INSECT ENDOCRINE SYSTEM

Hormones

Chemical messenger that are secreted directly into blood, that carries them to organs and tissues

Insect hormones

1. Brain hormones

2. Molting hormones

3. Juvenile hormones

Concept of Hormonal Control of Molting and Metamorphosis

• Sir Vincent Wigglesworth - used blood-sucking bug (Rhodnius prolixus), used juvenile hormone that prevents development of adult characteristics

• Critical period - period when brain is necessary for its hormonal influence to be exerted

Endocrine Glands

• neurosecretory cells within the central nervous system

• specialized endocrine glands: corpora cardiaca, corpora allata, prothoracic glands

Neurosecretory Cells

• located in protocerebrum of insects

• responsible for coordination and control of bodily functions (feeding, metabolism, excretion, reproduction, development)

Corpora cardiaca

• pair of organs closely associated with aorta

• it stores and release brain hormones from neurosecretory cells of the brain

• Also produce and release Adipokinetic hormone

Corpora allata

• connected to corpora allata and sub esophageal ganglion

• secretes juvenile hormones

Prothoracic glands

• pair of diffuse glands at the back of the head

• stimulated by the brain hormone to produce molting hormone also known as ecdysone

Prothoracicotropic hormone

• also known as “brain hormone”

• secreted by corpus cardiacum

• released in response to environmental stimuli

• stimulates the production of ecdysone by prothoracic glands

Juvenile hormone

• also called as “Neotenin”

• discovered by Vincent Wigglesworth

• ensures growth or larva but prevents the development of metamorphosis, thus it is called Inhibitory or Status Quo

• secreted by corpora allata

• At the last larval stage or nymphal stage, the corpora allata become atrophied (shrink) and stops producing juvenile hormone

Ecdysone / Molting hormone

• secretes by prothoracic gland

• generally called as ecdysteroids

• ecdysone and ecdysteroids also appear in plants as protection agents (toxins) against herbivorous insects

Eclosion hormone

• triggers ecdysis behavior at the end of each molt

• the end of apolysis, ecdysteriod concentration falls, and neurosecretory cells in the ventral ganglia begins secreting eclosion hormone

Bursicon

• hormone that causes hardening and darkening of the integument (tanning) due to sclerotization

Amounts of juvenile hormone

• Enough juvenile hormone - ecdysone promotes larva to larva molts

• Lower juvenile hormone - ecdysone promotes pupation

• Complete absence of juvenile hormone - formation of adult