Final answer:
The decline in JH concentrations during larval development may be due to an increase in JH degrading enzymes or a decrease in JH synthesis, allowing ecdysone to trigger the pupa-to-adult molt.
Step-by-step explanation:
The decline in Juvenile Hormone (JH) concentrations during larval development is a crucial factor for the normal metamorphosis of caterpillars into adult insects. Two mechanisms that could potentially explain this decline are:
- An increase in the production of enzymes that degrade JH as the larvae mature, thus reducing its concentration.
- A decrease in the synthesis of JH by the corpora allata, the glands responsible for its production, which could be due to developmental cues or changes in hormonal regulation pathways.
Both of these mechanisms are crucial for allowing the production of ecdysone, the hormone that promotes the pupa-to-adult molt, to take precedence, as ecdysone triggers larval molts only when JH levels are adequate. Without JH, the transition to the next developmental stage can proceed.