Late age Rearing
Scientific cultivation of mulberry and adoption of new technologies in silkworm rearing plays an important role in the production of quality raw silk. The larval duration in the life cycle of the silkworm, ranges from 24-28 days. The larval stage comprises of 5 instars, and 4 moults. Rearing of silkworms from 3rd or 4th instar up to spinning stage is called the late age silkworm rearing. During this period the silkworms consumes more than 94% of total mulberry leaves required, 133 times increase in body size, 125 times increase in body weight and 1000 times increase in the silk gland weight from the time of hatching. Since the late age silkworms are sensitive to high temperature and humidity, scientific rearing methods and rearing skill method are necessary for achieving maximum growth and survival of the larvae, thereby increasing the cocoon yield and silk production.
A separate rearing house with good ventilation, light and space has to be constructed for late age rearing. The height of the rearing building has to be appropriate, with provisions for maintaining the required temperature and room humidity. The rearing room has to be clean and hygienic and suitable for conducting effective disinfection. It should have an anti chamber for the prevention of uzifly entry and have a separate leaf storage room.
Silkworm Rearing in Bamboo Trays:
In tropical country like India, rearing houses should be constructed East-West longitudinally with corridors all around and window on the South and North sides of the building. For easy exchange of air, the windows should be constructed opposite to one another. All the doors and windows should be fixed with uzifly mesh. For effective exchange of air, ventilators are to be fixed above and below the windows. The rearing space required for one dfls is 8 sq.ft.
The rearing rooms and rearing appliances to be disinfected before and after the completion of silkworm rearing.
Rearing silkworms in bamboo rearing trays has been the traditional method of rearing in our country. Late age silkworm larvae require a temperature of 22-25� C, 70-80% RH, 16:08 hrs of light and darkness. The rearing room has to be adequately ventilated. Depending on the season and environment, the silkworms are to be fed 3 to 4 feedings per day. The mulberry leaves to be harvested during the cooler hours of the day and transported in bamboo leaf baskets coved with wet gunny cloth to the leaf storage room. The leaves are stored in leaf storage bins which are coved with wet gunny cloth; this will preserve the leaf moisture for a longer period and maintain the quality of leaves. Perforated PVC pipes can be placed inside the heap, this helps to reduce temperature buildup inside the leaf chamber.
Shoot Feeding Method Of Rearing:
During moulting periods, the rearing bed has to be dried by dusting lime powder and aeration inside the room increased by opening the window and ventilators to the required extent. After more than 95% of the larvae come out of moult, the rearing bed disinfection has to be done by dusting the bed disinfectants as per recommendation and feeding resumed after 30 minutes. If any diseased larvae or unequal size larvae are observed they have to be immediately separated and disposed to a basin containing formalin or bleaching powder solution. Regular rotation of the position of rearing trays from the top to the bottom will provide uniform temperature and humidity to the larvae. Depending on the season and weather conditions the ventilators and windows can be opened or closed to facilitate maintaining of rearing temperature and humidity inside the room.
To bring down the labour cost and increase the productivity, shoot feeding methods of rearing has been developed, standardized for tropical conditions and recommended for the sericulturists. This new technology reduces the labour cost to an extent of 50%. Irrigated mulberry gardens are suitable for adoption of shoot feeding method. 5 to 6 crops can be harvested in a unit area of mulberry garden with an interval of 40-45 days between crops. In this method of rearing, 15 to 20% leaf saving can be achieved which can be used by brushing additional dfls, increasing the cocoon productivity per unit area of land. Since the leaves are attached to the shoots, the quality of leaves is maintained for a longer period, facilitates effective feeding and reduces the leaf cocoon ratio significantly.
Handling of spinning larvae, harvesting of cocoons and transportation:
The mulberry shoots to be cut using sharp secateurs or sharp sickle leaving 2 -3 buds from the previous cut and harvested during the cooler hours of the day, covered with wet gunny cloth and immediately transported to the leaf storage room. The shoots are place upright and covered with wet gunny cloth.
