DISEASES AND PESTS OF MUGA FOOD PLANTS

Muga food plants are also attacked by various diseases and pests. They mainly depend upon the following parameters:

1. Variety of the plants,

2. Climate of the place,

3. Ecological condition and

4. Soil.

It is the primary duty of the planter to select the disease resistant suitable variety and good soil before plantation. Proper care must be taken to –protect the plants from diseases and pests including their enemies. In case of Muga food plants, prevention of the disease or pest is more important than control, as leaves are used for rearing of Muga worms.

1. Common diseases of Muga food plants are-

1. Leaf spot-caused by a fungus and it may be controlled by spraying insecticides with proper care.

2. Grey blight- It is also caused by a fungus. To control this disease picking and burning of diseased leaves in early, stage are required.

3. Red rust- caused by a parasite (alga). Pruning, removal of affected twigs and burning them is necessary to control this disease. Besides the above diseases some other diseases are also there for which controlling measure are to be taken in time.

2. Common diseases of Muga food plants are-

There are many pests which damage the Muga food plants. Some of them are-

1. Stem borer- It is also called carpenter worm. This may be controlled by applying fumigants soaking in cotton wool and putting it into the hole and close it with mud.

2. Leaf gall - Gall is tumour like growth caused by different gall wasps. This may be controlled by plucking the gall infected leaves and pruning the trees.

3. Sucking pests – Thrips, Jassids are the common sucking pests. These can be controlled by application of insecticides.

4. Leaf rolls- cause by insects secreting gummy substance by larvae forming roll of leaves. Leaf rolls are to be collected and burnt for control of this insect.

5. Hairy caterpillars- Remarkable damage done by many hairy caterpillars like cricula. They are to be collected and burnt for controlling them.

Plants may have their deficiencies also. Various cultural practices will help in preventing/controlling many of the diseases and pests. Besides, mechanical measure is to be taken to kill the adult pests. Collection of infected leaves and live cocoons of various insects is to be made and burnt them. Closure of holes made by borers is also essential by required materials. Application of some chemicals may suitably be made after proper experimentation. Spraying of insecticides is to be done before1-1½ months of rearing to avoid residual effect.    Top

DISEASES AND PESTS OF MUGA WORMS

1. DISEASES

There are four common diseases of muga silkworm. They are pebrine, grasserie, flacherie and muscardine. Transmission of all the diseases except pebrine is mainly infectious. pebrine is infectious and inherited. The incidence of different diseases varies from place to place and season to season. Grasserie and Muscardine are very rare in case of muga.

a) Pebrine (Phootukia): Pebrine is the most dangerous disease of muga silkworms. It is cause by protozoa (Nosema species). The spores of Nosema are bright and oval in shape when seen under microscope. It effects in all seasons but higher in autumn and winter seasons. The germ of pebrine loses its viability after six months in case of muga worms. It attacks in all stages of the life cycle of muga worm. Flies can carry pebrine germs infecting all worms in an outdoor rearing.

The important symptoms of this disease in larval stage are less appetite, worms becomes weak, sluggish, lose their natural luster and become dull in colour, unnatural small dots-like black spots appear all over the body especially in 4^th/5^th instar, and they become irregular in growth and moulting. Cocoons formed by infected worms are not uniform. Emergence of moths is very irregular. Infected female moths lay few eggs. The embryo dies inside the egg.

The following precautionary measures should be taken to control pebine disease:-

1. Exposing the cocoons to high temperature (34° C) at pre-pupal stage for 16 hours a day with 55-65 % humidity reduces the chance of pebrine infection of the eggs.

2. Keeping the eggs in hot water at 40° C for 30 minutes after 36-40 hours of oviposition will also help in disinfection and in killing pebrine spores.

3.  Seed cocoons should exclusively be procured from the uninfected areas.

4. Transportation of cocoons from infected to uninfected area should be avoided.

5.  Resistant stocks are to be encouraged for rearing.

6. Infected cocoons should be used for reeling or spinning.

7. Male moths, dead larvae, excreta from infected progenies and the smears of female moths should be burnt in pits at a distance and buried.

8. Layings must be selected on the basis of strict microscopic examination and proper disinfection with formaline.

9. If the infection is detected in a lot, all the worms along with plucked leaves of the particular tree should be burnt and buried.

10. Microscopic examination in all stages of Muga is essential. The hands of persons are to be washed with ¹ per cent formaline to avoid contamination.

11.  The field staff should undertake survey works in the field from time to time so as to forecast the possibility of _spread of disease.

b) Grasserie (Phularog)- It is a virus and contagious disease. It occurs in the gut and later to skin, fat bodies, blood cells, nerve ganglia, trachea, etc. It occurs mainly in summer and may occur in winter also. It is of rare occurrence in Muga.

Worms lose appetite, discharge soft excreta become sluggish and immobile. The dody becomes soft, flabby and turns brownish, loses its natural shape. The worms die after about 24 hours of attack. It gets ruptured after death with a slight injury and omits obnoxious smell. Body colour turns to blackish and ultimately tissues are melted. Cocoons formed by infected worms are flimsy.

Worms die during spinning, after pupation and even on emergence/ Dead pupae melt and make the cocoons dirty. The infected moths possess flaccid body with crumpled small wings.

On examination under microscope, polyhydral bodies are seen. They are nuclear and cytoplasmic in nature.

It may becontrolled by washing the eggs by formaldehyde, Sodium hydroxide, hydrochloric acid and Potassium permanganate of appropriate strength, following Sericultural hygience, selection of disease resistant strains, and suitable plantation for rearing, etc. It can be avoided by reducing summer rearing (mid June to August).

c) Flacherie (Mukhlage) - Flacherie is very common in Muga worms. It is caused by different kinds of bacteria. It is an infectious diseases. Some authors consider it as a virul disease. This disease infects the alimentary tract of the worms but blood cells, hypodermis and fat bodies may also be infected. Sudden fluctuation of weather is the main cause of the disease. Unsuitable leaves, over-crowding, heavy rain or long drought, etc., are also responsible for spread of the disease. Last stage worms are more susceptible to it. Worms die before spinning. It is common in rainy season.

Common symptoms of this disease are larva has swelling body, lethargic, motionless, weak and reduced feeding, body becomes soft, hangs its head downward and dies. They defecate coloured, sticky, semi-solid excreta, chain of faecal beads; protusion of the recrum has been observed.

Proper incubation of eggs, care of worms at theearly stages with quality leaves, protection from direct sun and rain, use of healthy and examined seeds, collection of seed cocoons from healthy and uninfected areas the precautionary measures to be taken for the disease. Worms should be handled less. Appropriated rearing season should be derermined carefully.

d) Mascardine (Bhekur Rog) — It is a fun fungal disease. The infected worms become harder, paler and completely inactive followed by bending of the body dorsally. It dies in about 20-24 hours of attack. Dead worms are compressed, reduced body fluid and spongy with fragile skin. A white encrustation appears round the body becomes laterally compressed, dry, hard, brittle and ,mummidied. The infected pupae become mummified and hard like that of the larvae. It is of very rare occurrence in Muga. Its occurrence is reported during winter rearing only.

This disease may be avoided by reducing the rearing of winter season (December to February).

2. PESTS

Common pests which damage the larvae of Muga are described below. The prevalence of these pests usually synchronises with rearing period of Muga worms.

a) Fly pest-Uzi fly is a parasite to larvae and pupa of Muga. The female lays eggs (30-40 Nos) on the body of the larvae. The eggs hatch out within three days. Maggots come out within 10-15 days. They pupate inside ground or in any dark corner and sometimes in the cocoons. They emerge out as fly ultimately. During winter season the pupae remain under hibernation. The adult will emerge in the following spring. Common fly (Trycolyga bombycis) attack Muga but the extent of damage is not so much. Sturmia sericariae attacks the Muga worms in the same way like other flies.

The incidence of this parasite is less (about 15%) in spring and autumn crops but about 50% in winter and the late Summer Crops.

b) Ichneumon Wasp — The adult is 2-2.5 cm in length with two pairs of transparent wing and a pair of prominent antennae. The insect is yellow/black in colour having dorsolateral black spots on each sternum. The prothroracic shield also bears four black spots The female has nearly on centimeter long prominent needle like ovipositor with long stylets.

al body by inserting its ovipositor ell. The maggot after hatching consumes the entire pupa/larva. It forms cocoons around the host, pupate and finally comes out as fly. It is found more during late autumn crop.

Pimpla punctuator also infects Muga worms in the same way as the Ichneumon wasp and other species of the moths.

Besides these, predators like (1) Canthesone bug  (2) Red ants, (3) Preving mantis (4) Reduviid bag, (5) Wasps, etc, are also damaging to the cocoon crop. 

3. CONTROLLING MEASURES

The controlling measures are only mechanical as we cannot apply any insecticides or pesticides due to harmful effects on Muga worms. So, constant watch and wards is the only remedy to this problem, some attractants and chemesterilants are employed with success. The use of odour baited lure has been helpful in traping various flies, wasps and predators. Tugon bait with fish refuse or flesh and Tugon bait with refuse of country liquor ar used and found effective. Thick liquid gum putting at the end of bamboo poles may be used to catch various flies, wasps, etc on the tree. Lali of molasses mixing with Tugon bait may also be used to attract them. Pitcher plants may be planted around the site of rearing, which will also help us to kill flies, etc. Sex pheromone may be used for luring insects into lethal traps. It is found very useful in controlling harmful insects. It has been reported that males of saturniids can be lured to their females upto a distance of about 4 K.M. Regular inspection of cocoonages (Jalis) is required to collect and destroy the fallen maggots on the floor. The floor of the cocooning room should be plastered so that maggot cannot go inside. Early stifling of reeling cocoons is to be done to kill the maggots of uzifly and others.

Besides disease and pests of Muga, there are many enemies, such as crows, bats, rats, ants, lizards, owls’ kites, snakes, mice, monkey, jackal, etc. Careful watching is most essential to avoid damage of the crop. Birds are scared away by bows and pallets and by other bird scaring instruments. Rearers should be educated for controlling various pests, predators and diseases of Muga worms.  Top

MULBERRY DISEASES AND PESTS – CONTROL MEASURES

A. MULBERRY DISEASES

The leaf of mulberry (Morus spp) is the basic food of silkworm (Bombyx mori L). The role of leaf quality in the success of silkworm rearing and cocoon yield is well established.

