MODULE 4: Silkworm Rearing Technology

B.Sc. Zoology (RTU Hojai University)

Comprehensive Study Material

Introduction to Silkworm Rearing Technology

Silkworm rearing technology refers to the scientific methods and techniques used for the successful cultivation and management of silkworms for silk production. In non-mulberry sericulture, proper rearing technology is extremely important because the health, growth, cocoon quality, and silk yield of silkworms depend largely on the rearing environment and management practices. Eri and Muga silkworms are highly sensitive to environmental conditions, food quality, hygiene, and diseases. Therefore, scientific rearing methods are essential for obtaining healthy larvae and high-quality silk.

Silkworm rearing involves several activities such as preparation of rearing house, maintenance of environmental conditions, feeding management, cleaning and disinfection, handling of larvae, cocoon formation, and harvesting. Proper rearing technology reduces mortality, prevents diseases, and increases silk productivity.

Rearing House and Rearing Site

The rearing house is the place where silkworms are kept and reared throughout their larval stages. A good rearing house provides suitable environmental conditions such as proper temperature, humidity, ventilation, and protection from predators and diseases. The success of sericulture depends greatly on the condition and management of the rearing house.

The rearing house should be constructed in a clean, elevated, and well-drained area to avoid waterlogging and dampness. The building should receive adequate sunlight and fresh air but should also protect silkworms from direct sunlight, heavy rain, and strong winds. Proper ventilation is necessary because silkworms require sufficient oxygen and fresh air for healthy growth.

The walls and floors of the rearing house should be smooth and easy to clean. Windows should be covered with nets to prevent entry of insects, rodents, lizards, ants, and birds. The rearing room must be spacious enough to accommodate rearing trays and allow easy movement for workers.

Hygiene is extremely important in the rearing house. The room should be cleaned regularly to remove leftover leaves, larval waste, dead larvae, and dust. Dirty conditions encourage the growth of pathogens and pests. Before each rearing cycle, the entire rearing room must be disinfected properly.

For Muga silkworms, rearing is generally carried out outdoors on host plants under natural conditions because Muga silkworms are semi-domesticated. However, early-stage larvae may sometimes be protected indoors before transfer to outdoor plantations. Eri silkworms are completely domesticated and are mainly reared indoors.

Rearing Appliances

Various appliances and equipment are used during silkworm rearing for feeding, cleaning, handling, and cocoon formation. Proper use of rearing appliances improves hygiene, labour efficiency, and larval survival.

Rearing Trays

Rearing trays are shallow trays made of bamboo, plastic, or wood used for keeping silkworm larvae during feeding and growth. They provide sufficient space for larvae to feed and move comfortably. Overcrowding in trays should be avoided because it may lead to disease spread and poor growth.

Feeding Stands and Shelves

Shelves or stands are used to arrange rearing trays vertically to save space and improve ventilation. They also make management and cleaning easier.

Bed Cleaning Nets

Bed cleaning nets are used to separate larvae from leftover leaves and waste materials. Fresh leaves are placed over the net, and larvae crawl upward for feeding, leaving the waste below. This method helps maintain cleanliness and reduces disease incidence.

Leaf Choppers

Leaf choppers or knives are used for cutting host plant leaves into small pieces suitable for young larvae. Tender chopped leaves are easier for early instar larvae to consume.

Mountages

Mountages are structures provided to mature larvae for cocoon spinning. They may be made of bamboo, straw, twigs, or other materials. Proper mountages allow larvae to spin healthy cocoons without overcrowding.

Hygrometers and Thermometers

These instruments are used to measure humidity and temperature inside the rearing house. Environmental monitoring is essential because silkworms are highly sensitive to climatic changes.

Disinfection in Silkworm Rearing

Disinfection is one of the most important aspects of silkworm rearing technology. Silkworms are highly susceptible to bacterial, viral, fungal, and protozoan diseases. Proper disinfection helps prevent infection and maintain hygienic rearing conditions.

The rearing house, trays, appliances, and equipment should be thoroughly disinfected before the beginning of each rearing cycle. Workers should also maintain personal hygiene while handling larvae.

Two important disinfectants commonly used in sericulture are formalin and bleaching powder.

Formalin

Formalin is a solution containing formaldehyde gas dissolved in water. It is widely used as a disinfectant in silkworm rearing houses. Formalin kills bacteria, fungi, and other microorganisms present in the rearing room and equipment.

Before rearing begins, formalin solution is sprayed on floors, walls, trays, shelves, and appliances. After spraying, the room is kept closed for several hours for effective disinfection. Proper ventilation is necessary afterward because formalin fumes may be harmful to humans.

Bleaching Powder

Bleaching powder is another important disinfectant used in sericulture. It contains calcium hypochlorite and releases chlorine, which destroys harmful microorganisms.

