Sericulture
Silk is the finest and most beautiful natural fibers of the world & is said to be the
“Queen of fibers”. They are very fine and light wt.& soft. They are very strong
having high elastic property. Silk producing is an insect called silk moth. Altogether
a no. of sp. Founded produces silk but only few species are used for sericulture.
Types of silk:
Mainly 4 species of silk have been recognized which are secreted only by different
sp. of silk worm.
Mulberry silk -Bombyx mori- It belongs to the family – bombicidae which feeds on
mulberry leaves. They are superior in quality to the other types due to its shining
and creamy white colour.
Tasar silk- It is belonging to family saturnidae which feeds on the leaves of arjun,
sal, oak and various secondary food plants. Tasar silk is secreted by the caterpillar
of Antherea mylita, A.paphia, A.royelli and A.pernyi etc. This is copper colour.
Eri silk- it is produced by phylosomia ricini which feeds on castor and keseru leaves.
It is creamy-white but less shining.
Muga silk- it is obtained from the caterpillar of Antheria assama which feeds on
som, suwalo, champa, mejankari etc.
LIFE HISTORY OF SILK:
Out of 4 different types, mulberry and eri are manufactured from domesticated
silkworms, where as tasar and muga silk worms are wild in nature. The life cycle of
these 4 types of silk moths are much common as they lay eggs from which
caterpillar hatches. They eat and grow and produces cocoon for their protection,
then pupate inside cocoon.
After some time, moth emerge from the cocoon male and female mate, lay
eggs, and repeat their life cycles.
Mulberry silk worm: The race of silkworm by which one crop is taken in one year
is called univoltine, more than one is multivoltine and two crops is taken in one
year is called bivoltine races. Different crosses are generally chosen for spring and
autumn rearing.
Life history of mulberry silk worm: The adult B. Mori is about 2.5 cm. in length and
pale creamy white in colour, flight is not possible in female because of its heavy
body wt. the moth is unisexual in nature and does not feed during its very short
period of 2-3 days.
Fertilization- Is internal preceded by copulation. Just after emergence, male moth
copulates with female about 2-3 hrs. and if not separated they may be dying after
few hrs. of copulating with female. One moth lay eggs400-500 eggs depending
upon climatic condition and supply of food material to the caterpillar from which
the female moth is obtained. They lay eggs on the upper part of the mulberry leaves
and attached gelatinous secretion of female moth.
Eggs. Eggs are laid by the female is rounded and white in colour. There are two
types of eggs - diapause and non-diapause. Eggs are called seeds.
Hatching: The eggs after 10 days of incubation hatch into a larva called caterpillar.
After hatching caterpillar needs continuous food supply because they are voracious
feeder and non-adequate food supply causes problems in growth in caterpillar.
Caterpillar: The newly hatch caterpillar is yellowish white in colour. The caterpillar
is provided with well-developed mandibulate type of mouth parts adapted to feed
easily on mulberry plant leaves. As they are voracious feeder, they grow rapidly
which moult by moulting and 5th instar respectively. It takes 21-25 days after
hatching. A full-grown caterpillar develops salivary glands, stop feeding and
undergo pupation. The time taken for the full growth of caterpillar from young to
well grown stage various with regards to temp., humidity and food supply and types
of races.
Pupa: - The caterpillar stops feeding and moves towards corner among the leaves
and secretes a sticky fluid through silk glands. The secreted fluids come out through
the spinneret and takes the form of long fine threads of silk which hardens with the
exposure to air and wrapped around the body of caterpillar in the form of covering
called the cocoon.
Cocoon: - They are white coloured bed of pupa whose outer thread is irregular and
inner threads are regular. The length of continuous threads secreted by a pupa for
the formation of a cocoon is about 1000-12000m., which is required 6 days to
complete. The pupal period last for 10-12 days and the pupa cuts the cocoon and
emerge into the adult.
Emergence of Imago: - Due to active metamorphic changes during pupation period
the abdominal pseudo legs disappear, and two pairs of wings develops. The silk
worms within the cocoon secretes an alkaline fluid to moisten it’s one of the ends
and as a result moistened and become soft where the threads are cut open by the
silkworm. Finally, a hole is formed through which a feeble adult moth squeezes out
of the cocoon.
ECONOMIC IMPORTANCE OF SILK/USES OF SILK:
Bulk of silk fibers produced is utilize in preparing silk clothes, uses of pure silk
decreased gradually due to its high-cost value and costly maintained. Clothes in
which silk fibers are combined with other natural and synthetic fibers are in great
demands not only in India but also in foreign countries. Besides silk being used as
garments, it is also used in other industries and for military purpose. It is used
manufacture of fishing fibers, parachutes, cartridge bags, insulation coils for
telephone and wireless receiver, tires of racing cars, filter cloths, for floor mills and
in medical dressing and suture material, fabrics for garments in various weaves,
plains, twill, stain, crepe, georgette and velvet, knitted goods such as vests, gloves,
socks, stocking dyed and printed ornaments, fabrics for saris’, jackets, shawls and
wrappers are made out of these materials.
DISEASES OF SILKWORM:
This profitable industry is often threatened not only by various disease resulted
from the viral, fungal bacterial and protozoan infection but by insect predators,
birds and other higher animals.