Mulberry is a fast growing plant and leaf contents are rich in protein, sugar and moisture. The nutritional value of leaf, however, varies greatly owing to a number of factors among which the diseases play an important role. Being a perennial plant, mulberry is exposed to the environmental vagaries and pathogens prevailing in the area throughout the year. As a result, many fungi, bacteria and nematodes cause number of diseases.

Feeding the leaves of infected plants to the silkworms adversely affects their growth and health resulting in partial or sometimes complete failure of cocoon crops and reduced marketing quality of cocoons produced. Hence, a close watch, timely control measures and regular monitoring are very essential to manage the problems posed by diseases.

1. Cercospora leaf spot

Causative organism: Fungus, Cercospora moricola

1.1 Symptoms: Initial symptoms of the disease are small light brown specks on leaves. These spots later enlarge into nearly circular, dark brown lesions with chlorotic margin. Whitish conidial masses appear on the lesions solitarily or in a circular fashion. Severely infected leaves turn yellow and fall-off prematurely. The loss due to the disease ranges from 10-20 per cent depending on the age of the garden, temperature and frequency of rain.

1.2 Seasonal incidence: The disease occurs during South-West monsoon season. Maximum disease severity is seen during August to October. The disease may also prevail on plants during November and December depending on the receipt of North-East monsoon. Young leaves within the age of 18 days are susceptible to infection.

1.3 Control: All the infected leaves should be collected and burnt prior to receipt of each rain to reduce availability of the inoculum in the garden for further spread.

Spray of 0.2% Carbendazim (2 gram of chemical/litre of water) twice at 15 days interval is used as chemical control. Safety period of Carbendazim is 15 days.

2. Powdery mildew

Causative organism: Fungus, Phyllactinia corylea

2.1 Symptoms: White powdery patches appear on the under surface of leaves. Corresponding to these patches on the upper surface, the leaves turn chlorotic. Under favourable conditions, the symptoms may progress to form an almost total white superficial covering on the under-surface of leaves. As the lesions become older, they may turn black due to the growth of a hyperparasite on the mildew fungus. Infected leaves turn yellow, lose the moisture and become easily friable leading to defoliation. The loss incited by the disease ranges from 10-15 per cent.

2.2 Seasonal incidence: The disease generally occurs during August to January. Maximum severity is noticed during October-December. Close spacing of plants and excessive nitrogen application favours disease severity.

2.3 Control: Adopting wider spacing to facilitate adequate aeration penetration of sunlight helps to reduce disease severity. Removal of weak branches and weeds checks the humidity build-up under the plant canopy thereby reducing the severity of the disease.

Chemical control of mildew becomes necessary in hilly areas and regions receiving heavy rainfall. Fungicidal spray of 0.2 per cent Carbendazim/Dinocap (2 gram/ml of chemical in one litre of water) should be applied as soon as the symptoms appear on plants which may be repeated after 15 days, if necessary. Leaves can be fed to worms after 15 days if Carbendazim is used and 20 days if Dinocap is sprayed.

3. Leaf rust

Causative organism: Fungus, Peridiospora mori

3.1 Symptoms: Numerous, small, light brown specks appear on the under surface of leaves which later turn into dark brown rusty spots.

3.2 Seasonal incidence: The disease is most common during winter months of November-January. Medium and coarse leaves are susceptible to infection. The loss due to this disease is about 5 per cent.

3.3 Control: Timely utilization of leaves during winter months is most essential to prevent inoculum build up in the garden.

Chemical control using foliar sprays of 0.2 per cent Carbendazim/Chlorothalonil (2 grams of chemical/litre of water) can reduce the disease severity. Leaves can be fed to silkworms after 15 days.

4. Bacterial leaf spot

Causative organism: Bacterium, Pseudomonas mori

4.1 Symptoms: Lesions initially consist of small, irregular, water soaked areas on the under surface of leaves. Later, they enlarge and become dark brown to black necrotic lesions. In wet weather, a sticky bacterial ooze can be seen on the lesions. If young leaves are infected, they curl and drop off, while medium aged leaves turn yellow prior to defoliation. The pathogen can also cause lesions on tender stem portions.

Yield loss as a result of disease is generally not high. Occasionally it may cause 1-2 per cent loss in yield.

4.2 Seasonal incidence: The disease occurs in most mulberry growing areas during June-December.

4.3 Control: Infected leaves should be removed and burnt to reduce the inoculum load in the garden. Chemical control using 100 ppm Streptocycline solution (1 gram of chemical in 10 litres of water) as foliar spray twice at 4 day intervals has been found to be effective. Residual toxicity to silkworm is absent.

5. Stem canker

Causative organism: Fungus, Lasiodiplodia theobromae

Mulberry is propagated mainly through stem cuttings. The cut ends of the cuttings provide the main portal for the entry of many pathogens. One such important pathogen is Lasiodiplodia theobromae (Botryodiplodia theobromae), a wound parasite causing stem canker in mulberry. Canker is a disease causing death and /or decay of the bark.

5.1 Disease symptoms in nurseries

• Failure of cuttings to sprout.

• Sudden withering and death of sprouts.

• Discolouration and drying of stems and buds above the soil.

• Rotting and peeling off bark on stem below the soil surface.

• Black mycelial strands seen below infected bark.

• Black eruptions on the bark of the infected stem portion.

5.2 Disease symptoms on grown-up plants

•  Greyish brown discolouration of the bark at the cut ends of the stem.

• Delayed sprouting.

• Death of buds and sprouts.

• Black eruptions on the bark in the infected region.

• Death of plants.

The above symptoms can be observed few days after the plants are pruned.

5.3 Disease management: The pathogen is soil-borne and spreads through irrigation, farm activities, insects and wind. Effective management of stem canker can be achieved through cultural and chemical methods.

5.3.1 Cultural methods

a)      Roguing: This method involves removal and burning of the infected cuttings and saplings in nurseries. In established gardens, the affected stem parts should be cut and burnt.

b)      Field sanitation: Field sanitation is essential especially in the control of L. theobromae which survives in the soil and on host debris. Destruction of crop debris by burning reduces inoculum build-up. Stalking of pruned stems and twigs by the side of mulberry garden should be avoided since it aids in the growth, multiplication and survival of the pathogen which serves as an important source of inoculum.

c)       Land use: Raising saplings repeatedly in the same site should be avoided as it helps in inoculum build-up in the soil, making it sick. Such sick soil supports a very high incidence of disease and mortality of cuttings.

d)      Planting season: Planting during winter months should be avoided since cold weather delays normal sprouting thereby predisposing the cuttings to infection.

e)      Proper pruning: Damaging the bark or buds while pruning should be avoided to prevent entry of pathogen. Pruning the stem close to the buds helps normal sprouting and prevents fast colonization by the fungus. Cutting close to the buds should also be followed while preparing cuttings to avoid delayed sprouting.

5.3.2 Chemical control

a)      Pre-treatment of cuttings: The cuttings should be dipped in 0.2 per cent Carbendazim solution (2 grams of chemical in one litre of water) for 30 minutes prior to planting followed by a spray after 15 days planting.

b)      Protecting established plants: Soon after pruning, the cut surfaces of the stems should be dressed with a spray/smear of 0.2 per cent Captan or Carbendazim solution. This is a very important step to be followed in gardens where shoot harvesting is practiced for rearing silkworms. The treatment forms a toxic barrier on the wound surface preventing the entry of pathogenic inoculum.

c)       Soil disinfection: This method is suitable for the treatment of sick soils in nursery beds. Carbendazim or Captan at the rate of 8 kg/acre should be broadcast after loosening the soil followed by irrigation. After 10-12 days, well decomposed farmyard manure should be applied and thoroughly mixed with soil for planting the cuttings. Post treatment application of farmyard manure is a pre-requisite prior to planting in treated soils.

5.3.3 Biological control

Nursery Guard, a bioformulation of Trichoderma pseudokoningii can be used for long term protection, better survivability and growth of saplings.

Mix 1 kg of nursery Guard with 60 kg of finely powdered, well decomposed farmyard manure/neem cake. Moisten the mixture to a maximum 30% moisture, store it under shade in the form of a heap and cover with a wet gunny cloth. This enhances the multiplication of biocontrol agent in the mixture.

Broadcast the mixture @ 2 kg/m over the well prepared nursery beds and thoroughly mix with soil by light digging. Apply the mixture only to the planting area in nursery beds. 

6. Root rot disease

Causative organism: Fungus, Fusarium solani and F. oxysporum

Fusarium solani is more virulent and cause maximum damage. The disease appears in all types of soil and climate throughout the year. The disease incidence with plant mortality ranges from 2-10%.

6.1 Symptoms and nature of damage: Sudden wilting/withering and defoliation of leaves followed by drying/death affected plants. The underground symptoms include decaying of root bark and rotting of primary and secondary roots. Rotten roots turn black and contain black powdery debris below the bark. The severely affected plants loose the hold in the soil.

The disease is soil-borne and appears in isolated patches in the gardens and quickly spreads to surrounding areas through irrigation and farm operation.

6.2 Management (chemical method): Chemical control involves the root dipping of saplings in 0.2% Carbendazim solution for half an hour and planting in pits dusted with 5g Mancozeb.

6.3 Method of application:

6.3.1 For existing plantation (disease in initial stage): As soon as the initial symptoms like wilting of leaves and drying of branches are noticed, dust 5g Mancozeb/plant after removing the soil around the infected plants to a depth of 5-6". And also apply the same dose of Mancozeb to the plants in 2-3 surrounding rows around the infected plants.

6.3.2 For replantation

• Uproot the severely affected plants and destroy. Prepare one foot deep pit and remove the soil including rotten stump of roots and allow the pit for sun drying for a month before planting. Prior to planting, dip the roots of the saplings in 0.2% Carbendazim solution (2g of chemical in one litre of water).

