Thursday, October 26, 2017

REARING OF SILKWORM AND PRODUCTION OF COCOON

Rearing program
In sericulture areas which enjoy temperate or subtropical climates, silkworm rearing is carried out twice a year in the spring and the autumn or three times, in the spring, the summer and the autumn, coinciding with the growth and production of mulberry leaves. In tropical areas, however, where mulberry growth is continuous throughout the year silkworms are reared five to six times in a year. Whether rearing is conducted frequently or only two or three times a year it is always beneficial to have a planned program. It is advisable to rear a greater number of lying at a time than to rear much bathos at very short intervals. The program of silkworm rearing in a farm is determined by the following considerations:
1.  Conditions of mulberry growth and yield of mulberry leaf.
2.  Availability of labor for rearing silkworms.
3.  Facilities for rearing silkworms, i.e. suitable buildings and equipment.
                
Conditions of mulberry tree growth and yield of mulberry leaf: The time to rear silkworms is when there is a proper sprouting of mulberry leaves and a plentiful supply of good quality leaves. The yield and the quality of the leaf depend to a great extent on the agronomic practices followed for the cultivation of mulberry trios namely irrigation, application of fertilizers and proper activation.

Availability of labor: Since sericulture is a labor‑intensive rural industry requiring much labor the volume of rearing to be undertaken will also depend on the adequate availability of labor at a reasonable wage. If labor costs are high economic production costs will also increase.

Facilities for rearing silkworms: The facilities required for silkworm rearing are a rearing space or houses, and rearing equipment.

Rearing space or houses: Silkworm rearing demands certain specified environmental conditions particularly as regards temperature and humidity. Rearing houses are planned and constructed to provide and maintain proper environmental conditions to ensure good quality cocoons.

Equipment for silkworm rearing: The equipment required for a model rearing house for shelf rearing is as follows: in the model rearing house in each of the rooms 200 ‑ 250 layings or 800‑1000 layings in the entire rearing house can be reared under shelf rearing.
Rearing stands
Ant wells
Rearing trays
Rectangular wooden trays or boxes
Paraffin pape
Foam rubber strips
Chop sticks
Feathers
Chopping board
Chopping knives
Mats
Leaf chamber
Cleaning nets
Mountages
Hygrometers and thermometers
Feeding stands

Other equipment: Among the other items required are feeding basins, preferably plastic, to, hold chopped leaves, and buckets and basin stands, etc., A sprayer is also required for disinfecting the rearing room, for spraying water on to the leaf chambers, etc. Leaf baskets made of bamboo are used for carrying the leaves from the garden to the rearing rooms.

Sanitation and preparations for rearing silkworms: The silkworms must be reared with the utmost care since they are very susceptible to disease. Bacteria, moulds and some protozoan attack the silkworms readily and any disease, once it breaks out, spreads quickly. To prevent disease, good sanitation methods and hygienic rearing techniques must be meticulously followed.

Hatching, feeding, cleaning and spacing
Hatching: Hatching of silkworms generally starts early in the morning. The process of transferring the silkworms to rearing trays is called "brushing". A suitable time for brushing is about 10.00 as most of the larvae hatch by 08.00 and develop good appetites within two hours of hatching.

Feeding silkworms: Silkworms are fed to satisfy their appetites and to ensure their, healthy and uniform growth. It is therefore necessary to preserve the quality of leaf during feeding and to keep the rearing beds clean.

Bed cleaning: Removing the old mulberry leaves, faecal matter of silkworms, exuviae, any dead or unhealthy silkworms, etc., from the rearing bed is called bed cleaning. Accumulation of any such matter creates environmental conditions detrimental to the health of silkworms.

Spacing: Provision of adequate rearing seat space is of great importance for the vigorous and full growth of silkworms. As the worms grow in weight and size, the density in the rearing bed increases and conditions of overcrowding are faced.

Overcrowding of silkworms means insufficient space for the free movement and free feeding of the worms and so the larvae crawl over one another.


