Sericulture: Introduction, Types, Life cycle,Disease and Management ( Zooconcept. In)

Sericulture:

In this article we will discuss about the sericulture :

Contents:

1.Introduction

2.Historical background of the sericulture

3.Types of Silk worm

4.Life cycle of Silk worm

5.Sericulture process

6.Disease and Management

INTRODUCTION

Silk was one of the world’s most exclusive fibers because of matchless characteristics like lustre, sensuousness, comfort and remarkable mechanical properties (high breaking strength, toughness and initial stiffness). Silk has been under use by human beings for use of various purposes since ancient times. pure silk is one of the finest and most beautiful natural fibers of the world and is said to be ‘The Queen of Fibers’ and ‘Bio steel’ because of its strength.
Silk clothes have a look and feeling of affluence that no other cloth can equal. Due to its great value and usefulness there have been many attempts in various parts of the world for the large-scale production of silk. Different rearing techniques are applied in different parts of the world for large scale production of silk threads of fine quality, this is known as sericulture.

Sericulture scenario in India

Sericulture, the cultivation of silkworm and their food plants to produce silk is a cottage industry. It provides ample opportunity to the rural agrarian population particularly to the tribals and poor people of India to generate money for maintenance of their sustainable livelihoods as it involves low capital investment, short gestation period and high returns.
India is blessed with production of five kinds of silk viz. Mulberry, eri, muga, tasar (Tropical) & temperate (oak) tasar. Mulberry sericulture is mainly practiced in five states namely Karnataka, Andhra Pradesh, Assam, Jharkhand, West Bengal, Tamil Nadu major silk producing states in country. Eri silk produced in Odisha, west Bengal, Bihar etc. Assam famous for muga oak tasar in Himalayan belt region. In international scenario, India earns the reputation to occupy the second position in the production of silk. The raw silk production of India amounted to over thirty-five thousand metric tons in fiscal year – 2020.

Historical Background of the sericulture

There is no authentic information regarding the origin and use of silk. The ancient literature gives two views. According to one view, silk industry originated for the first time in India at the foot of the Himalayas, and from there it spread to other countries of the world.
Second view, which has greater acceptance, says that this industry originated in China about 3000 B.C. According to this, a Chinese Princess Siling Chi was the first to discover the art of reeling an unbroken filament from a cocoon. This art was kept a close secret for nearly 3000 years. This art later on spread to the rest of the world through several agencies like civil war refugees, war prisoners’ marriage of royal families etc.

TYPES OF SILK AND SILKWORM

Moths belonging to families Saturniidae and Bombycidae of order Lepidoptera and class Insecta produce silk of commerce. There are many species of silk-moth which can produce the silk of commerce, but only few have been exploited by man for the purpose. Mainly five types of silk have been recognised which are secreted by different species of silk worms.Silkworm types are-

1.Mulberry silkworm
2.Silkworm
3.Tasar silkworm
4.Oak tasar silkworm
5.Muga silkworm

1. mulberry silkworm :

The bulk of the commercial silk produced in the world comes from this variety and often silk generally refers to mulberry silk. This silk is supposed to be superior in quality to the other types due to its shining and creamy white colour. It is secreted by the caterpillar of Bombyx mori which feeds on Solely mulberry leaves. In India the major mulberry silk producing states are Karnataka, Andhra Pradesh, west Bengal, Tamil Nadu and Jammu & Kashmir which together account for 92% of countries total mulberry raw Silk production.

2. Eri silkworm :

Eri silk us the product of silkworm Philosamia ricin that feeds on mainly castor leaves. Eri culture is a household activity practiced mainly for protein rich pupae, a delicacy for the tribal. The silk is used indigenously for preparation of cheddar for own use by the tribal. Its colour is also creamy white like mulberry silk, but is less shining than the latter. In India this is cultured mainly in the north-eastern state, Assam, Odisha, West Bengal, Bihar etc.

3. Tasar silkworm :

Tasar silk secreted by caterpillars of Antheraea mylitta, A. Paphia, A. Royeli, A. Pernyi, A. Proyeli etc. This silk is of coppery colour. They feed on the leaves of Arjun, Asan, Sal, Oak and various other secondary food plants. Tasar silk mainly produced in the state Jharkhand, Odisha, West Bengal, Bihar, cattish garh, Andhra Pradesh.

4.Oak Tasar silkworm:

It is fine variety of Tasar generated by the silkworm Antheraea proyeli J. They feed in natural food plants of oak, found in abundance in the sub Himalayan belt of India, covering the states of Manipur, Himachal Pradesh, Uttar Pradesh, Assam, Jammu & Kashmir.