• Dust 5g Mancozeb/pit and plant the treated saplings in the pit and cover with fresh soil.

• Also apply the Mancozeb alone @ 5g/plant for 2-3 rows of plants surrounding the infected plants.

• Apply second dose of Mancozeb @ 5g/plant a month after replantation.

6.4 Biocontrol: A biofungicide ‘Raksha’, containing Trichoderma harzianum has proved to be effective and is under large-scale field trial. The biofungicide can be used for the management of the disease.

6.4.1 Method of application:

Preparation of mixture of ‘Raksha’

• Mix one kg ‘Raksha’ with 50 kg FYM/neem cake (sufficient for 1000 plants) and keep under shade for a week covered with a wet gunny cloth to enhance the multiplication of Trichoderma.

6.4.2 For existing plantation (Disease in initial stage): As soon as the initial disease symptoms appear, apply the mixture of ‘Raksha’ @ 500g/plant at a depth of 5-6" below the soil including surrounding 2-3 rows of plants.

For new plantation, apply Raksha @ 500g/pit and plant the Mancozeb (0.2%) treated saplings in the pits (Mancozeb is not toxic to biocontrol agent).

Apply second dose of Raksha after 3 months of replantation.

7. Lasiodiplodia root rot disease

Causative organism: Lasiodiplodia theobromae (Botryodiplodia theobromae)

7.1 Symptoms

• Sudden wilting and withering of leaves.

• Drying and death of branches and plant.

• Appearance of black eruptions (pycnidial clusters) on the bark near the soil surface.

• Rotting and pealing of bark from roots.

• Greyish black mycelial strands appear on the under surface of bark and on wood portion of root.

• In presence of adequate soil moisture, rotting and pealing of bark extends even to the basal portion of the stump.

7.2 Seasonal occurrence: The disease occurs throughout the year.

7.3 Disease management

• Pruned stem portion should not be stacked near the garden to prevent multiplication of the pathogen and further spread.

•  Uproot and burn the diseased plant along with roots.

• Soil from where the infected plant was uprooted should be thoroughly drenched with 0.2% Carbendazim or Captan solution. After 15 days, apply well decomposed farmyard manure and plant a new sapling with its root pre-treated with 0.2% Carbendazim solution.

• Immediately after pruning, the cut surfaces and the stumps should be sprayed with 0.2% Carbendazim.

8. Root knot disease

Root knot is one of the major diseases limiting crop production throughout the world. It occurs throughout the year mainly in sandy soils low in organic matter. The severity of the disease increases with increased age of the garden. The estimated yield loss due to the disease is 15-30 per cent. Infected plants become weak and predisposed to other disease while severely infected plants ultimately die.

8.1 Causative organism: The organism causing root knot disease, is a nematode (Meloidogyne incognita), an endoparasite inhabiting mulberry roots.

8.2 Symptoms

• Stunted growth.

• Poor and delayed sprouting.

• Reduced leaf size and yield.

• Chlorosis and marginal necrosis of leaves, yellowing and wilting of leaves inspite of adequate soil moisture availability.

• Death of plants in severe cases.

These symptoms first appear in isolated patches, slowly spreading over the entire garden.

8.2.1 Symptoms on the underground parts

• Formation of galls/knots on roots.

• Reduced and stubby root system.

• Retarded root growth.

• Necrotic lesions on the root surfaces and death of active rootlets.

8.3 Disease management

Cultural methods

• Saplings free of nematode infestation should be used for planting to prevent the introduction of nematodes from diseased area into a disease free area.

• Heavily infested soils should be deep ploughed to expose the nematodes and their eggs to solar radiation. Keeping the land free of vegetation during summer kills the nematodes due to desiccation by solar radiation.

• Application of neem cake @ 2 MT/ha/year in 4 split doses reduces the disease incidence.

Chemical methods: Chemical methods of nematode management become necessary in sick soils and heavily infested gardens as they give quick results. Furadon 3 G (40 kg/ha) can be applied either in furrows of broadcast to the soil after light harrowing followed by irrigation. The leaves from treated plots can be fed to silkworms after 45 days.

Biological control: A bionematicide verticillium chlamydosporium can be applied with neem cake. One kg bionematicide to be mixed with 200 kg FYM and 24 kg neem cake is sufficient for 1000 plants. Prior to application, the mixture should be kept in shade for a week covered by wet gunny cloth. Apply the mixture @ 200 g/plant around the root zone and repeat the treatment every 4 months for 2 years.

Note: Do not use any fungicide/insecticide to the soil when bionematicide is applied.

B. MULBERRY PESTS

9. Mulberry Leaf-Roller,Diaphania pulverulentalis

The leaf-roller, Diaphania pulverulentalis (Hampson) (Lepidoptera: Pyralidae) is a pest of mulberry. The leaf-roller infestation causes considerable reduction in leaf yield, resulting in economic loss to sericulturists. The infestation is observed in mulberry plantations from 15 days through 70 days after pruning or leaf harvest. Up to 100% infestation is recorded in several areas.

9.1 Period of occurrence: Though, leaf-roller infestation is observed round the year but for May, infestation is severe from July to November.

9.2 Symptoms and nature of damage: The young caterpillars within the unopened young leaves secrete delicate, white, silky filaments, which bind the leaf blades together and feed on the soft green tissues on the leaf surface. Sometimes a single leaf is rolled up and the caterpillar is found within this rolled up leaf formed by the filaments and hence the name leaf-roller. Grown up caterpillars fed voraciously on tender leaves and their faecal matter can be seen on the leaves below the affected portion.

The leaf-roller not only feeds on the leaves at the apical portion of the affected plants, but also damages the young shoot. As a result, the plants become stunted. In such plants, tender leaves required for chawki rearing become scarce. In addition, the leaf-roller is highly susceptible to pebrine disease of silkworms. The pest larva infected with pebrine spores in the field can contaminate mulberry leaves. When such contaminated leaves are fed to silkworms, it can cause an outbreak of pebrine disease in silkworms. Thus, this pest causes dual damage.

9.3 Life-cycle: Moths are greyish brown in colour and measure about 1 cm in length. Wings have brownish wavy stripes. Moth lays 1 or 2 eggs on the apical portion of each shoot. Each female lays about 100 eggs. Incubation period is 3-4 days. Grown up caterpillars are greenish brown in colour with black markings on the lateral and dorsal regions of the body segments. The head is black in colour. Larval duration lasts for 10-15 days. Pupae are dark brown in colour. Pupation occurs in dry leaves and pupal duration is 8-10 days. The pest completes its life-cycle in 21-29 days.

9.4 Management practices: Adopt an integrated pest management (IPM) strategy comprising cultural/mechanical, chemical and biological control methods.

Cultural/Mechanical measures

• Clip the affected apical portions, collect them in polythene containers and dip in 0.5% soap solution (5g of soap in 1 litre of water) to destroy the larvae.

• Collect and burn dry leaves and weeds found on the surface of soil in infested mulberry gardens to destroy pupae.

• Dress mulberry shoots before transporting them to other areas for new plantations in order to check the pest from spreading.

• Promote the activity of bird predators by providing them with water in small containers in and around mulberry plantations.

9.4.2 Chemical control: Spray 0.076% DDVP [1 ml of DDVP (76% EC) in 1 litre of water] on the apical portion of plants when infestation is noticed. A second spray is necessary 10 days after the first spray, if infestation exceeds 20%. Use mulberry leaves for silkworm rearing 10 days after spray. About 150 litres of DDVP solution is required/spray/acre. Freshly prepared solution should be used.

The aforesaid management practices should be adopted simultaneously by Sericulturist in pest infested areas.

9.5 Precaution

• Undertake the insecticide spraying during the cooler hours of the day.

• Check the expiry date of insecticides while purchasing.

• Keep the container of the insecticides airtight after use.

• Keep the insecticides away from reach of children and pet animals.

10. Bihar Hairy Caterpillar, Spilosoma oblique

The Bihar hairy caterpillar, Spilosoma obliqua Walker (Lepidoptera: Arctidae) is a polyphagous pest infesting several crops including mulberry, sunflower, green gram, soya, jute, etc.

10.1 Period of occurrence: It occurs almost throughout the year and infestation is severe from August to December and also January.

10.2 Symptoms and nature of damage: Young caterpillars are gregarious and they feed on the green soft tissues of tender leaves, leaving behind only the veins. Grown up caterpillars are solitary and feed voraciously on entire mulberry leaves, thus defoliating the plants.

10.3 Life-cycle: Moths have light brown coloured wings, brick red abdomen, peppered with dark row of spots laterally and dorsally. Gravid females lay 1,000 to 2,000 eggs in a group on the under surface of mulberry leaves. Eggs are pale green in colour and hatch in 5-7 days. Caterpillars moult 6 times. Grown up caterpillars measure 4-5 cm in length and are covered with bristles. Anterior and posterior ends of the caterpillar are black in colour, while the rest of the body is reddish brown. There are seven instars and the larval duration is 27-32 days. They pupate in crevices found between stones on bunds, crevices of tree trunks and corners of nearby buildings. Pupae are dark brown in colour and measure about 2 cm in length. Pupal duration is 12-14 days. The life-cycle is completed in 44 to 53 days.

10.4 Management practices: Adopt an Integrated Pest Management (IPM) strategy comprising culturally/mechanical, chemical and biological control methods.

Cultural/Mechanical measures

• Collect and destroy egg masses and gregarious young caterpillars by crushing them.

• Use light traps to attract moths by placing a tray with 0.5% soap solution below the light source.

Chemical control: Spray 0.15% DDVP [2 ml of DDVP (EC=76%) in 1 litre of water], 15 days after release of T. chilonis. Mulberry leaves ca be fed to silkworms 10 days after spraying.

Biological control: Trichogramma chilonis is an egg parasitoid of many lepidopteran pests. It is widely used as a biocontrol agent of several crop pests. Release twice T. Chilonis at the rate of 5 tricho-cards (20,000 parasitised eggs in each tricho-card) per acre, at an interval of 3 days. Parasitoid releases have to be undertaken 20 days after pruning or harvesting.

