Diseases and Pests Management

Diseases and pests of silkworms

Diseases and pests of mulberry silkworm

Grasserie

• Causal organism: Nuclear Polyhedrosis Virus.
• Peak Season: The disease prevails all through the year but is intensive during summer and rainy seasons

Symptoms:

• The skin of worms becomes shiny before moulting and fails to moult.
• The infected worms move restlessly along the rim of the trays.
• The inter segmental swelling appears and the color of the body becomes yellowish.

Source of infection:

Silkworm get infected when it feed on contaminated mulberry leaves, disintegrating diseased silkworms, its body fluid , alternate host and contaminated rearing house & appliances.

Pre disposing factor: High temperature, high humidity and poor quality of mulberry leaves.

Management

• Practice disinfection of silkworm rearing house, surroundings, appliances and silkworm egg surface.
• Disinfect the rearing room and appliances with 0.5% bleaching powder solution.
• Do not feed tender leaves in the late instars.
• Avoid overcrowding.
• Remove and disposed diseased larvae carefully.

Flacherie

• Causal organism: Infectious flacherie Virus.
• Peak Season: April-September.

Symptoms

• The infected worms show loss of appetite.
• Head and thorax become translucent.
• Growth and development of the worms become irregular due to shrinkage of the body.
• Retarded growth, empty foregut and midgut.
• The worms die due to diarrhea followed by vomiting of gastric juice.

Source of infection: Silkworms get infected when it feeds on contaminated leaves.

Pre disposing factor: High temperature, humidity and poor quality mulberry leaves.

Management

• Disinfect the rearing room and appliances with 0.5% bleaching powder solution and use labex.
• Rear silkworm under optimum temperature and humidity.

Black Thorax Septicimia

• Causal organism: Bacillus spp.
• Peak Season: April-June.

Symptoms

• Swollen body.
• The thoracic region of the infected worms become blackish, body shrinks.
• Excretes soft and liquid like excrements, rotting of the body follows with excretion of dark brown fluid.
• Sluggish movement and low appetite.
• Immediately after death thoracic region becomes black.

Source of infection: Through wound injury.

Pre disposing factor: Mishandling of worms during transfer.

Management

• Maintain hygienic condition in and around rearing room.
• Avoid injury to the larvae.
• Avoid overcrowding and accumulation of faeces in the rearing beds.
• Rear silkworm under optimum temperature and humidity.

White Muscardine

• Causal organism: Beauveria bassiana.
• Peak Season: November to April.

Symptoms

• Presence of moist specks on the skin.
• Larvae lose appetite and become inactive.
• Vomiting and diarrhea, hard and stiff body.
• Mummified larvae covered with white woody aerial mycelia and presence of conidia.

Source of infection: Through wound injury.

Management

• Disinfect the rearing room and appliances with 0.5% Bleaching powder solution.
• Avoid low temperature and high humidity during rearing.
• The diseased larvae should be removed from the tray before they get mummified.
• Use 0.6% formalin charff/ Labex or Dithane-M45/ Captan with Kaolin.

Pebrine

• Causal organism: Nosema bombysis.
• Peak Season: Non- seasonal.

Symptoms

• Irregular size of the body as well as irregular hatching of eggs and moulting.
• Larval body shows wrinkled skin.
• Black pepper-like spots appear on the body of the infected worms.
• White postules appear on the silk gland when examined under microscope with presence of spores.

Management

• Disinfect the rearing room and appliances with 0.5% Bleaching powder solution.
• Strict mother moth examination and surface sterilization of dfls.
• Control mulberry pests in the field.
• Feed worms with mulberry leaves sprayed with 3-4% Bavistine.

Uzi fly (Exorista bombycis)

Nature of damage: The uzi fly is a serious endoparsitoid of silkworm inflicting of cocoon yield of 10-30%. The fly lays eggs on the integument of the worms in the dorsal and dorso-lateral side. After hatching from the eggs, the maggots of the fly penetrate into the larval body and feed on the tissue of the worms. The mature maggots come out of the larvae/pupae and undergo pupation in the rearing field or grainage hall. The uzi infested mulberry silkworm dies during larval or pupal stage.

Season of incidence: April to September with maximum infestation wet

summer months (July-September).

Management: For successful control of uzi infestation integrated management strategy is taken up involving physical, chemical and biological method judiciously in combination.