The spacing to be provided for different ages of silkworms of 50 layings or a box of 20 000 eggs are given below:
                                            At the beginning              At the end
                                              of each age                     of each age
                                                   (M2)                              (M2)
Univoltines and bivoltines species:
Age
lst                                                0.2                                  0.8
2nd                                              1.0                                  2.0
3rd                                               2.0                                  4.5
4th                                               5.0                                 10.0
5th                                             10.0                                 20.0

Multivoltines and bivoltines species in tropical areas:
Age
1st                                              0.2                                   0.5
2nd                                             0.5                                   1.5
3rd                                             1.5                                   3.0
4th                                             3.0                                   9.0
5th                                             9.0                                 18.0


Care at molting
Uniform growth of silkworms of any batch depends on the care given to rearing. Among the various steps involved in the rearing of silkworms the handling of silkworms during molt is of particular importance. Silkworms under proper rearing conditions would all settle uniformly for molt and also come out of molt uniformly.

Environmental conditions
Since silkworms have been domesticated for many centuries, they are by nature quite delicate and very sensitive to environmental conditions. In the commercial production of cocoon crops optimum environmental requirements ensuring maximum productivity of good quality cocoons of very high silk content are aimed at.

Temperature: Temperature plays a vital part in the growth of silkworms. Silkworms are cold, blooded animals and as such temperature will have a direct effect on the various physiological activities of their systems.

Since the temperature is in direct correlation to the growth of the silkworms’ excessive fluctuations in temperature are harmful and should be avoided. The optimum temperatures for rearing silkworms of different instars are as follows:
In stars                                                                                   0 C
     lst                                                                                  26 ‑ 28
   2nd                                                                                  26 ‑ 28
    3rd                                                                                 24 ‑ 26
    4th                                                                                 24 ‑ 25
    5th                                                                                 23 ‑ 24
Light: Silkworms are photosensitive and generally have a tendency to crawl towards dim light. They do not like either strong light or complete darkness. In complete darkness the larval period is shortened and in bright light there is a tendency towards production of heavy cocoons.

Leaf quality
The mulberry leaf is the exclusive food of the silkworm Bombyx mori. It is essential that the mulberry leaves axe not only in abundant supply but are also of good and suitable quality. Leaf quality has much to do with the success of silkworm rearing and the quality of the cocoons produced. Similarly in the case of fertilizer application, higher doses of nitrogen fertilizer induce more vigorous growth in mulberry trees and the leaves from such trees contain more water and protein.

Harvesting and storage of leaves: Leaves picked from mulberry plants lose water rapidly due to withering and as a result the leaf quality is considerably affected. Leaves that lose moisture beyond a certain level are no longer relished by the silkworms which do not feed adequately on such leaves with the result that they are not nourished properly.

Rearing early-age silkworms
Different methods of rearing the early ages are practiced. In all methods importance is given to maintenance of leaf quality and correct humidity and temperature in the rearing bed so that vigorous and healthy development is ensured. The two methods used at present are: 1. paraffin‑paper rearing and 2. box rearing.

Paraffin paper rearing: Paraffin paper is used as a bottom layer and as a cover for the rearing beds in the usual rearing trays. The object is to maintain the optimum humidity in the bed and to keep the leaves fresh for a longer period by preventing moisture loss through evaporation. Feeding is restricted to two or three times a day and so the labor required for feeding is reduced.

Box rearing: Boxes or trays made of wood or plastic or galvanized iron at least 10 ‑ 15 cm deep are used for box rearing. The boxes used may be with or without lids.

Rearing in boxes with lids: In this case a sheet of paraffin paper is spread over the bottom of the tray. The rearing bed is prepared over this and covered with another sheet of paraffin paper after putting in place the wet foam rubber pads.

Rearing in boxes without lids: Wooden boxes of uniform size and 10 ‑ 15 cm deep are used. Each box is provided with a sheet of paraffin paper for the base, over which the rearing bed is prepared, wet foam rubber pads axe placed on all the four sides and the bed is covered with another sheet of paraffin paper.