10.5 Economics (Per acre, per year)

(i)    Expenditure

(ii) Receipts 

a)      Average recovery in mulberry leaf                      =          2,386 kg

b)      Value of mulberry leaf @ Rs.2/ per kg)                 =          Rs. 4,772

c)       Net gain                                                            =          Rs. 3,568

d)      Cost-benefit ratio                                              =          1:2.96

11. Cutworm, Spodoptera litura

The cutworm, Spodoptera litura F. (Lepidoptera: Noctuidae), is a polyphagous pest infesting several crops, such as mulberry, tobacco, castor, several vegetable crops, etc. It occurs sporadically on mulberry, where vegetable crops are commonly grown.

11.1 Period of occurrence: It occurs mostly in between August to December and upto February months.

11.2 Symptoms and nature of damage: The cutworm caterpillars attack shoots of young mulberry plants and cut them, hence the name cutworm. The cut portion of the shoot dries up and falls off. They also feed on mulberry leaves.

11.3 Life-cycle: Moths are stout, forewings are dark with wavy white markings. Hindwings are white with brown margins. Eggs are laid in clusters of 200-300 underneath the leaves and are covered with brown bristles. Incubation period is 4-5 days. Fully grown caterpillars are stout, cylindrical and pale greenish brown in colour, with dark markings. They have transverse and longitudinal grey and yellow bands. The caterpillar is nocturnal in habit, and lies hidden in crevices of loose soil at the base of the plant during day time. It measures 3.5-4 cm in length and pupates in soil. Larval period is 2-3 weeks. Pupae are dark brown in colour and measure 1 to 1.5 cm in length. Moth emerges from pupa in about 2 weeks. Life-cycle is completed in 36 to 40 days.

11.4 Management practices: Adopt Integrated Pest Management approach comprising of cultural/mechanical, chemical and biological control methods.

Cultural/Mechanical practices

• Collect and destroy egg masses and young caterpillars.

• Plough the pest-infected garden and dig near the base of mulberry plant to expose the pest to sunlight and predators.

• Use light traps to attract moths by placing a tray with 0.5% soap solution below the light source.

Chemical control

• Spray 0.15% DDVP [2 ml DDVP (EC=76%) in 1 litre of water] in the evening, 20 days after pruning or leaf harvest. Feed silkworms 10 days after pesticide application.

• Dust 5% Malathion near the base of the plants immediately after pruning or leaf harvest.

Biological control: Use ‘Spodolure’, a pheromone trap @ 2 lures/acre twice at an interval of 15 days, starting from 25 days after pruning or leaf harvest to attract and kill male moths.

12 “Tukra”(Maconellicoccus hirsutus)

“Tukra” is caused due to infestation of mulberry plants by the mealy bug, Maconellicoccus hirsutus (green) (Hemiptera: Pseudococcidae).

12.1 Period of occurrence: Though “Tukra” infestation is observed throughout the year, it is severe in summer.

12.2 Symptoms and nature of damage: Malformation of the apical shoot due to flattening and/or thickening of the affected portion of shoot, reduction in internodal distance and wrinkling and curling up of apical leaves is observed. Affected leaves become dark green in colour and turn pale yellow, in the case of severe attack. Affected portion of plants become brittle. Presence of white mealy substance on infested portion of plants confirms mealy bug infestation.

The mealy bugs suck the sap, resulting in stunted growth of the plant and reduction in leaf yield.

12.3 Life-cycle: Each gravid female deposits about 250 eggs. The eggs hatch in 5-8 days. The crawlers are orange in colour and this stage lasts for a day. They settle on the plant and secrete a white mealy substance on their body. Females have three nymphal instars, while males have four. Life-cycle is completed in 24-26 days. Adult males are slender and possess a pair of wings and caudal filaments, each. They predominantly reproduce parthenogenetically.

12.4 Management practices: Adopt an Integrated Pest Management (IPM) approach comprising cultural/mechanical, chemical and biological methods.

Cultural/mechanical practices

• Clip the affected portions of the plants, collect them in polythene containers and dip in 0.5% soap solution (5g of soap in 1 litre of water) to destroy the pest. This practice should be employed about a week before commencement of leaf harvest.

• Do not grow alternate host plants such as croton, hibiscus, guava, grapes, lady’s finger, cotton, etc., in the vicinity of mulberry garden.

Chemical control: Spray 0.15 DDVP [EC=76%) in 1 litre of water] in 0.5% soap solution on pruned or leaf harvested plants, twice at an interval of 10 days. Leaves can be fed to silkworms, 10 days after spraying the insecticide. This practice should be adopted during summer (February-May).

Biological control: Release the predatory coccinellid ladybird beetle, Cryptolaemus montrouzieri (Muls) (Coleoptera: Coccinellidae) @ 125 adults per acre twice, during August-September and October-November.

12.5 Precautions

• Before pruning the infested mulberry plantation, clip the affected portions, collect in a polythene bag and dip in 0.5% soap solution.

• When cuttings from “Tukra” affected plantations are procured for planting, dip them in 0.15% DDVP solution for 2-3 minutes before planting.

• Ants play an important role in spreading “Tukra” infestation in mulberry plantations. Locate ant nests in and around mulberry plantations and treat them with 5% Malathion dust soon after pruning or leaf harvest.

13. Wingless Grasshopper, Neorthacris acuticeps nilgirensis

The wingless grasshopper, Neorthacris acuticeps nilgirensis Uvarov (Orthoptera: Acrididae) is a serious pest in rainfed mulberry plantations. The rate of infestation ranges from 0 to 95%. Besides causing extensive damage to mulberry, this pest infests sunflower, ragi, groundnut, beans, potato, etc.

13.1 Period of occurrence: The pest occurs throughout the year and the infestation is severe during July-August.

13.2 Symptoms and nature of damage: Nymphs and adults feed voraciously on sprouting buds and leaves of mulberry. Sometimes, they also feed on green bark of affected plants. When the infestation is severe, mulberry plants are completely devoid of leaves.

13.3 Life-cycle: Adults of the grasshopper are light in colour. Gravid females lay 6-8 eggs pods in loose soil at a depth of 2-3 cm. Each egg pod contains 8-18 eggs. Eggs hatch in 28-31 days. The I, II and III instar nymphs are straw coloured, whereas the remaining instars are light green in colour. Nymphs pass through 6 instars in 90-95 days. Females are larger in size than males and live for 45-60 days. The pest completes its life-cycle in 163-186 days.

13.4 Management practices

Cultural/mechanical measures

• Plough the infested mulberry plantations immediately after the onset of monsoon, to expose the egg masses to sunlight and predators.

• Maintain field sanitation by keeping the mulberry garden free from alternate host plants.

Chemical control: Spray 0.076% DDVP [1 ml of DDVP (EC=76%) in 1 litre of water] on mulberry foliage to kill nymphs and adults. If infestation is severe, a second application is necessary, 10 days after the first spray. Harvest mulberry leaf for silkworm rearing 10 days after the last spray.

14. Preparation of Insecticides

14.1 Calculation of dilutions: The active toxicant in a commercial formulation suitable for direct application is rarely available because small quantity of active ingredient has to be distributed on a large area. Dilution, therefore, becomes another important aspect for consideration.

To obtain the weight or volume of solid or liquid formulation of commercial insecticide available in market for the preparation of a solid or liquid containing a desired (or recommended) percentage of toxicant, the following formula can be applied.                          

A.                     d = (aXb)/c

where

a = % of toxicant desired (recommended).

b = Wt (in g or kg) of dust or volume (in ml or lt) of liquid required for application.

c = % of toxicant available in the commercial insecticide formulation.

d = Wt (in g/kg) or volume (ml or lt) of commercial formulation required.

B.  After obtaining the value of d, the following calculation formulation should be carried out to obtain the weight or volume of diluent (e),

                  value of (b) – value of (d) = e

C.  Mix well the diluent (value of e) by weight (in case of solid formulation) or by volume (in case of liquid formulation) to commercial formulation (value of d) to obtain the required quantity of desired strength of particular insecticide.

Example: Prepare 150 lts of 0.2% dimethoate, from the commercial formulation dimetoate 30% EC.

      a =       0.2% dimethoate

      b =       150 litres

      c =       30% EC

      d =       ?

                       ( 0.2 x 150)/30 = 1 litre (d) 

      150 i.e., (b) – 1 i.e.,(d) = 149 litres i.e., (e)

Therefore, to obtain 150 litres of 0.2% dimethoate from dimethoate 30% EC (Commercial formulation), 1 litre of dimethoate 30% EC should be added to 149 litres of water. In case of dust formulation, levigated china clay can be used as inert material to reach commercial formulation for application.

To determine the weight of solid formulation of commercial formulation sold in market for the preparation of a liquid for spray containing a desired (recommended) percentage of toxicant, the step mentioned above under (B) need not be carried out. After obtaining the volume of d (in g/kg), the determined weight of solid formulation should be added to the volume of liquid diluent considered for b.

Example: Prepare 100 litres of 0.5% BHC from commercial formulation BHC 50% WP available in the market. Follow step mentioned above under (A)

  (0.5x 200 (lts))/50 = 2.00 kg or      (0.5 x 200000 (ml))/50 = 2000 g

Mix 2 kg or 2000 g of BHC 50% WP in 200 litres of water.

14.2 Safe period for various insecticides available commercially: Insecticides are widely used for the control of insect pests of several field crops. Improper use and their application results in undesirable drift residues to adjacent field crops. Accordingly, mulberry gardens have also been found contaminated due to use of insecticides in the nearby crops.

Since silkworms are highly sensitive to insecticides, harvest of mulberry leaves before the safe period should be completely avoided. In case, this is not followed scrupulously and contaminated leaves are harvested from the garden either located adjacent to field crops applied with insecticides or directly treated with insecticides, silkworm larvae develop toxic symptoms followed by the loss of the crop. These symptoms include:

• Vomiting of the digestive juice

• Swinging of the anterior half of the body

• Shortening of the body due to loss of the body fluid

• Muscle contraction and

• Paralysis is followed by death of the silkworm larva.

To avoid loss of silkworm crops (due to feeding of contaminated leaves), mulberry leaves should be harvested on or after the number of days shown against each insecticide given below.