5 .Muga silkworm:

Muga obtained from semi domesticated multivoltine silkworm, Antheraea assamensis. This golden yellow colour silk is prerogative of India and the pride of Assam state. Muga Silk is high value product used in products like sarees, mekhales, chaddars.

THE LIFE CYCLE OF SILKWORM

The life cycle of silk moth starts when a female silk moth lays egg. The caterpillar or larvae are hatched from the eggs of the silk moth. The silkworms feed on mulberry leaves and give rise to pupa. In the pupa stage, a weave is netted around by the silkworm to hold itself. After that it swings its head, spinning a fibre made of a protein and becomes a silk fibre. Several caterpillars form a protective layer around pupa and this covering is known as the cocoon. The silk thread (yarn) is obtained from the silk moth’s cocoon.

The life cycle of the silkworm is explained by following stages: –

Stage1: Egg

An egg is the first stage of the life cycle of the silkworm. The egg is laid by a female moth which is mostly the size of small dots. A female moth lays more than 350 eggs at a time. In the springtime, the eggs hatch due to the warmth in the air. This procedure happens once in every year.

Stage 2: Silkworm

A hairy silkworm arises after the eggs crack. In this stage of silkworms, the growth happens. They feed on mulberry leaves and consume a large amount of these leaves for around 30 days before going to the next stage.

Stage3: Cocoon

In this stage, silkworms spin a protective cocoon around itself. It is the size of a small cotton ball and is made of a single thread of silk.

Stage 4: Pupa

The pupa stage is a motionless stage. In this stage, people kill the pupa by plunging the cocoon into boiling water and unwind the silk thread.

Stage 5: Moth

In this stage, the pupa changes into an adult moth. The female moth lays eggs after mating and thus the life cycle of silkworm begins again.

SERICULTURE STAGES OF PRODUCTION (PROCESSES)

The following Nine main steps involved in rearing process of silkworm. The steps are:

1.Disinfection
2 .Egg hatching
3.Egg incubation and larval Brushing
4. Feeding the Larvae
5. Spacing
6. Bed Cleaning
7. Caring during Moulting
8. Mounting
9.spinning the cocoon and reeling process

Disinfection:

It is the most important operation that to be carried out prior to the commencement of rearing. Clean the rearing site by removing weeds, grass and other bushes from around the tasar plantation. Disinfection of everything including rearing places is carried out by physical, chemical or radiation methods.

(i) Physical methods:

These are cheap, con­venient and easy to operate, e.g.

Sunlight:

Dry­ing of rearing appliances in sunlight can cause disinfection. However, sun drying cannot be carried out during winter and rainy seasons, and some appliances are likely to be damaged by exposure to sunlight.

Steam:

Disinfection by steaming may be used for rearing room and some appliances (not made of bamboo or wood). However, initial cost for installing the steaming apparatus like boiler and pipeline is high.

Hot air:

It is also a good sterilising method but cannot be used in routine sericulture because of its production cost.

(ii) Chemical method:

Most frequently used chemicals for disinfection method in sericulture include chlorine as chloramine, iodine as iodophores, phenol as cresol and hexachlorophene, formaldehyde as formalin (2%), bleaching powder 2% in slaked lime (add 20 gram bleaching powder and 5 gram slaked lime in 1 litre of water), before using for rearing, wash all the rearing applicences by spraying with 5% formalin and then keep them for sun drying etc. These are used as spray or fumigant. Precautions should be taken during and after the applications of such chemicals.

Egg hatching:

The first stage in Sericulture process is the production of silkworm egg in a controlled environment. Female moth deposit about 400eggs at a time. Hatching of egg is normally done by spreading eggs over shallow trays. Eggs are kept in hatching shed, which is closely regulated at 80°F for about 8-10days. Finally, tiny eggs are hatched into larvae caterpillar, at this point the larvae is about quarter of an inch.

Egg incubation and larval Brushing technique:

It ensures proper embryonic development and higher hatching of eggs. Incubate the egg at 28-300c temperature and 70-80% humidity for a period of 8-10 days. just before hatching place the egg in basin in single layer and cover them in small twig of fresh tender leaves of tasar food plant. Allow hatched larva to crawl over the leaves and transfer the left-over larvae to basin with the help of brush. Brushing is the separation of newly hatched larvae from their egg shells and transferring them to rearing trays from the egg cards. The newly hatched larvae are black, bristly and called ants. Brushing is usually starting at 10 am when peak hatch­ing occurs. Brushing can be done by various ways:

(a) Brushing from loose eggs:

Fine meshed net or thin muslin cloth can be placed over the newly hatched larvae. Then freshly chopped mulberry leaves are sprinkled over that net / cloth. The larvae start to crawl up through the holes onto the leaves. After sometimes, the larvae along with leaves are gently tapped on the rearing bed.

