ENDOCRINE SYSTEM IN INSECTS
The hormones are synthesized and secreted from glands. It can be endocrine (without ducts) or
exocrine (with ducts). Like other animals, insects possesses an array of hormones that regulate
their diverse physiological and biochemical processes.
Endocrine system:
Slow means of communication and coordination of long-term events, such as growth,
differentiation and development
Endocrine glands secrete chemicals called hormones (=1st messengers) into bloodstream.
Hormones circulate inside the body by blood and serves messengers between internal
tissues and organs
Slow response and the effects are usually long-term or permanent
HORMONAL SOURCES IN INSECTS INCLUDES
1. Neurosecretory Cells (NSC)
2. Prothoracic Glands
3. Corpora cardiaca
4. Corpora allata
5. Epitrachael glands
6. Weismann’s ring/ring gland
The first endocrine sequence to be considered is that controlling molting. Two endocrine sources
are involved: the neurosecretory cells of the brain and the prothoracic glands. The importance of
the brain in metamorphosis was discovered by Kopac (1922) and the further analysis was begun
by Wigglesworth (1940), who worked on the bug, Rhodnius.
, The axons of the medial neurosecretory cells run downward in the brain, cross to the opposite
hemisphere, and then leave the brain, gathered together as a thin nerve (Fig. 1). The nerve runs
backwards in the head and ends in a distinct organ, the corpus cardiacum
NEUROSECRETORY CELLS
A pair of median and lateral NSC in prothoracibrum. It connects to C. cardiac and C. allata
Wigglesworth's evidence suggested that the hormone triggering molting is secreted by the medial
neurosecretory cells situated in the pars intercerebralis of the brain. Many insects also have a
second, lateral group of Neurosecretory cells in each hemisphere of the brain. Meaning there are
a pair of median and lateral NSC.
Master regulator and controls most physiological and metabolic process including
secretion of hormones that control metamorphosis, moulting and reproduction
It also regulate the synthesis of lipids, carbohydrates, proteins
Regulates other basic physiological process such as feeding activity and excretion
It secretes:
1. Prothoracicotroic hormone (PTTH). This hormone activates prothoracic glands to release
ecdysone (moulting hormone)
2. Allotropin: a peptide which regulates the synthesis of juvenile hormone
3. Allostatin: a peptide that inhibit the synthesis of juvenile hormone
4. Diuretic /antidiuretic hormone: water balance (diuresis)/inhibit urine production
5. Eclosion hormone and ecdysone triggering hormone (emergence/eclosion)
The neurosecretory cells of the brain have been implicated in: a) Triggering the prothoracic glands,
b) Stimulating oviposition, c) Promoting water retention, d) Controlling activity rhythms, e)
Stimulating proteinase synthesis in the gut
Hormone is formed in the cell bodies of the neurosecretory cells
It appears that the hormone is formed in the cell bodies of the neurosecretory cells, is gathered
into membrane-bounded granules about 1000 A in diameter (Meyer and Pflugfelder, 1958), and
the granules are then transported down the axons to the corpora cardiaca. The transport was
demonstrated by showing that the secretory granules pile up on the proximal side of a cut through,
or a ligature around, the axons.
It seems that two factors are produced by the two cells types. Either both factors are needed for
endocrine activity, or the two factors are combined to produce a single hormone. In some insects
the lateral neurosecretory cells are seen only in the later stages of larval life, which again suggests
that they have a special role to play.
The next question is how the release of the brain hormone is controlled. In Rhodnius,
Wigglesworth showed that secretion begins when the abdomen is swollen by the bloodgorged
gut. It was the swelling and not the blood which was important. Molting can be blocked by
transecting the ventral nerve cord, which suggests that sensory impulses, elicited by stretching,
ascend the ventral nerve cord and stimulate neurosecretion. Recent work shows that in Rhodnius
The hormones are synthesized and secreted from glands. It can be endocrine (without ducts) or
exocrine (with ducts). Like other animals, insects possesses an array of hormones that regulate
their diverse physiological and biochemical processes.
Endocrine system:
Slow means of communication and coordination of long-term events, such as growth,
differentiation and development
Endocrine glands secrete chemicals called hormones (=1st messengers) into bloodstream.
Hormones circulate inside the body by blood and serves messengers between internal
tissues and organs
Slow response and the effects are usually long-term or permanent
HORMONAL SOURCES IN INSECTS INCLUDES
1. Neurosecretory Cells (NSC)
2. Prothoracic Glands
3. Corpora cardiaca
4. Corpora allata
5. Epitrachael glands
6. Weismann’s ring/ring gland
The first endocrine sequence to be considered is that controlling molting. Two endocrine sources
are involved: the neurosecretory cells of the brain and the prothoracic glands. The importance of
the brain in metamorphosis was discovered by Kopac (1922) and the further analysis was begun
by Wigglesworth (1940), who worked on the bug, Rhodnius.
, The axons of the medial neurosecretory cells run downward in the brain, cross to the opposite
hemisphere, and then leave the brain, gathered together as a thin nerve (Fig. 1). The nerve runs
backwards in the head and ends in a distinct organ, the corpus cardiacum
NEUROSECRETORY CELLS
A pair of median and lateral NSC in prothoracibrum. It connects to C. cardiac and C. allata
Wigglesworth's evidence suggested that the hormone triggering molting is secreted by the medial
neurosecretory cells situated in the pars intercerebralis of the brain. Many insects also have a
second, lateral group of Neurosecretory cells in each hemisphere of the brain. Meaning there are
a pair of median and lateral NSC.
Master regulator and controls most physiological and metabolic process including
secretion of hormones that control metamorphosis, moulting and reproduction
It also regulate the synthesis of lipids, carbohydrates, proteins
Regulates other basic physiological process such as feeding activity and excretion
It secretes:
1. Prothoracicotroic hormone (PTTH). This hormone activates prothoracic glands to release
ecdysone (moulting hormone)
2. Allotropin: a peptide which regulates the synthesis of juvenile hormone
3. Allostatin: a peptide that inhibit the synthesis of juvenile hormone
4. Diuretic /antidiuretic hormone: water balance (diuresis)/inhibit urine production
5. Eclosion hormone and ecdysone triggering hormone (emergence/eclosion)
The neurosecretory cells of the brain have been implicated in: a) Triggering the prothoracic glands,
b) Stimulating oviposition, c) Promoting water retention, d) Controlling activity rhythms, e)
Stimulating proteinase synthesis in the gut
Hormone is formed in the cell bodies of the neurosecretory cells
It appears that the hormone is formed in the cell bodies of the neurosecretory cells, is gathered
into membrane-bounded granules about 1000 A in diameter (Meyer and Pflugfelder, 1958), and
the granules are then transported down the axons to the corpora cardiaca. The transport was
demonstrated by showing that the secretory granules pile up on the proximal side of a cut through,
or a ligature around, the axons.
It seems that two factors are produced by the two cells types. Either both factors are needed for
endocrine activity, or the two factors are combined to produce a single hormone. In some insects
the lateral neurosecretory cells are seen only in the later stages of larval life, which again suggests
that they have a special role to play.
The next question is how the release of the brain hormone is controlled. In Rhodnius,
Wigglesworth showed that secretion begins when the abdomen is swollen by the bloodgorged
gut. It was the swelling and not the blood which was important. Molting can be blocked by
transecting the ventral nerve cord, which suggests that sensory impulses, elicited by stretching,
ascend the ventral nerve cord and stimulate neurosecretion. Recent work shows that in Rhodnius
