Sponsored by
NSTMIS Division
Department of  Science and Technology
Government of  India, New Delhi.

Implemented by
Karnataka State Sericulture Research and Development Institute , Bangalore


Technology No. : 006
Organization : Central Muga Eri Research & Training Institute, Jorhat, Assam
Subject : Non-Mulberry Sericulture
Category : Muga Culture
Technology Name :

Muga Silkworm Diseases and Pest Management

Salient Features of the Technology :

A. Pests and Predators

Uzi fly : Uzi fly (Blepharipa zebina and Exorista sorbillans) is the major pest of muga silkworm.  It is prevalent throughout the year attaining the peak during December to March.  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 worm. 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.

Control

·     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 ‘Jail’.

·     Harvest and stifle the uzi infested cocoons on 4th or 5th day of spinning.

·     Collect and destroy the maggots/pupae of the fly.

·     Burn the heavily infested worms.

Apanteles : Apanteles glomeratus usually infects the early stage silkworms. It is prevalent during summer and winter months of the year.  Apanteles lays eggs inside larval body of the silkworm by inserting the ovipositor through tubercles. The maggots of the fly feed on the tissue of the silkworm and come out through the tubercles after maturation. The mature maggots form pupae in aggregation outside the body of the silkworm larvae.

Control :

·     Rearing of silkworm under nylon mosquito net prevents Apanteles infestation.

·     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.

Ants, Wasps, Hornets, Canthecona bugs, Praying mantids, Birds, Owls, Bats, Monkeys, etc., are the major predators of muga silkworm.  Rearing under nylon mosquito net and mechanical control are the only methods to prevent the attack of predators.

B. Diseases

Pebrine : 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 mother moth.

Occurrence : The disease may occur in all seasons of the year.

Symptoms :

Early stage of infection : The infected muga silkworm larvae appear normal. Only microscopic examination of the silkworm larvae may indicate the presence of spore stage of the pathogen.

Later stage of infection: The silkworm larvae loose appetite, vary in size, retard in growth, moult irregularly and the colour of the larvae become light yellowish green instead of deep green colour of normal healthy larvae. Infected late stage larvae of muga silkworm show black dots or specks on the surface of the body and hence, the disease is known as ‘Phutuka’ i.e., spotted disease in Assamese.

Infection: The disease is transmitted from the infected mother to the offspring by transovarial/transovum means and this is called primary infection. If infection is primary, more than 50% larvae die before 3rd moult and rarely any larva go for spinning. When healthy larvae get infected through contamination during rearing, it is called secondary infection. Secondary infection during early 4th larval stages leads to formation of flimsy cocoons. Whereas larvae infected during 5th larval stage form well formed cocoons.

Infection source :

Egg stage

·     Transovarially.

·     Surface contamination of eggs (transovum).

·     Contaminated grainage appliances.

Larval stage

·     Contaminated egg laying kharika.

·     Transovarially infected larvae.

·     Faecal matters of infected larvae.

·     Exuviae of infected larvae.

·     Contaminated foliage.

·     Contaminated rearing site.

·     Contaminated rearing appliances.

Moth stage

·     Purchase of infected seed cocoons

·     Infected moth

·     Infected grainage appliances.

·     Meconium and moth scales.

·     Grainage dust.

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

Prevention/control of the disease:

·     Follow the scientific inspection method of individual mother moth testing for detection of pebrine in egg production.

·     Practice disinfection of grainage appliances before and after every grainage operation with 2% formalin.

·     Ensure use of microscopically tested disease free disinfected eggs only.

·     Practice surface sterilization of the eggs with 2% formalin for 5 minutes.

·     Maintain hygienic conditions in egg production room and rearing sites.

·     For basic stock maintenance, follow cellular method of rearing.

·     Practice disinfection of rearing appliances 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.

Viral disease : Nuclear polyhedrosis, commonly known as Grasserie is a major viral disease of muga silkworm caused by a baculovirus.

Occurrence: The disease prevails althrough the year but is predominant during rainy summer months of the year.

Symptoms: The silkworm larva fails to moult.  The integument becomes fragile and intersegmental region becomes swollen and that is why, the disease is known as ‘Phularog’ or 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.

Infection: The silkworm larvae get infected on feeding of contaminated foliage of the host plants.

Infection source : Disintegrating diseased silkworm, its body fluid and contaminated rearing site and appliances.

Pre-disposing factor: High temperature clubbed with high humidity, poor quality host plant leaves.

Spread of disease: The diseased silkworm larva extrudes the pathogen along with oozing of body fluid due to injury and breakage of dead 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 as well as the use of contaminated appliances during rearing.