Bleaching powder is used for disinfecting floors, rearing equipment, and surrounding areas. It is also useful for maintaining sanitation around host plant gardens and drainage systems. Proper use of bleaching powder helps reduce disease outbreaks.

Early Age Rearing

The early larval stages of silkworms are known as chawki or early age stages. Usually, the first and second instar larvae are considered early age larvae. These larvae are delicate, sensitive, and require special care.

Young larvae require soft, tender, fresh, and nutritious leaves because their mouthparts are not fully developed. Leaves should be chopped into small pieces for easy feeding.

During early age rearing, strict control of temperature and humidity is essential. Young larvae need relatively high humidity and moderate temperature for healthy growth and moulting. Cleanliness is extremely important because young larvae are highly susceptible to diseases.

The larvae should be protected from overcrowding, direct sunlight, sudden temperature changes, and excessive moisture. Bed cleaning should be performed regularly to remove waste and prevent microbial growth.

Proper care during early age rearing significantly improves survival rate and ensures healthy development during later stages.

Late Age Rearing

The later larval stages, usually third to fifth instars, are known as late age larvae. During this stage, the larvae consume large quantities of leaves and grow rapidly. Silk gland development becomes highly active, and the larvae prepare for cocoon spinning.

Late age larvae require larger feeding space and good ventilation because overcrowding may cause stress, disease spread, and accumulation of heat and moisture. Mature leaves are suitable for late instar larvae because they can consume tougher plant material.

The quantity of food increases greatly during late age rearing. Therefore, sufficient supply of fresh leaves is necessary. Bed cleaning becomes more important because late age larvae produce large amounts of waste materials.

Temperature and humidity should be maintained carefully. Excessive humidity may encourage fungal diseases, while low humidity may lead to dehydration and poor cocoon formation.

Late age larvae are more resistant than young larvae but are still vulnerable to diseases and environmental stress. Proper management during this stage ensures formation of healthy cocoons with good silk yield.

Environmental Conditions in Silkworm Rearing

Environmental conditions play a major role in silkworm growth, metabolism, disease resistance, and silk production. The most important environmental factors are temperature, humidity, light, and air circulation.

Temperature

Temperature greatly affects feeding activity, growth rate, moulting, cocoon formation, and silk production. Silkworms require moderate temperature for normal physiological activities.

Young larvae generally require slightly higher temperatures, while late instar larvae perform better under slightly lower temperatures. Extremely high temperatures may cause stress, dehydration, and mortality. Very low temperatures reduce feeding and slow down growth.

Sudden fluctuations in temperature are harmful because they disturb larval metabolism and increase susceptibility to diseases.

Humidity

Humidity refers to the amount of moisture present in the air. Proper humidity is essential for larval growth and successful moulting.

Young larvae require higher humidity because it prevents drying of tender body tissues and facilitates moulting. Older larvae require moderate humidity. Excessively high humidity promotes fungal growth and disease outbreaks, while very low humidity causes dryness and poor feeding.

Proper humidity management helps maintain healthy larval development and good cocoon quality.

Light

Silkworms are sensitive to light conditions. Moderate light is generally suitable for rearing. Very strong light or direct sunlight may stress larvae and increase room temperature.

During moulting, dim light and quiet surroundings are preferred because larvae remain inactive. Proper light management contributes to smooth growth and development.

Air Circulation and Ventilation

Fresh air is essential for silkworm respiration and healthy growth. Poor ventilation causes accumulation of carbon dioxide, moisture, foul smell, and harmful gases inside the rearing room.

Good ventilation removes excess heat and moisture and reduces disease occurrence. However, strong winds or drafts should be avoided because they may dry out larvae and leaves.

Proper air circulation maintains a healthy rearing environment and improves larval performance.

Feeding Management

Feeding management is one of the most important aspects of silkworm rearing technology. Silkworms require fresh, clean, nutritious, and disease-free leaves for healthy growth.

Leaves should be harvested carefully and fed immediately to maintain freshness. Wilted, dry, dusty, or diseased leaves should never be used because they may harm larvae.

Young larvae are fed chopped tender leaves several times a day, while mature larvae receive larger whole leaves. Feeding intervals should be regular to ensure continuous nutrition.

Proper feeding management improves larval growth, cocoon weight, silk quality, and disease resistance.

Mounting of Mature Larvae

At the end of the larval stage, mature larvae stop feeding and become restless in search of suitable places for cocoon spinning. At this stage, mountages are provided.

Mountages provide support for cocoon formation and prevent overcrowding. Proper mounting ensures uniform cocoon shape, better silk quality, and reduced cocoon damage.

The spinning process generally takes several days, during which the larva secretes silk continuously from the silk glands to form the cocoon.

Importance of Hygiene in Silkworm Rearing

Hygiene is essential throughout the rearing process. Dirty conditions encourage growth of pathogens, pests, and parasites that may cause severe disease outbreaks.

