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 Sericulture  

A.     SILKWORM EGG PRODUCTION 

1.     Techniques to be adopted in grainages to produce quality silkworm eggs

Success of sericulture depends on quality silkworm eggs. Therefore, management of seed production, transportation and incubation play important role on overall return. To produce quality seed, it is very important to adopt scientific methods of egg production right from seed crop rearing to egg incubation.

1.1 Disinfection of grainage and implements: The grainage rooms along with its appliances should be thoroughly disinfected prior to commencement of operation and kept ready to receive seed cocoons. A day before disinfection, the rooms and appliances are to be washed with 5% bleaching powder solution; the appliances are to be sun dried for 3-4 hours. A day after, the rooms and appliances should be properly disinfected with a mixture of 2% formalin, 0.5 to 1% lime and 0.5% detergent solutions. Room is to be disinfected at the rate of 1 litre per square metre floor area.

1.2 Transportation of seed cocoons: The seed cocoons are to be always loosely packed either in perforated plastic crates or bamboo baskets or gunny/cloth bags and transported to respective destinations during cooler hours of day. However, transportation of seed cocoons to be preferred in crates or baskets.

1.3 Pupal examination: Before selection of seed cocoons, it is very important to know the disease freeness of a lot, melted, flimsy and good cocoons are also to be separated. The gut portion is taken out and subjected to microscopic examination. In case there is incidence of pebrine, the lot has to be rejected. Before the arrival of new lots, it is very much important and essential to disinfect the contaminated rooms.

1.4 Preservation and protection of seed cocoons: Immediately after the receipt of seed cocoons, they are to be spread on trays in a single layer to facilitate good aeration. Sorting of seed cocoons like melt, uzi infested, flimsy and those which are not conforming to the characteristics of parent races are to be taken out and rejected. The healthy seed cocoons alone should be preserved in trays for further processing, there should be cross ventilation in the preservation room, 25 1˚C temperature, 75 5% relative humidity, 16 hour light and 8 hour dark conditions to be maintained in the cocoon preservation rooms. Complete darkness to maintain on the previous day of emergence, to avoid irregular emergence of moths.

1.5 Early eclosion/artificial eclosion/forced eclosion of moths: This helps in determining the disease freeness of a batch and helps in minimizing the loss to grainage.

1.5.1 Early moth eclosion box: A simple box made up of wood and plywood sheet with a glass door is used having dimension 90 x 75 x 60 cm. The bottom is fitted with asbestos sheet. A heating element is connected to the electric main through a thermostat (0 - 60˚C). On the top of the box at the centre, a 15 cm diameter ventilator covered with wire mesh is provided. It is fitted with sliding top to regulate ventilation. At the bottom of the box and on the lower portion of side walls, small holes are drilled to facilitate aeration. To measure the temperature, a thermometer is fixed from inside of glass door. Within the box, a provision has been made to place 4-5 plastic trays in two tiers for keeping seed cocoons inside.

For early emergence of moths, 50-60 seed cocoons are taken from individual lots and placed into an artificial eclosion box. The temperature in the box is adjusted to 32-33˚C with the help of thermostat. This accelerates the development of pupae and moth emerges early. The early emerged female moths of respective lots are taken and subjected for microscopic examination to know the disease freeness of lots.

1.6 Synchronization of emergence of moths, pairing, depairing and oviposition: Before the expected day of emergence of moths, the cocoon preservation rooms should be kept dark. In case of variation in development of male or female pupae, the development of male pupae can be arrested by preserving them at 5-7˚C and 75 5% relative humidity for 3-4 days. Only healthy and active moths are taken for pairing. After 1-2 hours of emergence, the male and female moths of respective combination are allowed for 3.5 to 4 hours of pairing. At the time of depairing, the male and female moths are to be moved side ways so that the moths are separated easily without causing injury to reproductive organs. The mated female moths are taken in a separate container and induced for urination. Moths are placed on egg sheet and covered with cellules and kept in semi dark condition for oviposition. Under proper preservation (5-7˚C), male moths can be used for second pairing by giving 1-2 hours rest. Throughout the process of pairing, depairing and oviposition, optimum temperature of 25 1˚C and relative humidity of 75 5% should be maintained.

1.7 Moth examination: The pebrine disease in Bombyx mori is caused by a parasitic sporozoan, Nosema bombycis. The mother moth examination can be taken up either (i) individual moth or (ii) mass moth examination. The details are discussed in chapter silkworm diseases and pests control measures.

1.8 Surface sterilization of silkworm eggs: After ascertaining the disease freeness of layings, egg sheets are dipped in 2% formalin for 10-15 minutes. This helps in removal of pathogens adhering to the egg shell and further prevents secondary contamination. Washing of eggs in formalin solution helps in firm adherence of eggs to the sheet.

1.9 Incubation of silkworm eggs: Incubation facilitates uniform development of embryo. In addition, it greatly influences the voltinism of the eggs in succeeding generation, larval growth and success of cocoon crop. Therefore, the eggs are subjected to ideal conditions of incubation.

Optimum temperature of 25 1˚C, relative humidity of 75 5%, 16 hours of light and 8 hours darkness is ideal. During the pinhead stage or before two days of hatching, the eggs are black boxed to aim at uniform development of embryo and hatching of larvae at a time on a single day.

2.     Loose Egg Preparation

Loose eggs are getting popular for obvious advantages such as

  • Standard/uniform egg number (irrespective of the race, season, zone)

  • Increased egg recovery and

  •  Easy and better management.

2.1 Methodology

2.1.1 Preparation of starched: Dissolve 40 to 50g of maida in one litre of water and boil it to make it a paste. Smear the paste uniformly in a thin film on the craft paper sheet of appropriate size and dry

2.1.2 Oviposition: Spread the starched egg sheet in the oviposition tray so as to cover the entire floor surface besides the four of the frame.

  1. Spread the female moths uniformly at the rate of 40 to 50 (bivoltine) or 50 to 60 (multivoltine) per sq foot in the trays for oviposition.

  2. Keep the trays inside oviposition stand and allow the moths to oviposit under dark conditions.

  3. Maintain optimum temperature of 25 1 C and relative humidity of 75 5 % for better egg recovery, both in terms of quality and quantity.

