A sizeable population (60.5%) of muga silkworm (Antheraea assama Westwood, Saturniidae: Lepidoptera) enters pupal diapause in its natural environment in the wild state whereas the development is continuous when reared in the plains (0 to 20 m MSL) under human care (in this practice the larvae are mounted on the food plants with suitable leaves and protected from natural enemies and pass the entire larval stage in the out-door and rest of the development, viz. cocooning, pupation, moth emergence, courtship, copulation, oviposition and embryonic development etc. take place in in-door conditions; the ripe worms are collected from the food plants and put in the cocoonage; after cocoon formation the cocoons are placed in cages for moth emergence; if the moths do not couple naturally, mechanical coupling by gentle rubbing of the genital segments of the opposite sexes is resorted; finally the coupled moths are tied on a straw bundle for oviposition). Inbreeding of diapausing population in plain inhibits dormancy but intercross with the non-diapausing population channels a few pupae (3.5%) into diapause. Low temperature (6–10°C) and short photophase (9 to 10 hr) prevailing in winter in the hills (100 to 450 m AMSL) appear to be the threshold level to induce diapause in muga silkworm.