Safe periods of various insecticides against silkworm

*    Names in parentheses are the trade names of insecticides

**  Safe periods have also been indicated with each insecticide recommended for mulberry pest control.

14.3 Meaning of the commonly used terminology on the containers of insecticides

14.4 Compatibility chart of plant protection chemicals

14.5 Precautionary measures for spraying of fungicides/insecticides 

• Do not allow children for spraying

• Do not spray in hot sun, spray in cool hours

• Do not blow nozzle, use a needle or thin wire to clean

•  Do not spray against wind, keep away from spray mist and dust drift

• Do not mix by hand, use rod for mixing

• Wash the hands or take bath before eating

C. DISINFECTANTS AND DISINFECTION METHODS

Disinfection forms an integral part of healthy and successful silkworm rearing. It aims at the total destruction of disease causing pathogens. Several diseases caused by bacteria, viruses, fungi and protozoa affect the silkworms. These pathogens released by diseased silkworms easily accumulate and spread in the rearing environment through different routes. They are not easily destroyed and can persist/survive for long periods under congenial conditions. The spores of the pathogens, especially those of fungi are light and can easily be drifted by air current resulting in easy spread of diseases. There are no curative methods for any of the silkworm diseases and they are best prevented than cured. This is achieved by adoption of proper and effective methods of disinfection and stepwise maintenance of hygiene during rearing. To realize the benefit of disinfection to the full extent, attempt should be made to have synchronized disinfection (mass) and rearing at village or block level considering them as one unit.

1. Chemical disinfectants available for use in sericulture

1.1 Formalin: It is commercially available as 36% formaldehyde in solution form. A mixture of 2% formalin + 0.05% detergent is an effective solution that can be used for disinfection purpose as spray. Formalin is effective only in rearing houses, which can be made airtight and it is faster and more pronounced at temperature above 25˚C and humidity more than 70%.

1.2 Bleaching powder: It is a white amorphous powder, with a pungent smell of chlorine. For effective disinfection, a high grade bleaching powder with an active chlorine content of 30% must be used. It should be stored in sealed bags, away from moisture, failing which it will be rendered ineffective. The action of bleaching powder is optimal under wet contact conditions and therefore the surfaces of equipment and walls should be drenched with this solution.  A 2% bleaching powder in 0.3% slaked lime solution is used for disinfection as spray.

1.3 Slaked lime: A very useful bed disinfectant in sericulture, especially against viruses. It absorbs moisture and can be used to regulate bed humidity and maintain hygiene. Application of lime dust in combination with bleaching powder in an around rearing houses and premises improves hygiene in the environment.

1.4 Chlorine dioxide: Chlorine dioxide marketed as Sanitech is an ideal disinfectant for sericulture. The disinfectant available at 20,000 ppm concentration is a strong oxidizing agent, effective at broader pH range and at 2.5% concentration in combination with 0.5% slaked lime is effective against all silkworm pathogens. It is stable and may be activated at the time of its use. It possesses tolerable odour and least corrosive at the suggested concentration.

1.5 Materials required for disinfection: Disinfectants, detergent, sprayer – Rocking or power sprayer, buckets, measuring jar, weighing scales, gas masks, metal pans, room heaters, slaked lime powder. Hand gloves and muslin cloth.

D. TECHOLOGY FOR PREVENTION/CONTROL OF DISEASES IN SILKWORM

The technology for prevention/control of silkworm diseases during silkworm rearing is provided as sequential steps.

1. Cleaning of rearing house and appliances (after completion of silkworm rearing and cocoon disposal)

Immediately after the disposal of cocoons, collect at one place inside the rearing house, all diseased and dead larvae, pupae, floss, left over mulberry, bed refuse, silkworm faeces, dust, dirty, etc., and disinfect by sprinkling 5% bleaching powder solution and dispose off by burying at 2ft. depth or burning.

2. Disinfection of rearing house and appliances (with appliances inside the rearing house)

2.1 Measurement of area of rearing house: Measure the length and breadth of the rearing including leaf preservation room, mounting room/place, etc. and calculate the floor area for disinfection.

Floor area = Length x Breadth (of the floor)

Example: Length of floor 20’, breadth of floor 15’

Area of floor = 20 x 15 = 300 sq. ft. = 28 m²

2.2 Estimation of the quantity of disinfectant required: The disinfectant required for disinfection of rearing house is 2 lt/sq.m floor area or 185 ml/sq. ft. floor area.

To estimate the quantity of disinfectant solution required, multiply, the floor area in square metre by 2.0 or the floor area in sq. ft. by 0.185 which gives the actual disinfectant required in litres for disinfection of inside or rearing house.

Example:

Area for disinfection 28 m ² Quantity of disinfectant required = 28 x 2.0 = 56 lts. The requirement of disinfectant for outside of the rearing house and appliances are to be added. To disinfect the appliances inside the rearing house, add 25% and 10% for outside of the rearing house to the total quantity of disinfectant solution required for disinfection of inside of rearing house.

Example:

Disinfectant solution required = 56 lts. Additional disinfectant solution required for appliances is 25% of 56 lts. i.e., 56 x 25/100 = 14 lts. Additional disinfectant solution required for outside rearing house is 10% of 56 lts. i.e., 56 x 10/100 = 5.6 lts. Total quantity of disinfectant required for disinfection of rearing house and appliances is 56 + 14 + 5.6 = 75.6 lts (75 lts). Add 0.05% detergent to total quantity of disinfectant solution required if formalin is used.

0.05% of 75 lts of disinfectant solution is 75 x 0.05/100 = 37.5 g, Add 37.5g of detergent to 75 lts of 2% formalin disinfectant solution.

3. Disinfection

Disinfect the rearing house using 2% bleaching powder in 0.3% slaked lime, 2.5% Sanitech (Chlorine dioxide) in 0.5% slaked lime or 2% formalin + 0.05% detergent solution. 

3.1 Preparation of 2% bleaching powder in 0.3% slaked lime solution: Prepare the disinfectant solution using highgrade stable bleaching powder containing 30% chlorine and having ISI mark. Always prepare disinfectant solution prior to disinfection. To prepare the solution, determine the quantity of disinfectant solution required as suggested above and calculate the quantity of ingredients to be added.To prepare 1 lt. of 2% bleaching powder in 0.3% slaked lime solution, the requirement is 1 lt. of water, 20 g bleaching powder and 3 g slaked lime powder. Make a paste of 20 g bleaching powder and 3 g of slaked lime in 100 ml of water and to this paste, add water to make 1 litre solution.

Example:

Preparation of 75 lts. of disinfectant solution, the requirement is 75 x 1 lt = 75 lts. of water,75 x 20 g = 1.500 kg bleaching powder + 75 x 3 g = 225 g of slaked lime powder.

Mix 225 g of slaked lime powder and 1.5kg of bleaching powder in small quantity (3 lt) of water and make into a paste by stirring. Then add the remaining quantity of water (72 lts) and mix thoroughly. Allow the solution to stand (covered) for some time (10 min) and then use the supernatant for disinfection/or pass (filter) the disinfectant solution through muslin cloth an use only the supernatant for spraying. The undissolved particles can be used in the compost pit while burying diseased materials.

3.2 Preparation of 2% formalin + 0.05% detergent solution: To prepare 2% formalin + 0.05% detergent solution, mix one part of 36% formalin with 17 parts of water. Then add 0.05% detergent to the total formalin solution.

To prepare a known volume of 2% formalin + 0.05% detergent solution, divide the total quantity of the solution required by 18 to get the quantity of formalin required. To this formalin, add water to make it up to the required quantity. Mix 0.05% (0.5 g/lt) detergent to the total disinfectant.

Example:

Required quantity of 2% formalin + 0.05% detergent solution = 75 lts. To prepare 75 lts. divide the required quantity by 17 to obtain the quantity of formalin required, i.e., 75/17 = 4.17 lts. To obtain 75 lts. of disinfectant, mix 4.17 lts. of formalin (36%) to water (75.00 – 4.17 = 70.59) and make upto 75 lts. i.e., 4.17 + 70.83 = 75 lts. To obtain 0.05% detergent in 2 % formalin, the quantity of detergent to be added is 0.5 g in one lt. For 75 lt. of 2% formalin, mix 75 x 0.5 = 3.75 g of detergent.

3.3 Preparation of 2.5% Sanitech (Chlorine dioxide) in 0.5% slaked lime solution: Required quantity of 2.5% Sanitech in 0.5% slaked lime = 75 lts

To prepare 1 lt. of Sanitech in 0.5% slaked lime solution, the requirement is 25 ml of Sanitech + 2.5 g activator crystals + 5 g of slaked lime.

Preparation

Solution A:  Add 2.5 g of activator crystals to 25 ml of Sanitech solution, stir and allow 5 minutes to stand. Colour changes to light yellow.

Solution B:  Mix 5 g of slaked lime powder in water and make it up to 975 ml of water. Mix solution A with solution B. The disinfectant (~ 1 lt) is ready for disinfection.

To prepare 75 lts. of Sanitech in 0.5% slaked lime solution; the requirement of Sanitech is 75 x 25 ml = 1.875 lts.,activator crystals 75 x 2.5 g = 187.5 g (188 g),slaked lime powder 75 x 5 g = 375 g,water 75 x 975.5 ml = 73.125

Preparation

Solution A:  Add 188 g (3¾ packets) activator crystals provided with every litre Sanitech to 1.875 lts. of Sanitech, stir and allow 5 minutes to stand. Colour changes to light yellow.

Solution B:  Mix 375 g of slaked lime powder in water and make it up to 73.125 lts. of water. Mix solution A with solution B (1:40). The disinfectant (75 lts) is ready for disinfection.

