonic egg state

Answer

The larva undergoes metamorphosis to form a pupa
Juvenile hormone inhibits metamorphosis and keeps the insect in its immature larval state. When its concentration drops to a low level while ecdysone remains active, the insect undergoes metamorphosis from the larval stage into a pupa.

Step-by-Step Solution

1
Identify the primary hormones involved in insect growth and metamorphosis.
Ecdysone triggers moulting, while juvenile hormone maintains larval structural features.
Understanding hormone interaction is key to determining developmental pathways in arthropods.
2
Analyze the effect of changing hormone concentration ratios.
High juvenile hormone + Ecdysone = Larval moult; Low juvenile hormone + Ecdysone = Pupal metamorphosis; Absence of juvenile hormone + Ecdysone = Adult emergence.
Juvenile hormone acts as a suppressor of adult and pupal gene expression.
3
Deduce the outcome for a significant decrease in juvenile hormone.
The larva transitions into the pupal stage.
Lowering juvenile hormone level allows pupal genes to be expressed during the ecdysone-stimulated moult.

Key Concept

Hormonal regulation of metamorphosis in insects
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Topics

Growth, Development, and Metamorphosis

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