Diseases of Silkworm and Its Management

DISEASES OF MULBERRY SILKWORM 1. Viral Disese Symptom: The larvae will be sluggish with swollen intersegmantal region The integument of diseases larvae will be fragile and brakes easily On infury milky fluid containing many polyhedral inclusion bodies oozes out from the larval body The diseases larvae do not settle for moult and showshining integument The larvae appear to be restless The dead larvae hand by hind legs head downward Management Sun drying of rearing appliances for one/two days Disinfection of rearing room and appliances with 5% bleaching powder Disinfection of worms, trays and discarding of diseased worms Ensure proper ventilation and air circulation Provide proper bed spacing Feed the larvae with nutritious mulberry leaves Collect and burn infected larvae, faecal matter and bed refuses Early diagnosis and rejection of infected lots Dust the bed disinfectant, Vijetha (or) Resham Keet Oushadh on the larvae, after   each  moult and ½ hr. before resumption of feeding (3 kg/100 dfl). Spray 1% of extract of Psoralea coryleifolia on mulberry leaves, shade dry and feed worms once during third instars. 2. Bacterial Diseases Bacteria and viruses cause the disease individually or in combination. Fluctuating temperature and humidity and poor quality mulberry predispose the  disease development. The diseased larvae will be stunted in growth, dill lethargic soft and appear flaccid The cephalothoracic region may be translucent The larvae vomit gut juice, develop dysentery and excrete chain type fecus. The larvae on death putrefy, develop different and emit foul smell Management Maintenance of hygienic condition Disinfection of rearing room and appliances Disinfection of worms, trace and discarding of sick worms Avoid injury to the worms, overcrowding of trays and accumulation of faeces in the rearing bed Sound management, improving the rearing environment and feed stuff Feeding the larvae with healthy nutritious leaves. Early diagnosis and rejection of infected lots Avoid spraying commercial B. t. insecticides in nearby mulberry field. Apply antibiotics like Streptomycin/Tetracyclin/Ampicillin 3. Fungal Diseases White muscadine is caused by a fungus Beauveria bassiana and the green muscadine is caused by a fungus Spicaria prasina. Aspergillosis is common in young age silkworms and the infected larvae will be lustrous and die. Dark green (Aspergillus flavus) or rusty brown ( Aspergillus tamari)mycelial cluster are seen on the dead body. The diseases larvae prior to death will be lethargic and on death are flaccid oil specks may be seen on the surface of larvae They gradually be fome hard, dry and mummify into a white or green coloured structure The diseases pupae will be hard, lighter and mummifies Magagement Sundry the rearing appliances. Disinfect the rearing room and utensils with 5 per cent bleaching powder Avoid low temperature and high humidity in the rearing room Keep the rearing bed thin and dry Early diagnosis and rejection of infected lots Apply Dithane M45 (3 kg/100 dfls) / Vijetha supplement as disinfectant on the larvae Disinfect rearing rooms and trays with 4 per cent pentachlorophenol to control Aspergillosis. 4. Protozoan disease : Pebrine Diseases larvae show slow growth, undersized body and poor appetite. Diseases larvae reveal pale and flaccid body. Tiny black spots appear on larval integument. Dead larvae remain rubbery and do not undergo putrefaction shortly after death. Management of  Pebrine Produce healthy eggs Disinfection of rearing room and utensils Maintain strict hygienic conditions during rearing Surface disinfect the layings in 2 per cent formalin for 10 minutes before incubation. Collect and burn the diseased eggs, larvae, pupae and moths, bed refuses, faecal pellets, etc

Management of Silkworm Rearing, mounting & production of cocoon.

Silkworm Rearing: -

Silkworm is domesticated over thousands of years and the sole food for the growth of silkworm is mulberry leaf.

Climatic requirements: -

Under ideal conditions silkworm completes cocoon formation in 24-28 days from the day of hatching. However, there is variation in number of days due to fluctuation in temperature and humidity. As the temperature increases the development of larvae activates. The following required temperature/humidity/spacing should be provided:

S. No.	Stage	Temper- ature 0C	Humi- dity %	Spacing (for 100 dfl’s) in Sq. ft
1	1st Instar	26-28	85-90	4-14
2	2nd Instar	26-28	85-90	15-45
3	3rd Instar	25-26	80-85	46-90
4	4th Instar	24-25	70-75	91-100
5	5th Instar	23-24	70	181-360

The larval development will be maximum during the 5th Instar after 4th moult. Generally the moulting period delays due to fluctuation in climatic conditions. Temperature plays an important role in the development of larva. Larva under goes four moults in case of tetramoulters with in a span of 26-28 days to spin the cocoon.

