Through this slide share the users will know about the moulting, factors affecting and how moulting is controlled by hormonal secretions.

1. MOULTING AND
HORMONAL STUDIES
KUNTAMALLA SUJATHA M. SAI ABHISHEK,
Asst. Prof., Sericulture Department, Project Officer,
Kakatiya University, BDL,
Hanamkonda, Warangal Hyderabad.
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3. MOULTING
The periodic cast of body covering at a particular interval in life cycle of an insect is known
as moulting or ecdysis or apolysis. It is controlled both genetically and harmonically. There
are 2 phases in the larval stage of insects.
• Feeding phase
• Moulting phase
Feeding phase:- At this phase larva eats voraciously.
Moulting phase:- It is also known as moulting phase. In this phase worm’s skin become
loose, wrinkled and keep its mouth upward, translucent, dull and stops feeding.
There are 3 different kinds of moulters based on number of moulting.
• Trimoulter:- Moulting takes place 3 times in its larval stage. Ex: Primitive silkworm.
• Tetramoulters:- moulting takes place 4 times in its larval stage. Ex:- Bombyx mori L
• Penta moulters:- Moulting takes place 5 times in its larval stage. Ex:- Bombyx mandarina.
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4. Types of moulting
There are at least 5 different types of moulting in silkworm, namely di, tri, tetra, penta and
hexa moulters. The most common type in the primitive domestic silkworm varieties and in
the wild moths are trimoulters, where almost all present day commercial strains are tetra
moulters.
Tetra moulting characters has been considered as the standard type in silkworm genetics.
The expression of moulting characters is also affected partly by the sex linked maturity
genes.
Factors affecting the moultinism
• Low temperature (200C).
• High temperature and humidity during the young stage.
• The young and soft mulberry leaves.
• Some mulberry races are liable to produce three moulters than other races.
• The length of light and dark times per day.
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6. HORMONAL STUDIES
Moulting in silkworms is controlled by secretions of harmone in the brain, the corpora
altata and the prothoracic gland. The secretion of these harmones is controlled by
environmental conditions.
The brain in B.mori secretes brain harmone that activates the prothoracic gland to secrete
ecdysin which initiate maturation or moulting. Soon after this hormone goes into action, the
corpora altata secretes juvenile hormone (JH) which inhibits further maturation and
perpetuates the larval characters resulting in moulting out and emergence of the next stage
larva. At the time of metamorphosis the balance in effects of JH and ecdysin is in favour of
metamorphosis.
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8. At the time of moulting the content of the exuvial gland and malphigian tubule flows out
between the new and old skins to help casting the exuvia. Action of prothoracic gland is
controlled by the moulting genes while that of corpus altataum by sex linked maturity genes.
Enzymatic
• Enzymes are the biocatalysts which speed up the reaction.
• Moulting requires certain enzymes like polyphenol oxidases dopa carboxylase and acetyl
transferase.
• Polyphenol oxidases are said as key enzymes in moulting.
• Phenol oxidase level is higher during moulting stage and decreases after moulting.
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10. Hatching Larval duration Moulting time
I instar 2 – 3½ days 1st moult (24 hrs)
II instar 2 – 2½ days 2nd moult (20 hrs)
III instar 3 - 3½ days 3rd moult (24 hrs)
IV instar 4 - 4½ days 4th moult (24 hrs)
V instar 6 – 7 days Spinning
Total 22 – 25 days AVG 23 – 24 days
Table showing moulting durations
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