The location of a host at the time of larval emergence of a parasitoid is important for successful parasitism and also influences the parasitoid population. Nonparasitized and parasitized hosts stayed in a concealed location (e.g., in soil [vermiculite] or in the leaf fold of the corn plant) during the photophase; whereas during the scotophase, they moved about exposed on the corn leaves. However only parasitized hosts remained in this exposed location at the time of emergence of the parasitoid larvae. Emergence of the parasitoid larvae always occurred during the photophase. Even when parasitization was delayed by 6 h, larval emergence occurred only during the photophase in all cases, suggesting that parasitoid emergence occurred selectively during the photophase and was not dependent on the duration of development. The time from oviposition to emergence was not related to the number of eggs laid. When a photoperiod of 12:12 (L:D) h was reversed 8 d after parasitization, the parasitoid larvae showed a tendency to emerge according to the new reversed photophase. They appeared to emerge in response to the light stimulation. We evaluated development by measuring both the size of the cordal vesicle and the volume of the parasitoid larva. The increase in size or volume was slower from 2200 hours on day 9 after parasitization, suggesting that the larvae awaited an appropriate chance to emerge from the host and were able to regulate the time of emergence. High humidity at the time of emergence caused scattered cocoon masses and many naked pupae. Desiccation after larval emergence promoted high mortality in cocoons.