Regular cleaning, proper disposal of waste, disinfection of equipment, use of disease-free leaves, and maintenance of personal hygiene by workers help reduce infections.

Good hygiene practices improve survival rate, cocoon quality, and overall silk production.

Economic Importance of Scientific Rearing Technology

Scientific silkworm rearing technology increases silk production, improves cocoon quality, and reduces losses caused by diseases and environmental stress. Proper rearing practices support sustainable sericulture and provide employment opportunities in rural areas.

In Assam and North-East India, scientific rearing of Eri and Muga silkworms contributes significantly to the economy and preservation of traditional silk industries. Adoption of improved rearing technology enhances productivity and income generation for farmers and sericulturists.

Conclusion

Silkworm rearing technology is the scientific foundation of successful non-mulberry sericulture. Proper rearing house management, use of suitable appliances, maintenance of environmental conditions, disinfection practices, feeding management, and hygienic care are essential for healthy growth of Eri and Muga silkworms. Early age and late age larvae require different management techniques for optimal development. Scientific rearing technology improves cocoon production, enhances silk quality, prevents diseases, and supports sustainable sericulture development. Therefore, efficient silkworm rearing practices are essential for the economic success of the silk industry in Assam and North-East India.

What is Scientific Rearing?

Scientific rearing methods in sericulture involve a systematic approach to managing silkworms to ensure maximum survival and high-quality silk production. For RTU Hojai students, these methods are categorized into environmental control, nutritional management, and hygienic practices.

1. Preparation and Disinfection

Before rearing begins, the entire environment must be sterilized to eliminate pathogens.

Disinfection: The rearing house and all appliances (trays, stands, nets) are treated with Formalin (2%) or Bleaching Powder.
Hygienic Maintenance: A "disinfection basin" containing a bleaching powder solution is often kept at the entrance for workers to wash their hands and feet.

2. Early Age Rearing (Chawki Rearing)

This refers to the care of the 1st and 2nd instar larvae. Because they are delicate, they require specialized "Chawki" methods:

Nutritional Care: They are fed tender, succulent leaves (top leaves of the plant) chopped into small pieces to match their small mouthparts.
Climate Control: They require a higher temperature ($26-28^{\circ}\text{C}$) and higher humidity ($80-90\%$) to facilitate easy growth and smooth moulting.

3. Late Age Rearing

This involves the 3rd, 4th, and 5th instar larvae. As the worms grow, the focus shifts to mass management:

Spaced Feeding: To prevent the spread of diseases and overheating, the larvae are spread out across more trays to increase "floor space."
Leaf Quality: They are fed mature, whole leaves. During the 5th instar, their consumption increases dramatically, as this is when the silk glands develop most rapidly.
Bed Cleaning: Using cleaning nets, the "bed" (waste, leftover leaves, and excreta) is removed regularly to prevent the buildup of ammonia and moisture, which causes fungal diseases.

4. Environmental Management

Scientific rearing relies on maintaining an "optimum micro-climate" inside the rearing house:

Temperature: Ideally maintained between $24^{\circ}\text{C}$ and $27^{\circ}\text{C}$. High heat can cause dehydration, while low heat slows down metabolism.
Ventilation: Proper air circulation is vital to remove the carbon dioxide produced by thousands of breathing larvae and to prevent "stagnant air," which leads to the spread of Grasserie and Flacherie.

5. Mounting and Spinning

When the larvae turn translucent and stop feeding, they are transferred to mountages (Chandrika or bamboo hurdles).

Density: Scientific methods dictate that larvae should not be overcrowded on the mountage to avoid "double cocoons" (two worms spinning one cocoon), which cannot be reeled properly.
Environment: During spinning, the room should be well-ventilated with low humidity ($60-70\%$) to help the liquid silk solidify quickly.

Summary of Scientific Steps

Step	Action	Purpose
Disinfection	Spraying Formalin/Bleaching Powder	To kill bacteria, viruses, and fungi.
Chopping Leaves	Cutting leaves for Chawki	To assist tiny larvae in feeding.
Bed Cleaning	Using nets to remove waste	To maintain hygiene and prevent disease.
Spacing	Increasing tray area as worms grow	To prevent suffocation and infection.
Mounting	Transferring to bamboo frames	To provide a structure for spinning cocoons.

How does the process of bed cleaning change as the silkworm progresses from the 1st instar to the 5th instar?

MODULE 5: Cocoon Harvesting & Silk Processing

B.Sc. Zoology (RTU Hojai University)

Comprehensive Study Material

Introduction to Cocoon Harvesting and Silk Processing

Cocoon harvesting and silk processing are among the most important stages of sericulture because they directly determine the quantity and quality of silk produced. After silkworm larvae complete their growth, they spin cocoons around themselves using silk secreted from the silk glands. These cocoons are then collected, processed, and converted into silk fibres for textile production.