Preventive measure of the disease:

·     Practice disinfection of rearing site before rearing with 2% formalin solution spray.  Dusting of 0.3% slaked lime in addition to usual disinfection procedure is recommended for rearing site and appliances disinfection in case of high incidence of disease in previous rearing.

·     Pick out growth retarded/lethargic/irregular moulters and destroy.

·     Ensure measures of destruction of diseased/doubtful worms by burning or burying with 5% formalin solution.

·     Ensure hygienic conditions during rearing.

·     Use certified disinfected disease free layings only.

·     Ensure rearing on good quality leaves, because in case of silkworm, food is the major source of the diseases.

Bacterial disease: Flacherie is a syndrome of bacterial diseases in muga silkworm. Some flacherie diseases are caused by an ultra virus, which is in fact, an exciting agent, followed by secondary infection of bacteria.

Occurrence: The disease prevails in all seasons of the year but is intensive during rainy summer months (June to August) of the year.

Symptoms: The 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 a short time.

Infection: The muga silkworm larvae get infected on feeding of contaminated/poor quality foliage of the host plants.

Infection Source : 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 larvae feeding on the contaminated/poor quality leaves. Infected worms are oozing out body fluid containing pathogen throughout incubation period of infection and contaminate the leaves of the host plant 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 and humidity during rearing period also may lead to out break of the disease.

Preventive measures of the disease :

·     Use disinfected quality seeds of disease free zone.

·     Practice orientation of brushing to protect the young larvae from direct               sunlight.

·     Disinfection of rearing site before rearing with 2% formalin solution is mandatory. Ensure dusting of 0.3% slaked lime in addition to usual disinfection procedure recommended for rearing site and appliances in case of high incidence of the disease in previous rearing.

·     Inspect rearing field regularly and pick out stunted/sluggish/irregular moulters and destroy.

·     Ensure measures of destruction of diseased/doubtful worms by burying with 5% formalin solution.

·     Practice washing of hands with formalin solution at the time of transfer of worms.

·     Maintain hygienic conditions during rearing.

·     Ensure rearing on good quality leaves, because in case of silkworm, food is the major vector of the diseases.

·     Do not allow late stage worms to feed on tender succulent leaves.

Mascardine: Muscardine is one of the major diseases found in silkworm.  But in muga silkworm, while muscardine is less prevalent occurring under certain specific environmental influence only.  Observations over the last decade revealed that the disease appeared alternatively after 2-3 years intervals.  The causal organism of the disease is a fungus, which is not yet identified in case of muga silkworm.

Occurrence : The disease occurs during 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 : The infection may occur in any stage of the silkworm larvae. Infected larvae loose their appetite and become inactive. The colour of the larva turns pale, gradually ceases movement within 12-18 hours of infection. The larvae hangs on tree twig or trunk and hardens. Within another 6-8 hours, the larva dies in next 16-18 hours, a white encrustation appears on the larval body. Within another 24 hours, the whole body of the larva gets covered by the white encrustation and becomes dry, brittle and mummifies.

Predisposing factors : Low temperature with high humidity.

Source of infection : Mummified/diseased larvae contaminates the rearing environment and foliage of the host plants.

Spread of disease : The conidia or spores of the pathogenic fungus are dispersed by wind and through contact. The conidia on contact with host integument, germinate, penetrate into the host body and cause the infection.

·     Different chemical formulations viz., Labex, Resham Jyoti, Vijetha and Muga Guard as prophylactic measures were tested to control silkworm diseases.

·     Muga Guard, a new formulation developed at the institute was tested for controlling bacterial and viral disease in muga silkworm.

Preventive measure of the disease:

·     Practice orientation of brushing towards sunlight during winter.

·     Practice disinfection of rearing site before rearing with 2% formalin solution.

·     Practice dusting of slaked lime in the field to control humidity at the time of rearing.

·     Practice dusting of Tasar Kit Oushad developed by CTR&TI, Ranchi on the body of the larvae at the time of transfer.

·     As prophylactic measure, spray 0.5% Sodium hydroxide solution on the worms after 24 hours of each moult.

·     Maintain hygienic conditions during rearing.

Collection and destruction procedure of dead/diseased larvae:

·     Pick out sick or dead worms by forcep or chopstick and keep in a container with 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.

·     Don’t allow the birds, ants and poultry to eat the carcasses.

Source of Information :

Package of Practices of Muga, Eri and Mulberry Sericulture for N-E region of India - CMER&TI, 2005 pp.12-20 and A Decade of Research in Muga, Eri and Mulberry - CMERTI Publication pp.12.

Photo of technology

:
Flacherie infected Muga larva Muscardine muga larvae