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. : 031
Organization : Central Sericultural Research and Training Institute, Pampore, Jammu & Kashmir
Subject : Mulberry Sericulture
Category : Silkworm Pathology
Technology Name :

Silkworm Disease Management Practices

Personnel : Md.Isa, Mir MI, Khan MA,
Year of Recommendation : 2003
Salient Features of the Technology :

Pebrine disease : Pebrine is caused by Nosema bombycis, which is a protozoan.  The disease is transmitted through contaminated leaves or from mother moths through eggs.  It is the most serious disease in silkworms as it is highly infectious and infects the young silkworm larvae causing considerable loss.

Symptoms : The symptoms of this disease are observed in all life stages viz., egg, larva, pupa and adult.

Symptoms of egg stage :

  • Poor egg number.
  • Reduction in size and weight.
  • Lack of adherence of substratum, disuniform with more of dead and unfertilized eggs.
  • Irregular hatching.

Symptoms at larval stage :

  • Loss of appetite, retarded growth and disuniformity in size
  • Irregular moulting.
  • Heavy mortality after 2nd moult if infected at egg stage.
  • Larvae shrink in size and vomit gut juice.
  • Dark brown or black spots may be seen sometimes on the body.

Symptoms at the pupal stage :

  • Pupa looks floppy and swollen.
  • Irregular black spots on the body.
  • Heavy mortality at pupal stage.

Symptoms at the moth stage :

  • Improper development of moth.
  • Deformed wings and distorted antennae.
  • Poor mating and egg laying.
  • Scale of wings and abdominal area come off easily.

Control measures of pebrine disease :

  • Follow strict mother moth microscopic examination method to produce disease free layings. Individual moth examination or group moth examination for industrial seed must be resorted to, in order to eradicate pebrinized layings.
  • Periodical microscopic examination of silkworm larvae during rearing. If pebrine spores are detected, the whole lot should be discarded /rejected.
  • Carry out surface sterilization of disease free layings by dipping egg cards in 2% formalin solution for 10 minutes followed by washing in running water.
  • Follow strict disinfection of rearing room, appliances and surroundings of rearing area.
  • Maintain strict sanitation and hygienic conditions during rearing.
  • Apply bed disinfectant as per recommended schedule and quantity. Infected silkworm faeces and bed refuse are important source of infection and should be disposed off to prevent cross infection and spread of disease.

Grasserie disease: Grasserie is a viral disease in silkworm caused by Nuclear Polyhedrosis (NPV), Cytoplasmic polyhedrosis (CPV) and infectious flacherie. Nuclear polyhedrosis (NPV) is a major viral disease in silkworm.  It is caused due to the presence of high temperature, high humidity and feeding of poor quality mulberry leaves.  It is highly infectious.

Symptoms : In the early larval stage of infection, it is difficult to detect the disease. Microscopic examination of larvae may indicate the presence of polyhedral bodies. As the disease advances, the larvae loose appetite and skin becomes shiny before moulting. The inter-segment membrane becomes swollen.  The haemolymph or body fluid becomes turbid white.  Microscopic examination shows presence of large number of polyhedral bodies.

Control measures for grasserie:

  • Rear the larvae under clean and hygienic condition.
  • Thorough disinfection of rearing room, appliances and surroundings.
  • Ensure proper disinfection of egg surface.
  • Incubate eggs under hygienic conditions. Avoid touching with hands.
  • Provide suitable and timely feed during rearing.
  • Maintain proper spacing and adequate ventilation.
  • Pick out diseased, weak and injured larvae and destroy them  properly.
  • Apply bed disinfectants as per recommended schedule and quantity.

Flacherie disease : Flacherie disease of silkworm is caused by bacteria or virus individually or in association. Depending on symptoms and cause they are called as bacterial flacherie disease, septicemia, sotto disease, etc. The disease may occur due to fluctuations in temperature, humidity and feeding poor quality mulberry leaves.

