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 Sericulture  

Techniques of rearing the Muga Silkworms

Sericulture is an important agro-based cottage industry which provides gainful employment to the rural section of the society. The success of the silkworm rearing depends on the quality of leaves, suitable environment factors and proper management practices. The rearing process is a multifarious activity and attention is needed to following aspects to attain maximum yield. Sericulture in East Khasi Hills District is having ample scope for the development because of the locational characteristics and climatic parameters of the district.

ESSENTIAL ITEMS

The essentials items for  Muga rearing are as follows:

  1. Bamboo baskets,

  2. Mounting brushes (Kharikas),

  3. Secateur,

  4. Butterfly catching nets,

  5. Bow with pallets,

  6. Bird scaring instruments,

  7. Nylon mosquito nets,

  8. Wire-netted cages or Bamboo cages (chakaripera),

  9. Triangular bamboo shieves (chalani)

  10. Alluminium pans

  11. Bamboo poles,

  12. Gamaxin,

  13. Tugon bait,

  14. Gum,

  15. Lali, molasses,

  16. Dry leaf Jalis, etc.

All rearing appliances must be disinfected with 4 percent formal dehyde solution in time. The life cycle of Muga may be divided into four stages, viz.

  1. Egg,

  2. Larva,

  3. Cocoon (pupa) and

  4. Moth.

Muga silkworm (Antheraea assama; family Saturniidae) is semi-domesticated and multivoltine. It is possible to rear 4-6 crops in a year. The rearing is out-door and exposes to environment conditions and attack of parasites, predators and diseases. It results in heavy losses due to weather conditions, pests, diseases and natural calamities. These losses are due mainly to the faulty selection of rearing places (Muga chung) and food plants, improper handling of worms, poor supervision of rearing, intensity of natural enemies, etc. Smoke from various engines and workshops, dust from gravel roads, some of the pesticides and herbicides used in agricultural fields and tea estates, D.D.T. spraying for eradication of Malaria are also some of the factors hampering the healthy growth of Muga-culture.

2. REARING PLACE

A suitable rearing place (Muga chung) is to be selected. It should not be low lying and shady. Medium size full-grown Som/Suala trees with more branches and fresh leaves are to be selected for rearing. Early stage worms should preferably be reared on dwarf plants for reducing loss of worm. Tall trees will reduce the production. It is also difficult to hang “Kharikas” and to transfer the worms to other trees after exhaustion of leaves on tall trees. Worms also find it difficult to crawl up the tall trees in search of suitable leaves. It increases the mortality of worms of course, flies wasps etc., may not be able to attack the worms easily in tall trees as they can fly to a particular level only.

The rearing place (Muga chung) should be cleaned including the base of all trees to avoid pests. The dry and diseased branches, twigs and leaves, nests of ants and wasps, etc, are also to be removed before starting the rearing. Plants infected with ants, aphids, wasps, termites are to be avoided for rearing. A band of straw should be wrapped around the trunk of each tree at a height of about one meter. This will act as a barrier for the worms from coming down and prevents ants, etc., from going up. Banana or pine apple leaves may be put above this band so that worms cannot come down after exhaustion of leaves. These will facilitate to collect them easily. Ashes, lime and sand mixed with kerosene may be put at the base of trees. Gamaxin may also be sprinkled at the base of trees to prevent ants but it must be done at least before a fortnight of mounting the worms. Fish refuse, mollases etc., may be kept at the base of trees to attract the ants. Ants should be burnt regularly in the morning and evening. The nests of ants/wasps from nearby bushes/grasses are also to be cleared. It is better if the apical buds in the branches may be removed before two weeks of rearing as buds and every tender leaves are not suitable for rearing. Insecticides/fungicides should not be sprayed before rearing. 

3. HATCHING

The eggs of muga silkworms are brownish in colour. They hatch out within 1 to 12 days of eviposition during summer and a16 to 25 days in winter. The worms start hatching from early in the morning till about 10:00 a.m. under normal condition. Hatching will be ever within 24 days. Newly hatched worms eat their egg shells. Worms hatched out during first two days are to be considered for farm rearing as they graw uniformly and are healthy. Larvae hatched up to 4 days are to be kept for commercial rearing. The percentage of hatching is 40% to 95 according to the season. Hatching will delayed during summer by keeping the eggs at 6°C to 10°C and hastened during winter by exposing them to 28°C to 30°C as experimented at Muga Research Station, Dhakuakhana (Assam). Eggs kept in controlled condition and incubated eggs will hatch uniformly and worms would complete maturing with 3-4 days. Eggs should be kept in perforated boxes in an disinfected room and ants, lizard, etc. should not be there.