Physical

• Fixing of fly-proof wire mesh or nylon nets on ventilators. Windows and doors to prevent the entry of Uzi flies into the rearing house.
• Creation of physical barrier by covering a fly-proof curtain around the rearing stand to exclude the gravid flies from silkworms.
• Sealing of cracks and crevices in the floor to prevent maggots from getting shelter under the floor for pupation followed by emergence of adult flies inside the rearing house.
• Dusting of levigated china clay on the body of the spinning silkworms on the mountages @ 3-4 g/100 worms/ sq. ft. of the montages prevents sticking of uzi-eggs laid on the body of the silkworms.
• Regular collection of uzi maggots & pupae and infested silkworm larvae from rearing trays and mountages and destroying them immediately by putting them into hot water.
• Drying of commercial cocoons should be made immediately after harvest on the 5th day to kill the maggots inside the cocoons.
• Regular collection of uzi maggots and puparia in the cocoon markets and reeling establishments and destroying them immediately.
• Killing of adult flies at once if found inside the rearing house.
• Transportion of the seed cocoons having uzi infestation must be stopped to such an area where there is no incidence of uzi infestation.
• Rearing holiday for a period of 45-60 days should be maintain between the rearing seasons for natural regulation of uzi population.
• Use uzitrap; a chemotrap to attract and kill the adults of uzi fly.

Chemical

• Spraying of 2% bleaching powder solution to uzi infested silkworms during 2nd & 4th day of 3rd instar, 2nd, 4th & 6th day of 4th instar and 2nd, 4th, 6th & eight day of 5th instar can kill uzi eggs laid over the silkworm body and able to protect 3-5 kg of cocoons.
• Use of uzicide on silkworm larvae can kill the eggs of uzi fly.

Source:

• Package of practices of Muga, Eri and Mulberry Sericulture for North Eastern region of India, 2005, Central Muga  Eri Research & Training Institute, Lahdoigarh, Jorhat, Assam.
• Directory of Sericulture Technology 2008, Karnataka State Sericulture Research and Development Institute,  Bangalore- 560 062.

Diseases and pests of muga silkworm

Pebrine disease

Pebrine is the most serious disease of muga silkworm caused by a protozoan of Nosema sp. It is unique in being transmitted to offspring by transovarial/ transovum means from other moths. If infection is primary, more than 50% larvae die before 3rd moult and rarely any larva goes for spinning. When healthy larvae get infected through contamination during rearing, it is called secondary infection. Secondary infection during early 4th larval stage leads to formation of flimsy cocoons, whereas larvae infected during 5th larval stage form well formed cocoons.

Peak season: Throughout the year.

Symptoms

Early stage of infection

• The infected silkworm larvae appear normal. However, microscopic examination of silkworm larvae may indicate the presence of spores of the pathogen.

Later stage of infection

• The silkworm larvae loose appetite, vary in size, retarded growth, moult irregularly and the colour of the larvae become light yellowish green instead of deep green colour (normal healthy larvae).
• The infected late stage larvae show black dots or specks on the surface of the body and hence the disease is known as Phutuka (spotted disease in Assamese).

Sources of infection

Egg stage

• Transovarial.
• Surface contamination of eggs (transovum).
• Contaminated grainage appliances.

Larval stage

• Contaminated egg laying kharika.
• Transovarially infected larvae.
• Faecal materials of infected larvae.
• Contaminated foliage.
• Contaminated rearing site.
• Contaminated rearing appliances.

Moth stage

• Infected seed cocoons.
• Infected moth.
• Infected grainage appliances.
• Meconium and moth scales.
• Grainage dust.

Spread of the disease: Pebrinized larvae extrude faecal material, gut juice and vomit which contaminate the rearing environment, appliances and host plant foliage. Mostly, consumption of contaminated foliage/ egg shell results in spread of the disease.

Management

• Scientific inspection of individual mother moths for detection of pebrine during egg production.
• Disinfection of grainage appliances with 2% formalin before and after every grainage operation.
• Use microscopically tested disease free disinfected eggs only.
• Surface sterilization of eggs with 2% formalin for 5 minutes.
• Maintain hygienic condition in egg production room and rearing sites.
• Follow cellular method of rearing for basic stock maintenance.
• Disinfection of rearing appliances before use.
• Check the faecal materials, unequal/ lathergic/ unsettled irregular moulters periodically.
• If pebrine spores are detected, reject the entire infected crop.