In non-mulberry sericulture, especially Eri and Muga culture, cocoon harvesting and processing require careful scientific handling because improper methods may damage the silk fibres and reduce commercial value. The quality of cocoons depends on several factors such as healthy larval growth, suitable mountages, environmental conditions, and proper harvesting techniques.

Silk processing includes cocoon harvesting, cocoon storage, boiling or cooking of cocoons, reeling or spinning of silk fibres, drying, twisting, weaving, and finishing. The methods used differ between Eri and Muga silk because of differences in cocoon structure and silk filament continuity.

Mountages in Sericulture

Mountages are structures or devices provided to mature silkworm larvae for spinning cocoons. When larvae complete feeding during the final instar stage, they stop eating and search for suitable places to spin cocoons. Proper mountages provide sufficient support and space for cocoon formation.

Good mountages are essential because they help produce healthy, clean, compact, and uniform cocoons. Improper mountages may lead to deformed cocoons, poor silk quality, overcrowding, and increased disease risk.

The mountages used in sericulture should possess certain qualities. They should provide enough space and ventilation, prevent cocoon sticking, be easy to clean and disinfect, and allow easy harvesting of cocoons.

The two important types of mountages commonly used in non-mulberry sericulture are bamboo mountages and rotary mountages.

Bamboo Mountages

Bamboo mountages are traditional mountages widely used in rural sericulture, especially in Assam and North-East India. They are made from bamboo strips, twigs, or woven bamboo structures. Bamboo is easily available, inexpensive, lightweight, and eco-friendly, making it suitable for village-level sericulture.

In bamboo mountages, mature larvae climb into the spaces between bamboo strips and spin cocoons individually. The spaces between the strips allow proper air circulation and prevent overcrowding. Bamboo mountages are simple in design and easy to construct.

The advantages of bamboo mountages include low cost, local availability, easy handling, and suitability for both Eri and Muga culture. However, bamboo mountages may absorb moisture and become contaminated with pathogens if not cleaned properly. Therefore, regular cleaning and disinfection are necessary.

Traditional bamboo chandrikas, spiral mountages, and twig mountages are commonly used forms of bamboo mountages.

Rotary Mountages

Rotary mountages are improved scientific mountages designed to enhance cocoon quality and labour efficiency. These mountages are generally made of plastic, metal, or specially designed lightweight materials.

Rotary mountages can rotate or move, allowing better space utilization, improved aeration, and uniform cocoon formation. They help reduce cocoon deformities and facilitate easy harvesting. Since the larvae remain separated, the chances of cocoon sticking and disease spread are reduced.

Rotary mountages are more hygienic and durable than traditional bamboo mountages. They are easier to clean and disinfect and can be reused for long periods. However, they are more expensive and may not be easily affordable for small-scale rural farmers.

Scientific sericulture centers and commercial silk farms often use rotary mountages to improve cocoon production and silk quality.

Cocoon Formation

After mounting, the mature silkworm larva begins spinning silk around itself using secretions from the silk glands. The silk passes through the spinneret and hardens on contact with air to form a continuous filament.

Initially, the larva spins a loose outer layer called floss. Gradually, it spins dense layers of silk to form the cocoon shell. Inside the cocoon, the larva transforms into a pupa.

The spinning process generally takes two to three days. Proper environmental conditions such as suitable temperature, humidity, and ventilation are essential during cocoon formation. Excessive moisture or poor ventilation may damage cocoons and encourage fungal growth.

Cocoon Harvesting

Cocoon harvesting refers to the collection of cocoons from mountages after completion of spinning. Harvesting is an important stage because improper handling may damage cocoons and reduce silk quality.

Cocoons are usually harvested after the larva completely transforms into a pupa and the cocoon shell hardens properly. Harvesting too early may damage immature cocoons, while delayed harvesting may allow adult moth emergence, which breaks the silk filament and reduces commercial value.

During harvesting, defective, stained, diseased, pierced, and deformed cocoons are separated from healthy cocoons. Only healthy and compact cocoons are selected for silk processing.

Harvesting should be done carefully to avoid crushing or tearing the cocoon shell. Workers generally remove cocoons manually from mountages and clean off loose floss fibres.

In Muga culture, harvesting is performed before the moth emerges so that continuous silk filaments can be obtained during reeling. In Eri culture, however, the moth is generally allowed to emerge naturally because Eri silk is commonly processed by spinning rather than reeling. Therefore, Eri silk production is considered more humane and is often called Ahimsa silk production.

Sorting and Grading of Cocoons

After harvesting, cocoons are sorted and graded according to quality. Sorting helps separate good cocoons from defective ones.

Healthy cocoons are compact, uniform, properly shaped, and free from stains or holes. Defective cocoons may include double cocoons, thin-shelled cocoons, malformed cocoons, stained cocoons, or diseased cocoons.

Grading is important because high-quality cocoons produce better silk yield and superior fibres. Proper grading improves market value and industrial efficiency.