Eggs with kharikas (bamboo orthatch) or the loose eggs in bamboo/paper baskets are to be tied with or hang on suitable leafy branches and on the trunk when the majority of the worms are hatched out (4 A.M. to 10 A.M.).

4. MOUNTING

The newly hatched tiny worms will crawl up by themselves to the leave of Som/Suala by their natural instinct. They start eating from the margin of suitable leaves. They eat up the midrib and even the petiole of the leaf during the last two instars. Another method of mounting the newly hatched Muga worms is that small twigs bearing soft and tender leaves are lightly put ever the newly hatched worms on the “Kharikas” or in the egg boxes/baskets. They will crawl up to the leaves. The twigs with the worms are then tied with suitable branches at different places of the Som/Suala trees for uniform distribution. They are to be put either on the east or north side of the trees to get sufficient sunshine by the help of bamboo poles. The suitable time for mounting the newly hatched worms is morning. It is not advisable to mount during heavy showers, heavy wind or storm. It is better if a limited number of worms can be mounted on a particular tree, where leaves will be sufficient upto maturing to avoid frequent transfer of worms. 5 layings may be a reared in a full grown Som/Sualu tree and about 200 cocoons may be harvested in one crop. Overcrowding by mounting more worms on a tree by the rearers compel them to eat hard leaves unsuited to their age. It is the main cause of flacherie desease of Muga. It is desirable to mount the worms hatching in different days on separate plants. Kharikas/bamboo baskets are to be collected, disinfected with 2% formaldehyde solution and preserved properly for future use. The younger worms prefer soft and tender leaves and matured leaves at the advance instars stages. It has been observed that the rate of feeding is higher at night than in the day time. They take rest (about 5 minutes) after every stretch of feeding. Healthy worms take the whole leaf even soft twigs from the top of the tree. Larvae move much during the first instar-1 stage in search of the suitable leaves than during the other instars. If and when change of food plant is necessary, worms should be mounted first on Sualu and then transferred to Som. Worms find difficult to eat Sualu leaves due to presence of gall wasps and of flowers. Likewise, fly pests are more in Digloti rearing and the fruits of Digloti also hamper the worms to a great extent.

5. MOULTING

Muga worms are green in colour with thorny warts. They shed their skin (moult) four times their larval period. Worms move more before moulting to find out proper place for shelter. Moulting period varies from 24 to 36 hours depending upon this season of rearing. The larvae eat their cast off skin. No disturbance and transfer of worms should be there during moulting. The transfer of worms after exhaustion of leaves should be done after 3-4 hours of moulting (ecdvsis). Day and night constant and close watching is indispensable to avoid pests and to scare birds, bats, etc. This will also help to assess the condition of the worms. Dead worms should be collected twice daily in the morning and evening. They are to be burnt and buried away from the rearing place. Microscopic examination of dead and diseased worms should be done to detect diseases. It is advisable to conduct rearing of unhealthy and weak worms separately on fresh plants. Muga worm start descending of their food plants when leaves are exhausted. They are picked up, sorted out according to their stages and hung on few leafy branches of other suitable tress with the help of triangular bamboo shieves (chalani) and bamboo poles. Another method for transferring the worms is keeping leafy twigs alongwith the worms may be put on other suitable trees with the help of bamboo poles. One should handle them carefully to avoid injury to worms by forcible detachment. Worm falling from the trees should be picked up by some suitable leaves (branches). Worms defecate orange shaped litters with six longitudinal furrows. Worms usually hide on the under surface of the leaves and have a strong gripping power. They are very sensitive and disturb easily. They stop eating leaf and shrink their body (expressing their anger) when disturbed by movement, sound or touch etc. If removed by force, they vomit a liquid. Rough surface (bark) of the trunk of the tree should be made smoth. It will help in picking up worms easily without damage during transfer. Smaller worms would be picked up first and the bigger worms later. The blue colour larvae are bigger and heavier than the normal green colour larvae.