Source: Central Muga Eri Research & Training Institute, Lahdoigarh, Jorhat, Assam

Flacherie

Flacherie; commonly known as anal protrution is a syndrome of bacterial diseases in muga silkworm caused by Pseudomonas sp. Sometimes it is caused by an ultra virus, which acts as an exciting agent followed by secondary infection of bacteria. Sudden fluctuation in temperature and humidity, bad weather, poor quality leaves with high water content are predisposing factors. Peak season: Throughout, intensive during rainy summer months (June to August).

Symptoms

• The infected larvae become lethargic and motionless.
• The colour of the haemolymph turns black.
• Excreata looks like chain.
• Sealing of anal lips.
• Rectal protrusion.
• Infected larvae die within a short time.

Source of infection

• Larvae get infected upon feeding of contaminated/ poor quality leaves of host plants.
• Diseased larvae, its gut juice, faecal material, body fluid.
• Contaminated rearing site and appliances.

Spread of the disease

• Secondary infection of larvae due to feeding on contaminated leaves.
• Infected worms ooz-out body fluid containing pathogen throughout the incubation period and contaminate the rearing environment.
• Feeding of late stage worms with very tender succulent leaves.
• Sudden fluctuation of temperature and humidity during rearing period.

Management

• Use disinfected good quality seeds of disease free zones.
• Orient the brushing to protect the young larvae form direct sun shine.
• Disinfection of rearing site with 2% formalin solution before rearing.
• Dust 3% slaked lime in addition to formalin in case of high incidence of the disease in the preceding year.
• Inspect rearing field regularly and pick out stunted/ sluggish/ irregular moulters and destroy.
• Destruction of diseased/ doubtful worms by burying with 5% formalin solution.
• Wash the hands with formalin solution at the time of transfer of worms.
• Maintain hygienic condition during rearing.
• Feed with good quality disease free leaves.
• Do not feed late stage worms with tender succulent leaves.

Grasserie

It is a major viral disease of muga silkworm caused by a baculovirus. High temperature clubbed with high humidity, poor quality host plant leaves are predisposing factors.
Peak season: Throughout the year, predominant during rainy summer months of the year.

Symptoms

• The silkworm larvae fail to moult.
• The integument becomes fragile and intersegmental region becomes swollen and that is why the disease is known as Phularog (swelling disease in Assamese).
• The body tissues and haemolymph of the infected larvae get disintegrated into turbid white fluid and the larvae hang upside down with the anal claspers after dying.
• The turbid fluid contains large number of hexagonal polyhedral bodies.

Source of infection

• Feeding of contaminated foliage.
• Disintegrating diseased silkworms, their body fluids.
• Contaminated rearing sites and appliances.

Spread of the disease: The diseased silkworm larvae extrude the pathogen along with oozing of body fluid due to injury and breakage of dead and/ or diseased larvae. The body fluid and broken body parts of the larvae contaminate the foliage, rearing site and appliances. The disease spreads to healthy worms on feeding of the contaminated leaves and/ or use of contaminated appliances during rearing.

Management

• Disinfection of rearing site with 2% formalin solution before rearing.
• Dust 3% slaked lime in addition to usual disinfection in case of high incidence of disease in preceding rearing.
• Pick out growth retarded/ lethargic/ irregular moulters and destroy.
• Ensure destruction of diseased/ doubtful worms by burning or burying with 5% formalin solution.
• Ensure proper hygiene during rearing.
• Use certified disinfected disease free layings only.
• Ensure rearing on good quality leaves.

Mascardine

Mascardine is one of the major diseases of silkworm. However, it is less prevalent in muga silkworm and occurs under certain specific environmental influence only. The disease appears at an interval of 2-3 years. The causal organism is a fungus and it is yet to be identified for muga silkworm. Low temperature with high humidity is predisposing factors. Peak season: Winter months of the year when night temperature falls down and the day temperature remains comparatively high associated with high humidity i.e. foggy weather.

Symptoms

• Infected larvae loose appetite and become inactive.
• Colour of the larvae turns pale.
• Gradual cease of movement within 12-18 hours of infection.
• The larvae hang on tree twig/ trunk and harden.
• The larvae die within 16-18 hours of infection.
• A white encrustation appears on the larval body and it covers the whole larval body within 24 hours of death.
• The dead larval body becomes dry, brittle and mummified.

