About Lesson
The moulting process
The moulting process, also known as ecdysis, is crucial for the growth and development of insects, as it allows them to shed their old exoskeleton and form a new one. The process is a complex sequence of events that involves three primary stages: Apolysis, Ecdysis, and Sclerotization. Here’s a detailed breakdown of each stage and the hormones involved in moulting:
- Apolysis (Formation and Dissolution):
- Definition: Apolysis refers to the dissolution of the old cuticle and the formation of a new one.
- Process:
- Cell Division: The process begins with repeated mitotic division of epidermal cells. This increases both the number and size of these cells, creating pressure on the cuticle.
- Tension and Separation: As the epidermal cells grow, they exert tension on the old cuticle, causing them to separate from it. This results in the creation of a subcuticular space between the epidermis and the old cuticle.
- Secretion: The epidermal cells start producing moulting fluid and cuticular material, which accumulate in this subcuticular space. The moulting fluid dissolves the old cuticle, and the new cuticular material begins to form.
- Ecdysis (Shedding of the Old Cuticle):
- Definition: Ecdysis is the stage where the insect sheds its old cuticle and emerges with the new one.
- Process:
- Formation of New Cuticle: During this stage, both the epicuticle and procuticle of the new exoskeleton are already formed beneath the old cuticle.
- Splitting of Cuticle: The ecdysial membrane (a thin layer formed between the old and new cuticle) splits along predetermined lines of weakness due to the insect’s inner muscular activity.
- Physical Changes: The insect also swallows air and water, which helps distend its gut, and blood is pumped from the abdomen to the thorax through muscle contractions, causing further pressure.
- Shedding Process: The old cuticle breaks, and the insect, now in its new instar, begins to emerge. The head comes out first, followed by the thorax, abdomen, and appendages.
- Sclerotization (Hardening and Tanning of New Cuticle):
- Definition: Sclerotization is the process by which the newly shed cuticle hardens and darkens to become a more durable, rigid exoskeleton.
- Process:
- Tanning: The new cuticle, initially soft and milky white, undergoes tanning (or sclerotization) to become darker and harder.
- Chemical Changes: Sclerotization involves the cross-linking of proteins and other substances in the cuticle, which makes it more resilient to physical damage, dehydration, and pathogen invasion.
Hormones Involved in the Moulting Process:
The moulting process is regulated by specific hormones that control different stages of development:
- Juvenile Hormone (JH):
- Source: Produced by the corpora allata (glands located near the brain).
- Role: JH plays a critical role in maintaining the insect in an immature, larval or juvenile stage. It prevents the insect from undergoing metamorphosis by inhibiting the action of the moulting hormone. As the insect matures, JH levels decrease, allowing the process of moulting and metamorphosis to occur.
- Moulting Hormone (MH):
- Source: Produced by the prothoracic glands of the brain.
- Role: MH triggers the moulting process by stimulating the synthesis and release of enzymes that break down the old cuticle, facilitating the shedding process. It also plays a key role in the formation of the new cuticle.
- Eclosion Hormone:
- Source: Released from neurosecretory cells in the brain.
- Role: This hormone is responsible for initiating the actual process of ecdysis (shedding of the old cuticle). It triggers the ecdysial membrane to split and activates the behavioral changes required for the insect to emerge from its old exoskeleton.
Summary of the Moulting Process:
- Apolysis: The old cuticle dissolves and the new cuticle begins to form in the subcuticular space.
- Ecdysis: The old cuticle is shed, and the insect emerges with its new cuticle.
- Sclerotization: The new cuticle hardens and darkens, providing the insect with protection and strength.