6. LARVAL PERIOD      

The larval period varies from 22 to 50 days according to the season of rearing. At the end of fifth instar the worm attains maturity, stops feeding and empties its alimentary canal by passing out the last excreata (green semi-solid) mass followed by coloureds slimy substace). Worms consume about 20 per cent leaves during first instars and 80 percent during the last instar alone. Matured Muga worms become slightly smaller, flabby and transluscent and make a hallow sound on touch. They come down from the tree in the evening due to effect of negative geotropism. It makes the collection of worms easier for the nearers. They are collected by the rearers in bamboo baskets quickly and may be put on ‘Jalis’ directly. The effective rate of rearing varies from 20-60 Cocoons per laying, depending on the season rearing.

7. FEEDING

Mugaworms feed on Mejankari and chapa leaves produce creamy white silk. It fetches a higher price. Of course, the growth of Mugaworm on Mejankari is said to be slow and unhealthy in comparison to that of som Plants. However, rearing on Majankar may be conducted where it is growing abundantly for producing creamy-white ‘Mejankari’ silk.

8. MATURING

Generally a crop completes maturing within 3-4 days. Of course, some crops take upto two weeks to complete maturing. The worms maturing earlier produce male moths, those that mature later produce more female moths and worms maturing in between (Bhor-pok days) produce an approximately equal number of male and female moths.

The matured worms are then taken to the seed preparation house or any other suitable place and put them into the Jali prepared earlier from suitable dry leafy twigs and kept hanging vertically in dry place for spinning cocoons after being counted. The number of worms in a ‘Jali’ are to be adjusted according to the space available in it. ‘Jalis’ may be arranged on bamboo mats where mutured.

The mature worms are then taken to the seed preparation house or any other suitable place and put them into the Jali prepared earlier from suitable dry leafy twigs and kept hanging variety in dry place for spinning cocoons after being counted. The number of worms in a ‘Jali’ are to be adjusted according to the space available in it. ‘Jalis’ may be arranged on bamboo mats where matured worms are kept and they will crawl up to the ‘Jalis’ easily. Some one should observe the worms atleast for an hour after hanging the ‘Jalis’ as some worms way fall down from the ‘Jalis’ while searching for suitable place for cocooning. Those worms are to be kept on ‘Jalis’ again. Sex in larval stage can easily be distinguished by the external genital markings. Four dots in case of female and a V-shaped marking the in male worms are seen in between the 8th and 9th segments on central side. Sex markings in pupa are more prominent than in worms. Separate cocoonage should be used for males and females in case of production. ‘Jalis’ are to be prepared from the leave of suitable trees. The quality, size, colour, etc of the cocoons differ according to the food plants on which they feed. It is said that the age of the tree has a great effect on the colour of the silk produced. The cocoon spun by Muga worms feeding in Diglati leaves is smaller to that of other Muga food Plants.

9. COCOONING

Cocooning is completed within 3-4 days in summer and 7 days in winter. Pupation is completed after 15-30 days of cocooning. No disturbance should be there to the Jalis up to a week during cocoons formation. The female worms spin bigger cocoons than the males. Usually cocoon formation starts during the day time. Cocoons are harvested normally after a week of spinning during summer. Of course, it is delayed up to 1½ weeks during winter. The normal and the inferior cocoons should be harvested separately. Cocoons are cleaned of the adhering leaves at the time of harvesting. Good and healthy cocoons are kept for seed production, and the others for reeling and spinning purposes. The weight of cocoons, silk shell, pupa and the length of filament varies according to season.

10. INDOOR REARING

The indoor rearing for the whole larval period may be practiced for producing basic seed cocoons and for maintaining the parent stocks. It may be done by bringing leafy branches or Som/Saulu trees and putting them in some container (non corrosive) having cold water. These branches are to be changed from time to time whenever necessary to keep the freshness of the leaves. It should be done after proper experimentation for better harvesting. It may result about 95 per cent success of the cocoon crop. It does not require regular watching like that of outdoor rearing, reduces expenditure, loss of worms and mortality. It also protects the Muga worms from their enemies like ants, wasps, birds, bats, etc. Continuous indoor rearing for many generations throughout the larval period may weaken the strain. So, indoor rearing up to second moult or third stage and outdoor rearing for the remaining instars preferably under net covering with proper care will help to maintain the health and vigour of the race intact and in harvesting more cocoons. Muga worms like to take water drops accumulated on the leaf for which sprinkling of water once a day on the twigs is advisable in case of indoor rearing. Windows should be kept open from time to time as required. Sericultural hygiene must be followed. Disinfection is to be done to the rearing houses used for indoor rearing of Mug worms and also the rearing appliances like that of Eri and Mulberry silkworm rearing houses. Chowki rearing especially during summer may be adopted for better rearing results.