Source of infection

• Mummified / diseased larvae.
• Contaminated rearing environment.

Spread of the disease

• The conidia/ spores of the pathogenic fungus are dispersed by wind.
• The conidia on contact with larval integument germinate, penetrate into the larval body and cause infection.

Management

• Orientation of brushing towards sun shine during winter.
• Disinfection of rearing site with 2% formalin solution before rearing.
• Dust slaked lime in the field to control humidity at the time of rearing.
• Dust Tasar Kit Oushad developed by CTR&TI, Ranchi on the body of the larvae at the time of transfer.
• Spray 0.5% sodium hydroxide solution on the worms after 24 hours of each moult as prophylactic measure.
• Maintain hygienic condition during rearing.
• Collection and destruction of dead/ diseased larvae
• Pickout sick or dead worms with forceps/ chopstick and put in 2% formalin solution.
• Bury the carcasses in a pit and cover the soil.
• Wash hands with formalin or dettol solution after handling dead or infected larvae.
• Do not allow birds, ants or poultry to eat the carcasses.

Uzi fly (Exorista sorbillans)

Nature of damage: It is the major pest of muga silkworm. The fly lays eggs on the integument of the worms in the dorsal and dorso-lateral side. After hatching from the eggs, the maggots of the fly penetrate into the larval body and feed on the tissues of the worms. The mature maggots come out of the larvae/ pupae and undergo pupation in the rearing field or grainage hall. The uzi infested muga silkworm dies during larval or pupal stage. Season of incidence: Prevalent throughout the year, peak during December to march.

Management

• Rear the silkworm under nylon mosquito net during peak infestation period (December to March), which ensures 80-90% control.
• During transfer of late stage worms, remove the fly eggs from the integument of the silkworm larvae with the help of forceps.
• Keep the rearing field clean and dust with bleaching powder during rearing.
• Mount uzi infested worms in separate Jali.
• Harvest and stifle the uzi infested cocoons on 4th and 5th day of spinning.
• Collect and destroy the maggot/ pupae of the fly.
• Burn heavily infested worms.

Apanteles (Apanteles stantoni)

Nature of damage

Usually infect the early stage silkworms. Apanteles lays eggs inside the body of silkworm larvae by inserting the ovipositor through the tubercles after maturation. The mature maggots form pupae in aggregation outside the body of the silkworm larvae.
Season of incidence: Prevalent during summer and winter months of the year.

Management

• Rearing of silkworm under nylon mosquito net.
• Keep the rearing field clean and dust with bleaching powder during rearing.
• Collect and destroy the maggots/ pupae of the fly along with the silkworm larvae.

Spider: Attacks 1st instar worms

Wasp (Vespa orientalis)

It occurs during June-July to August-September months. It attacks early stage worms by lacerating and picking young age worms. It can be controlled by covering silkworm rearing by nylon nets and destroying hives.

Red ants

The red ants are also serious pest in many muga growing areas. It attacks 1st stage worms. The lost due to red ants are reported to be 5-10%. They can be controlled with the spray of 2% Rogor (insecticide) before 15 days of rearing or burning down their nest well before the rearing.

Grass hopper: They attack the 2nd to 3rd stage worms. Lost due to grass hoppers are minimal

Source:

• B.K. Singh, N. Tiken Singh, 2010, Muga Silkworm Seed Organization (MSSO), P-4 Unit, Mendipathar, East Garo  Hills, Meghalaya.
• Package of practices of Muga, Eri and Mulberry Sericulture for North Eastern region of India, 2005, Central Muga  Eri Research & Training Institute, Lahdoigarh, Jorhat, Assam.
• Directory of Sericulture Technology 2008, Karnataka State Sericulture Research and Development Institute,  Bangalore- 560 062.

Diseases and pests of eri silkworm

Pebrine

• Causal organism: Protozoan- Nosema sp.
• Peak season: Summer season of the year.

Symptoms

• At early stage of infection: The infected early stage worms do not show any morphological abnormality. Only microscopic examination of the silkworm larvae may indicate the presence of spores of the pathogen.
• Later stage of infection: The silkworm larvae loose appetite. Varies in size, retard in growth, moult irregularly and the colour of the larvae becomes pale.
• Infection: It is unique in being transmitted to offspring by trasovarial / transovum means from mother moth and this is called primary. If infection is primary, more than 50% larvae die before third moult and rarely any larva goes to spinning stage. When healthy larvae get infected through contamination during rearing, it is called secondary infection. Secondary infection during early 4th larval stage leads to formation of flimsy cocoons, where as larvae infected during 5th larval stage spun well formed cocoons.

