ENT 305 Molting

Molting

• Molting limits insect size

  • Exoskeleton must be molted for growth

  • Newly molted insect has no support (if volume is larger, they would simply collapse or burst)

• Molting hormone released by gland in the head

• Since insects have a tough, non-living outer covering (exoskeleton), they cannot grow steadily, but instead have to grow in stages by periodically shedding the exoskeleton (molting or ecdysis)

• Molting: the process where an insect replaces its old exoskeleton which allows for growth

• Production of a new cuticle (exoskeleton) and the subsequent shedding of the old cuticle

• Triggered by hormones that are released when the insect reaches its size limit for the current exoskeleton

• The new exoskeleton is produced inside the old one and then hardens after shedding

Ecdysone

• Molting hormone

• Released by prothoracic gland and triggers molting and maturation

Juvenile Hormone

• Molting hormone

• Release by corpora allata gland and keeps larvae from pupating during larval molts

Molting Process

• Apolysis

• Secretion of inactive molting fluid by epidermis

• Production of new cuticulin layer for new exoskeleton (protects epidermal layer from digestion)

• Activation of molting fluid

• Chemical digestion and absorption of old endocuticle by molting fluid

• Epidermis (living layer) secretes new procuticle

• Ecdysis

• Expansion of new integument

• Tanning and sclerotization of new exocuticle (darkening and hardening)

Apolysis

Physical separation of old exoskeleton from epidermis

Ecdysis

Shedding of old exo- and epicuticle and includes external and linings of tracheae, foregut, and hindgut (not midgut because it is not lined with cuticle)

Ecdysial suture

A Y-shaped cranial suture found in larvae and some adults along which the integument is ruptured during molting.

Exuvium

Old shed cuticle

Teneral

Newly emerged insect/arthropod with soft exoskeleton (soft and pale)