Silkworm Diseases

Infection travels by four routes: diseased and dead silkworms, their faecal matter, contaminated leaf and contaminated appliances. Every measure below closes one of those four doors.

Muga silkworm diseases

Disease	Causal organism	Symptoms	Management
Pebrine	Nosema sp. AA1 (microsporidian); locally phutuka	Irregular growth and moulting; black specks on the body surface of late-stage larvae; deformed moths with distorted antennae	MME-certified, surface-sterilised DFLs; individual mother moth examination; disinfect appliances with 5 % bleaching powder or 0.02 % NaOCl; 9:1 lime and bleaching powder dusting around field and grainage
White muscardine	Beauveria bassiana	Pale sluggish larvae, dark intersegmental areas, death in 3–5 days, body then covered in white powdery fungus	Field disinfection; quality stage-specific leaf; 0.1 % LAHDOI on plants and soil 7 days before brushing, then every 15 days
Black / green muscardine	Metarrhizium sp. / Nomuraea sp.	As white muscardine, with differing conidial colour	As above
Aspergillosis	Aspergillus flavus, A. parasiticus, A. tamarii	Localised infection mainly of early instars; kills early instars in 2–3 days, later instars in 4–6 days	As above; strict early-age hygiene
Grasserie	Nucleopolyhedrovirus	Loss of appetite, swollen body, loss of clasping power, turbid white fluid from the larva	Egg disinfection with 0.2 % NaOCl; careful site selection; remove and destroy infected larvae; lime dusting to cut humidity; bury dead worms and litter
Bacterial flacherie	Bacterial pathogens	Loss of appetite, pale body, vomiting of gut juice, semi-solid faeces	As for grasserie
Infectious flacherie	Bacteria with infectious flacherie virus or densonucleosis virus	Diarrhoea, motionlessness, haemolymph turning black, chain-type excreta sealing the anal lips, anal region swollen and ruptured	As for grasserie; feed healthy leaf only

Pebrine transmission

Transmission is both vertical — transovarial and transovum surface contamination — and horizontal, from contaminated appliances and the egg-laying kharika.
More than half of primarily infected larvae die before the third moult.
Larvae infected in the early fourth instar spin fragile cocoons; those infected in the fifth still form sound ones, which is why cocoon appearance cannot substitute for mother moth examination.

Muscardine and weather

Muscardine can take 60–90 % of the Jarua pre-seed crop. Low temperature with high humidity is the predisposing combination: at Lahdoigarh in December 2012, with a minimum of 5.5 °C and humidity of 72–92 %, the disease ran through Jarua in three successive years; in December 2016, with a minimum of 10.0 °C and humidity of 44–82 %, no incidence was reported. A single infected fifth-instar larva produces millions of conidia that detach, float and infect through the integument.

Heavy rainfall has moved the risk into Chotua and early Jethua crops, so the forewarning calendar should be read against actual rainfall rather than the month alone.

Eri silkworm diseases

Disease	Causal organism	Season and predisposing factors	Symptoms and management
Pebrine	Nosema philosomiae and N. ricini (Microsporidia: Nosematidae)	Throughout the year	Poor egg-laying capacity in infected mothers; affected eggs and irregular hatching. Control rests on mother moth examination, certified DFLs, egg surface sterilisation and grainage hygiene.
Muscardine	Beauveria and Metarhizium spp.	Winter, as temperature falls	Loss of appetite, sluggishness, cessation of movement, pale larval colour, then mummification. Control by disinfection, bed drying with lime and removal of infected larvae.
Grasserie	Samia ricini nucleopolyhedrovirus (SariNPV) / PcNPV, Alphabaculovirus, dsDNA	Rainy and summer seasons with excess leaf moisture; temperature and humidity fluctuation, tender or contaminated leaf, poor bed cleaning and ventilation, overcrowding	Attacks late fifth instar and maturing worms — bloated body with yellowish skin, restlessness, loss of clasping power, intersegmental swelling, vomiting and diarrhoea, translucent head and thorax. Lime dusting, sanitation, no overcrowding, avoid tender leaf in late age, wash hands after handling infected larvae.
Flacherie	Presumed viral, followed by secondary bacterial infection	Year-round; heaviest in summer and rains	Spread by contaminated leaf, dead and diseased worms, faecal matter, gut juice and body fluid, and by overcrowding. Managed by leaf quality control, bed hygiene and stocking discipline.

Grasserie and muscardine occupy opposite ends of the weather range — one is a wet-season disease of late-age worms, the other a cold-season disease. A single disinfection regime will not substitute for season-specific bed management.