Source of infection

Egg stage

• Transovarial.
• Surface contamination.
• contaminated grainage appliances.

Larval stage

• Contaminated egg laying kharika.
• Transovarially infected larvae.
• Faecal matters of infected larvae.
• Excreta of infected larvae.
• Contaminated foliage.
• Contaminated rearing room.
• Contaminated rearing appliances.

Moth stage

• Purchase of infected seed cocoons.
• Infected moth.
• Infected grainage appliances.
• Meconium and moth scales.
• Grainage dust.

Spread of disease: Perbrinized larvae excreat faecal matter, gut juice and vomit containing pathogens, which contaminate the rearing environment, appliances and foliage. Mostly, consumption of contaminated foliage or egg shell results in infection and spread of the disease.

Management

• Follow the scientific inspection method of individual mother moth testing for detection of pebrine during egg production.
• Practice disinfection of grainage hall and appliances before and after every grainage operation with 2% formalin.
• Ensure use of microspically tested disease free disinfected eggs only.
• Practice surface sterilization of eggs with 2% formalin for 5 minutes.
• Maintain hygienic conditions in egg production room and rearing room.
• Practice disinfection of rearing appliances and rearing room before use.
• During rearing, test the faecal matters, unequal/ lethargic/ unsettled/ irregular moulters periodically. If pebrine spores are detected, reject the entire infected crop.
• Ensure the measures for destruction of diseased silkworm larvae/ cocoons/ moths/ eggs.

Flacherie

• Flacherie is a syndrome of bacterial diseases in eri silkworm. Flacherie disease is caused by an ultra virus, which is an exciting agent, followed by secondary infection of bacteria.
• Peak season: All seasons of the year, intensive during rainy summer months (June to August).
• Symptoms: Infected silkworm larvae become lethargic and motionless. The colour of the haemolymph turns black. Chain type excreta, sealing of anal lips, rectal protrusion are some of the easily detectable symptoms of the disease. Infected larvae die within short time.

• Infection: Feeding of contaminated/ poor quality foliage.
• Source of infection: Diseased larvae, its gut juice, faecal matters, body fluid and contaminated rearing site and appliances.
• Pre-disposing factor: Sudden fluctuation in temperature and humidity, bad weather, poor quality leaves with high water content.
• Spread of disease: The disease is transmitted by secondary infection of the larvae feeding on the contaminated/ poor quality leaves. Infected worms ooze out body fluid containing pathogen throughout incubation period of infection and contaminate the leaves of the rearing bed and rearing environment. The disease spreads to healthy worms on feeding of the contaminated leaves. Feeding of late stage worms with very tender succulent leaves and sudden fluctuation of temperature & humidity during rearing period also lead to outbreak of the disease.

Management

• Use disinfected quality seeds of disease free zone.
• Disinfection of rearing room before rearing with 2% formalin solution.
• Dusting of 0.3% slaked lime in addition to usual disinfection for rearing room and appliances in case of high incidence of the disease in preceding rearing.
• Inspect rearing room regularly and pick out stunted/ doubtful worms by burying with 5% formalin solution.
• Practice washing of hands with formalin solution at the time of handling of worms.
• Maintain hygienic condition during rearing.
• Feeding of good quality leaves, because food is major source of infection.
• Do not allow late stage worms to feed on succulent tender leaves.

Insect pests

Unlike mulberry and muga silkworm, attack of insect pests is less in eri silkworm. However, use of nylon net in the windows & doors of the rearing room prevents uzi fly infestation in eri rearing. Usually fly pests come to the rearing room through the food plant foliage. Hence, preservation of plucked leaves in separate site also helps in checking the entry of fly pests.

Source:

• B.K. Singh, N. Tiken Singh, 2010, Muga Silkworm Seed Organization (MSSO), P-4 Unit, Mendipathar, East Garo  Hills, Meghalaya.
• Package of practices of Muga, Eri and Mulberry Sericulture for North Eastern region of India, 2005, Central Muga  Eri Research & Training Institute, Lahdoigarh, Jorhat, Assam.
• Directory of Sericulture Technology 2008, Karnataka State Sericulture Research and Development Institute,  Bangalore- 560 062.