Diseases are –
• Pebrine- Nosema
• Flacherie-Bacterial disease
• Grassarie- Viral
• Muscardine-fungal and
• Maggot disease- Tricolyga sorbillans, a fly.
FOOD PLANTS:
• Mulberry: mulberry
• Muga: Som, Suwalo (primary), Sal, Mayankuri, Champa, Gulanch (secondary)
• Tasar: Arjun, Asan, Sal, Oak, Bagari
• Eri: Castor (primary), Keseru.
REARING OF SILK WORM:
MULBERRY SILK
The word rearing does not mean only the feeding of caterpillars as often
understand, but a continuous care from egg laying through aestivation,
hibernation, incubation, early-stage larval care, late-stage larval care to the
production of cocoon.
Grainage Management:
The establishment of grainage is to provide good quality of seed to rearers
and maintenance of original quality of races. For this purpose, due care should be
taken of the crop of silk worm for seed production from the very beginning i.e., the
cater pilar stage, by providing them with proper nutrition and protection from the
attack of disease, keeping these points of views initial selection is made on the base
of percentage of dead pupae during normal development. First selection is made
by separating out dead cocoons and nest selection in the grainage.
After first selection cocoons are subjected to sex separating by cutting one
end of the cocoon either manually or cocoon opener.
For production of commercial eggs loose forms of cocoons are used and
collective mother examination is done either through mass Pebrine detecting
machine or general microscopic observation. They are then kept for mass
emergence.
Emergence of moth and fertilization: - When kept for emergence at room
temperature, mass emergence of adult takes place. As per their nature, just after
emergence, male moth starts moving around the female. Males are very much
active whereas the females which are loaded with eggs are incapable of flying. If
not separated at once in cages males starts copulating with the females but the
eggs obtained from this female fertilized from the male of the same stock is useless
for the seed. So that, males and female just after emergence have to be separated
into separate cages without their mating. Now one female of one lot is kept with
the male of the other lot and at once they form pairing and compute for 3 hours.
After completion of mating males should be separated and may be used for the
fertilization of other females. Now fertilized females are subjected to egg laying.
Egg laying:
After fertilization female starts egg laying and in the duration of 24 hours it
completes egg laying process. The eggs laid by one female are about 400-500
depending upon their races. Female dies after egg laying. These eggs are called
seeds. These eggs are kept in sterilized trays and stored at 4º C under laboratory
condition or sometimes kept at hill stations in diapause condition.
The stages of egg production are of three types-
i. Production and supply of parent’s eggs,
ii. Rearing of parent eggs and
iii. Production of commercial F1 seed. The grand parent and parent’s eggs
are produced by recognized and reputed organization. This commercial
seed is supplied to the rearers.
Hatching:
This is an important phage of sericulture industry because as soon as the larvae are
hatched, they start feeding voraciously. So only those sericulturists who would be
able to supply sufficient amount of fresh mulberry leaves to young hatched larvae,
could perform successful sericulture problem otherwise young ones will die
resulting great loss to sericulture Industry. This is why the hatching has to be
controlled accelerated or postponed by artificial treatment under refrigerated
condition. Proper hatching of seeds advanced techniques has been developed in
which eggs are collected and kept with mulberry leaves working as stimulant for
hatching in shady places on white sheet of paper in insect proof trays on a stool.
For this purpose, the legs of stool must be kept in water so that insects may not
crawl and damage the hatching eggs.
Post cocoons processing: - The method of obtaining silk thread from cocoon is
known as post cocoon processing. This includes-
Stifling- The process of killing the cocoon is termed as stifling. Sericulturist
should be very much careful that before the emergence of silk worm. Good sized
cocoons of 8-10 days old for further process and dropped into hot water or subject
to steam or dry heat, Sun exposure for 3 days or fumigation.
In this way pupae or cocoon are killed. The killing of cocoon in boiling water
helps in softening the adhesion of silk thread among themselves and loosing of
outer thread to separate freely, facilitating the unbinding of silk thread.
Reeling and spinning – the process of removing then thread from the killed
cocoon is called as reeling. 4 or 5 free ends of the threads of these cocoons are
passed through the eyelet and guides to twist into one thread and wound round a
large wheel from which it is transferred to spools. Thus, the silk obtained on the
spool is known as raw silk or reeled silk. The waste outer layer or damaged cocoons’
thread are separated, tested and then filaments are spun. The spunned silk is
known as ‘spun silk’ the raw silk is further boiled stretch and purified by acid or by
fermentation and then carefully washed over again and again to bring about the
well-known lustre on the thread.
Silk:
Silk is a pasty secretion of silk worm produced by the silk gland. The silk glands are
actually modified salivary glands which are long and sac like as this pasty secretion
comes in contact with air it becomes hard and forms strong and pliable silk strands.
This secretion forms 2 cores of fibroins and sericin protein.
i. A tough elastic insoluble protein consisting of 75% of fibers weight and
cemented with sericin from the middle region of the silk gland and the time of
secretion and
ii Sericin a gelatinous protein which is easily soluble in warm water. Some
quantity of wax and carotenoid pigments are also detected.
Fibroin is made up glycine, alanine, tyrosine.
Sericin is easily soluble in water and composed of sericin, alanine and
leucine.