Symptoms:

  • Larvae becomes sluggish and loose appetite.
  • Body shrinks, becomes soft and flaccid.
  • Growth is retarded, becomes dull and vomits gut juice.
  • Loose clasping power of prolegs.
  • Body ferments, turn to different colour and oozes out foul smell.

Control measures for flacherie:

  • Raise only healthy and strong silkworm races.
  • Maintain proper temperature (22-25C) and humidity (80-85%) during incubation of eggs.
  • Attend thorough disinfection of rearing room, appliances and surroundings.
  • Take strict hygienic measures during rearing.
  • Isolate infected larvae from the healthy one immediately and destroy by burning or dumping deep in the soil.
  • Provide quality leaves for feeding and maintain proper spacing and ventilation.
  • Maintain proper temperature and humidity during rearing.

Muscardine (Fungal disease) : Muscardine is a fungal disease in silkworm. Various types of muscardine diseases have been reported i.e. white, green, yellow etc. but white muscardine is commonly found in Kashmir valley. The white muscardine in silkworm is caused by a fungus, Beuveria bassiana. The disease is caused due to body contamination by the fungus. The fungus grows well under low temperature.

Symptoms:

  • The larvae loose appetite, become sluggish, ceases to move and finally die.
  • The dead larvae become harder and mummified.
  • The body after death is covered with white mycelia. Conidia develops in the body.
  • Finally whole body of dead larvae looks chalky white.
  • The pupa and moth are also infected by white muscardine disease. In heavy infection, pupal body gets cowered with conidia.

Control measures for muscardine disease:

  • Infected larvae should be picked up and burnt.
  • Maintain good ventilation and proper humidity in rearing room.
  • Regulate humidity by dusting lime at the time of each moult and in between.
  • Apply bed disinfectants as per recommended schedule and time.
  • Provide quality leaves and maintain proper spacing during rearing. Avoid dusty leaves.
  • Follow strict disinfection of rearing house, rearing appliances and surrounding area.
  • Practice proper disinfection of silkworm egg surface.
  • Maintain hygienic conditions during rearing.
  • As a specific measure, dust Diathene M-45 in Kaolin or Captan in slaked lime on silkworm body immediately after every moult as per following schedule.
  • I-II instar -1% dust
  • III-V instar-2% dust
  • Apply formalin chaff to silkworm body. The formalin chaff is prepared by partially burning paddy husk and mix formalin of 0.6% to 0.8% concentration (0.6% for chawki and 0.8% for late stage) in the ratio of 10:1. The chap is sprinkled uniformly on the silkworms 30 minutes before feeding.

Integrated silkworm disease management: Comprehensive integrated steps can result in prevention of silkworm diseases. Prevention is better than cure is the correct approach for controlling silkworm diseases. The following preventive measures will result in controlling silkworm diseases:

  • Follow strict disinfection of rearing houses, rearing equipments and surrounding areas.
  • Rear only disease free layings. Infected layings should be isolated through strict moth examination and discarded.
  • Control mulberry pests (alternate hosts of muscardine causing pathogens) in the field and provide disease free and quality leaves according to age of silkworms.
  • Maintain strict sanitation and hygienic conditions during rearing.
  • Enhance vigour of silkworms by providing suitable and timely feeding. This will enhance resistance against disease.
  • Isolate sick and diseased worms and dispose off properly.
  • Maintain appropriate spacing during rearing.
  • Isolate infected material/equipment and follow strict disinfection.
  • Faeces (silkworm litter) and bed refuse should be disposed off properly by burying it.
  • Adjust the humidity of rearing room and trays. Dust lime at the time of each moult.
  • Apply bed disinfectant (Vijetha/Labex/RKO) as per recommended schedule and time.
  • Intensive rearing management and close monitoring is essential.
Source of Information :

Bulletin No.7, CSR&TI, Pampore pp.1-6.

Photo of technology

:
Pebrinized larvae Muscardine larvae Grasserie larvae