Co‑operative rearing of young silkworms: Silkworms not reared properly in their young ages are prone to disease at later stages, and crops may even fail. Maintenance of optimum temperature and humidity, supply of suitable leaves, and handling of the young‑age rearing with utmost care, etc., demand highly technical skills, which are not often available to the ordinary silkworm rearer.

Rearing late‑age silkworms
Late‑age worms in the fourth and fifth instars need comparatively less humid rearing conditions and also preferably a lower temperature. These are real feeding stages when the worms consume about 90 ‑ 95 percent of the total feed, and therefore, adequate spacing and an adequate amount of feed should be given to these two ages.

Methods of rearing late‑age worms: Three methods of rearing are commonly known: shelf rearing, floor rearing and shoot rearing.

Shelf rearing : Rearing of silkworms in rearing trays arranged one over the other in tiers on rearing stands is called shelf rearing.

Floor rearing: This is another method of rearing silkworms on fixed rearing seats. The rearing seats are arranged in two to three tiers so as to accommodate as many silkworms as possible.

Shoot rearing: Shoot rearing is very similar to floor rearing. Silkworms are reared on big branches in one or two tiers. The big shoots harvested from the fields are fed straight away to the worms.

Mounting and harvesting
Toward the close of the final larval instars the silkworm stops feeding and gets ready to build the cocoon prior to transforming itself into the pupa inside the cocoon. The feeding during the final instars may last from five to seven days in the case of multivoltines and bivoltines races in the tropical areas, and seven to nine days in the case of bivoltines and univoltines races in sub‑tropical areas. With the cessation of feeding and as the stomach contents empty, the fully mature larva becomes translucent and yellowish in appearance which is a clear indication that the worm is fully ripe and is ready to be mounted on to montages or cocooning frames. Such ripening larvae normally crawl towards the periphery of the rearing trays in search of suitable supports for building their cocoons. Thus the process involved in picking the ripe worms and putting them on to the suitable montages for the spinning of cocoons is called mounting of worms.

Collecting mature worms for mounting: Collecting mature silkworms and mounting them on the montages is a laborious job. Usually the mature larvae are picked by hand by skilled labor capable of identifying the mature worms, which are collected in trays and later put on the montages.

Method of free mounting: With this method instead of collecting the mature worms from the beds, the montages are placed in the beds themselves and the worms crawl up onto them.

Density of mounting: In the case of revolving montages density is automatically adjusted since only the number required to fill the empty blocks in the cocooning frames are mounted. Ordinarily a single frame contains about 156 blocks and 10 such frames are put together to form a unit of turning cocooning frames which can mount 1560 worms.

Environmental conditions required for mounting: Maintenance of the required environmental conditions during mounting is important as it determines the quality of the cocoons spun. Silkworms under mounting normally require a comparatively drier 0 atmosphere. Ideal conditions for good spinning are temperatures not exceeding 26 0 C and relative humidity between 60 and 70 percent. If temperatures rise above 26 C the quality of the cocoon is affected. It is particularly important that during the first 50 hours after mounting ideal conditions are maintained for cocoon spinning.


Harvesting of cocoons: After spinning the cocoon the larva undergoes metamorphosis inside the cocoon and becomes the pupa. Generally pupation takes place on the fourth or fifth day of spinning. The pupa when formed has a thin cuticular skin which is soft to the touch and ruptures easily if disturbed; therefore early harvesting of cocoons should be strictly avoided. In course of time the pupal skin hardens and turns dark brown and it is at this stage that cocoon can be harvested. The proper time for harvesting cocoons is on the seven or eighth day of spinning in the case of bivoltines and univoltines races, and on the fifth day in the case of multivoltines races. Harvesting must not be unduly delayed beyond the period mentioned above lest any parasitic insects infecting the silkworm larvae emerge from the pupa and damage the cocoons.

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