Storage of Cocoons

Storage of cocoons is necessary before silk extraction or marketing. Proper storage maintains cocoon quality and prevents damage caused by moisture, pests, fungi, or moth emergence.

Cocoons should be stored in clean, dry, cool, and well-ventilated rooms. Excessive humidity encourages fungal growth and spoilage, while high temperatures may stimulate premature moth emergence.

During storage, cocoons are generally spread in thin layers on bamboo trays or racks to allow proper air circulation. Overcrowding should be avoided because it increases heat and moisture accumulation.

Protection from rats, ants, insects, and birds is essential during storage. Regular inspection helps detect spoilage or infestation.

In commercial sericulture, stifling is often performed before storage. Stifling involves killing the pupa inside the cocoon using heat, steam, or sunlight to prevent moth emergence. This preserves the continuous silk filament necessary for reeling.

However, in Eri culture, stifling is usually avoided because the moth is allowed to emerge naturally.

Stifling of Cocoons

Stifling is the process of killing the pupa inside the cocoon before the adult moth emerges. If the moth emerges naturally, it cuts through the cocoon and breaks the silk filament into small pieces.

Stifling is mainly important in Muga and mulberry silk production because continuous filaments are required for reeling. Common methods of stifling include hot air treatment, steam treatment, sun drying, and boiling.

Proper stifling preserves silk quality and increases reeling efficiency.

Silk Processing

Silk processing refers to the methods used for extracting silk fibres from cocoons and converting them into usable yarn. The two main methods of silk extraction are reeling and spinning.

The method used depends on the type of cocoon and the continuity of silk filaments.

Cocoon Boiling or Cooking

Before silk extraction, cocoons are usually boiled or cooked in hot water. This process softens the sericin, the gummy protein that binds silk fibres together.

Boiling loosens the silk filaments and makes them easier to unwind during reeling. It also kills the pupa inside the cocoon if stifling has not already been performed.

The temperature and duration of boiling must be carefully controlled because excessive boiling may weaken silk fibres, while insufficient boiling may make reeling difficult.

In some traditional methods, alkaline substances may be added to improve softening of sericin.

Reeling of Silk

Reeling is the process of unwinding continuous silk filaments from cocoons. This method is mainly used for Muga silk because Muga cocoons contain long continuous filaments.

After boiling, the outer floss is removed and the filament ends are located. Several filaments from different cocoons are combined and reeled together onto a reel to form raw silk thread.

Reeling produces smooth, strong, lustrous, and continuous silk yarn suitable for weaving high-quality silk fabrics. The quality of reeled silk depends on cocoon quality, boiling efficiency, and reeling techniques.

Traditional hand reeling and modern machine reeling methods are used in sericulture industries.

Spinning of Silk

Spinning is the process of converting short or broken silk fibres into yarn by twisting them together. This method is mainly used for Eri silk because Eri cocoons are open-mouthed and the silk filament becomes discontinuous after moth emergence.

In spinning, the cocoons are softened, opened, and the fibres are separated manually or mechanically. The fibres are then twisted together to form yarn.

Spun silk is softer, warmer, and more wool-like than reeled silk. Eri silk fabrics produced from spun yarn are highly valued for shawls, blankets, and winter garments.

Spinning allows the use of broken or pierced cocoons that cannot be reeled.

Difference Between Reeling and Spinning

Feature	Reeling	Spinning
Silk filament	Continuous filament	Short broken fibres
Cocoon type	Closed cocoon	Open or pierced cocoon
Silk quality	Smooth and lustrous	Soft and wool-like
Main silk type	Muga silk	Eri silk
Process	Unwinding filament	Twisting fibres
Commercial use	Fine silk fabrics	Warm clothing and shawls

Drying and Twisting of Silk Yarn

After reeling or spinning, silk yarn is dried properly to remove excess moisture. The yarn may then be twisted to increase strength and durability.

Twisting improves weaving quality and prevents fibre breakage during textile production.

Weaving and Finishing

The processed silk yarn is woven into fabrics using handlooms or power looms. Traditional Assamese silk weaving is famous worldwide for its artistic beauty and cultural significance.

After weaving, finishing processes such as washing, dyeing, polishing, and ironing are performed to improve appearance, texture, and durability.

Muga silk retains its natural golden colour, while Eri silk may be dyed into various colours.

Importance of Cocoon Harvesting and Silk Processing

Proper cocoon harvesting and silk processing are essential for obtaining high-quality silk and maximizing economic returns. Scientific processing techniques reduce silk wastage, improve yarn quality, and increase market value.

The silk industry provides employment to thousands of rural families, especially women, in Assam and North-East India. Traditional silk processing also preserves cultural heritage and supports cottage industries.

Muga silk is internationally famous for its golden shine and durability, while Eri silk is valued for its softness and eco-friendly production methods.

