Silkworm Diseases and Pest Management
Domain focus
This domain tests recognition, prevention and control of silkworm diseases and pests. The exam expects the causal agent, key symptom, transmission route and control measure for each major problem.
Core rules and concepts
- Pebrine is caused by Nosema bombycis and is transmitted through the egg. Diagnosis uses mother-moth examination; infected lots must be destroyed. There is no curative treatment.
- Flacherie is a complex bacterial-viral disease; larvae become sluggish, flaccid and may have foul-smelling excreta. Hygiene, good leaf quality and temperature control reduce losses.
- Grasserie is caused by Bombyx mori nucleopolyhedrovirus and shows turbid haemolymph and swollen larvae; polyhedra are visible under a microscope. Disinfection and removal of diseased larvae are essential.
- Muscardine is a fungal disease, commonly Beauveria bassiana, producing a white, hardened mummy. Avoid excess humidity and disinfect rearing rooms.
- Uzi fly, Exorista sorbillans, lays eggs on larvae; maggots kill the host. Use mesh screens, clip maggot-infested larvae and follow recommended fly control.
Worked example
In a mother-moth examination, 100 moths are smeared and examined. Two show pebrine spores. The percentage is 2 ÷ 100 × 100 = 2%. Reasoning: even one positive moth indicates infection in the seed lot; for seed production the lot is rejected, not treated, because the parasite is transovarian.
Traps that cost marks
Looking for a pebrine medicine; confusing muscardine with flacherie; ignoring uzi fly because cocoons look normal; disinfecting only after an outbreak; using the same room for diseased and healthy batches.