3.4 Disinfection of rearing house, appliances, etc. inside the rearing house

Spray using powerful jet sprayer, the required quantity of disinfectant @ 2.0 lt/m floor area of rearing house + 10% for outside of rearing house +25% of disinfectant solution for appliances) uniformly to drench all parts of rearing house inside and outside, and appliances. Keep the rearing house closed for a minimum period of 6-10 hours. Disinfect bamboo mountages with 2% formalin solution. Do not spray bleaching powder solution to the mountages. After minimum period of 18-24 hours, shift the rearing appliances out of rearing house and sundry for 10-12 hours. Do not smear cowdung to the rearing trays and store them inside the rearing house till 5 days prior to next brushing.  Top

HEALTH CARE MEASURES FOR BOMBYX MORI L

A. DISINFECTANTS AND DISINFECTION METHODS

Disinfection forms an integral part of healthy and successful silkworm rearing. It aims at the total destruction of disease causing pathogens. Several diseases caused by bacteria, viruses, fungi and protozoa affect the silkworms. These pathogens released by diseased silkworms easily accumulate and spread in the rearing environment through different routes. They are not easily destroyed and can persist/survive for long periods under congenial conditions. The spores of the pathogens, especially those of fungi are light and can easily be drifted by air current resulting in easy spread of diseases. There are no curative methods for any of the silkworm diseases and they are best prevented than cured. This is achieved by adoption of proper and effective methods of disinfection and stepwise maintenance of hygiene during rearing. To realize the benefit of disinfection to the full extent, attempt should be made to have synchronized disinfection (mass) and rearing at village or block level considering them as one unit.

1. Chemical disinfectants available for use in sericulture

1.1 Formalin: It is commercially available as 36% formaldehyde in solution form. A mixture of 2% formalin + 0.05% detergent is an effective solution that can be used for disinfection purpose as spray. Formalin is effective only in rearing houses, which can be made airtight and it is faster and more pronounced at temperature above 25˚C and humidity more than 70%.

1.2 Bleaching powder: It is a white amorphous powder, with a pungent smell of chlorine. For effective disinfection, a high grade bleaching powder with an active chlorine content of 30% must be used. It should be stored in sealed bags, away from moisture, failing which it will be rendered ineffective. The action of bleaching powder is optimal under wet contact conditions and therefore the surfaces of equipment and walls should be drenched with this solution.  A 2% bleaching powder in 0.3% slaked lime solution is used for disinfection as spray.

1.3 Slaked lime: A very useful bed disinfectant in sericulture, especially against viruses. It absorbs moisture and can be used to regulate bed humidity and maintain hygiene. Application of lime dust in combination with bleaching powder in an around rearing houses and premises improves hygiene in the environment.

1.4 Chlorine dioxide: Chlorine dioxide marketed as Sanitech is an ideal disinfectant for sericulture. The disinfectant available at 20,000 ppm concentration is a strong oxidizing agent, effective at broader pH range and at 2.5% concentration in combination with 0.5% slaked lime is effective against all silkworm pathogens. It is stable and may be activated at the time of its use. It possesses tolerable odour and least corrosive at the suggested concentration.

1.5 Materials required for disinfection: Disinfectants, detergent, sprayer – Rocking or power sprayer, buckets, measuring jar, weighing scales, gas masks, metal pans, room heaters, slaked lime powder. Hand gloves and muslin cloth.

B. TECHOLOGY FOR PREVENTION/CONTROL OF DISEASES IN SILKWORM

The technology for prevention/control of silkworm diseases during silkworm rearing is provided as sequential steps.

1. Cleaning of rearing house and appliances (after completion of silkworm rearing and cocoon disposal)

Immediately after the disposal of cocoons, collect at one place inside the rearing house, all diseased and dead larvae, pupae, floss, left over mulberry, bed refuse, silkworm faeces, dust, dirty, etc., and disinfect by sprinkling 5% bleaching powder solution and dispose off by burying at 2ft. depth or burning.

2. Disinfection of rearing house and appliances (with appliances inside the rearing house)

2.1 Measurement of area of rearing house: Measure the length and breadth of the rearing including leaf preservation room, mounting room/place, etc. and calculate the floor area for disinfection.

Floor area = Length x Breadth (of the floor)

Example: Length of floor 20’, breadth of floor 15’

Area of floor = 20 x 15 = 300 sq. ft. = 28 m²

2.2 Estimation of the quantity of disinfectant required: The disinfectant required for disinfection of rearing house is 2 lt/sq.m floor area or 185 ml/sq. ft. floor area. To estimate the quantity of disinfectant solution required, multiply, the floor area in square metre by 2.0 or the floor area in sq. ft. by 0.185 which gives the actual disinfectant required in litres for disinfection of inside or rearing house.

Example:

            Area for disinfection 28 m²

            Quantity of disinfectant required = 28 x 2.0 = 56 lts.

The requirement of disinfectant for outside of the rearing house and appliances are to be added. To disinfect the appliances inside the rearing house, add 25% and 10% for outside of the rearing house to the total quantity of disinfectant solution required for disinfection of inside of rearing house.

Example:

            Disinfectant solution required = 56 lts.

Additional disinfectant solution required for appliances is 25% of 56 lts.

i.e., 56 x 25/100 = 14 lts.

Additional disinfectant solution required for outside rearing house is 10% of 56 lts. i.e., 56 x 10/100 = 5.6 lts. Total quantity of disinfectant required for disinfection of rearing house and appliances is 56 + 14 + 5.6 = 75.6 lts (75 lts). Add 0.05% detergent to total quantity of disinfectant solution required if formalin is used. 0.05% of 75 lts of disinfectant solution is 75 x 0.05/100 = 37.5 g. Add 37.5g of detergent to 75 lts of 2% formalin disinfectant solution.

3. Disinfection

Disinfect the rearing house using 2% bleaching powder in 0.3% slaked lime, 2.5% Sanitech (Chlorine dioxide) in 0.5% slaked lime or 2% formalin + 0.05% detergent solution.

3.1 Preparation of 2% bleaching powder in 0.3% slaked lime solution: Prepare the disinfectant solution using highgrade stable bleaching powder containing 30% chlorine and having ISI mark. Always prepare disinfectant solution prior to disinfection. 

To prepare the solution, determine the quantity of disinfectant solution required as suggested above and calculate the quantity of ingredients to be added. To prepare 1 lt. of 2% bleaching powder in 0.3% slaked lime solution, the requirement is 1 lt. of water, 20 g bleaching powder and 3 g slaked lime powder. Make a paste of 20 g bleaching powder and 3 g of slaked lime in 100 ml of water and to this paste, add water to make 1 litre solution.

Example:

            Preparation of 75 lts. of disinfectant solution, the requirement is 75 x 1 lt = 75 lts. of water.  75 x 20 g = 1.500 kg bleaching powder + 75 x 3 g = 225 g of slaked lime powder.

Mix 225 g of slaked lime powder and 1.5kg of bleaching powder in small quantity (3 lt) of water and make into a paste by stirring. Then add the remaining quantity of water (72 lts) and mix thoroughly. Allow the solution to stand (covered) for some time (10 min) and then use the supernatant for disinfection/or pass (filter) the disinfectant solution through muslin cloth an use only the supernatant for spraying. The undissolved particles can be used in the compost pit while burying diseased materials.

3.2 Preparation of 2% formalin + 0.05% detergent solution: To prepare 2% formalin + 0.05% detergent solution, mix one part of 36% formalin with 17 parts of water. Then add 0.05% detergent to the total formalin solution.

To prepare a known volume of 2% formalin + 0.05% detergent solution, divide the total quantity of the solution required by 18 to get the quantity of formalin required. To this formalin, add water to make it up to the required quantity. Mix 0.05% (0.5 g/lt) detergent to the total disinfectant.

Example:

            Required quantity of 2% formalin + 0.05% detergent solution = 75 lts. To prepare 75 lts. divide the required quantity by 17 to obtain the quantity of formalin required, i.e., 75/17 = 4.17 lts. To obtain 75 lts. of disinfectant, mix 4.17 lts. of formalin (36%) to water (75.00 – 4.17 = 70.59) and make upto 75 lts. i.e., 4.17 + 70.83 = 75 lts. To obtain 0.05% detergent in 2 % formalin, the quantity of detergent to be added is 0.5 g in one lt. For 75 lt. of 2% formalin, mix 75 x 0.5 = 3.75 g of detergent.

3.3 Preparation of 2.5% Sanitech (Chlorine dioxide) in 0.5% slaked lime solution: Required quantity of 2.5% Sanitech in 0.5% slaked lime = 75 lts. To prepare 1 lt. of Sanitech in 0.5% slaked lime solution, the requirement is 25 ml of Sanitech + 2.5 g activator crystals + 5 g of slaked lime.

Preparation

Solution A:  Add 2.5 g of activator crystals to 25 ml of Sanitech solution, stir and allow 5 minutes to stand. Colour changes to light yellow.

Solution B:  Mix 5 g of slaked lime powder in water and make it up to 975 ml of water. Mix solution A with solution B. The disinfectant (~ 1 lt) is ready for disinfection. To prepare 75 lts. of Sanitech in 0.5% slaked lime solution; the requirement of Sanitech is 75 x 25 ml = 1.875 lts., activator crystals 75 x 2.5 g = 187.5 g (188 g), slaked lime powder 75 x 5 g = 375 g, water 75 x 975.5 ml = 73.125

Preparation

Solution A:  Add 188 g (3¾ packets) activator crystals provided with every litre Sanitech to 1.875 lts. of Sanitech, stir and allow 5 minutes to stand. Colour changes to light yellow.

Solution B:  Mix 375 g of slaked lime powder in water and make it up to 73.125 lts. of water. Mix solution A with solution B (1:40). The disinfectant (75 lts) is ready for disinfection.

3.4 Disinfection of rearing house, appliances, etc. inside the rearing house:

Spray using powerful jet sprayer, the required quantity of disinfectant @ 2.0 lt/m² floor area of rearing house + 10% for outside of rearing house +25% of disinfectant solution for appliances) uniformly to drench all parts of rearing house inside and outside, and appliances. Keep the rearing house closed for a minimum period of 6-10 hours. Disinfect bamboo mountages with 2% formalin solution. Do not spray bleaching powder solution to the mountages. After minimum period of 18-24 hours, shift the rearing appliances out of rearing house and sundry for 10-12 hours. Do not smear cowdung to the rearing trays and store them inside the rearing house till 5 days prior to next brushing.

