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

Silkworm Diseases: A Detailed Overview

Here's a detailed description of four prominent silkworm diseases:

1. Pebrine

• Causal Agent: Nosema bombycis (a microsporidian parasite)
• Source of Infection: Infected moths (through spores in faeces, scales, and eggs). Transovarial transmission (from mother to offspring) is common.
• Symptoms: Blackening of the larva’s gut, shrinking and hardening of the body, tremors, and reduced silk production. Infected larvae often die in the final instar. Adult moths show a characteristic pepper-like appearance on their wings (hence the name 'Pebrine').
• Management:
  • Selection of disease-free layings (DFL) – crucial for prevention.
  • Regular disinfection of rearing houses and equipment.
  • Proper hygiene during rearing.
  • Treatment with antibiotics (though resistance is a growing concern).

2. Grasserie

• Causal Agent: Bombyx mori Nuclear Polyhedrosis Virus (BmNPV)
• Source of Infection: Contaminated rearing environment (faeces, vomitus, scales of infected larvae). Mechanical transmission through workers and equipment.
• Symptoms: Initial symptoms include loss of appetite, sluggishness, and vomiting. Larvae become flaccid, develop a shiny appearance, and eventually die. The body fluid contains numerous viral polyhedra.
• Management:
  • Strict sanitation and disinfection of rearing houses.
  • Use of BmNPV-resistant silkworm breeds.
  • Avoidance of overcrowding.
  • Application of disinfectants like sodium hypochlorite.

3. Muscardine

• Causal Agent: Beauveria bassiana (a fungal pathogen)
• Source of Infection: Spores of the fungus present in the soil, air, and rearing environment. Infection occurs through the cuticle.
• Symptoms: Hard, spherical nodules (muscardines) develop on the body of the larva, often appearing white initially and turning greenish-black with age. Infected larvae become immobile and die.
• Management:
  • Maintaining optimal rearing conditions (temperature, humidity).
  • Disinfection of rearing houses and equipment with fungicides.
  • Removal and destruction of infected larvae.
  • Use of resistant silkworm breeds.

4. Flacherie

• Causal Agent: Primarily caused by bacteria like Bacillus thuringiensis and Serratia marcescens, but can also be associated with viruses and poor nutrition.
• Source of Infection: Contaminated mulberry leaves, rearing environment, and water.
• Symptoms: Larvae exhibit loss of appetite, become pale and watery, and develop a foul odor. Vomiting and diarrhoea are common. The gut becomes empty and fragile.
• Management:
  • Providing healthy, disease-free mulberry leaves.
  • Maintaining proper hygiene in the rearing house.
  • Disinfection of rearing equipment.
  • Use of probiotics to improve gut health.
  • Antibiotic treatment (under veterinary guidance).

The following table summarizes the key features of these diseases:

Disease	Causal Agent	Source of Infection	Key Symptoms	Management
Pebrine	Nosema bombycis	Infected moths & eggs	Blackened gut, tremors	DFL, Disinfection, Hygiene
Grasserie	BmNPV	Contaminated environment	Loss of appetite, shiny body	Sanitation, Resistant breeds
Muscardine	Beauveria bassiana	Fungal spores	Hard nodules on body	Optimal conditions, Fungicides
Flacherie	Bacillus thuringiensis etc.	Contaminated leaves/environment	Pale, watery larvae, vomiting	Healthy leaves, Hygiene, Probiotics