It is not possible to conduct large scale rearing of Muga worms indoor. The outdoor rearing for the whole larval period also increases loses to the commercial rearers. So, after rearing up to third instar indoor, worms should be transferred to dwarf leafy trees for outdoor rearing, for the remaining larval period. Dwarf plants covered with fine nylon mosquito nets or Wire-netted cages for outdoor rearing of young worms at least up to the second moult will also save the worms to a great extent from ants, wasps, flies, etc.

Worms hatched out from the eggs of different mother moths are to be reared on separate trees without mixing them Cocoons harvested from such rearing should be kept separately. Male and female moths emerging from these cocoons are to be allowed to pair disallowing brother sister mating (inbreeding). It facilitates in keeping the hybrid vigour in subsequent generations. It will help in the maintenance of the purity of the Strain without deterioration. Further research is necessary in evolving and developing some suitable interspecific hybrid for the greater interest of the Muga silk industry. Yellow body mutant of Maga should also be tried for outbreeding which would help in maintaining vigour and health of the worms. The body weight of Muga worms is abouts 0.008 gms to 5.5 gms from 1st instar to 5th instar. The weight of cocoon varies from 4.5-6.0. gms and the shall weight from 0.30 gms to 0.60 gms.

11. SEASON OF REARING

The rearing of two major commercial crops. (in four batches) a  years may suitably be practiced during spring (early and late) for producing reeling cocoons. The may be adjusted according to the local conditions. It is better to conduct rearing of summer crop in cold climate (at high altitude) as mortality and flies, wasps, etc, are more during summer in hot places. It will help in supplying the seed cocoons for the autumn crop. It will also provide hill amelioration to the worms. Maximum possible layings should be reared during springs (first crop and autumn third crop) rearing as these are the two most suitable seasons for rearing of Muga. It will increase the quantity and the quality of cocoons. Necessary steps must be taken to control different diseases and to get rid of various ants, wasps, flies, birds, bats, etc., for harvesting a successful cocoon crop. Tugon bait, gum, lali, molasses, etc. may be used in alluminium pans for controlling and killing ants, wasps, flies, etc., Birds scared away by bows and pallets and other bird scaring instruments.

Most of the wild Muga worms (yellow, blue and orange in colour) are bivoltine and do not emerge during winter. The collection of wild Muga seed cocoons from different places of hills and plains of Meghalaya and Assam and also from certain places will help the rearers in improving the production of quality cocoons by hybridising them with semi-domesticated strains. It is essential to multiply the hibernating strains of Muga worms as such breed will eliminate the hazardous winter rearing. They are vigorous and stronger and will solve the problem of seed cocoons to a great extent. Rearing of selected strains may be conducted in suitable green/glass houses (specially early spring crop when hail storm, pests are prevailing), under controlled temperature (24°C-30°C) humidity (75%-85%) and light. Suitable selected clonal plants on tubs may be used for the purpose for making nutritious leaves available. This may also help in reducing degeneration of Muga worms.

Rearers usually do not select the trees in advance before taking up rearing for which leaf quality varies and affects the growth of Muga worms.

Most of the activities of Muga culture happen to be in darkness such as the maturing of worms, emergencae of moths, pairing of moth, and laying of eggs. So, the Muga rearers will have to work even at night.

12. ECONOMICS OR REARING

About 300 Som/Sualu Plants may be planted in one acre (about 3 bighas) of land with a spacing of 3m x 3m. In this plantations about 900 layings of muga worm can be reared in one crop easily. Such, major crop for producing reeling cocoons may be taken up twice at year during April-May (till mid June) and September-October (up to middle of November). Thus a family having three adult members may rear 1800 layings) in two crops and harvest about 72,000 cocoons(40 cocoons per laying) within a period of three months (two crops). The income from the rearing thus would be Rs. 14,400.00 by selling 72,000 reeling cocoons at the Rs. 200/-, per 1000 cocoons.