Rearing shed: -

Rearing shed must be constructed with East/West direction, preferably with the thatched roofing, mud walls or any roofing must not reflect heat on the biological body growth of silkworm. Keeping good number of windows, proper ventilation, light, using country tiles for roofing will serve the purpose of maintaining required atmospheric conditions in the rearing house with reduced cost. The rearing house should have a good length of height and breadth.

Leaf quality: -

Quality of mulberry leaf in addition to proper maintenance of temperature/humidity plays significant role in the development of healthy silkworm.

Leaf quality plays an important role in the production of quality cocoons. The young age worms are fed with tender, succulent leaves which contain sugar, less amount of fibre, starch but, high moisture and protein that are suitable for chawki worms. Hence, the top tender leaves of mulberry plant are used to feed the young age worms. The late age worms are fed with matured leafs available at the bottom of the mulberry trees.

The leaf during its feeding time should not contain dust particles or water droplets on the surface of leaf. Disease attacked, wrinkled, weak leaves, poor quality leaves should not be fed to the worms. Feeding bottom matured leaves to chawki worms, tender leaves to mature worms should be avoided.

Preservation of Leaf:

Harvested leaf should be transported in wet gunny bags or baskets made up of bamboo. Such leaf should be preserved in a separate room or in a corner of rearing room or in specially designed leaf preservation chamber made up of wood with sufficient number of ventilators.

The leaf chamber should contain a good number of ventilators covered with wet gunny cloth. This will help in maintaining leaf quality. Other wise leaf should be scattered on the floor in a single layer so that the water droplets on surface of leaf will be evaporated. Leaf should never be preserved on heaps. This will increase the humidity. Leaf scattered on floor should be frequently sprinkled with water and tilted in summer.

Leaf requirement:

Silkworm attains nearly 10,000 times of weight starting from hatching to spinning stage, therefore, feeding quality leaf plays an important role in the development of silkworm.

Leaf Requirement (about 400 eggs per DFL’s)

S. No.	Silkworm Stage	Quantity of mulberry leaf Required (approx.) (Kgs)
1	1st Instar	2-4
2	2nd Instar	4-8
3	3rd Instar	30-40
4	4th Instar	80-90
5	5th Instar	600-650

The requirement of leaf will differ from race to race. The consumption of leaf also varies with season. During summer the quantity of leaf required will be a little higher since, drying of leaf will be faster hence additional feeding may be required.

Rearing Equipments:

The following equipments are required for silkworm rearing.

1)Mesh 2) Formalin 3) Sprayer 4) Mats 5)Leaf preservation chamber

Chopping board 7) Chopping knife 8) Chop sticks 9) Feathers

Ant wells 11) Foam pads 12) Paraffin Paper 13) Hygrometer

Thermometer 15) Bed cleaning net 16) Wash basin

Plastic buckets/Mugs 18) Rearing stands 19) Rearing trays

Feeding stand 21) Mountages

Disinfection:

Disinfection is a process of destructing the disease casual organisms. There is a possibility of carrying the pathogens or germs through the rearing equipment if there is any disease attack in the previous crop. Therefore, disinfection is necessary to protect the crop from disease attack. Before taking up rearing all the rearing equipments including the rearing house should be disinfected thoroughly. There are various methods of disinfection like physical and chemical. Physical disinfections are Sun drying, Steaming. In chemical disinfection, all the rearing equipment as well as the rearing house should be thoroughly disinfected with 2% formolin and dried.

Ultimate production of silkworm seed is to produce cocoons to get silk yarn. Advance planning, quality production, timely supply of seed are the critical factors in silkworm seed production.

The silkworm seed is produced in "Grainages". Grainages play a vital role not only in production of seed but also in the entire seed organization. During the Grainage operation one must know the seed suitability for a particular area before releasing commercially. A particular race is suitable to a particular area.

Transportation of Eggs:

The required number of DFL’s should be collected from either Govt. Grainage or licenced Pvt. Grainage. The transportation of eggs plays an important role in the development of embryo and successful crop harvest. Therefore, the DFL’s are collected safely in a wet hand bag in the early morning or in the late evening. Care must be taken to not to cause any damage to the inside embryo. In case of loose eggs, the transportation box containing loose eggs should be covered with wet cloth, good aeriation must be provided to the eggs.

Care should be taken while transporting the DFL’s and should be kept under incubation at 250C temperature and 80% humidity. Egg cards should be spread in the rearing trays which should be kept in cooler places only.

Incubation:

The eggs should be kept in cooler places at 250C temperature and 80% humidity, lesser the humidity poorer the hatching percentage or more the temperature weak the larva and poorer the hatch percentage.

For uniform hatching all the egg cards or loose eggs should be kept in dark and cooler atmosphere. On the day of pin head or blue egg stage all the eggs are covered with a black sheet or kept in black box and known as black boxing. On the day of hatching all the eggs are suddenly exposed to bright light in the early morning at around 8 A.M. so that 95% hatching can be achieved. It should be ensured that hatching should take place uniformly. With proper maintenance of temperature and humidity development of larvae will be uniform.

