Silkworm rearing

Silkworm hybrid

The improved bivoltine hybrids namely, CSR2 x CSR4 and double hybrid (Krishnaraja) are recommended under IVLP.

Chawki rearing

From hatching to its full-grown stage, the silk worms pass through five instars and the worms up to stage two are called young age worms or chawki.  As they are susceptible to infections and vulnerable to adverse weather conditions, special care is required for rearing of chawki. Hence, it is advisable to obtain silkworm reared under controlled conditions in separate chawki rearing centers.  The package of practices for chawki rearing is entirely different from late age rearing.

Late age rearing

Rearing of late age worms begins from third instar.  These worms are voracious feeders.  Various practices required for rearing are indicated below:

Rearing house

Mulberry silkworm rearing, being completely domesticated, demands specified environmental conditions like temperature (24-28 C) and relative humidity (70-85%).  It is therefore necessary to evolve measures for economic cooling through selection of proper material for wall and roof fabrication, orientation of building, construction method, design, etc.  Further, enough space must be available to carry out leaf preservation, chawki rearing, late age rearing and moulting.  It should also be convenient enough to conduct effective cleaning and disinfection.

The size of the rearing house depends upon the quantum and type of rearing.   A floor area of 400 sq ft. can provide rearing space for 100 dfls (dfl: Disease Free Layings; 1 dfl = 500 larvae)

Rearing appliances

The late age silkworms do not tolerate high temperature, high humidity and poor ventilation. Hence, the rearing house should have cross ventilation facilities to bring down the room temperature and for removal of vapour and harmful gases generated from large quantities of excreta produced by silkworms. The minimum requirement of equipments for 100 dfls (50,000 larvae) is given in Table .

Table : Rearing appliances required for rearing 100 dfls (50, 000 larvae)

Disinfection

Disinfection of rearing house and appliances should be made twice before rearing that is once with 5% bleaching powder (immediately after the completion of previous crop) and another time with 2.5% Sanitech (Chlorine di-oxide) solution just 2 days before the next crop. The schedule suggested for disinfection is given in Table 2.

Schedule of disinfection for rearing house and appliances

Shoot rearing –an economical way

In this method of silkworm rearing, the last 3 stages of rearing will be conducted by giving mulberry shoots instead of individual leaves. This method is the most economical method of rearing, as it helps to save about 40% of rearing labour. The other advantages are,

• Reduction in contamination and spread of diseases due to less handling of silkworms.
• Secondary contamination is reduced, as worms and leaves are separated from faeces.
• Maintenance of hygienic condition.
• Better preservation of leaf quality both during storing and on the bed.
• Better aeration in the bed.
• Better cocoon quality and higher survival of larvae.
• Less non-recurring expenditure.

Feeding

• Initiate feeding with 50-55 days old shoots harvested at the height of 3-4 feet in the cooler hours of the day preferably in the morning. 60-65 days old shoots should be fed to fifth age worms.
• The harvested shoots should be preserved loosely in vertical position in cool and moist place by covering with cleaned, disinfected and wet gunny cloth.
• The quantum of mulberry shoot required is 460 Kg in 4th instar and 2880 Kg in 5th instar for bivoltine silkworms.
• Daily 3 feeds (6 AM, 2 PM and 10 PM) schedule should be followed.
• Avoid feeding of soiled or over matured leaves.
• Distribute the larvae uniformly in the bed during every feeding. The bed space required for the worms of 100 dfls at the end of the fifth stage is 600 sq ft.
• Remove the under sized and all suspected diseased worms carefully with chopsticks before every cleaning / feeding to avoid the contamination. The picked larvae should be put into 2% bleaching powder in 0.3% slaked lime solution.

Bed cleaning

• Remove the unhealthy larvae, if any and put them into 2% bleaching powder in 0.3% slaked lime solution.
• Don’t spill the bed refuse on the floor of the rearing room while cleaning the bed.

Maintenance of temperature and humidity

• The ideal temperature for the late age rearing is 26 C for III instar larvae, 25 C for IV instar and 24 C for V instar larvae. 80% humidity is required for III instar larvae and 70% is required for IV and V instar larvae.
• Adjust the temperature and relative humidity as per requirement by using cooling, heating and humidifying appliances such as air cooler, room heater, charcoal stove, wet gunny cloth or by sprinkling water on the roof or using wet sand.
• Good cross ventilation will help to reduce the body temperature of the silkworm.

Care during moulting

• Ensure good ventilation and dry condition in the rearing house during moulting period.
• Spread the bed gently soon after the worms settle for moult and apply slaked lime powder uniformly over the bed to ensure drying of bed.
• Avoid high fluctuation of temperature and humidity as well as strong wind and bright light.
• Resume feeding when 95% of worms come out of moult

Maintenance of hygiene

• Wash hands and feet with disinfectant solution before entering in to the rearing house. To begin with, the hands and feet should be washed with alkaline soap and then dipped in disinfectant solution (2.5% Sanitech/ Serichlor in 0.5% slaked lime solution or 2% Bleaching powder in 0.3% slaked lime).
• Wash hands in disinfectant solution and water after picking of diseased worms, after bed cleaning and before feeding.
• Pick the diseased worms every day into a basin with lime powder and bleaching powder mixture and dispose off carefully by burning or burying at a distant place.
• Keep the rearing room clean and well aerated during silkworm rearing.

Application of bed disinfectant

Vijetha, Vijetha Green and Ankush are the silkworm body and rearing seat disinfectants for the prevention of silkworm diseases. The method of usage is as follows.

• Take the powder in a thin cloth and dust over the silkworms @ 5 g/square feet after every moult and once on 4th day of final instar after bed cleaning as given in Table 3.

Table 3: Schedule and quantity to be dusted (for 100 dfls)

Note: Vijetha supplement is recommended for the use during rainy season and winter months to control muscardine.

• If muscardine disease is high during rainy and winter seasons, the use of Vijetha supplement is recommended to prevent this disease.
• Don’t dust when silkworm are under moult or on eatable mulberry leaves.
• Feed silkworms 30 minutes after dusting.

Mounting of ripened worms

To obtain such quality cocoons, mounting the silkworm larvae at the appropriate time and good quality mountages are essential. In the fifth instar on seventh day silkworms enter into maturation and stop feeding and begin to search place to build the cocoons. Such larvae are picked immediately and mounted on to the mountages. Care should be taken that the number of larvae on mountages must not exceed the capacity of each mountage. When the larvae are in spinning stage, the room temperature of 24°C and 60-70 % of relative humidity along with good aeration facility are to be provided. Rotary mountages are recommended for the production of better quality cocoons. About 35 sets of rotary mountages are required for mounting worms of 100 dfls. For hanging rotary mountages, a separate mounting hall or verandah is required.

Harvesting and sorting

Harvest cocoons on 6th day. Remove defective cocoons. After sorting out the defective cocoons grade the cocoons according to the quality. In winter, delay the harvest by one day.

Marketing

Transport the cocoons during cooler hours of the day and market on 7th day. Cocoons need to be loosely packed in nylon netted bags of 30~40 kg capacity and transported in vehicle having shelves/partitions so that pressing of cocoons can be avoided.

Cocoon yield

The average yield is 60-70 Kg from 100 dfls. About 700-900 Kg cocoon can be harvested from one acre of mulberry garden in a year.

Source: Central Sericulture Research & Training Institute, Mysore

Related Resources

1. Mulberry silk reeling
2. Vanya silk reeling
3. Post yarn technologies