2.1.3 Collection of loose eggs

  • Conduct mother moth examination as per the standard procedure

  • Soak the disease free egg sheets in water for 20 to 30 minutes to dissolve the gums

  • Make ready the egg washing tray/collection unit by connecting to a water source, tie a nylon bag at the outlet for collection of eggs.

  • Spread the soaked egg sheet on the egg washing tray and release water.

  •  Gently dislodge the eggs with hand.

  •  The eggs easily get dislodge and are collected in to the nylon mesh bag.

2.1.4 Removal of gum

  • It is essential to remove the gum that is coated on the eggs.

  • Prepare 0.3 to 0.5 % bleaching powder solution and allow it to settle.

  • Release the eggs into the bleaching powder solution and wash for 10-20 minutes.

  •  Subsequently wash thoroughly in running water.

2.1.5 Drying of eggs

  • Collect the eggs into nylon bags.

  • Gently squeeze out the water.

  • Release the eggs on the platform of the drying unit.

  • Spread the eggs in thin layer.

  • Switch on the fan.

2.1.6 Acid treatment of bivoltine eggs

  • Collect the eggs in to nylon bags and tie the bags well.

  • Dip the bag in to hydrochloric acid for the stipulated period (1.075 specific gravity, 46.1 C, 5-6 minutes) and gently disturb the eggs for uniform acid stimulus.

  • After the treatment, withdrew the bag from the acid and wash thoroughly in running water for 20-30 minutes

  • Dry the eggs as described earlier.

2.2.7 Winnowing of eggs

  • For elimination of lighter eggs, feed the eggs into the hopper of the winnowing unit and switch on the fan.

  •  Discard the lighter eggs which are blown away.

2.2.8 Brushing of loose eggs

  • As per the probable date of hatching, transfer the eggs two days earlier when they are pin-head stage into a paper boat/brushing frame.

  • Black box the eggs

  • On the expected day of hatching, spread the paper boat, distribute the eggs in a thin layer using a feather and expose to light.

  •  Dust bed disinfectant on the hatched larvae.

  •  Sprinkle adequately, chopped mulberry leaves on the net.

  •  After one or two, lift the top net and transfer into a tray.

3.   Handling of silkworm eggs

3.1 Handling of bivoltine silkworm eggs: Depending on the need, the eggs could be made to hatch between 10 to 365 days by adopting different methods of preservation.

3.1.1 Artificial hatching: The bivoltine silkworm eggs before entering into dispause are acid treated with specific concentration of Hydrochloric acid at different temperatures.

3.1.2 Hot acid treatment for bivoltine silkworm eggs: Hydrochlorisation of bivoltine silkworm eggs is a common method to prevent eggs from entering into dispause. There is a correlation between the temperature and specific gravity of hydrochloric acid. When the hydrochloric acid is heated specific gravity falls. Adjustment of specific gravity hydrochloric acid ranging from 1.071-1.076 at normal room temperature 0f 25 C can safely be used for hot acid treatment of silk worm eggs, though ideal specific gravity at 46C is 1.0642. The specific gravity ranging from 1.0715-1.0764 at room temperature 25 C to 1.0728 at 35C room temperature are fit for acid treatment. Adjustment of proper specific gravity of the acid is essential before starting acid treatment. Acid adjusted for the above specific gravity is heated to 46 C for 5-6 minutes for acid treatment. Hot acid baths specially made for this purpose are to be used where the principle adopted is to heat the acid kept in the container in a water bath indirectly. Some old hydrochloric acid used earlier for acid treatment is mixed with fresh acid for better results as fresh acid does not give desired results.

The egg sheets are to be dipped in 2 % formalin for about 2-5 minutes to make the eggs adhere firmly the egg sheets during hot acid treatment and to disinfect the eggs against pebrine. The eggs are dried and later dipped in hydrochloric acid of same specific gravity as that used in treatment for 10 seconds and later treated in hot acid bath. This helps in maintaining the concentration and specific gravity of the acid during treatment of silkworm eggs. The eggs are washed in running cold water immediately after acid treatment to remote the acid completely as traces of acid on eggs lead to death of the eggs. Litmus paper may be used to check the presence of acid.

The standard duration of hot acid treatment for various silkworm races is given below:-

Japanese races                          5-6 minutes

Chinese races                            4-5 minutes

European races                          6-7 minutes

For treatment of hybrid eggs the duration of duration of dipping in acid is determined as the mid-value of the duration of the two parents. Care must be taken not to exceed the duration of acid treatment as the eggs get killed and damaged. A proper alarm timer is to be used during acid treatment to avoid damage.

3.1.3 Preservation of bivoltine silkworm eggs: Bivoltine silkworm eggs are preserved for hibernation for use in the next spring season. The eggs prepared in spring are kept in room temperature of 25C with humidity of 75% to 805 till October-November. The temperature should not go higher than 30 C during this period and not lower than 20 C. The eggs reach dispause stage during this period. They are allowed to be kept in natural temperature which gradually falls to 10C by December. If they are left in such conditions for long, they start hatching irregularly leading to unseasonal hatching. It is necessary to subject the eggs to low temperature of 7.5 C to 5C for 50 to 60 days in order to ensure that all the eggs are hatch on time for rearing later in spring. The eggs are generally kept in refrigerator of cold storage at 5 C from December to February. The eggs are transferred to 2.5 C-0C for 40-60 days by middle of February. This helps in checking the growth of embryo. The eggs are kept at 10 C to 15 C for 4-5 days at the end of March or beginning of April and released for incubation or further cold stored, at 2.5 C till release at a later stage. The duration of preservation scheduled may be adjusted for early spring rearing in February to March. The eggs are released from cold storage and kept at normal room temperature for 3 to 6 hours for checking of sudden exposure to high temperature.

