The processes involved in the induction and termination of facultative larval diapause in the parasitoid Colpoclypeus florus (Walker) was investigated in the laboratory. Larval diapause in C. florus is under maternal control. Photoperiod is the major factor governing the induction of larval diapause in C. florus. The pupa of the maternal generation is the most sensitive stage though the adult is also sensitive. Adult sensitivity increases with age, in particular at low temperatures. Photoperiod has no effect on the developing larva. The critical photoperiod for diapause induction for parasitoids maintained throughout the life cycle at 15 and 20°C was found to be 15 and 13.5 h, respectively. No diapause was induced at 25°C at any photoperiod examined. A chilling period of >5 wk is a prerequisite for diapause termination. After 8 wk at 5°C, all diapausing larvae pupate within 20 d whether held under short or long daylength. Chilling temperature and duration of chilling significantly affected diapause termination. Diapause development proceeds rapidly as chilling period increases and temperature decreases. The role of diapause in the biology of this parasitoid is discussed.