Economic Importance of Eri and Muga Silk

Non-mulberry silk production contributes significantly to the economy of Assam and North-East India. Silk products such as mekhela-chador, shawls, scarves, decorative fabrics, and handicrafts have high national and international demand.

Scientific cocoon harvesting and processing improve productivity, export value, and employment generation in the sericulture sector.

Conclusion

Cocoon harvesting and silk processing are vital stages in non-mulberry sericulture. Proper use of mountages, scientific harvesting methods, careful storage, cocoon boiling, and efficient silk extraction techniques determine the quality and quantity of silk produced. Bamboo and rotary mountages provide suitable support for cocoon formation, while reeling and spinning are the two major methods of silk extraction. Reeling is mainly used for continuous filament silk such as Muga silk, whereas spinning is used for discontinuous fibres such as Eri silk. Scientific silk processing improves silk quality, enhances economic value, and supports sustainable sericulture development in Assam and North-East India.

Explain cocoon processing steps

Cocoon processing is the critical bridge between rearing silkworms and producing high-quality silk yarn. For B.Sc. Zoology students at RTU Hojai, it is important to understand that the steps vary slightly depending on whether you are processing Muga (reeled) or Eri (spun) silk.

1. Harvesting

The first step is the collection of cocoons from the mountages.

Timing: Cocoons are harvested 7–10 days after the larvae begin spinning.
Sorting: During this stage, "defective" cocoons (melted, stained, double, or malformed) are separated from the healthy ones to ensure uniform silk quality.

2. Stifling (Killing the Pupa)

This process is primarily used for Muga silk to prevent the adult moth from emerging.

Purpose: If the moth emerges, it cuts through the silk layers, breaking the continuous filament into thousands of small pieces.
Methods: Cocoons are subjected to high heat via steam, hot air, or sun drying.
Note: For Eri silk, stifling is often skipped because the moth is allowed to emerge naturally (producing "Ahimsa silk"), and the broken fibers are later spun like wool.

3. Storage

After stifling, cocoons are stored in a cool, dry, and well-ventilated place. Proper storage prevents fungal growth and protects the cocoons from pests like ants and rats before they are sent for reeling.

4. Degumming (Cocoon Boiling)

Silk filaments are held together by a natural "gum" called sericin.

Process: Cocoons are boiled in hot water (sometimes with a mild alkali like soda) to soften the sericin.
Effect: This allows the long, continuous core of fibroin to be easily pulled away from the cocoon shell without breaking.

5. Reeling vs. Spinning

This is the final stage where the silk is extracted into thread.

Reeling (for Muga/Mulberry):
- Used for continuous filaments.
- The ends of several filaments (4 to 10) are found and twisted together to form a single, strong thread of raw silk.
- This is done using a Bhir (traditional) or a mechanized reeling machine.
Spinning (for Eri):
- Used for discontinuous (broken) fibers.
- Because the Eri moth leaves a hole in the cocoon, the silk cannot be reeled. Instead, the fibers are pulled apart and twisted together into yarn, similar to how cotton or wool is spun.
- Traditionally done using a Takli or a spinning wheel (Charkha).

Comparison of Processing Methods

Step	Muga Silk (Reeled)	Eri Silk (Spun)
Pupa Treatment	Stifled (killed) to keep filament intact	Moth emerges naturally (Ahimsa)
Boiling	Lightly boiled to soften gum	Thoroughly boiled to remove gum
Extraction	Reeling (continuous thread)	Spinning (twisted short fibers)
End Product	Fine, glossy, and smooth	Soft, warm, and wool-like

What are the specific chemical differences between fibroin and sericin that make boiling a necessary step in this process?

MODULE 6: Pests and Diseases of Eri and Muga Silkworms

B.Sc. Zoology (RTU Hojai University)

Comprehensive Study Material

Introduction to Pests and Diseases in Sericulture

Pests and diseases are among the greatest problems faced in sericulture because they reduce silkworm survival, cocoon quality, silk yield, and economic profit. Eri and Muga silkworms are highly sensitive organisms and are easily affected by insects, microorganisms, and adverse environmental conditions. Diseases and pests may attack silkworms during any stage of their life cycle, including egg, larva, pupa, and moth stages.

In non-mulberry sericulture, proper identification, prevention, and control of pests and diseases are extremely important for successful cocoon production. Poor hygiene, contaminated food plants, overcrowding, improper temperature and humidity, and lack of disinfection increase the chances of disease outbreaks. Scientific rearing management and sanitation are therefore essential to maintain healthy silkworm populations.

The major pests affecting Eri and Muga silkworms include Uzi flies, ants, and beetles. Important diseases include protozoan diseases such as Pebrine, viral diseases such as Grasserie, fungal diseases such as Muscardine, and bacterial diseases such as Flacherie.