Muga rearing is done generally by the rearers themselves and no paid labourer is engaged. So whatever amount is obtained by disposing the cocoons may be considered as income of the family. The capital investment is also reasonable, except counting the wages of their self-employment, cost of seed cocoons/seeds and rearing appliances, the plants as they can rear more layings. Inter-crops will also increase the income of rearers to some extent. Indoor rearing for early stages worms followed by outdoor rearing in later stages will also help in harvesting more cocoons (100 cocoons per laying). It is advisable to conduct the rearing of two major crops in two batches each (early spring, late spring and early autumn, late autumn) for accommodating more layings and to ensure harvesting of more cocoons.

Muga silk industry may be developed in rural areas where their food plants are available in nature. They may also be planted in vacant places and in waste land. The farmers having small land-holding may take up it easily. The people of Muga food plant growing areas are to be educated to preserve them for their own benefit. They should also be taught the improved rearing technique of Muga worms.          

13. PRODUCTION OF SEEDS

Seed production is the most important aspect of Muga silk Industry and the success of rearing mainly depends on it. Seed production may be divided into four divisions, viz. (A) Selection of seed cocoons, (B) Preparation of seeds, (C) Seed examination and (D) Seed supply.

The seed preparation houses should be spacious. They are to be provided with a microscope, heater, lights, air cooler, humidifier, incubator, refrigerator, sprayer including formaline, etc. They should be free from rats, lizards, spiders, ants, etc. Important characters for selection of Muga are viability, fecundity, larval period, larva weight, mortality, disease resistance, cocoon weight, shell weight, filament length, demier, etc. Selection may be done considering all required characters of the Muga silkworm (chromosome number n=15) through out its life cycle.

13.1 SELECTION OF SEED COCOONS

Better seed cocoons are always required to produce better silkworm seeds. If possible, it is better to select them during the larval stage. There are hibernating and non-hibernating Muga strains. We should try to increase the production of hibernating Muga broods. Experienced Muga rearers visit the Muga rearing in the last stage before maturity. They observe the worms, the mode of their eating leaves on the tree, visual examination of some of the worms, percentage of mortality, etc. Healthy worms usually eat the leaves from the top of a tree and even the twigs. They are bright green in colour. Their dry litres powder  when crushed, 2-3 littres are present at the rectal portion of a healthy worm. They show their sensitiveness without vomiting upto 4-5 times, while touched. Seed cocoons are usually selected and graded on visual examination through long practical experience, after the harvest. Seed cocoons should be selected from and around “Bhorpok”(mid-maturity) stage to obtain approximately equal number of male and female moths for seed preparation. Healthy, well built, robost cocoons with live pupae, fine denier silk, more percentage of silk content, good reelability, longer filament length, compact in texture, without any pest ialso have life like that of human beings. It is better to carry seed cocoons along with the ‘Jali’ to avoid damage during transportation. It is advisable to collect healthy disease free seed cocoons from a distant place so that change of food, climate, etc, occurs and better cocoon crop may be obtained.

Selected seed cocoons are to be kept in rat-proof well ventilated rooms in wire-netted and bamboo cages (chakaripera) in one layer. More space is required for preservation of Muga seed cocoons. Seed cocoons may be kept in garland when a large number of Commercial seeds are to prepared. Each garland should have 50-150 cocoons Seed cocoons received from different areas are to be kept separately Seed cocoon should not be stored in damp, poorly ventilated and in dark places. Wire-netted cages are to be used to maintain the purity of the strains of Muga, especially where parent stocks are maintained. The cages may bae arranged in tiers for economy of space. The four legs of the lower most cage should be kept on ant-wells. Preservation of spring and autumn breeds seed cocoons should be in cold storage for delay and regular emergence of moths. The period of diapause is in pupal stage. This will also help in controlling pebrine disease. Such preservation of seed cocoons will help in avoiding summer and winter crops. This will ensure the seed supply in autumn and spring rearing. It is better if the seed cocoons may be preserved under regulated temperature and humidity followed by proper incubation for uniform emergence. Seed Cocoons may be preserved in cold storage at 25°C first and then to reduce the temperature to 5°C after every 12 hours upto 5°C Seed Cocoons may be preserved upto 4 months. Similarly while releasing these preserved seed cocoons the temperature should gradually be increased by S°C after every 12 hours and then to keep at the room temperature. Seed cocoons also may be preserved in high altitude during summer with proper care in transportation. Necessary steps are to be taken to control the life-cycle of Muga silk-worm by artificial means subjecting the pupae to hibernate for avoiding the summer and the winter rearing. It may be induced by controlling the photoperiod at the larval stage. The photoperiod effect combined with temperature and humidity renders some Muga-worms to go for diapause and others to continue with the voltinism

The price of seed cocoons is too high but the rearers purchasing capacity is limited. So, marketing of seed cocoons should be regulated. Rearers co-operatives may also be formed to avoid exploitation by middlemen. Introduction of a crash programme for production of more muga seed cocoons would also ease the position.