Brushing: -

Brushing is transferring of newly hatched larvae into rearing trays. The newly hatched larvae after one hour of hatching get ready to feed on mulberry leaf. They are fed with finely chopped tender mulberry leaf. They are fed with finely chopped tender mulberry leaves. Chawki worms are fed with tender leaves with high moisture content. The brushing of newly hatched larvae can be done in various methods.

Newly hatched larvae can be covered with a net and chopped mulberry leaf can be sprinkled over the net. The larvae slowly crawls on to the net and start to feed on the mulberry leaf. Then transfer into rearing tray by gently tapping the net, this method is more convenient in case of the loose eggs.

In case of egg cards, the egg cards are placed in the rearing trays and chopped mulberry leaf is sprinkled over the newly hatched larvae, the larvae crawls on to the mulberry leaf later on the cards are removed.

Care should be taken not to touch the newly hatched larvae with hands while providing proper spacing, instead chop sticks are used to spread the worms in the rearing tray.

Feeding of Leaf: -

The leaf is finely chopped as per the recommended size and sprinkled on the larvae and after half an hour the newly hatched larvae slowly crawl on to mulberry leaf. Chopped leaf should be preserved from drying and loss of moisture content. For this purpose it should be collected in a basin covered with paraffin paper to protect from loss of moisture content.

First feeding to the newly hatched larvae should be given at 9 A.M. in the morning. During the 1st instar depending upon the silkworm strain and other factors (environmental conditions and leaf quality) the required mulberry leaf per 100 DFL will be around 2-2.5 kgs. The 1st instar stay for 3-31/2 days and under go moult. The moulting period last for about a day. This will depend upon the environmental conditions.

Gap should be maintained for feeding the worms before under going moult and immediately after moult. Generally two hours gap is given. Also over feeding should be avoided, especially before under going moult which will result in wastage of leaf.

Spacing: -

Larval growth will be very fast in the silk worms during the early stages. Too much crowd in the rearing tray results in increase in humidity, heat, fermentation of litter which results in un-hygienic conditions, wastage of leaf and under development of silkworm. The number of trays and space required for each instar will increase.

Stage of silkworm	No.of trays required for 100 DFL’s (Diameter of tray 3 ½’)		Space required (Bi and Multi x Bi hybrids)
	Beginning	End of stage	Begin	End
1st instar	2	2	4 to 15 Sq.ft
2nd instar	2	5-6	15 to 45 Sq.ft
3rd instar	5-6	10-12	46 to 90 Sq.ft
4th instar	10-12	20	91 to 180 Sq.ft.
5th instar	20	40	181 to 360 Sq.ft

Spacing should be given simultaneously at the time of bed cleaning or feeding and care should be taken not to disturb the worms very frequently.

Bed Cleaning: -

Silkworm after moulting leaves the exuviae. All the leaf fed to silkworm may not be consumed. Dried leaves, rejected leaf in the bed, silk worms excreta, dead worms, diseased larvae all will increase the humidity, fermentation, temperature in the bed. If proper bed cleaning is not done in time it leads to various complications viz. Ill health of larvae, disinterest of the larvae to fed due to unhygienic conditions, ultimately worms becomes weak.

Bed cleaning in silkworm rearing tray is done by various methods like using of paddy husk, straw, and bed cleaning net. During 1st instar bed clearing should be done once during pre-moulting, during 2nd instar – twice, once after moult and before next moult. During 3rd instar thrice i.e. after moult, before next moult and once in the middle. During 4th and 5th stage once in a day in case of shelf rearing. However, in case of floor rearing or shoot rearing once in each instar.

Feeding:

Not only the nutritive value but also the number of feeds in each instar plays a major role in the cocoon built. Three to four feeds are given to the silkworm. In a day the last feeding i.e., during the night should be a little more since the duration for the next feeding will be longer. During moulting period no feeding should be given. Before settling to moult and immediately after moult, first feeding should not be heavy. Feeding tender leaves to young age worms is essential. As the larval growth advances the mature leaf can be fed.

Maximum leaf is consumed during 5th instar only. During this stage only the maximum growth of silk gland can be noticed. It is estimated that 50% of the total weight will be increased in the 5th instar itself. The feeding schedule is: -

S.No.	1st feeding	2nd feeding	3rd feeding	4th feeding	5th feeding
1	6 A.M.-6.30 A.M	11-11.30 AM	3-3.30 PM	7-7.30 PM
2	7 AM – 7.30 AM	11-11.30 AM	2-2.30 PM	5-5.30 PM
3	6 AM – 6.30 AM	10-10.30 AM	2-2.30 PM	6-6.30 PM	10-10.30 PM

More number of feedings are given during summer since moisture content in the leaf will not be sufficient during summer and leaves will dry very easily.