Pests of Eri and Muga Silkworms

Pests are organisms that attack silkworms directly or indirectly and cause economic losses. They may feed on silkworms, damage cocoons, or spread diseases. Pest attacks reduce larval health, cocoon quality, and silk production.

Uzi Fly

The Uzi fly is one of the most destructive pests of silkworms. Its scientific name is Exorista bombycis. It is a parasitic fly belonging to the order Diptera. The adult female Uzi fly lays eggs on the body surface of silkworm larvae.

After hatching, the maggots penetrate the larval body and feed internally on the tissues and body fluids of the silkworm. The infected larvae become weak, stop feeding, and eventually die before cocoon formation or during the pupal stage.

The maggots later emerge from the dead silkworm and pupate outside. Heavy infestation by Uzi flies causes serious economic losses in sericulture because infected larvae cannot produce healthy cocoons.

The spread of Uzi fly is favoured by poor hygiene, improper netting, and lack of pest control measures. Protection of rearing houses using nets and destruction of infected larvae help control the pest.

Ants

Ants are common predators of silkworm eggs, larvae, pupae, and even cocoons. They attack weak or diseased larvae and may carry away small larvae and eggs.

Ant attacks are especially dangerous during early larval stages because young larvae are delicate and unable to defend themselves. Ants may also disturb larvae during moulting and cocoon spinning.

Ant infestation is common when rearing houses are dirty or when food materials are left scattered around the room. Ants enter through cracks, walls, doors, or floors in search of food.

Control of ants involves maintaining cleanliness, using water barriers around rearing stands, applying lime or ash around the rearing room, and sealing cracks and entry points.

Beetles

Certain beetles attack silkworm cocoons and stored silk materials. Beetles may damage cocoon shells, feed on pupae, or spoil stored cocoons and silk fibres.

Some beetles also attack host plant leaves, indirectly affecting larval nutrition. Damage caused by beetles reduces cocoon quality and increases silk wastage.

Proper storage conditions, sanitation, and regular inspection help prevent beetle infestation in sericulture units.

Diseases of Eri and Muga Silkworms

Diseases are abnormal conditions caused by microorganisms such as protozoa, viruses, fungi, and bacteria. Silkworm diseases spread rapidly under unhygienic conditions and may cause mass mortality.

The important diseases of Eri and Muga silkworms include Pebrine, Grasserie, Muscardine, and Flacherie.

Protozoan Disease: Pebrine

Pebrine is a serious protozoan disease of silkworms caused by Nosema bombycis, a microscopic spore-forming protozoan parasite. Pebrine is highly infectious and may spread from one generation to another through eggs. This type of transmission is called transovarial transmission.

The disease affects all stages of the silkworm life cycle, including eggs, larvae, pupae, and moths. Infected larvae become weak, sluggish, and irregular in growth. Black pepper-like spots may appear on the body surface, which is why the disease is called Pebrine, meaning “pepper-like.”

Diseased larvae show poor feeding, delayed moulting, reduced silk production, and high mortality. Cocoons produced by infected larvae are generally small, thin, and of poor quality.

Pebrine spreads through contaminated eggs, infected larvae, diseased moths, contaminated leaves, and rearing appliances. Since the disease spreads rapidly, it is considered highly dangerous in sericulture.

Prevention of Pebrine mainly depends on strict hygiene and use of disease-free eggs. Microscopic examination of moths and eggs is important for detecting infection. Infected larvae and moths should be destroyed immediately to prevent further spread.

Viral Disease: Grasserie

Grasserie is a viral disease caused mainly by nuclear polyhedrosis virus (NPV). It commonly affects silkworm larvae during later stages of development.

The infected larvae become swollen, fragile, and translucent. Their body appears shiny and oily due to accumulation of viral fluid inside the tissues. The larvae lose appetite, become sluggish, and stop feeding.

In advanced stages, the body wall becomes weak and easily ruptures, releasing milky fluid containing viral particles. Diseased larvae usually die before cocoon formation.

Grasserie spreads through contaminated leaves, rearing equipment, infected larval fluids, and poor environmental conditions. High temperature, excessive humidity, overcrowding, and poor ventilation increase disease incidence.

There is no effective cure for Grasserie once infection occurs. Therefore, prevention is extremely important. Proper hygiene, disinfection, removal of diseased larvae, and maintenance of suitable environmental conditions help control the disease.

Fungal Disease: Muscardine

Muscardine is a fungal disease caused mainly by the fungus Beauveria bassiana. It is one of the most common fungal diseases of silkworms.

The fungal spores enter the silkworm body through the cuticle and germinate inside the tissues. Infected larvae lose appetite, become inactive, and gradually die.

After death, the body becomes hard, dry, and covered with white fungal growth. This white powdery appearance is characteristic of white Muscardine disease. In some cases, green or yellow fungal growth may also occur depending on the fungal species involved.