13.2 PREPARATION of SEEDS

Muga seed preparation is time consuming and hazardous task. Usually for cocoons are required for preparation of a single laying.

Moths emerge from the seed cocoons after 2-4 weeks from the date of cocooning according to season. In normal condition the emergence of moth takes place from evening till midnight. Male moths emerge earlier than the female moths. They can easily be identified. The male moths are copper brown to deep brown in colour while the females are yellowish light brown. The males have broader antenna and narrow and small abdomen. The females have smaller antenna and large abdomen.

Seeds cocoons are to be refrigerated at 5-10˚C in early pupal stage and incubated at 34˚C to synchronize the time of emergence of moths of different strains of Muga for hybridization. Moths may be refrigerated for 3-4 days without adverse effect. Male moths may also be refrigerated for about a week. They may be utilized for a second time pairing, if and when necessary. Refrigeration for a longer duration is not advisable. Moths are to be selected after emergence considering their health; natural brown colour with thick wings, without any deformity, and urine like that of pure milk, etc.

The male and female moths are allowed to pair in the cage naturally. Some of them may not pair for which mechanical means, such as , moving them by hand and blowing air by mouth for early pairing are to be adopted by the breeder. Maximum care must be taken to avoid damage to the female moths. Unpaired female moths may also be kept outside in a safe place tying them on “Kharika” for pairing with wild males after darkness in the evening and should be collected in the early morning of the following day. Moths like darkness for pairing with comparatively lower temperature and high humidity. Male moths are more active and smart fliers. Female moths are passive and generally do not fly. The female moths are tied by one of the hind wings and fastened to a “Khasika” first and then allowed them to pair. Paired moths are taken out from the cage carefully and the female ones are tied, unpaired and kept for egg laying by hanging the “karika” and strings/wire arranged already for the purpose.

Moths are usually allowed to pair for about 12 hours due to practical reason though 4-5 hours are sufficient for fertilization. They start pairing in the evening and are unpaired in the following morning by hand. One must take care at the time of unpairing so that female moths will not be injured. Application of light or heat will help in separating couples by themselves. A single male moth can be used for a second coupling without affecting fertility and egg laying when male moths are less. After unpairing, the female moths are kept for egg laying on “Kharikas”. They prefer darkness for egg laying like that of other satuniids. They start laying eggs within 12 hours. They are allowed to lay eggs for 3 days, which are considered for rearing purpose. Eggs laid latter are less viable and the worms become weak, and development is poor. A female moth usually lays 150-300 eggs. Muga moths lay maximum eggs in spring and autumn, and minimum during summer. Eggs adhere to “Kharika” or in a small bamboo/paper basket with cover for basic seed preparation to help in proper examination. More moths may be allowed to lay egg together in longer bamboo Kharikas for large scale seed production. The moths with Kharika should not be exposed to sunlight and rain. Likewise, more unpaired female moths may be kept in paper/bamboo basket for preparation of large scale loose eggs but it is not advisable as it would be difficult to examine the mother moths. Sometimes smoke or light is to be introduced in the room as shock treatment to the female moths. It gives better effect in eggs laying. Deposition and preservation of eggs should be conducted in a cool room with sufficient humidity. Incubation may be practiced for regular and uniform hatching at 40˚C. It will also help in controlling pebrine disease. The moth is a non-feeding stage and dies within 7-15 days after emergence.

Continuous inbreeding will lead to degeneration of the merits of the race and also reduces vigour. Hybridization (out-breeding) in between two different group of Muga is essential for commercial rearing. Domesticated Muga may be hybridized with the hibernating wild Muga from time to time to give them hybrid vigour and to avoid the troublesome summer and winter broods. Muga silkworm is a primitive insect and has no means of large scale hybridization in absence of related strains. Government farms should maintain parent stocks of different strains correcting from various places to study their behaviours and inter or intra-specific hybridization for keeping hybrid vigour. It would help to prepare hybrid seeds in subsequent generations.