(b) Brushing from egg cards:

From egg cards, newly hatched larvae can be transferred by the following:

(i) Feather:

Here the egg card is held vertically above freshly prepared rearing bed and then by gentle strokes of a feather, the larvae are pulled out from the card on the rearing bed. How­ever, this method is little bit crude and may cause some injury to the larvae.

(ii) Husk:

Here powdered husk is sprinkled over newly hatched larvae on the egg card. Then freshly cut mulberry leaves are sprinkled over the centre of husk. The larvae crawl up the husk to reach the leaves. After sometimes, the larvae are brushed from husk by means of a feather on the rearing bed.
However, in all cases of brushing, care should be taken not to touch the newly hatched larvae with hands.

Feeding the Larvae:

Both the quality and size of the cocoons depend mainly on the quality of mulberry leaves fed by larvae during rearing. After a little practice, the amount of leaves that to be given per feeding to fulfill the appetite of the worms, is adjusted. The amount of food given also depends on races and voltinism of the moths.
However, maxi­mum amount should be given during the active feed­ing stage of instar and no food should be given dur­ing moulting. In Indian sericulture, nowadays four feedings per day is allowed. In case of shoot and floor rearing’s, three feedings per day are sufficient.
In all larvae, several feeding stages can be noticed during their development, viz., active feeding stage when larvae feed maximum during the instar, sparsely feeding stage when they eat less, usually at pre-moulting stage when larvae empty their gut; non-feeding stage when the larvae do not take any food usually during moulting.
Of the total ingestion during entire larval development, nearly 85% of food is taken during IVth and Vth instar stages. During feeding, generally a gap of 2 hours is given before and after each moulting. Young worms are always fed with tender leaves while late stages are given mature mulberry leaves. To enable the larvae to feed easily, young worms have to be given chopped leaves but for mature worms, full leaves or young branches or shoots may be given.

Spacing:

The silkworms grow very rapidly from age to age and increase many times their weight and size from the previous instar. The total increase in weight from hatching to the end of Vth instar is about 7,000 to 10,000 times.
Crowded situation in rearing trays results in increased humidity, heat, fermentation of litter, all of which will in turn cause under development of larvae, wastage of feeding leaf and unhygienic condition. To provide more and adequate space for the growing worm, the rearing space has to be extended at each stage and this is called spacing. Spacing is usually done along with bed cleaning and is given once a day.

Bed Cleaning:

The rearing tray of silkworms accumulates some unconsumed leaves after each feeding, exuviae after moulting, excreta, dead or diseased larvae, etc. All these if not cleaned, combine to form a thick and damp litter which promotes the growth of different micro-organisms, generation of heat and injurious gases and depletion of oxygen. Hence, it is very necessary to remove the litter perio­dically and the process of its removal is called bed cleaning.
Bed cleaning can be done by using paddy husk, straw and bed cleaning net. During 1st instar, bed cleaning should be done once during per moulting, during 2nd instar twice, once after moult and before next moult.
During 3rd instar thrice, i.e. after moult, before next moult and once in the middle. During 4th and 5th instars once in a day in case of shelf rearing. However, in case of floor or shoot rearing, bed cleaning should be done once in each instar.

Caring during Moulting:

In commercial races of silkworm, moulting occurs four times, lasting for 15-30 hours. During this time, the worm does not take any food, wriggles out of the old skin and comes out with a new, soft skin.
Care taken during moulting includes stopping and resuming feeding at appropriate time to ensure uniform growth, keeping the bed dry and disinfected either by dusting Resham Keed Oushad (RKO), formulated by CSR and TI, Mysore or by spraying Labex, formulated by Berhampur.
Besides disinfecting action, RKO can reduce grasserie in different seasons and can increase growth rate of larvae leading to improved cocoon quality. Labex has anti-muscadine effect and can inhibit early moulters from resuming feeding leading to uniform growth.

Mounting:

Mounting is the process of transferring the ripe worms to the mountages. On the mountage, the ripe worms exude silk, spin the cocoon around itself and transformed into the pupa inside it. The pupa after metamorphosing into adult moth comes out by piercing open the cocoon. The aim of sericulture is to rear the silkworm providing them optimum conditions and mountages so that they can spin good cocoon with high and best silk content.
Mounting is done by following methods:

(a) Hand picking:

Ripe worms are collected in a tray one by one by hand and then transferred to the mountages. Though some worms may be injured while picking and handling, but by this method, only ripe worms can be picked and distributed more uniformly in the mountages.