Muscardine spreads rapidly under high humidity, poor ventilation, damp conditions, and unhygienic rearing environments. Wet rearing beds and contaminated equipment favour fungal growth.

Prevention of Muscardine requires proper ventilation, maintenance of moderate humidity, regular cleaning, and disinfection of rearing houses and appliances. Diseased larvae should be removed and destroyed immediately.

Bacterial Disease: Flacherie

Flacherie is a bacterial disease of silkworms caused by several bacterial species affecting the digestive system. It is often associated with poor nutrition, contaminated leaves, improper environmental conditions, and physiological stress.

Infected larvae become weak, soft, and inactive. They lose appetite and show digestive disturbances such as vomiting and diarrhoea. The body becomes flaccid, darkened, and foul-smelling.

The digestive tract becomes damaged due to bacterial multiplication and toxin production. Diseased larvae usually die rapidly, especially during later larval stages.

Flacherie spreads through contaminated food, dirty rearing beds, infected faeces, and poor sanitation. High temperature, overcrowding, stale leaves, and poor ventilation increase the risk of infection.

Control of Flacherie involves feeding fresh and clean leaves, maintaining proper hygiene, avoiding overcrowding, and removing diseased larvae immediately.

Prevention and Control of Pests and Diseases

Prevention is the most effective method for controlling pests and diseases in sericulture because treatment after infection is often difficult and ineffective. Scientific management practices greatly reduce disease incidence and improve cocoon production.

Hygiene and Sanitation

Proper hygiene is the foundation of disease prevention. Rearing houses, trays, mountages, and appliances should be cleaned regularly. Leftover leaves, waste materials, and dead larvae must be removed immediately.

Workers should maintain personal cleanliness while handling silkworms. Hygienic conditions reduce the growth and spread of pathogens and pests.

Disinfection

Disinfection destroys harmful microorganisms present in the rearing environment. Formalin and bleaching powder are commonly used disinfectants in sericulture.

The rearing room and equipment should be disinfected before every rearing cycle. Proper disinfection reduces bacterial, fungal, and viral infections.

Proper Ventilation

Good air circulation removes excess moisture and harmful gases from the rearing house. Proper ventilation prevents fungal growth and reduces humidity-related diseases such as Muscardine.

However, strong winds and sudden temperature fluctuations should be avoided because they may stress the larvae.

Temperature and Humidity Management

Silkworms require suitable temperature and humidity for healthy growth. Excessive humidity encourages fungal diseases, while extreme temperatures weaken larvae and increase susceptibility to infections.

Environmental conditions should therefore be maintained carefully according to the larval stage.

Use of Healthy Food Leaves

Fresh, clean, and disease-free host plant leaves should be supplied to silkworms. Stale, wet, dusty, or contaminated leaves should never be used because they may carry pathogens.

Nutritious leaves improve immunity and resistance to diseases.

Removal of Diseased Larvae

Infected larvae should be identified and removed immediately from the rearing trays to prevent disease spread. Dead larvae should be burned or buried safely.

Keeping diseased larvae in the rearing room increases contamination risk.

Use of Disease-Free Eggs

Healthy and disease-free eggs are essential for successful rearing. Microscopic examination of moths and eggs helps detect Pebrine infection and prevents transmission to the next generation.

Protection Against Pests

Rearing houses should be protected using nets, screens, and barriers to prevent entry of Uzi flies, ants, beetles, rodents, birds, and lizards.

Water barriers, lime powder, and regular cleaning help control ants and crawling insects.

Importance of Disease Management in Sericulture

Disease management is essential for maintaining healthy silkworm populations and improving silk production. Pests and diseases may cause heavy economic losses by reducing larval survival, cocoon weight, and silk quality.

Scientific disease prevention methods improve productivity, increase farmer income, and ensure sustainable sericulture development. Proper pest and disease management is especially important in Assam and North-East India, where Eri and Muga silk industries are economically and culturally significant.

Economic Importance

Healthy silkworm rearing leads to increased cocoon production, better silk quality, and higher market value. Effective pest and disease control reduces mortality and improves the profitability of sericulture.

The silk industry provides livelihood opportunities to thousands of rural families in Assam and contributes significantly to traditional handloom and textile industries.

Conclusion

Pests and diseases are major challenges in non-mulberry sericulture and greatly affect silkworm health and silk production. Important pests of Eri and Muga silkworms include Uzi fly, ants, and beetles, while major diseases include Pebrine, Grasserie, Muscardine, and Flacherie caused by protozoa, viruses, fungi, and bacteria respectively. These diseases spread rapidly under unhygienic and unsuitable environmental conditions. Proper hygiene, disinfection, ventilation, environmental management, use of disease-free eggs, healthy food supply, and immediate removal of infected larvae are essential for prevention and control. Scientific pest and disease management plays a crucial role in improving cocoon quality, silk yield, and the economic success of sericulture in Assam and North-East India.

The "Natural Rights"