Survey of potential seed producing areas and collection of several strains from different area are necessary. These may be reared in small batches in a farm and all the cocoons harvested from such rearing may be mixed allowing them to have random mating which will give hybrid vigour. An alternative to this, these strains may be reared separately in different farms and only male cocoons are to be exchanged to prepare hybrid seeds among them.

13.3 SEED EXAMINATION

Visual examination play an important role in seed examination one may select better layings through his long practical experience. Eggs with glue bigger in size, laid in clusters with fibrous body dust and brown in colour are said to be healthy. Weak and dead moths irregular layings, less number of eggs in a laying, under developed and unfertilized eggs, etc, are to be rejected before seed examination. This is to be followed especially for parent stock maintenance. It will also help in quick microscopic examination. It is advisable to conduct examination in all the stages of the life-cycle of the Muga silkworm.

Microscope, glass slides with cover, mortar and pestle, scissors, caustic potash solution, etc., are essential for seed examination.

After egg laying for three nights, the abdominal portion of mother moths are cut by scissor and crushed with the help of mortar and pestles, sprinkling a few drops of distilled water or ½ drop of 2 percent caustic potash solution. Then a drop of the suspension is placed on glass slide by stick/rod covered with glass cover and examined under microscope. The eye-piece, objective, etc. of the microscope should properly be cleaned and accurate focusing must be there for correct microscopic examination.

It is better to examine a mother moth at a time and in case of basic seeds it is a must. In case of large scale industrial seed production, examination of ten moths taking at random from a particular lot is to be examined at a time.

The organisms that cause diseases of Muga silkworms are virus, bacteria, fungus and sporozoa. Generally, the eggs laid by moths having mild viral, bacteria or fungal infections may be use for rearing as there is difficulty to get sufficient seed cocoons. But we should not consider any when they are infested by sporozoa (pebrine), which is transmitted from mother to the off-springs, through eggs. Such infected mother moths and their eggs must be destroyed without delay by burning and burying them at a distant place. Loose eggs are to be collected on the fourth day of oviposition after examination of mother moths and washed (disinfected) with 2 percent formalin.

Washing of eggs for about 5 minutes with 2 percent formaldehyde solution followed by washing in clear cold water and drying in shade is essential to avoid contamination of diseases before supplying to rearers. Heat treatment for pebrinished pupae and eggs may be done like that of oak tasar after proper experimentation. Disinfection with Kharika is more advantageous. Disinfected eggs are to be kept without overcrowding in cool and moist place.

Hatching may be delayed for few days by refrigerating the eggs if and when necessary after 48 hours of oviposition. But is should not exceed more than a week for normal hatching.

Loose eggs after disinfection may be preserved in a box having an arrangement for light on the top and for air on the sides. Eggs in boxes may be incubated at a required temperature and humidity which will help in uniform hatching. The eggs inside the box should be kept in one layer and not in heaps.

13.4 SEED SUPPLY

The process of transportation of seeds has a direct effect in the cocoons crops. Every one must remember that there is life inside the eggs. No abnormal heat and direct sun should be experienced by the eggs during transit. Otherwise, it may result the failure in rearing, especially as it causes mortality in the 5th instar before maturity. One must realize that the embryo is being developed inside the egg like that of the development of the baby in the mother’s womb. Seeds should reach the destination within the seventh day of oviposition.

A well-perforated wooden box with a thin cloth lining inside is to be used for sending seeds (loose-eggs) with proper operation. It is advisable to transport eggs on 4th/5th day of incubation. Quantity of eggs is to be put inside the box according to its capacity and in no case it should be over loaded to avoid damage to developing embryos. Eggs may be supplied along with “Kharikas” for nearby places. Eggs are to be transported preferably in cooler hours. Tender leaves may be put in the eggs carrying boxes, if hatched eggs are transported. It is better to supply seed cocoons with “Jali” instead of seeds wherever and whenever possible with proper care in transportation. Seed cocoons should be transported carefully after 6-9 days of spinning. Government should take appropriate steps to supply muga seed cocoons and disease free seeds to the rearers at reasonable cost in required seasons. Rearers usually cannot continue the rearing for more than three generations of a particular lot of muga due to successive inbreeding. Field Staff should arrange for microscopic examination of mother moths in rearers’ house to get disease free eggs.

   

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