6 chapter steps in silkworm egg production at grainage, egg sheets and loose egg production technology

6 - Chapter Steps in silkworm egg production at grainage, egg sheets and loose egg production technology

1. Chapter 6 Steps in Silkworm in Egg production at Grainage, egg sheets and loose egg production Technology By, Nayana , B. P. Msc . (Agri.) SRF UAHS, Shivamogga

2. Egg Production in Mulberry Silkworm Success of Sericulture depends on quality silkworm eggs. Therefore management of seed production, transportation and incubation play important role on overall return Therefore:- It is very important to adopt scientific methods of egg production right from seed crop rearing to egg incubation

3. Disinfection of grainage and Implements The grainage rooms along with its appliances should be disinfected thoroughly prior to commencement of operation and kept ready to receive seed cocoons Transportation of seed cocoons The seed cocoons are to be loosely packed in perforated plastic crates or bamboo baskets or gunny cloth bags and transported to respective destination during cooler hrs of the day

4. Pupal Examination Before selection of seed cocoons, it is important to know the disease freeness of a lot Therefore:- The gut portion is taken out and subjected to microscopic examination If there is incidence of pebrine, the lot has to be rejected Preservation & protection of seed cocoons Immediately after receiving seed cocoons, the healthy cocoons are to be spread on trays in a single layer to facilitate good aeration . There should be cross ventilation in the preservation room having 250C and 75% RH, 16 hours light and 8hrs dark condition Complete darkness to be maintained on the previous day of emergence to avoid irregular emergence of moths.

5. Early Eclosion / artificial eclosion / forced eclosion of moths Early emergence / eclosion of moths help in determining the disease freeness of a batch and helps in minimizing the loss to grainage . For this, a simple box made up of wood and plywood sheet with a glass door is used with a dimension of 90 x 75 x 60 cms The bottom is fitted with asbestor sheet A heating element is connected to the electric main through a thermostat at 60 C On the tap of box at centre a 15 cm diameter ventilator covered with wire mesh is provided. It is fitted with sliding top to regulate ventilation

6. At the bottom of the box & on the lower portion of side walls, small holes are drilled for aeration To measure the temperature, a thermometer is fixed from inside of glass door Inside the box, there is a provision to place 4-5 plastic trays in 2 tiers for keeping seed cocoons For early emergence of moths, 50-60 seed cocoons are taken from individual lots and placed into an artificial ecolosion box The temperature in the box is adjusted to 32-33 C using 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.

7. Synchronization of emergence of moths, pairing, deparing and ovposition 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 % RH for 3-4 days. After 1-2 hrs of emergence the male and female moths of respective combination are allowed for 3 1/2 to 4 hrs of pairing

8. At the time of depairing the male and female moths are to be moved side ways so that the moths are separated easily without injury to reproductive organs The mated female moths are placed in a separate container and induced for urination Then the moths are placed on egg sheet and covered with cellules and kept in semi dark condition for oviposition Under proper preservation (5-7 0 C ) male moths can be used for second pairing by giving 1-2 hrs rest Throughout the process of pairing, depairing and oviposition , optimum temperature of 25 C and RH of 75% should be maintained

9. Mother Moth Examination The mother moth examination is done to know the pebrine disease in B. mori caused by a parasitic sporozoan , Nosema bombycis Surface sterilization of silkworm eggs After ascertaining the disease freeness of layings , egg sheets are dipped in 2% formalin solution for 10-15 minutes This helps in removal of pathogens adhering to egg sheets and further prevents secondary contamination Washing of eggs in formalin solution helps in firm adherence of eggs to the sheets

10. Incubation of Silkworm eggs In order to facilitate uniform development of embryo the eggs are subjected to ideal conditions of incubation like Optimum temp. of 25 C and RH of 75%, 16 hrs light and 8 hrs darkness is ideal During pin head stage or before 2 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

11. Egg Laying Process Egg laying can be carried out by following methods Cellular bag method Cellular card method Flat card method Loose egg method

12. Cellular Bag Method It was invented by Louis Pasteur Small bags made of paraffin paper perforated with many holes are used Male and female moths are introduced into these bags for copulation and deposition of eggs Female moths after egg laying are examined microscopically for pebrine disease  

13. Disadvantages It is costly Laborious method where in individual bags are required However perfect disease free layings can be obtained by this method since each bag is tested and 100 % moth testing is ensured It pebrine is found, the entire lot is rejected in case of reproductive seeds This method is useful in reproductive seed selection

14. 2. Cellular Card Method It is conveniently used in industrial egg production and in less laborious than the earlier bag method 7x4 = 28     Here, a card paper of 28 compartments with 4 rows &7 sections is used

15. One mother moth is kept in each compartment for deposition of eggs. Mother moths are tested for pebrine free microscopic examination If any pebrine spores are noticed, the particular card can be easily destroyed 3. Flat Card Method About 40 mother moths are allowed to lay eggs on a card paper Eggs are laid on the whole surface of the flat card

16. Mother moths are examined for pebrine after deposition of eggs If the testing of mother moths shows more than 10-20% of the females are infected with pebrine, the entire lot is reject.

