Abstract
Lamerin breed of the silkworm, Bombyx mori L. for Northeastern India hosts a vertically transmitted microsporidian parasite for generations, which does not harm significantly the cocoon production. The transversally infected progenies do not exhibit marked external sign or symptom. The microspordian causes inapparent infection and over $(80\%)$ of the infected progeny survives and spin cocoons. There is possibility of co-existence between the breed and the associated micosporidian parasite. To evaluate the impact of the microsporidian on breed the present study was conducted in respect of tranovarial transmitted (observed as T1), secondarily infected (observed as T2) and healthy silkworm (observed as T3). The larval and pupal mortality was $12\%$ and $6\%$ in T1 and $10\%$ and $3\%$ in T2 batch, while in case of T3 batch there was no mortality. Significant changes were also observed in single cocoon weight, single shell weight, denier, reelibility, raw silk recovery $\%$ and neetness. There is no significant impact of the infection on the fecundity and hatchability. The hatchability of the eggs laid by healthy or infected moths are equall as much as control but the progeny had the infection transmitted from the parent.