Hormonal Control of Metamorphosis in Insects

Summary

This video explores the hormonal regulation of insect metamorphosis, focusing on two key hormones: 20-hydroxyecdysone and juvenile hormone. 20-hydroxyecdysone, a steroid, drives the transformation from larva to pupa and adult, while juvenile hormone, a lipid, controls larval stages and prevents premature metamorphosis. The brain's corpora allata and corpora cardiaca secrete these hormones, with juvenile hormone ensuring larval molts and 20-hydroxyecdysone inducing the transition to the pupal and adult stages when juvenile hormone levels are low. This hormonal interaction ensures the proper timing of insect development stages.

Takeaways

• 😀 20-hydroxyecdysone (20E) is a steroid hormone that plays a crucial role in insect metamorphosis, driving the transition from larva to pupa and from pupa to adult.
• 😀 Juvenile hormone (JH) is a lipid hormone that helps maintain the larval state by preventing the action of 20E during high concentrations.
• 😀 The interaction between 20E and JH determines the insect's developmental progression, with JH preventing the effects of 20E at high levels.
• 😀 When juvenile hormone concentration decreases, 20E is able to induce the transition from larva to pupa and adult stages.
• 😀 Neurosecretory cells in the insect's brain release prothoracicotropic hormone (PTTH), which stimulates the release of ecdysone from the prothoracic glands.
• 😀 Ecdysone is converted into 20E in the mitochondria, and this 20E drives the expression of genes responsible for pupal and adult structures.
• 😀 Juvenile hormone, when present in high concentrations, prevents 20E from initiating molting and keeps the insect in the larval form.
• 😀 Juvenile hormone receptor binding to JH in the nucleus drives the expression of larval genes, ensuring the formation of larval structures.
• 😀 The hormonal process involves multiple glands, including the corpora allata, which secretes juvenile hormone, and the corpora cardiaca, which releases PTTH.
• 😀 The process of PTTH-mediated metamorphosis involves both juvenile hormone and 20E, with the presence of 20E facilitating adult and pupal development when juvenile hormone levels are low.

Q & A

What are the two main hormones responsible for insect metamorphosis?

The two main hormones responsible for insect metamorphosis are 20-hydroxyecdysone and juvenile hormone.

What is the function of 20-hydroxyecdysone in insect metamorphosis?

20-hydroxyecdysone is a steroid hormone that drives different molts in insects, such as larva to pupa and larva to adult transitions.

What role does juvenile hormone play in insect metamorphosis?

Juvenile hormone is a lipid that influences larval molts and prevents the transition from larva to pupa or adult by inhibiting the action of 20-hydroxyecdysone.

How do juvenile hormone and 20-hydroxyecdysone interact in insect metamorphosis?

Juvenile hormone prevents the effect of 20-hydroxyecdysone on molting. When juvenile hormone concentration is high, 20-hydroxyecdysone has no effect on the molts, keeping the insect in the larval stage.

What happens when juvenile hormone concentration decreases?

When juvenile hormone concentration decreases, 20-hydroxyecdysone becomes active and drives the transition from larva to pupa and eventually to the adult stage.

What is the role of the corpora allata in hormonal control of metamorphosis?

The corpora allata is responsible for secreting juvenile hormone, which combines with its receptor and regulates the expression of larval genes.

What is the function of the corpora cardiaca in insect metamorphosis?

The corpora cardiaca secretes the prothoracicotropic hormone (PTTH), which stimulates the prothoracic gland to secrete ecdysone, which is converted into 20-hydroxyecdysone.

How does 20-hydroxyecdysone contribute to the molting process?

20-hydroxyecdysone drives the expression of genes that lead to the formation of adult and pupal structures, but only when juvenile hormone levels are low.

What happens when juvenile hormone is present in high concentrations?

When juvenile hormone is present in high concentrations, it prevents 20-hydroxyecdysone from affecting the molting process, keeping the insect in its larval stage.

How does PTTH mediate metamorphosis in insects?

PTTH, secreted by the corpora cardiaca, acts as the molting signal in insects, leading to the secretion of ecdysone from the prothoracic gland and initiating the hormonal changes required for metamorphosis.