Grasserie is common during final instar or befor spinning. Why?
1. It depends on the instar / time the silkworm got infected by the pathogen. 2. If silkworm gets infected during the 4th or early 5th instar, the symptoms of the disease will be observed prior to spinning or pre-pupal stage. 3. In silkworm infected with the high dose of virus, the ecdysone harmone required for moulting and maturation will be destroyed. The larval period will be simply continued due to lack of ecdysone till the larae develop the disease. Thus we see the disease associated with worms that failed to moult / spin the cocoon 4. If the infection level is low, larva pupate but die in pre-pupal or pupal stage resulting in melting.