(Silkworm rearing using the mulberry shoot do not require the rearing trays but uses the platform. Rearing trays are the main source of infectious agent and most difficult and expensive to achieve disinfection. To avoid this, changing over to rearing silkworm on shoot is advantageous. This method does not require additional disinfectant for appliances as only the rack and nylon nets are used.)

3.4 Disinfection prior to brushing: Disinfection process should start 4-5 days prior to brushing. However, the eggs may be incubated in a separate disinfected incubation room.

3.4.1 Five days before brushing: The rearing house and appliances are cleaned, washed in water. If trays and other appliances namely, basins, vinyl sheet, leaf basket, etc., are used, conduct additional disinfection by dipping them in disinfectant or spraying disinfectant.

a) Dipping in disinfectant: Disinfect the rearing appliances that could be disinfected with 2% bleaching powder in 0.3% slaked lime solution by dipping them for 10 minutes in the solution in a disinfection tank. A tank of 2 feet depth and 4 feet diameter is suitable for disinfection. Prepare the disinfectant solution to fill half of the height of the tank. To determine the quantity of disinfectant solution to be prepared in the tank, calculate the volume of the tank using the formula л r²h.

Example:

            Tank of 4 feet diameter and height of 2 feet, then the volume is л r²h (radius: r) = d/2, d = diameter (half the height = 1 foot)= 3.14 x 2 x 2 x 1 = 12.56 cubic feet.1 cubic foot holds 28 lts of solution. 12.56 cubic feet holds 12.56 x 28 = 352 lts. Prepare 2% bleaching powder in 0.3% slaked lime solution (352 lts) as described above. To prepare 1 lt of 2% bleaching powder in 0.3% slaked lime solution, the requirement is 3 g of slaked lime and 20 g bleaching powder. Mix the slaked lime into water after making paste as suggested earlier.

Example:

To prepare 352 lts of 2% bleaching powder in 0.3% slaked lime solution, the requirements are 352 litres of water, 352 x 20 g of bleaching powder = 7.040 kg and 352 x 3 g of slaked lime = 1.056 kg. Mix 1.056 kg of slaked lime powder and 7.040 kg of bleaching powder in 12 lts of water and make it into paste by stirring. Then pour it into disinfection tank and add remaining quantity of water (340 lts) and mix thoroughly. For disinfection, prepare the disinfectant solution to fill half the tank and dip the appliances to submerge completely. Dip as many appliances as possible to submerge in the disinfectant solution. Leave the appliances submerged for at least 10 minutes. Dip another set of appliances for disinfection. 8-10 dips may be made in the disinfectant solution. Fresh solution should be prepared and used after 10 dips. After dip disinfection, shift the appliances directly into disinfected rearing room and allow them to dry.

b) Disinfection by spraying: Disinfection of appliances by dipping in disinfectant is the best method. However, where the facility of disinfection tank is not available, the following method is advised. Disinfect the appliances using 2% formalin + 0.05% detergent solution or 2.5% of Sanitech in 0.5% slaked lime or with 2% bleaching powder in 0.3% slaked lime solution. Spray the disinfectant @ 35 ml/sq. ft. surface area or 700 ml for a tray of 3.6 feet diameter. After the spray, put them together and keep completely covered with vinyl sheet for a minimum period of 6 hours. Disinfect the mountages also, following the above method.

3.4.2 Four days before brushing: Sun dry the appliances. If the prevalence of viral diseases (Grasserie and Flacherie) were high during the previous crop, spray 0.3% slaked lime in water (3 g/lt) to the rearing house and appliances @ 2 lt/sq.m floor area + additional requirements. Sun dry the appliances after 1-2 hour of spray.

3.4.3 Three days before brushing: Conduct second disinfection of rearing house and appliances. Shift all the disinfected appliances into the disinfected rearing house and arrange in the room. Disinfect the rearing house and appliances by spraying 2% bleaching powder in 0.3% slaked lime solution or 2.5% Sanitech in 0.05% slaked lime or 2% formalin + 0.05% detergent solution. The quantity of disinfectant solution required is calculated and sprayed as per the first disinfection. After disinfectant spray, keep the room closed preferably for 24 hours. The second disinfection may follow the first if the gap between the two is not much.

3.4.4 Two days before brushing: Dust 5% bleaching powder in slaked lime powder @ 200 g/sq.m at the entrance of the rearing house and the passage to it. Sprinkle water @ 1 lt/sq.m floor area. Open the windows of the rearing house and ventilate to drive off all the adour of disinfectant. Prevent the entry of unauthorized persons into the rearing room to avoid contamination of rearing house and appliances.

Estimation of requirement of disinfectant dust for floor disinfection:

Floor area (sq.m) x 0.200 = kg of dust required for dusting

Floor area (sq.ft) x 0.018 = kg of dust required for dusting

Preparation: 5% bleaching powder in slaked lime powder.

Preparation of 1 kg: Mix 50 g of bleaching powder in 950 g of fine slaked lime powder.

3.4.5 One day before brushing: Arrange appliances for chawki rearing and maintenance of hygiene. Keep the later instar rearing room and mounting hall closed and open only one day before the later instar larvae are to be shifted into the rearing house.

3.5 Disinfection and maintenance of hygiene during silkworm rearing: 

• Avoid borrowing the rearing appliances. Do not use appliances without disinfection. Avoid overlapping rearings.

• Maintain personal and rearing hygiene throughout the rearing. Special consideration for maintenance of hygiene be given during the chawki stage. Restrict the entry of persons into the rearing house.

• Surface disinfects the silkworm eggs before head pigmentation stage with 2% formalin for 5-10 minutes and wash with water. Dry them in shade and incubate following the guidelines.

• At the passage to entrance of rearing house, sprinkle 5% bleaching powder in slaked lime @ 18 g/sq.ft. An area of 6 x 8 feet may be covered.

• Rearer and any person entering into the rearing house must disinfect foot and hard before entry. These persons should step on foot mat at the entrance containing a mat soaked in 2% bleaching powder in 0.3% slaked lime solution. Ultimately a disinfection tank of 2 x 1½ ft. x 3 inch may be made and filled with 2% bleaching powder in 0.3% slaked lime solution. Replace the disinfectant everyday.

• Wash hands with two 2% bleaching powder in 0.3% slaked lime solution or “Suchi” and then rinse with clean water. Replace the disinfectant everyday.

• Pick up diseased/unequaled/suspected disease worms and disposed into 5% bleaching powder in slaked lime in basin. Keep in basin covered with a lid and change every 3-4 days.

• Disinfect the hand after picking the diseased worm by washing in 2% bleaching powder in 0.3% slake lime solution or by “Suchi” solution.

• Clean the silkworms rearing bed using bed cleaning net and disinfect after every use by dipping in 2% formalin solution for 10 minutes. Wash hands with disinfectant.

•  Spread vinyl sheet for collection of bed refuse and shift bed refuse into manure pit. Disinfect the vinyl sheet after use every day by dipping in 2% bleaching powder in 0.03% slaked lime solution.

• Rare silkworms always on rearing seat paper (newspaper). Change as and when soiled.

• Wipe the floor after cleaning with 2% bleaching powder in 0.3% slake lime solution or by “Suchi” solution. If the floor is a mud floor, dust 5% bleaching powder in slaked lime at an interval of 3-4 days.

• Dust the bed disinfectant as per the schedule, quantity and precaution. Feed 30 minutes later. While extending the bed also, apply bed disinfectant to the empty tray.

• Do not store mulberry leaves inside the rearing room. Store in a separate disinfected room.

• Feed good quality and sufficient quantity mulberry leaves for robust larval growth. Provide recommended spacing sufficient ventilation for healthy growth of later instar worms.

• Avoid contamination of mulberry. Use separate baskets for collection of mulberry and feeding worms.

• Avoid injury to silkworms while rearing and mounting for spinning cocoons. Sprinkle bleaching powder in mounting place.

• Pick diseased and non-spinning larvae from mountages and dispose them into 2% bleaching powder in 0.3% slaked lime solution in a basin. Wash hands and feet while coming out or rearing house/mounting hall, etc. after completion of work at every visit.

3.6 Disinfection of silkworm body and rearing seat: It is most important to disinfect the silkworm body and rearing seat with bed disinfectants for containing secondary contamination and to improve the hygiene during rearings.

Precautions

• Do not dust on the silkworms settled for moult or under moult.

• Do not dust on the silkworms where eatable mulberry leaves are available.

• Dust uniformly as per schedule, quantity and with precautions. Feed after 30 minutes.

• While dusting, protect eyes, nose, ear and mouth. Wash hands thoroughly after dusting bed disinfectants.

•  Keep disinfectants away from children.

COST WORKED OUT FOR DISINFECTION AND MAINTAINING HYGIENE DURING SILKWORM REARING FOR CROP OF 150 DFLS

Primary disinfectants : Formalin

SUMMARY: Total quantity of disinfectant required

*= Detergent; += Slaked lime

Adoption of silkworm rearing on mulberry shoot reduces the expenditure on disinfection and hygiene by Rs. 120 – 140/-

Primary disinfectant: Bleaching powder

C. SILKWORMS DISEASES AND PESTS-CONTROL MEASURES

I. SILKWORMS DISEASES -CONTROL MEASURES

a. MUSCARDINE AND APERGILLOSIS: Muscardine and Aspergillosis are fungal diseases of silkworm.

1.  Occurrence

The diseases prevail during winter and rainy season in all sericultural areas. The chawki rearing conditions are congenial for aspegillosis.

2.   Causative agent

White muscardine is caused by a fungus, Beauveria bassiana. Apergillus is caused Aspergillus flavus, A. oryze and A. tameri.

 i.        Symptoms: The larvae loose appetite, become inactive and on death, gradually, they become harder and finally mummifies. The fungus overgrow the larvae, develops fruiting body and produce conidia on the surface giving white colour to the mummified diseased silkworm. (White muscardine). Aspergillosis generally infect early instar silkworm. The early instar silkworm becomes inactive and dies without clear morphological symptoms. Late instar silkworm develops black spot at the site of infection and dies due to Aflotoxin by the fungus.

ii.          Predisposing factors: Low temperature and high humidity to white muscardine. High temperature and high humidity for Aspergillosis.

iii.  Source of pathogen: Mummified/diseased silkworm, contaminated rearing environment, rearing house, appliances and alternate hosts (Most lepidopteran pests). Aspergillus sp. are common in the environment growing as a saprophyte.

iv.           Transmission: The conidia of the pathogen are dispersed by wind or contact. The conidia on contact with host integument, germinate, penetrate into the body cavity and cause disease. The contaminated rearing environment, house, appliances and alternate hosts also form source for the spread of the disease.

 v.            Prevention/control of Muscardine and Asprgillosis

1. Practice disinfection of silkworm rearing house, surroundings, appliances and silkworm egg surface. Aspergillus sp. are comparatively more tolerant to formalin hence, 3% formalin solution is suggested.