4.  Basic infrastructure required for seed production

  1. Cocoon stage room

  2. Moth pairing room

  3.  Oviposition room

  4.  Moth Examination room

  5.  Acid Treatment room

  6. Egg preservation room

5.  Equipments required for seed production

  1. Refrigerator

  2. Incubator

  3. Wooden Racks

  4.  Wooden trays

  5.  Antwells

  6.  Working Stand and Tables

  7. Exhaust fans

  8.  Moth crushing Sets

  9. Microscopes

  10.  Round Bamboo Trays

  11.  Acid treatment baths

  12. Thermometers/Hygrometers

  13. Seed production registers

  14. Specific gravity meter

  15. Glass-slides with cover

  16. Glass disc

  17. Glass pipette

  18. Measuring jar

  19. Water filter

  20. Egg sheets

  21.  Cellules

  22.  Wash basin

6. Chemical required for seed production

  1. Formaldehyde

  2.  Hydrochloric acid

  3. Potash

  4. Potassium Hydroxide

  5. Lime

  6.  Bleaching powder

  7.  Xylol

B.     SILKWORM REARING

1.  Rearing Plan

Planning of the rearing amounts to the completion of work by 50%. It helps in synchronizing mulberry growth, silkworm rearing in addition to augmenting productivity and material arrangement. The size and time of rearing mainly depends on the leaf availability in quantity and maturity. However, the rearing facilities to rear a unit quantity of eggs should be considered. The following points and parameters are to be considered for annual planning.

  • Cropwise leaf production per unit area

  • Rearing period

  • Number of crops per year

  • Rearing facilities

  • Labour arrangement

2.  Parameters to be considered

2.1 Leaf yield: The yield of leaf fluctuates depending upon the season. This aspect should be considered for estimating the quality of the layings to be brushed. 12-15 kg of leaves are required to rear 1dfl of bivoltine hybrid.

2.2 Division of plots

a)    Single plot system: This arrangement gives 5 to 6 crops per year. It requires one rearing house with leaf storage-cum-chawki rearing room.

b)    Two plots system: In this arrangement, rearing facility can be exploited two times and annually double the quantity of layings can be reared. But the important factor in this system is that a separate chawki rearing building is a must.

2.3 Mulberry garden management: Proper mulberry garden management has to be ensured so as to provide sufficient between two rearings (a minimum of ten days gap should be provided).

3.  Rearing House

The rearing house is designed based on the brushing capacity and the method of rearing. In general, 2 sq.ft/dlf floor-area is required for tray rearing and 3 sq.ft/dfl in case of shoot feeding method. The same room can be used for chawki rearing and subsequently for leaf preservation in case of a single plot system. But in the case of 2 plot system, a separate chawki room away from the late age rearing house is essential. Each rearing house must have:

  • A main rearing hall

  • Ante room

  • Leaf preservation room

Rearing houses are to be built in such a way to create a congenial atmosphere for the growth of the silkworm at the minimum operational cost. they are to be equipped with facilities to create required environment such as temperature and relative humidity. Raising evergreen trees, even mulberry trees around the rearing house help by maintaining a better rearing environment.

Rearing houses are to be designed for effective disinfection, like smooth surface of walls, use of lime white wash, facility for making the building air tight, and less reactive to disinfectants and washable smooth floor. The ideal location for leaf chamber is the north-east corner of the rearing house which is the coldest place of the building. It should not be well ventilate as it needs high moisture. The place must be cool, humid and dark. 

3.1 Ante room: Ante room acts as barrier for entry of uzi fly, which should have minimum width and breadth of stretched arm (span) length of about 8 feet. The doors fitted with self-closing facilities are advantageous. 

3.2 Chawki rearing house: A separate chawki rearing rearing building with facilities to raise temperature and humidity is a must for 2 plot rearing system. This may be located away fro late rearing house and least accessible for the working group. The size of chawki rearing house is decided based on the quantity of eggs brushed. For a mulberry garden of 1 arce, the chawki room of 10′ х14′  is ideal. The size of the chawki rearing building should not be big. It is ideal to have false roofing with smooth surface material.

3.3 Preparation of rearing house The rearing house should be kept ready in advance by disinfecting effetively using recommended procedure, at least 4 days in advance. Care must be taken to avoid accumulation of disinfecting chemical during rearing followed by preconditioning of the rearing house by arranging required numbers of rearing stands and trays and also adjusting rearing temperature and humidity one day in advance.

4.  Rearing Appliances

Following are the appliances required for rearing silkworms for 1 arce of mulberry garden (300 dfls):

          Non recurring (General)

Quantity

1. Disinfection mask and protective gum shoes             

1 set

2. Sprayer (power sprayer, multipurpose pump or rocking sprayer for disinfection)

1 set

3. Room heater with thermostart 2 KV blowing type or charcoal stove

3

4. Water air cooler (Heavy duty)

3

5. Kerosene blow lamp

1

6. Wet and dry bulb thermometer

3

7. Forceps 6 " long

3

8. Plastic sieve

1

   

          Non recurring (Specific)

Quantity

1. Rearing building

  • Chawki rearing room, leaf preservation-cum-preparation room, ante room

  • Late age rearing hall, ante room, leaf preservation room

1

2. Egg transportation box

1

3. Egg incubation chamber

1

4. Loose egg incubation frame

6

5. Black box

1

6. Chawki rearing trays (wooden 3'x4'x2.5')

24

7. Chawki rearing bottom stand

2

8. Rearing stands to accommodate 12 trays in arow

2

9. Feeding stands

1

10. Ant wells

72

11. Leaf chopping board

1

12. Leaf chopping knife

1

13. Leaf mat (4' x 6' rexin)

2

14. Leaf chamber

1

15.Bed cleaning nets (3'x4', mesh size inch x inch)

48

16. Earth pot

1

17.Litter basket

2

18. Late age rearing trays (bamboo 3.5' dia)

      (for feeding method only)

120 for CB     140 for BV        

19. Rearing stands

12 for CB        14 for BV        

20. Feeding stands

3

21. Shoot rearing rack 5'x35'x3 tiers (For shoot feeding method only)

2

22. Mountages (bamboo chandrike)

120

23. Plastic basin (big 18'' dia and small 9'' dia)

2

24. Plastic bucket with lid (big 20 ltr cap.).

2

25. Plastic mugs

2

26. plastic boxes with different colours

2

27. Foam pads

50

28. Foot rugs

2

29. Leaf chamber for late age

2

30. Leaf basket (Bamboo)/(Plastic)

8/3

31. Cleaning nets (4'x4')

280

32. Cora cloth

8

33. Gunnny cloth

10

Recurring

Quantity

1. Parafin paper (20 m/crop)

20

2. Old new papers

10 kg

3. Formalin

15 kg

4. Bleaching powder

7 kg

5. lime

25 kg

6. Bed disinfectant

12 kg

7. Power and fuel

 