In this method of rearing, bamboo trays or rearing stands are not required, instead shoot rearing racks are constructed/fabricated. The rack should be 5 ft in width and length as long as the rearing hall. The rearing rack can have 3 to 4 tiers with a gap of 2 to 2.5 ft between the racks for effective aeration. 600 to 750 sq.ft. rearing space is required for hybrids while the CSR hybrids require 800 to 850 sq.ft. bed area.
After resuming from the moult, the 2nd or 3rd instar larvae are to be evenly spread on lime powder dusted old new paper spread on the shoot rearing rack. Mulberry shoots should be gently placed on the rearing bed opposite to one another. Depending on the season 3 to 4 feedings can be given per day and as the larvae grow, bed spacing should be increase.
When more than 90% of the larvae settle for 4th moult, feeding should be stopped, aeration inside the rearing room increased and rearing beds should be dried by dusting active lime powder. When more than 90% of the larvae come out of the moult, the rearing bed should be disinfected by dusting the recommended quality of disinfectants and after 30 minutes feeding should be resumed. In the shoot feeding method, rearing bed is cleaned once after 4th moult by using rearing nets or rope, larvae spread evenly as per the recommendation and feeding resumed. If the rearing room humidity is very low, the rearing beds can be covered with old news paper.
Once the larvae exhibits spinning behavior, feeding quantity has to be reduced and stopped. Spinning larvae has to be separated from the bed and shifted to the mountages. During spinning stage, 24 - 25� C temperature and 60-70% relative humidity has to be maintained in the mounting hall. This helps in getting quality cocoons. Adequate aerating should be provided during spinning period and the spinning larvae should not be exposed to direct sun light or heat. Cocoons can be harvested after 5 to 7 days, dead, flimsy, irregular and stained cocoons should be separated and good cocoons transported to the cocoon market in a cotton bags.
Types of Mountages:
Bamboo mountages are the traditional type use in Karnataka. Bamboo strips are fixed in a spiral/circular fashion on the bamboo mats. The idea size of the mountage is 1.8 x 1.2 meters and gap between the spirals should be 5 to 6 cms. 40 to 60 larvae per sq. ft. can be mounted. During spinning stage, two mountages placed one behind the other at an inclination of 45�, this reduces the number of bad or rejected cocoons.
Plastic corrugated mountage:
Plastic corrugated nets are specially designed for mounting spinning larvae. The height of the corrugation should be 6 cms and each mounatge should have 11 corrugations in number. The ideal size of the mountage should be 60 x 90 cms, and this can be easily placed in wooden rearing tray. 300 to 400 can be mounted on these mountages. Before mounting the larvae, old news paper should be spread below the mountage, this will help to absorb the urination, reducing the humidity build up. These types of mountage, require less mounting space and can be easily disinfected. Cocoons can be easily harvested from this type of mountage. Adequate aeration should be provided in the mounting hall or rack particularly for CB larvae, as urination is more in these larvae.
This is an improved, Japanese type of mountage made with thick paper boards. Each mounting frame has 13 rows and 12 columns containing 156 mounting slots. Each slot is 4.5 x 3 x 3 cms in size and the dimension is 55 cms in length, 40 cms in width and 3 cms in depth. 10 such mountages are arranged in metal frame with a distance of 8 cm from one another. The rotary mounting frames are hung from the ceiling during spinning stage and can be packed and stored after cocoon harvesting.
Before mounting the larvae, the rotary frames are placed on old news paper; about 1200 larvae are measured and distributed between the rows on the news paper. Once all the larvae climb on the mountage, the frames are lifted and hanged from the ceiling. Since the spinning larvae exhibit negative-geotrophic behavior, they climb and move up, because of the weight displacement, the mountage rotates, helping the larvae to search an empty slot and settle for spinning. Therefore, this type of mounatge is called a rotary mountage.