- The infected embryo dies within the egg.
- The hatching percentage of eggs is low.
Early stage of infection:
- The infected muga silkworm larvae appear normal. Only microscopic examination of the silkworm larvae may indicate the presence of spore stage of the pathogen.
- The larvae become yellow.
- Irregular growth of larvae is clearly visible and more than 50 per cent of the larvae die before third moult.
Later stage of infection:
- Under condition of heavy infection, black spots appear on the skin as the parasite invades the hypodermal cells of the skin. These cells die here and there showing melanosis and appear as dark peeper like spot. It is called as “”phutuka” (spotted) in Assamese. Infected larva is known as “Balipara muga”. Two types of spots are reported from Upper Assam, if the spots are larger in size, it is known as “Hatiphutuka” and if small it is known as “Baliphutuka”. When the infection is primary, most of the worms die in the second and third instar. If the infection is secondary, the worms may spin the cocoon of inferior quality, “Hatiphutukia”, larva may moult five times instead of the usual four moults.
- The silkworm larvae loose appetite.
- Vary in size
- Retard in growth
- Moult irregularly
- The colour of the larvae become light yellowish green instead of deep green colour of normal healthy larvae.
- The infected larva becomes undernourished and lethargic.
- In mature larva, the silk glands are infected heavily and silk formation is hampered thereby.
- Infection during early fourth larval stage leads to formation of flimsy cocoon, whereas infection during fifth stage leads to vigorous growth of the larvae and produce well formed cocoons.
Pupal stage: Chrysalid shows black dots or specks on the body surface
- Moth shows black dots or specks on the body surface
- The infected female moth deposits lesser number of eggs than the healthy individual.
- A flimsy cocoon is formed
- Low shell weight
- Less filament length
- The thread breaks easily.