8. Man power (Up to chawki rearing including leaf picking and after the IV instar only for rearing)

 

 

Leaf rearing

Shoot rearing

a. Cleaning

3 men x1 day

3x1

b. I age rearing

4x1

4x1

c. II age rearing

2x4

2x4

d. III age rearing

2x4

2x4

e. IV age rearing

4x4.5

2x4.5

f. Bed cleaning

-

2x1

g. V age

6x8

3x8

h. Harvesting

12

12

i. Leaf harvest

54

 

j. Marketing

2

2

5.  Egg Transportation

Silkworm eggs are to be handled with special care during transportation without desiccation. Usually, farmers use cloth bags, paper bags, etc to carry silkworm eggs. In these bags the eggs are directly exposed to various adverse climatic conditions, which lead to poor hatching of the eggs and poor health of the larvae. In addition to the physical compression, there are chances of contamination of toxic chemicals emanated from chilly, tobacco, detergents, etc. To overcome this problem, a few simpler and cheaper transportation bags or egg carrying boxes utilizing locally available materials are fabricated having a better humidity and temperature maintaining abilities. Each box or bag has provision of supplementing the required humidity and thermo-insulation property to avoid temperature fluctuations and provide rigid structure to avoid compression.

The bag is made or rigid plastic mesh lined with thin foam pad. It is supported by a rigid metal frame where as, the egg carrying box is made of rigid card board lined inside with thermocol and a provision to increase humidity and ventilation. Each box/bag has a capacity of 300 dfls. The transportation bag is kept wet till the transportation is complete. In box, wet foam pad is kept at the bottom for this purpose. It is ideal to transport eggs on the 2nd and 3rd day of the oviposition during cooler hours.

6.  Egg Incubation 

Providing ideal conditions to the eggs during embryonic growth for the complete, healthy and robust growth and development can be referred to as incubation. The silk worms eggs are to be incubated properly up to the 9th day from the day of oviposition and after examination of healthy development of embryos, and to avoid irregular hatching. Embryos grow robust using most of its reserve food under <25C and >80% RH conditions. On the 9th day the egg sheets are re-arranged. About 25 dfls after disinfection are kept in the chawki-tray in single layer in incubator to enable brushing and proper spacing for young worms later. The egg sheets are covered with sheet of black paper or paraffin paper. On the due dated of hatching when a few larvae have started hatching, black paper or paraffin is removed and the eggs are exposed to dim light for about an hour. This facilitates uniform hatching of larvae. Care is to be taken not to over-crowd the eggs. Hygiene condition ensures prevention of disease contamination. Various used for incubation should be thoroughly cleaned, washed and disinfected before incubation. 

6.1 Low Cost Incubation Chamber (LCIC): In order to maintain optimun temperature and humidity during embryonic developmental stage of eggs a simple electrically independent and easy to handle Low Cost Incubation Chamber (LCIC) is developed which is efficient in providing conducive conditions for the growth of silk worm embryo durinf incubation of silkworm eggs.

LCIC, mainly consists of two chambers (outer and inner), the outer chamber of 18 inches height and opening at one end is made up of clay, of diameter of 21 inches at the top opening and 15 inches at the bottom closed end. The wall of the outer chamber is provided with 5mm diameter holes at the top half-portion of the chamber, in rows in longitudinal pattern. The inner chamber is 18 inches in height and also made up of soil. The top end opening is having  diameter of 15 inches that taper to 12 inches to the closed bottom end. This inner chamber is also provided with rows of holes of 5mm similarly. Clean and formalin disinfected sand bed of 1 inch depth is kept at the bottom of the outer and inner chambers. Sand in the chambers is kept moist sufficiently conditioned at least 12 hours before keeping eggs for incubation.

The egg sheets are aligned vertically with the help thin bamboo strip (with enough space for air circulation between sheets) and cover the mouth of both the chambers with loosely knit gunny cloth and preserve the eggs till black boxing.

LCIC provides ideal temperature and RH for incubation of silkworms eggs. LCIC units can be prepared easily, as the material used for fabrication arelocally available and cheap. The system is found to be very effective as it ensures optimum condition for the growth/development of silkworm eggs thereby hatching is optimized and higher is ensured.

6.2 Loose egg incubation: After transporting the loose eggs during cooler hours of the day, eggs should be incubated in incubation frames, which are made up of 2cm. Thick, light, wooden strips with two frames (outer and inner). The outer frame is 36x24cm and the bottom of the frame is lined with a thick black cloth. Inner frame is of 32x20 cm and it fits exactly inside the outer frame. One such frame can accommodate 1 box (20000 eggs or 50 dfls). Black boxing can be done in the incubation frame it self. Care should be taken to spread the eggs uniformly.

7. Black Boxing

Light has propound effect on hatching. Preserving the developed eggs in total darkness for a day or two before hatching is called black boxing. This helps in uniform hatching on a single day. During the black boxing, those embryos in advanced stage of development stop further development and this facilitates other to catch up.

Any device that provides complete darkness can be used for this purpose. Simple black sheet of paper (thick drawing sheets quality) or cover, which gives total darkness, is ideal. Eggs are grouped (25 to 50 dfls) in a tissue paper and covered on the day of pin head stage. They are transferred to black boxes. Such black boxes are placed under required humidity and temperature conditions. These eggs are exposed to light between 6 to 7 am.

