Abstract:The effects of photoperiod on the prepupal diapause and larval development were examined in the green lacewing，Chrysopa pallens (Rambur) at 22℃.Photoperiodic responses of Ch. pallens showed short-day type, and the critical photoperiod for diapause induction was estimated to be between 10.5L-13.5D and 11L-13D. The second instar larvae was the most sensitive stage for prepupal diapause induction，the prepupae could go into diapause only when the second instar larvae was subjected to the diapause-inducing short-day conditions.Diapause incidence became higher when the induction throughout larval instars 1-3 than only the larval instar 2. This results suggested that the first and third instar larvae had a certain degree of sensitivity to diapause-inducing photoperiods.Effects of the different photoperiods on the developmental periods of larvae stage and prepual weight of Ch. pallens were also investigated.The results showed that the second instar larvae stage was extended when they were kept under the short-day photoperiods，and the developmental duration of the second instar larvae grown under the photoperiods of 9L-15D and 11L-13D were significantly longer than that of 12L-12D and 15L-9D. The weight of diapauseing prepupae grown under the diapause-inducing short-day conditions was significantly higher than that of the non-diapause prepupae grown under the long-day or short-day conditions.