2. Practice hygienic measures during silkworm rearing. Ensure the measures for destruction of diseased silkworm.

3. Regulate humidity by dusting slaked lime at the time of every moult and in between, if necessary to keep the rearing bed dry. Provide good ventilation.

4.  Apply bed disinfectant as per recommended scheduled and quantity.

5. As s specific measure, dust 1-2% for 3^rd, 4^th and final instars) of Dithane M45 in Kaolin or Captan in slaked lime on silkworm body immediately after every moult and on the 4^th day final instar @ 3-5 g/sq. ft. Alternately, apply formalin chaff to surface disinfect silkworm body. Formalin chaff is prepared by partially burning paddy husk and mix formalin of concentration of 0.6%/0.8% (0.6% formalin chaff is for chawki worms and 0.8% for later stages) in the ratio of 10:1. The chaff is sprinkled uniformly on the worms after every moult and paraffin/old newspaper is covered for 30 min. Feeding should be given afterwards.

6. Feed good quality of mulberry, provide requisite spacing and ventilation. Maintain the required temperature and humidity.

b. NUCLEAR POLYHEDROSIS (GRASSERIE)

Nuclear polyhedrosis is a major viral disease commonly known as Grasserie or Haluthode.  

1.  Period of occurrence: The disease prevail although the year but is insentive during summer and rainy seasons.

2.   Causative agent: Bombyx mori nuclear polyhedrosis virus, a baculovirus.

3. Symptoms and nature of damage

3.1 At the early stage of infection: The infected silkworm appears normal and microscopic examination of the haemolymphy may indicate the presence of nuclear polyhedra with in the nucleus of haemocyte.

3.2 Late stage of infection: The skin becomes shining before moulting and fails to moult. The integument will be fragile and the intersegmental region becomes swollen. The haemolymph becomes tubid white and contains large number of polyhedra which are hexagonal.

3.3 Infection: Silkworm gets infected when it feeds on contaminated mulberry leaves.

3.4 Sources of infection: Disintegrating diseased silkworm, its body fluid, alternate hosts and contaminated silkworm rearing house and appliances.

3.5 Pre-disposing factor: High temperature, humidity and poor quality of mulberry.

3.6 Transmission: The disease is transmitted by secondary infection of larvae feeding on the contaminated mulberry.

3.7 Spread of disease: The diseased silkworm extrudes the pathogen along with oozing body fluid during to injury and breakage of dead diseased larvae. The body fluid and dead broken larvae contaminate the rearing house, appliances, surrounding and mulberry. The disease spreads to the healthy silkworm on feeding the contaminated mulberry.

3.8 Control/prevention of the disease

• Practice disinfection of silkworm rearing house, surroundings, appliances and silkworm egg surface. A spray of 0.3 % slaked lime solution in addition to usual disinfection procedure is recommended for rearing house and appliances in the case of high incidence of disease.

• Practice hygienic measures during silkworm rearing. Ensured the measures for destruction of diseased silkworm.

• Identify and picked out infected larvae in the early stages.

• Apply any bed disinfectant as per recommended schedule and quantity.

• Maintain optimum rearing temperature and avoid drastic changes in temperature.

• Feed good quality of mulberry in sufficient quantity.

c. FLACHERIE

Flacherie is a syndrome associated with Infectious Flacherie, Densonucleosis, Cytoplasmic polyhedrosis, Bacterial diseases and Thatte roga in silkworm.

1.  Period of occurrence

The disease prevail although the year but is insentive during summer and rainy seasons.

2.  Causative agent

The disease is caused by Bombyx mori virus (infectious Flacherie) and Bombyx mori densonucleosis virus (Densonucleosis) and Kenchu virus. Flacherie may be caused by these viruses individually as well as in association or each in association with Streptococci/Staphylococci bacteria (Thatte roga). Cytoplasmic polyhedrosis is caused by a Reovirus, Bombyx mori cytoplasmic polyhedrosis virus. Streptococci sp., Streptococci sp. Basillus sp. and Serretia bacteria, individually and in association cause bacterial flacherie.

3. Symptoms

3.1 At the early stage of infection: Symptoms are typical at the early stage of infection. Larva becomes lethargic and loose appetite.

3.2 At the later stage of infection: The Larva becomes soft and flaccid. Retards in growth, becomes dull, vomits gut juice and faeces becomes sort with high moisture content. The cephalothoracic region becomes translucent (Infectious Flacherie, Densonucleosis and Cytoplasmic polyhedrosis).  The midgut becomes turbid white due to formation of polyhedra and the faeces whitish black (Cytoplasmic polyhedrosis).  The larvae ferments, turn different colour and smell foul (Bacterial diseases). Sometime symptoms of toxicosis are observed (Bacterial toxicosis).

3.3 Infection: Silkworm gets infected when it feeds on contaminated mulberry leaves.

3.4 Sources of infection: Dead/diseased silkworm, its faecal matter, gut juice, body fluid, alternate hosts contaminated rearing house and appliances.

3.5 Pre-disposing factor: Fluctuation in temperature, humidity and poor quality of mulberry.

3.6 Transmission: The disease is transmitted by secondary infection of larvae feeding on the contaminated mulberry. The diseased silkworm extrudes the pathogen along with gut juice and faecal matter throughout the incubation period of infection. The disintegrating diseased larvae also extrude pathogen into the environment. The pathogen contaminates the rearing house, appliances, surrounding and mulberry. The disease spreads to the healthy silkworm on feeding the contaminated mulberry.

3.7 Control/prevention of the disease

• Practice disinfection of silkworm rearing house, surroundings, appliances and silkworm egg surface. A spray of 0.3 % slaked lime solution in addition to usual disinfection procedure is recommended for rearing house and appliances in the case of high incidence of disease.

• Practice hygienic measures during silkworm rearing. Ensured the measures for destruction of diseased silkworm.

•  Identify and picked out infected larvae in the early stages.

•  Apply any bed disinfectant as per recommended schedule and quantity.

• Pick out diseased as early as possible and destroy them in disinfectant or by burning.

• Feed good quality of mulberry, provide requisite spacing and ventilation. Do not feed wet mulberry. Provide good environment. Maintain the required temperature and humidity.

II. SILKWORM PESTS -CONTROL MEASURES

a.  USI FLY, Exorista bombycis

The uzi fly, Exorista bombycis (Louis) (Diptera: Tachinidae) is a serious endo-larval parasitoid of the silkworm, Bombyx moriL. The pest was introduced accidentally into Karnataka in 1980. Since then, the pest has been inflicting considerable loss to sericulture industry. At present, he loss is estimated to be ranging from 10 to 20%.

1.     Period of occurrence

The pest occurs throughout the year. Its incidence is maximum from August to November.

2.     Symptoms and nature of damage

Presence of black scar on the body of parasitised silkworms and maggot emergency hole in cocoon indicate uzi infestation.

The silkworms parasitized in early stars are killed before attaining spinning stage, while those parasitised in the late V instar spin cocoons of weak built and from such cocoons uzi maggots emerge by piercing, thus rendering cocoons unfits for commercial reeling.

3.   Life-cycle

Every gravid fly lay 1-2 eggs on each silkworm. The eggs hatch in 2-3 days and young maggots pierce into the host body and devour the body tissues. The maggots after spending 5-8 days of parasitic life, emerge from the host body.

After emergence they lead 12-20 hours of post-feeding life and pupate in the loose soil, crevices on the rearing house floor, dark areas on the floor in the rearing house. The pupal stage last for 10-12 days  the life cycle is completed in 18-24 days.

4.  Management practices

4.1 Cultural/mechanical

• Collect and destroy the uzi fly infected silkworms, uzi maggots and pupae.

•  Keep the rearing house free from cracks and crevices.

• Uzi infected larvae spins cocoon a day or two earlier than the other silkworms. Such cocoon should be harvested separately and stifled.

4.2 Exclusion method: Fix wire mesh or nylon net to the windows of the rearing house with an arrangement for ante-room at the entrance of the rearing house.

4.3 Chemicals

4.3.1 Uzitrap: It is a chemotrap used for attracting and killing the adults. Dissolve one tablet in one litre of water and the solution should be taken in light coloured flat trays or plates (10" diameter, or 10" Lx 8" B) ad place near the window (at the height of their base) both inside and outside the rearing house. The window needs to be provided with nylon net/wire mesh. In case there is a nylon net enclosure in the rearing house, on or two containers with uzitrap solution should be placed. The solution should be used starting from III instar of silkworm through spinning stage. If dust, dead insects, etc. , accumulate in the trap solution, fresh solution should be prepared and used. One tablet of uzitrap containing 12 tablets is sufficient for 100 dfls rearing.

4.3.2 Uzicide: It is a liquid ovicidal formulation. It is sprayed on the body of the silkworms starting from the second day of the the 2nd day in III instar through 4th or 6th day in V instar on alternate days except the period of moulting. Uzicide should be sprayed after bed cleaning or 2-3 hours after feeding. Silkworms should be fed half an hour after spraying uzicide. Four to five litres of uzicide is required for rearing silkworms from 100 layings.

4.3.3 Uzi powder: It is an ovicidal dust formulation. It is dusted on the body of the silkworm on 2nd during III instar, 2nd and 4th days during IV instar and 2nd, 4th and 6th days in V instar. Uzi powder should be dusted after bed cleaning and silkworms should be fed half an hour after dusting. Four to five litres of uzi powder is required for rearing silkworms from 100 layings.  Top