8. Brushing

Transfer of the newly hatched larvae from eggs on the wax paper or rearing bed is called brushing. In 4'x3' tray, 50 dfls can be brushed and reared up to I moult and 25 dfls up to II moult. The egg sheets are distributed in required numbers per tray before hatching. Fresh, tender and succulent mulberry leaves (with 80-85 % moisture) from a well maintained garden are collected and chopped to a convenient size of 0.5 to 1.0 sq. cm. This is sprinkled over the hatched larvae on the egg card. After 30 minutes, when all the worms have crawled on to the leaf, the leaves along with the worms are transferred on to the wax paper in the rearing tray with the help of a soft feather and arranged in the form of a thin bed of required size. Clean wet foam pads are kept around the rearing bed covered with another paraffin paper to maintain the required humidity. Pile up trays one above the in the form of a box. This arrangement conserves leaf moisture to a longer period for better feeding conditions, leading to vigorous and healthy growth of larvae.

In case of brushing loose eggs, inner incubation frame should be removed. Two layers of cotton/nylon net (mosquito net) is spread over the loose eggs and exposed to light. About 2 to 3 hours later, hairy small worms crawl out through the net. Then the chopped leaves are spread over the net. Cover the incubation frame with paraffin paper and keep undisturbed for an hour. Then the frame worms along with the top net is lifted from the incubation frame and brushed in a chawki tray.

For the chawki rearing, blue polythene sheets can be used in place of paraffin paper. The polythene sheet should be 400 gauge. During high humid conditions, wet foam pad and bottom sheet can be dispensed with. About 3 inch gap should be maintained between covering sheets and rearing bed. Finely chopped leaf bits can be used for brushing. This will help in controlling the initial thickness of bed effectively.

9. Harvest, Transport and Preservation of leaf

Well grown fresh and succulent leaves (80-85% leaf moisture) raised under recommended package of practices, should be used for chawki stage. The leaf harvesting must be carried out during the cooler hours of the day and should be transported in clean, wet gunny bags or baskets to the rearing house. Store the leaf in humid place. During summer, the efficiency of leaf preservation is increased by sprinkling water on the leaves and then covering with wet gunny cloth.

For young silkworm, the first two to three full blown leaves below the glossy leaf, which are tender, succulent and dark green in colour are suitable. As the worms grow, medium leaf should be used for feeding the worms.

The nutritional conditions of chawki leaves can be maintained when they are preserved under low temperature, high humid and dark conditions. This can be effectively done by preserving them in earthen pots buried in wet sand.

10.  Chawki Rearing

Rearing of young age silkworm up to III moult is called chawki rearing. Rearing of young age silkworms under ideal environmental conditions, feeding succulent, nutritious, tender leaves will make the larvae grow robust and make more stress tolerant during the advanced age of development.

10.1 Temperature: The silkworm body temperature will be little higher than the atmospheric temperature by 1℃ the ideal temperature for healthy growth of silkworm varies according to its developmental stage and variety. Increase of temperature increases the growth of silkworm. However, very high temperature imbalances the metabolic activity and the silkworm, thus becomes unhealthy. High temperature also affects the quality of leaf in the rearing bed. In case of lower temperature, the larval duration is extended due to low metabolic activities. Finally, the silkworm may end up susceptible to diseases. Therefore, the optimum temperature for the chawki worms is 27-28 ℃ for I instar and 26-27 ℃ for II and III instars. Ideal temperature can be maintained by adopting the following methods.

Low temperature can be increased by using electric heater preferably connected with thermostat or by burning charcoal with out emitting smoke. High temperature can be brought down by keeping the premise cool through shade, sprinkling, providing false ceiling or covering roof with dried plant material.

10.2 Humidity: Atmospheric humidity influences the silkworm growth mainly through mulberry leaf in addition to its direct effects on the silkworm. In case of low, the rate of multiplication of pathogens is slow and though hygienic conditions are better, the leaf withers fast, rendering it unfit for the silkworm to eat. As a result, growth of the larvae slow down causing inanition (weakness) with difficulty in moulting. On the other hand, high humidity keeps the quality of the leaf better, the larvae grow fast, becomes fat and weak in resistance to external conditions. At high humidity conditions, pathogens multiply at higher rate,. Hence an optimum humidity during rearing seasons has to be maintained for healthy growth of the larvae and superior quality of the cocoons the optimum humidity is 85-90% for I and II instars. The humidity can be attained easily by using the following techniques:

  • Use paraffin paper or blue polythene sheet as bottom and covering sheets in the rearing tray to conserve humidity.

  • Keep clean, pathogen free and wet foam pads around the rearing bed.

10.3 Light: Light has varied effect on the silkworm behaviour and growth. Silkworm prefer dim light (20-30 lux). The intensity of this light should be uniform throughout the rearing building. The dim light during the day and darkness during the night is more congenial for healthy growth of the larvae.

10.4 Aeration: The rearing room is polluted by carbon dioxide, carbon monoxide, sulphur dioxide and ammonia due metabolic activity of the silkworm, mulberry leaves, workers and fermentation process in the bed. These unwanted gases have to be replaced by fresh air containing more oxygen for healthy growth of the silkworms. Keeping in view, stagnation of air should be avoided by proper ventilation.

10.5 Feeding and Spacing: Chawki worms are to be fed 3-4 times a day with tender, succulent leaves. The quality of leaf to be fed each time should not be more than required; otherwise it leads to wastage of leaves. Before feeding, the bed have to be spread and dried to facilitate all the larvae to crawl on to the surface, which helps them to feed on fresh leaf. Further, it helps in maintaining better bed hygiene and micro-climate of the bed.

As the larvae grow in size, they require more bed are. Over crowding of the silkworms lead to competition of the available food space, which weakens the worms to a great extent. Regulate the spacing and feeding quality for healthy growth of the silkworms. Everyday after bed cleaning, optimal bed area has to be provided. Care should be taken for uniform distribution of larvae in the bed. Details of the feeding time, leaf size, quantity of feed and bed size, etc. should be followed:

STANDARD CHART FOR YOUNG SILKWORM REARING OF 40,000 (100dfls)

Stage of larvae

Age (Days)

Feeding time

Leaf size in cm.

Leaf quantity in gms.

Bed area in sq. ft.

Remarks

 

 

 

1

10 AM

Finely chopped

500

4

Expose from the black box to light around 7a.m. Brush the larvae around 9a.m. using finely chopped tender leaves. Make the bed after 30 minutes

4 PM

0.5x0.5

 

10 PM

 

0.5x0.5

 

 

7.5

 

I instar 27-28 C

 

2

5 AM

1.0x1.0

 

1800

7.5

Spread the bed half an hour before feeding for drying.