Types of Rearing:

Rearing of silkworm is done in various methods in different areas. Mainly the rearing of silkworm is of two types

a. Chawki Rearing:

Rearing of young age silk worms is called Chawki rearing. Here worms are reared upto third moult and distributed to the rearers for late age rearing. Chawki rearing in mass at each CRC will not only control the attack of diseases but also facilitate the rearing on most scientific lines and cost wise it is most economical. To maintain coolers, heaters, exhaust fans, etc., by individual rearers is a costly affair, however, all these facilities can be maintained in Chawki Rearing Centres.

b. Late Age Rearing:

Late age rearing after third moult does not require high temperature and humidity compared to chawki rearing. Late age rearing is a little easier process than chawki rearing. During late age the quantity of mulberry leaf required is more than 90% of total larval period. During 5th stage particularly the larvae eat voraciously worms feel maximum appetite larvae loses water from its body hence, less temperature, low humidity, good ventilation is required.

Mounting:

This is the last stage of rearing operation. At this stage silkworm becomes matured completely and ready to spin into cocoon. These silk worms after 5 days of 4th moult becomes yellowish and translucent, stops feeding on mulberry leaves, starts to search for a corner and try to crawl on the feeding trays further liquid like substance oozes out of the mouth from the spinneret. These movements clearly indicate to transfer the mature larvae into the mountages.

Transferring of matured silkworm on to the mountage or cocoon frames is called "mounting". This is an important and skilled operation. Any deviation in identification of maturity of worms adversely effect on cocooning.

During mounting though, selection of ripen worms is not a difficult task, but, due care is needed. Most of rearers pick up ripen worms with hands to transfer them on to mountage. This is the most common method used in our country, however this is laborious and due care is needed while handling the mature worms. A few rearers use rearing nets, in some parts, rearers use mulberry branches to separate the matured worms. As the matured worms stop feeding they crawl on to the twigs searching for a support to spin the cocoon.

Another method called frame method is also used, fresh mulberry leaf is applied with a frame, matured worms crawl above the frame which are picked up and tranferred on to the mountages. While mounting care should be taken to avoid over crowding. Proper spacing should be given to avoid formation of double cocoons strained cocoons/urinated cocoons. For the purpose the density of worms in the mountage should be limited to 40-50 worms per sq.ft.to avoid formation of double cocoon, stained cocoon. However, the number of worms in each mountage depends upon the size of mountage and type of silkworm race.

The matured worms picked up in any of the methods mentioned above are transferred to the mountages. In an area of 1 mt 800-900 worms can be mounted to avoid too much density in the mountage. Mountage should be kept in inclined position so that, excreta of worms fall on ground.

In certain strains of silk worms around 250-300 worms can be conveniently mounted in a standard mountage of 90 x 60 cm size. However the size of mountage varies from place to place. In case of bamboo made chandrike that has a mat on the back ground of size 6’ x 4’, it easily carries above 1000 worms.

During mounting care should be taken to use the right type of chandrike in convenient size and shape. There are different types of chandrike that are used for the purpose of mounting.

Plastic mountage

Bamboo made chandrike

Straw mountage

Bottle brush

Revolving mountage, etc.

Cocooning:

The matured silkworm spins the outer protective covering called cocoon and remains in dormant stage inside as pupa.

After mounting the ripen worms in chandrike the larvae sticks on to the mountage by oozing out the silk fluid which will harden immediately after coming in contact with air and sticks itself to the mountage. It starts to ooz out the silk by continuous movement of its head in a very specific manner to form the silk filament in the shape of arithmetic figure `8’.

Larvae moves its head continuously about 70-80 times per minute till the compact shell called cocoon is formed and detaches itself from the last layer of silk of then transforming into pupa. The Cocoon will have three layers.

Outer floss

Middle compact layers

Inner pelade

The outer floss layer which will be 8-10% of weight of cocoon though formed of a continuous filament, is not reelable. The floss percentage varies from race to race. The middle order compact layer only is reelable and is a continuous filament easily reelable and the inner pelade layer is not reeled.

Silkworm completes the spinning in 2-4 days depending upon the silkworm strain and climatic conditions provided.

Harvesting of Cocoons:

Harvesting of cocoons is done on the fifth day of spinning. Whereas seed cocoons should be harvested on eighth day or ninth day of spinning depending upon atmospheric temperature.

Harvesting should not be done immediately after pupation. Further, harvesting should be done before the moth emerges out. Too many days delay in harvesting will result in formation of pierced cocoons due to emergence of adult moth or uzi maggots.

Cocoons are harvested generally with hand. In advanced temperate countries like Japan simple devices are used to harvest the cocoons from rotatory mountage