(b) Simultaneous mounting:

In this method, a number of mature larvae is collected simultaneously and transferred to the mountage. Here, mature, immature and over-mature worms are mounted together; hence, cocoon formed by them may not be uniform.

(c) Net method:

In the rearing tray, when worms are ripened, straw rope nets / rush nets or cleaning nets are spread over the rearing beds and left for some time. Ripe worms crawl alone on the nets while unripe worms continue feeding. The nets with ripe worms are then shaken on the mountages to transfer them without touching by hand.

(d) Branch method:

Here small branches of mulberry are spread over the rearing bed. Ripe worm’s craw ling over them are then shaken off on the mountages. Besides branch, dried weeds (Russia) or cut straw (Japan) can also be used for transferring the ripe worms to mountages. Number of ripe worms per mountage is very important. In general, one ripe worm requires an area that is the square of its body length for spinning its cocoon. Too wide spacing may cause wastage of silk for spinning the preliminary web. Again, too close spacing may result in formation of double cocoon (which are not reliable), staining of cocoons with excreta of the worms and also formation of damp cocoons. The optimum density for Chandrika is 50 worms per 0.1-2m.
Precautions to be taken during mounting:
• Only ripe worms should be mounted. Unripe worms spoil other cocoons with their excreta while overripe worms hastily spin cocoons which are malformed, flattened, sticky and inferior.
• An optimum temperature (24°C) should be maintained in spinning place. Too low temperature causes delayed formation of cocoons, and affects colour, lustre and texture of the silk. Too high temperature results in the formation of deformed cocoons with thick filament.
• The ideal humidity for spinning is 60-70%. Ventilation is needed to dry the wet silk into firm cocoon and to evaporate the water or excreta released by the worms during spinning.
• The mountages should be disinfected before and after use.
• The spinning worms should not be disturbed which otherwise would result suspension of spinning and breaking of thread.

Spinning the cocoon

The silkworm now starts spinning of cocoon and liquid silk secretions extrude from two glands, this viscous clear liquid is forced through the openings on the mouthpart of larva, harden on exposure to air and form filaments. A second pair of glands nearly secrets a gummy binding fluid called sericin which binds two filaments (fibrous) together steadily the silkworm rotates its body into a movement over some 3,00,000 times constructing a cocoon and producing a about a mile of a silk filament. With in the few days of making its coccons the silk producers kill the pupa in the cocoon. The unusual method of killing one-
• Immersing the cocoon in the steam for few minutes
• By baking cocoon in hot oven
• By placing the common in the boiling water
• By freezing the common to death

After killing pupa take it to Process for: (a) Reeling ,(b) Throwing ,(c) Degumming

(a) Reeling:

The process of unwinding of the filament from the cocoon is called reeling, this process is carried out in a building called reeling plant. The cocoon is soaked in boiling water to softer the sericin gum that is holding the filament in place. The cocoons are taken out and loose fluffy silk on outside is cleaned off which is then used in production of spun silk yarn.
The coccons are again placed hot water basin and Labour use a brush or broom to push cocoon up and down in the water until some look and a filament becomes attached to broom. The filament is drowning out gently, the cocoon tumbles around in water and gradually unreel itself.
Reeling done by the following reeling silk reeling machines-
• Pedal-cum-motorized reeling-cum-twisting machine
• Hand operated wet reeling machine
• Motorized Tasar reeling machine
• KAMDHENU; improved vertical reeling-cum-spinning machine

(b) Throwing:

It is a process in which two or more mutual filament stands are combined and twisted together to form heavier threads.

(c) Degumming:

The process of removing the sericin from raw silk or thrown is called degumming the gum is removed from finished yarn by boilers with soap and water.

SILKWORM DISEASE AND THEIR MANAGEMENT

The success of silkworm rearing mainly depends on the protection of crop from the diseases. Despite the ideal climate, superior quality of leaves. Following are the diseases-

Grasserie

Grasserie disease is the most serious viral disease in silkworm. It is also known as nuclear polyhedrosis, milky disease or hanging disease.

Causative agent:

B. mori nucleopolyhedrovirus (BmNPV)

Route of infection :

Virus enters through mouth with the contaminated leaf into the silkworm body, multiplies inside, ruptures the skin, oozes the milky white haemolymph and spreads the infection to other individuals.

Symptoms :

Shining and fragile skin, restlessness, swollen inter-segmental regions, rupture of skin, oozing of milky white haemolymph and hanging of larvae by their prolegs.

Viral Flacherie

The BmIFV and BmDNV do not produce any highly visible external symptoms and mostly interfere with the growth, development and reduce the reproductive capacity of silkworm.