10 AM

1.0x1.0

 

4 PM

1.5x1.5

10 PM

1.5x1.5

10.5

 

 

 

3

5 AM

1.5x1.5

 

1200

10.5

Spread the bed half an hour before feeding for drying. Clean the bed by using a net. Observe for moulting behaviour. If symptom of moulting observed, reduce the leaf size and quantity appropriately.

10 AM

1.5x1.5

4 PM

1.5x1.5

 

10 PM

 

0.5x0.5

 

10.5

I moult 26-27 C 75 %RH

 

 

 

4

5 AM

 

 

 

0.5x0.5

 

 

 

200

 

 

 

15.0

Give light feeding if necessary. Stop feeding when about 90% of larvae settle for moult. Break/spread the bed gently and apply fresh active lime powder to the dry bed.

10 AM

4 PM

10 PM

 

 

5

5 AM

1.5x1.5

 

3500

 

15.0

Give feeding if 90% of the larvae are out of moult. Disinfect the larvae/bed before feeding. Clean the bed using net.

10 AM

1.5x1.5

4 PM

1.5x1.5

 

30.0

10 PM

2x2

II instar 26-27C 85-90%RH

 

6

5 AM

2x2

 

4250

30.0

Spread the bed half an hour before feeding for drying.

10 AM

2x2

4 PM

2x2

10 PM

2x2

45.0

 

 

 

 

7

5 AM

2x2

1100

45.0

Observe for moulting behaviour. If symptom of moulting observed, reduce the leaf size and quantity appropriately. Clean the bed before settling for the moult.

10 AM

1x1

 

 

II moult 26-27 C 75 %RH

4 PM

 

 

 

 

 

 

Stop feeding when about 90% of larvae settle for moult. Break/spread the bed gently and apply fresh active lime powder to the dry bed.

10 PM

 

8

5 AM

 

 

 

45.0

Disinfect the larvae/bed with bed disinfectant. If >90% of the larvae are out of moult, feed & clean the bed using net. Distribute the larvae during cooler hours of the day

10 AM

 

 

 

4 PM

2x2

3300

45.0

10 PM

3x3

 

 

9

5 AM

3x3

9000

45.5

Spread the bed half an hour before feeding for drying. Clean the bed and give feeding.

 

10 AM

3x3

 

 

4 PM

3x3

 

 

60.0

 

10 PM

4x4

III instar 26-27C 85-90%RH

 

10

5 AM

4x4

12000

60.0

Spread the bed half an hour before feeding for drying. Clean the bed and give feeding.

 

10 AM

4x4

4 PM

4x4

10 PM

4x4

90.0

 

 

11

5 AM

4x4

 

8000

 

90.0

Clean the bed using net.

10 AM

4x4

4 PM

2x2

If symptom of moulting observed, reduce the leaf size and quantity appropriately.

10 PM

2x2

III moult 25C

75 %RH

 

12

5 AM

 

 

90.0

 

 

90.0

Stop feeding when ~90% of larvae settle for moult. Spread the bed gently and apply fresh active lime powder to the bed dry.

10 AM

4 PM

10 PM

It is important to remove paraffin paper cover and foam pads every morning prior to feeding. Chopsticks/forceps should be used while handling the chawki silkworms.

10.6 Bed cleaning: As the larvae grow the unconsumed leaves and litter in the bed increases and may cause the multiplication of pathogens and release of obnoxious gases. Hence periodic cleaning of the larval bed is necessary. This is carried out using cleaning net with suitable mesh size.

10.7 Moulting and moulting care: Under optimum rearing conditions, the worms take 3 to 3 days to settle for I moult and 2 to 2 days to settle for the II moult. Moulting duration is 18 to 24 hours. When the worms start settling for the moult, the top paraffin paper and wet foam pads are removed. Feeding is also reduced during this period. When all the worms settle for moult, then slaked lime should be dusted @ 4-5 g/sq. ft. During moulting, the bed thickness should be reduced as far as possible. Adequate spacing allows the left-over leaf and bed for quick drying. The above steps enable the moulting worms to settle uniformly.  Increase in the bed humidity is harmful for moulting.

Feeding is resumed half an hour later dusting bed disinfectants when more than 95% of the worms are out of the moult. Tender leaf is given for the first one or two feedings after the moult.

10.8      Disease management: Like any other animal, silkworm is also affected by various diseases caused by virus, bacteria and fungi. These diseases can be effectively prevented/controlled by killing the pathogens in and around the rearing house through disinfection before the commencement of rearing and by maintaining hygienic conditions and regular use of disinfectants during rearing. Chawki worms in general are more resistant to diseases than late age worms. However, the common diseases during chawki are fungal (muscardine and aspergillosis). Diseases are more common when rearing bed is thick, bed humidity is high, worms kept in crowded conditions, less nutrition leaf, etc. As a control measures, the bed disinfectant has to be used, as recommende.

In the event of outbreak of diseases, all the suspected/diseased larvae have to be removed carefully to avoid further contamination and placed in 2% formalin or lime solution before burning or buying. After this, the rearing bed is disinfected after every moult. Maintenance of ideal temperature, humidity, aeration, spacing and feeding the larvae with nutritionally rich leaf improves hygiene and helps in prevention/controlling the diseases effectively. Periodic dusting of the mixture of bleaching powder and lime powder to the surroundings, floor and path leading to the chawki building helps in preventing the diseases.

10.9 New techniques in chawki rearing: Various new technologies have been developed to simplify rearing and increase productivity and decrease the cost of production. Use of paraffin paper, foam pad and box rearing are some of the appropriate technologies incorporated for the chawki rearing. Some more new technologies have also been developed during recent years as detailed below.

10.9.1 Isolation chamber: Successful chawki rearing needs ideal environmental conditions, good quality leaf and appropriate technologies. In the present situation, it is very difficult for the farmers to provide such ideal environmental conditions as most of them are conducting rearing in part of the dwelling house. Therefore, Isolation chamber has been developed top provide better environmental conditions and hygiene at the farmers level with low input cost, The isolation chamber can easily satisfy the average farmer as it can easily be accommodated inside his dwelling house. Isolation chamber can be made either with wood or brick masonry.

