Field and laboratory experiments showed that under certain conditions adult females of the predatorJalysus spinosus(Say) have a facultative reproductive diapause in North Carolina. Diapausing females appeared in the Oxford, NC area in late August, as day length declined to 13.5h and less. In the laboratory at 26.7°C, the percentage incidence of diapause rose abruptly from ca. 9% at 13.5 photophase to 98% at 12.5 h. The diapause-induction curve was a Type III shape, with 0% diapause at constant darkness. A long day (14 h light and 10 h dark) and warmer temperatures shortened the length of diapause.