Diapause induction and cold storage of diapause cocoons in Agrypon flexorium (Hymenoptera:Ichneumonidae)

To understand the effects of temperatures and photoperiods on diapause induction of Agrypon flexorium( Thunberg),the process of induction,the sensitive stage that was susceptible to photoperiod and the effect of low temperature on the storage was investigated. The results showed that when the temperature was between 17- 23℃ and day length was 10- 14 h,the diapause rate significantly increased with the decrease of temperature and day length. High temperature counteracted the effect of short day length. When the temperature was 26℃,photoperiod had no effect on diapause. Thus,lower temperature and shorter day length were the major factors that induced diapause of the parasitoid. The parasitoid accepted the signal for diapause at the egg and 1st instar larval stages. The pre-pupae entered diapause only if the eggs and 1st instar larvae had been reared in the temperature and the photoperiod for diapause induction till they matured. The emergence rate and the parasitic ability showed no significant difference between adults emerged from the diapause cocoons stored in the temperature of 4℃ for 80 d and those from the non-diapause cocoons without cold storage. After cold storage for 120 d,the emergence rate of the diapause cocoons still reached 71. 7%. The results suggested that the photoperiod of 8L∶ 16D at 17℃ had diapause induction effect on parasitized host larva. The optimal storage time of diapause cocoons is 80 d and should not be more than 120 d. The study provided some reference information for indoor propagation,preventing wasp degeneration and field releasing.