10.9.1.1 Advantages of isolation chamber:

  • Uniform temperature and humidity can be effectively maintained with minimum power.

  • Moisture loss in the leaf is minimized.

  • Larval growth and moulting behaviour is uniform

  • Chances of contamination with dust and pathogens minimized

  • Larval duration is reduced

  • Larval weight increases.

  • ERR improves and enhances the crop stability.

10.9.2 Blue polythene sheet: To maintain optimum humidity conditions use of paraffin paper, wet foam pads and box rearing are popular in tropical conditions. Because of the natural wear and tear, high cost and non-availability of paraffin paper, the idea of using of blue polythene sheet came. It is used in silkworm beds in place of paraffin paper for bottom and cover, It is much cheaper and durable than paraffin paper.

10.9.2.1 Advantages

  • Humidity for chawki rearing can be maintained in the bed.

  •  Driage of the leaf is reduced in the bed.

  • Yield and cocoon characters are improved.

  •  Polythene sheets are easily available.

  •  Polythene sheets can be washed and disinfected.

  •  Polythene sheets can be used for more crops.

  • It reduces the input cost.

10.9.2.2 Points to remember

  1. Use of thicker gauge polythene sheet (more than 400) should be avoided.

  2.  During high humid conditions, wet foam pads and bottom polythene sheets can be dispensed with.

  3.  A gap of 3 inches should be maintained in between the covering sheet and the rearing bed.

  4. Pin hole perforations should be made @ 1 hole per sq. cm. on the upper polythene sheet.

10.10 Transportation of chawki worms: The transportation of chawki silkworms reared in the chawki rearing centre is inevitable. It is always better if they are transported in the following conditions:

  • Stage: Under II moult or two feeds after the II moult.

  • Packing: Covered in wax paper.

  • Time: During cool hours particularly in the evening.

  • Distance: Shorter the better.

  • As soon it reaches the rearing house, spread and keep them in the rearing stand.

11. Late Age Silkworm Rearing

The rearing of grown up silkworms, i.e. from 4th age of spinning is termed as late age rearing and is usually completed in 14-16 days. Silkworms attain sufficient growth during this stage, representing more than 94% of the leaf consumption, 133 times increase in body size, 125 times increase in body weight, and nearly 1000 times increase in silk gland weight. Moreover, the late age worms are more sensitive to high temperature and humidity conditions and diseases. Maximum growth and survival, which directly influence cocoon crop yield and this can be achieved only through scientific and skillful rearing.

11.1 Rearing house: A separate rearing house with adequate rearing space, sufficient ventilation and light is essential. This will enable effective disinfection and also to maintain required humidity, temperature and other hygienic conditions which helps to get good cocoon crop. The rearing building should be constructed in the outskirt of the village or in the garden in a centrally located place for easy access and to prevent cross contamination. The size of the building should be as per the requirement, with the height of about 12 ft. This helps in effective maintenance of temperature and humidity. The building should be fly and rodent proof with smooth finished walls, floor and rounded corners. Each rearing house should have an independent rearing hall with leaf storing room and ante-room.

11.2 Quality of leaf: The success of silkworms rearing mainly depends upon the quality of leaf. The IV and v instar worms require less moisture content in the leaf than the chawki worms. But the leaves should be nutritious. The worms are to be fed with medium and coarse leaf in the late age.

Harvesting of the leaf is done during cooler hours of the day. Leaf can be either harvested by individual leaf plucking or in the form of shoots from the garden, which is 50 to 60 days mature. After harvest the leaf is transported to the rearing room, packed loosely in wet gunny bags or bamboo baskets covered by wet gunny cloth.

The leaves should be preserved properly in leaf chamber, covered with wet gunny cloth. The leaf moisture could be retained by spraying water over the leaf at frequent interval during summer. This enables the leaf to remain fresh for longer time and results on good cocoon yield. Do not feed the worms with withered leaf as it leads to reduction in consumption and growth of worms. In the case of shoot preservation, mulberry shoots should be preserved vertically and covered with clean wet gunny cloth in dark room with low temperature and high humidity.

11.3 Environmental conditions: Though temperature range of 24 to 26 C is ideal for rearing late age worms, the rearing cold be successfully conducted even at higher temperature by proper manipulation through effective cooling, regulation of humidity, frequency of feeding and aeration. 

11.4 Bed spacing and feeding: Crowding of silkworm in the rearing trays and poor ventilation leads to the building up of toxic gases in the rearing room, which is harmful to the silkworms. Proper spacing and good aeration keeps the worms healthier. Crowding of worms in the rearing trays also leads to under-nourishment and poor growth resulting in low cocoon yield. For obtaining better silkworm growth, optimum spacing and quantum of feed should be given as in the following table:

OPTIMUM SPACING AND FEED FOR LATE STAGE SILKWORMS

Stage

Temp C

Humidity %

Quality of leaf

Frequency of feed

Spacing per 100 dfls

(sq ft)

Feed quantity kg/ 100  dfls

 

 

 

 

 

BV

MV

BV

MV

 

4TH

 

25-26

 

70-75

 

Medium

 

3-4

9-20 (115-225)

8-16 (100-200)

 

195

 

160

 

5th

 

24-25

 

70-75

Medium to course

 

3-4

20-40 (225-500)

16-32 (200-400)

 

1120

 

960

Rearing trays should not be smeared with cow dung.

11.5 Care during moult: Silkworm takes 4 to 4 days in IV age to settle for moult. It takes nearly 30-36 hours in IV moult. At the time of moulting, the worms require comparatively dry atmospheric conditions. To achieve this, keep the bed thin, spread the bed gently, dust lime powder over the bed, provide good spacing and increase aeration in the rearing house. This reduces the bed humidity and dries the left over leaves quickly. As the worms show signs of moulting, the feeding for moult, should be reduced. When 90 to 95 % of the worms settle for moult, feeding should stop. Resumption of feeding of only done after 95 % of the worms have come out of the moult. Tender leaf is given at the time of resumption after applying disinfectant. Unsettled worms should be separated and rejected before dusting the lime. If the unsettled larvae are more and are healthier, keep them separately, give feeding and allow to settle for moult.