Causative agent :

B. mori Infectious Flacherie Virus (BmIFV) and B. mori Densovirus (BmDNV)Route of infection :Ingestion

Symptoms :

BmIFV: Gradual reduction in size, retarded growth, reduction in body weight, transparent thorax, flaccid condition of body, dissolved alimentary canal followed by vomiting of digestive juice. BmDNV: Body flaccidity, thorax transparency, diarrhoea and pale yellow alimentary cana.

Bacterial Flacherie

The diseases caused by bacterial pathogens in silkworm is collectively known as flacherie due to the flaccid nature of the diseased larvae. Bacterial diseases of silkworms are divided into three major types namely bacterial diseases of the digestive tract, bacterial septicaemia and Bacterial toxicosis. Flacherie is also caused by the combined infection of bacteria and viruses.

Causative agent:

Bacterial diseases of digestive tract: Streptococcus faecalis, S. Faecium; Staphylococci sp., Septicemia: Serratia marcescens, Toxicosis: Bacillus thuringiensis
Route of infection: Ingestion, Wounding – direct entry of bacteria in the silkworm haemocoel can occur after Breaking of the cuticle

Predisposing factors:

High temperature, high humidity, feeding poor quality mulberry leaves, unhygienic conditions, Overcrowded rearing and poor ventilation

Symptoms:

The larvae become flaccid, the growth of infected larvae retards, become inactive and vomit gut Juice, digestion in the infected larvae gets disturbed, voids foul smelling semisolid excreta (chain type excreta), faeces become soft with high moisture content and rectal protrusion Occurs, cephalothoracic region becomes translucent

Septicemia:

Dead larvae turn red in colour; Toxicosis: Diseased larvae paralyse, dead Larvae turn black in colour, rot and emit foul smell

Muscardine

Muscardine in silkworm is caused by many species of such as Beauveria bassiana, Metarrhizium anisopliae, Nomuraea rileyi, Spicaria prassina. They are Often named for the colour of the layer each fungus leaves on its host.
Causative agent: White muscardine by Beauveria bassiana, Green muscardine by Metarrhizium anisopliae and Nomuraea rileyi.

Route of infection:

Skin, the conidia from infected silkworm / alternate hosts contaminate rearing environment, Rearing house and rearing bed.

Symptoms:

The infected larvae become inactive, stop feeding, experience loose elasticity and Die. The fungus leaves the body of its host covered in powdery conidia (white in case of Beauveria and green in case of Metarrhizium and Nomuraea) and finally the body hardens.

Pebrine

Pebrine is the most dreaded disease of the silkworm where the spores can survive outside the Host for several years.

Causative agent:

Several kinds of microsporidia such as Nosema bombycis, Vairimorpha sp., Pleistophora sp. and Thelophania sp.

Route of infection:

The disease spreads through ingestion of mulberry leaves contaminated with the pebrine spores and also by transovarial (from infected mother moth to embryo) and transovumtransmission (from surface contaminated eggs at the time of hatching)

Symptoms:

Retarded growth of larvae, delayed moulting, loss of appetite. In the advanced stage of infection, the larvae become flaccid with vomiting and anal discharges, the colour of the larvae changes to rustic brown or red with black spots.

Aspergillosis

Aspergillosis is a fungal disease in silkworm which occurs during Chawki stage (I & II instar worms).

Causative agent:

Aspergillus flavus and A. tamarii
Route of infection:

Skin, the conidia from infected silkworm / alternate hosts contaminate rearing environment, rearing house & rearing bed. Infection starts when conidia comes in contact with silkworm body.

Symptoms:

Infected larvae stop feeding, become lethargic and the larvae die soon due to aflatoxin produced by the fungus in the host. Aerial hyphae appear a day after death and later conidia cover the body giving particular colour according to the Aspergillus species (dark green in case of A. flavus and dark brown in case of A. tamarii.

Prevention and management of silkworm diseases:

• Practice two times thorough disinfection of rearing house, its surroundings and appliances with any recommended disinfectant (Asthra / Sanitech / Serichlor / Serifit / Decol).
• Select carefully the disease free layings (dfls).
• Maintain personal and rearing hygiene during silkworm rearing.
• Collect the diseased larvae at early stage of infection and ensure their proper disposal.
• Maintain optimum temperature and humidity in the rearing house.
• Feed good quality mulberry leaf, avoid overcrowding in the rearing bed and provide proper ventilation in the rearing house.
• Apply bed disinfectants as per schedule and quantity (Ankush / Vijetha / Rakshak / Resham Jyothi).
• Feed Amruth (botanical based curative formulation against silkworm diseases) as per schedule and quantity.

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