17. 4. Loose Egg Preparation Technology The mother moths (50-100) are kept on starch coated craft paper & allowed to lay eggs After egg laying mother moths are examined for pebrine disease If found infected all the eggs are discarded Generally, during this process the moths which do not take part actively in mating are eliminated from the paper After deposition of eggs the paper is immersed in water for 30 mins to detach the eggs from the egg sheet. The loosened eggs are washed again in a salt solution of specific gravity 1.06 – 1.10

18. The eggs which float on the surface are removed as well as the unfertilized and dead eggs The loose eggs are washed with 2% formalin solution and once again with fresh water Finally, the eggs are dried under shade and are weighed & packed comfortably in egg boxes Each unit of egg box contains approximately 20,000 eggs For convenience 1 g of eggs is weighed and the number counted accurately to calculate number of eggs per gram This will help the farmer to estimate the quantity of eggs to be purchased for rearing depending upon the mulberry leaf available in the garden

19. Advantages In case of egg sheets, it is hard to find the actual no. of eggs in each egg card which may range from 300-400 numbers In loose eggs the fertility of eggs is assured Farmers do not find any loss for their payment. Unlike approximate number of hatching percentage in case of egg cards, 100% hatching is assured for each gram of loose eggs thus farmer do not find any loss Easy to transport and easy to procure Occupies less space, during preservation and transportation Farmer easily estimate the quantity of eggs required for the quantity of leaf available in his garden

20. Transportation of Eggs Eggs are very sensitive to light and temperature Eggs should be transported only during cool hours ( eigther early hours or late evening) of the day Eggs must be packed in a wet hand bag and not to be carried during day at high temp. and should never be exposed to direct sun light and strong winds Egg transportation should be avoided during egg pigmentation stage (blue stage) and immediately after egg laying Therefore to be transported on or before 5 th day of incubation

21. Incubation Eggs will hatch in 10 days after laying in multi- voltine Incubation of eggs is necessary in order to hatch the eggs simultaneously on the required day The purpose is to obtain uniform growth and uniform embryonic development The eggs purchased should be incubated in room where the required temp. of 25°C and humidity (80%) can be controlled and light hours 17 to 18 hrs / day In case of hibernating eggs, they are acid treated, then either refrigerated or cold stored to delay hatching These eggs should never be brought to room temp. (25°C) suddenly A passage of 15°C for half a day should be maintained The incubating eggs should be washed in 2% Formaldehyde before incubation

22. Before hatching, the eggs shows certain characteristics Head pigmentation stage : Just 2 days before hatching Body pigmentation stage : Just one day before hatching To ensure uniform hatching all the eggs must be kept in dark for 2 days before stipulated hatching period in multivoltine eggs (IP: 10days) Therefore on 8 th day i.e., at egg pigmentation stage, eggs are kept in dark for 2 days In case of body pigmentation stage eggs are kept in dark for 1 day These eggs kept under dark should be exposed to light suddenly on the day of hatching and this is called black boxing With this method maximum hatching of eggs is ensured

23. There are Two types of eggs Non-Hibernating Hibernating 1. Non-Hibernating These eggs do not enter into diapause or dormancy Multivoltine silkworm races lay non-hibernating eggs which hatch after 10 days of laying Here the embryo will continue to develop at normal temperature and humidity conditions

24. 2. Hibernating Eggs The Univoltine silkworms lay only hibernating eggs These eggs do not hatch till the following spring until artificial methods are adapted for hatching The most common method of artificial hatching is acid treatment Bivoltine races lay one brood of diapausing and one brood of non-diapausing eggs Acid Treatment The hibernating eggs should be treated with HCL within 24 hrs of laying to stop the eggs from undergoing diapause

25. Postponement of Acid Treatment Eggs within 20 hrs of oviposition should be cold stored at 5°C & 80% RH up to 5 days Later these cold stored eggs should be brought to room temperature of 25°C through an intermediate temperature of 15°C for 2 hrs, to avoid sudden exposure to hot temperature and then acid treated

26. Cold Acid Treatment HCl of specific gravity 1.1 at 15°C should be used to prepare a solution The egg cards should be dipped in 2% formaldehyde within 20-24 hrs of laying to enable the eggs to adhere to egg cards firmly and Then dipped in HCl soln. for 60-90 minutes at a room temperature of 25°C – 26°C

27. Hot Acid Treatment HCl of conc. of specific gravity 1.075 at 15°C is used Eggs must be treated for 5-6 minutes at 46°C However, this time period (5-6 mins ) will be higher in case of Univoltine races when compared to bivoltines The eggs then are washed with running water after acid treatment Later dried in the shade without exposing them to direct sunlight

28. Acid Treatment after chilling The eggs after 40-50 hrs of oviposition at 25°C can be chilled by keeping them in cold storage at 5°C up to 60 days In order to prolong the cold storage period for more than 60 days, the temperature should be further decreased to 2.5°C and humidity should not exceed 80% Before undertaking the process of acid treatment after chilling, the eggs should be passed through a middle temp. of 15°C in room for 3 hrs

29. The eggs should be dipped in Hcl for 5-7 minutes depending upon the silkworm race The specific gravity of HCl should be 1.1 at 15°C and heated to 48°C The acid treated eggs should be dried in the shade and should not be exposed directly to sunlight for drying They should be kept at 25°C room temperature and RH of 80-85% favours good hatching percentage