Describe the names of any four diseases of silkworm and their causal agents (scientific names), sources of infection, symptoms and management. (IAS 2020/20 Marks)

Introduction

Silkworms are economically important insects that are reared for the production of silk. However, they are susceptible to various diseases that can significantly impact silk production. 

Diseases of Silkworm and Their Causal Agents

1. Bacterial Flacherie

• Causal Agent: Bacillus thuringiensis
• Sources of Infection:
  
  • Contaminated feed and environment.
  • Infected larvae shed spores in feces.
  • Mechanical transmission through workers’ hands and tools.
• Symptoms:
  
  • Softening of the body.
  • Lethargy and reduced movement.
  • Discoloration of the larval body.
  • High mortality rate in late instars.
  • Occurrence of a foul odor from infected larvae.
• Management:
  
  • Maintain hygiene in rearing areas.
  • Use of disinfectants to clean equipment.
  • Avoid over-crowding of silkworms.
  • Implementing proper feed management.
  • Early removal of sick larvae to prevent spread.

2. Nuclear Polyhedrosis

• Causal Agent: Baculovirus
• Sources of Infection:
  
  • Infected larvae and their droppings.
  • Contaminated surfaces in rearing environments.
  • Mechanical vectors like tools and equipment.
• Symptoms:
  
  • Paralysis of larvae.
  • Sudden drop in feeding and activity.
  • Body becomes limp and turns yellowish.
  • Formation of polyhedral bodies in the hemolymph.
  • High mortality rates during late larval stages.
• Management:
  
  • Use of resistant silkworm strains.
  • Strict sanitation practices.
  • Isolation of infected individuals.
  • Proper disposal of dead larvae.
  • Monitoring of environmental conditions to minimize outbreaks.

3. Fungal Disease (Green Muscardine)

• Causal Agent: Beauveria bassiana
• Sources of Infection:
  
  • Infected host larvae in the environment.
  • Soil contamination.
  • Spores transmitted through air.
• Symptoms:
  
  • Larvae exhibit greenish coloration due to fungal growth.
  • Death occurs within a few days of infection.
  • Reduced movement and feeding behavior.
  • White cottony growth on the body surface.
  • Potential spread to healthy larvae.
• Management:
  
  • Regular monitoring of humidity and temperature.
  • Use of fungicides when necessary.
  • Proper ventilation in rearing areas to reduce moisture.
  • Removal of infected individuals promptly.
  • Use of fungal-resistant silkworm varieties.

4. Viral Disease (Grasserie)

• Causal Agent: Nuclear Polyhedrosis Virus (NPV)
• Sources of Infection:
  
  • Infected larvae and their secretions.
  • Contaminated feed and equipment.
  • Environmental exposure to viral particles.
• Symptoms:
  
  • Distended body and white coloration of larvae.
  • Slow movement and lethargy.
  • High mortality rate among late-stage larvae.
  • Presence of mucous and fluid in the body cavity.
  • Sudden death in large numbers.
• Management:
  
  • Maintain strict hygiene protocols.
  • Quarantine of new stock.
  • Avoidance of temperature fluctuations.
  • Use of probiotics to strengthen immunity.
  • Continuous education for farmers on disease identification and control.

Conclusion

Silkworms are susceptible to various diseases caused by different pathogens. Proper management practices, including hygiene, sanitation, and timely intervention, are crucial for controlling these diseases and ensuring a healthy silkworm population for silk production.