11.6 Bed cleaning: Rearing worms in tray system requires bed cleaning everyday during instars. Cotton/nylon nets can be used for bed cleaning.

11.7 Crop protection: In the uzi fly infected area, silkworm rearing must be conducted in well protected nylon net enclosure or in fly proof rooms. Use of uzicide, uzitrap, uzi powder or any other recommended chemical reduces the uzi fly infection. Recommended bed disinfectants which can be used to prevent grasserie and muscardine diseases are applied half an hour before resuming feed after each moult and once again on the 4th day of V age.

11.8 Mounting and harvesting: At the end of 5th age i.e., on6th or 7th day, larvae reduces feeding, shrink in size, body becomes translucent and change their colour to light yellow and start crawling in the bed with raised head and release wet faecal matter,. This is the indication of spinning larvae, and thereafter the feeding quantity should be reduced and aeration should be increased. Once the spinning larvae appear in the bed, pick them by hand and put them on mountages. Take away the big branches with leaf, if any, in the bed before picking spinning larvae. When more of the worms are matured for spinning, they can be easily separated by shaking the branches and collecting the larvae enmass. Net can also be used for separating the spinning larvae. Mount the spinning larvae on bamboo mountages. Temperature of 24 c and humidity of 60-65 % and aeration are ideal for spinning. Therefore, take necessary care during spinning time to get quality cocoons. Harvest cocoons on the 5th or 6th day after spinning during summer seasons, respectively. For better cocoon quality and quantity, rotary mountages are ideal.

12. Shoot Feeding for Late Age Silkworms

Sericulture is highly labour intensive, contributing more than 50 5 of the cost in silkworm rearing, further, the labour requirement particularly of leaf harvest is also very high. Keeping in view, shoot feeding technology is recommended for late age silkworm to enhance margin of profit in sericulture.

The popular silkworm rearing, in general, is by harvesting individual leaf and feeding them to silk worms in trays which are kept 10 to 12 in number one above the other in a rearing stand up to a rearing stage. This traditional method of rearing involves high labour of leaf picking, feeding and for everyday bed cleaning. In the shoot feeding method, the last two stages of rearing is done, by giving whole mulberry shoot instead of individual leaves, and it is out in plat form type rearing rack. There will be one bed cleaning after 4th moult.

12.1 Rearing and appliances: A separate house preferably in the garden or nearer to the garden is convenient. The rearing house should be built on a raised platform with shady trees around to provide good aeration and cool surroundings. The rearing house should be rodent and uzi proof with an ante-chamber and a shoot storing-cum-chawki room. Approximately, 3 sq. ft. per dfl floor area is the requirement. The details or rearing by shoot feeding are given as follows:

STANDARD CHART FOR REARING BY SHOOT FEEDING METHOD FOR 40,000 (100dfls)

Stage of larvae

Age (Days)

Feeding time

Quantity of shoots in Kg*

Bed area in sq. ft.

Remarks

 

 

 

 

 

 

 

 

 

 

IV instar 22-25 C 70-75 %RH

 

 

1

8 AM

 

3 PM

 

10 PM

6

 

8

 

10

 

 

5'x15'

After III moult disinfect the bed, apply net and give cut leaves. Separate the larvae from the bed, shift them to shoot feeding racks, sprinkle bed disinfectant over shoot feeding bed before putting the worms and feed.

 

2

8 AM

3 PM

10 PM

12

15

17

 

5'x20'

 

Expand the bed before feeding.

 

3

8 AM

3 PM

10 PM

19

22

24

 

5'x20'

 

Expand the bed before feeding.

 

 

4

8 AM

3 PM

10 PM

5 AM

22

20

16

8

 

5'x30'

 

 

Examine larvae for moulting behaviour and feed appropriately. Provide covering (thin feeding).

 

 

 

3 PM

10 PM

8 AM

3 PM

 

 

 

5'x30'

 

 

If 90% of the larvae have settled for moult, stop feeding, apply active lime powder, and check for good aeration.

 

IV moult

 

1

10 PM

8 AM

3 PM

10 PM

16

19

22

26

 

 

 

5'x30'

 

If 90% of the larvae are out of moult, sprinkle bed disinfectant and give feeding. Clean the bed ** after 2 to 3 feeds and then disinfect the bed.

 

 

2

8 AM

3 PM

10 PM

30

34

38

 

5'x35'

 

 

Expand the bed before feeding.

 

 

3

8 AM

3 PM

10 PM

42

46

48

 

 

5'x55'

 

Expand the bed and disinfect before feeding.

 

4

8 AM

3 PM

10 PM

50

54

60

 

5'x60'

 

Expand the bed, observe for healthiness of the larvae.

 

 

IV instar 22-25C 70-75%RH

 

 

 

5

8 AM

3 PM

10 PM

62

66

72

 

5'x70'

 

Expand the bed, disinfect the bed and give normal feeding.

 

6

8 AM

3 PM

10 PM

76

78

80

5'x70'

 

Give normal feeding.

 

7

8 AM

3 PM

10 PM

82

82

70

 

5'x70'

 

Give normal feeding. Disinfect the bed, if necessary.

 

8

8 AM

3 PM

10 PM

8 AM

65

50

40

10

 

5'x70'

Observe for spinning behaviour.

Mount the spinning larvae at the rate of 40-45 larvae pee sq. ft. on the mountage.

 

  • *About 60-70 days old (harvest to harvest) with about 60% leaf and 40 % stump weight.

  • *For bivoltine, give 10% more feed.

  • **Bed cleaning: Use bigger size nets (2''x2'') or 2 to 3 ropes of 5 to 6 ft. length tied to a rod, give 2 to 3 feed and lift the net/rope to separate the new bed from the old, disinfect the bed after cleaning.

12.3 Transportation and marketing of cocoons: After harvesting, the cocoons should be cleaned by removing litter. Double cocoons and flimsy cocoons are separated out and transported in loosely filled gunny/cloth bag during cooler hours of the day for marketing

   

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