Study On The Diapause Induction Of Mallada Basalis And Dichochrysa Hespera

The green lacewing of Mallada basalis?Walker?and Dichochrysa hespera?Yang et Yang?are two important biological agents distributed in South C hina widely.To understand the diapause mechanism of these two predators,the effects of photoperiod on their development and fecundity were observed,the diapause stage and critical photoperiod of D.Hespera were clarified,and the synergistic effect on the diapause induction of D.Hespera through transfering photoperiod and temperature during its development were also examined.The results could help us to understand the seasonal adaptation mechanism of these two species of green lacewing in theory,and provide technical supports for the stroage of mass-rearing natural enemy products and their field application in practice.The main results of this paper were as followed:1.Effects of photoperiod on the development of Mallada basalis and Dichochrysa hesperaUnder the photoperiod 16L:8D,14L:10D,12L:12D,10L:14D,8L:16D?temperature25??,M.Basalis could successfully finish its generation development,and the survival rate of the different developmental stage maintained above 90%.All survived female adults could lay eggs,but the photoperiod affected their development rate and fecundity of female adults.The 2^nd instar larvae,the 3^rd instar larvae and pupae developed quickly under the long light photoperiod?eg.16L:8D?,and shortened the preoviposition period,while had the high fecundity.With the decreasing day light,the developmental rate of the 2^nd instar larvae to pupae decreased,the preoviposition period prolonged,and fecundity of female adults reduced.The effects of photoperiod on the development and fecundity of D.hespera were simily to that of M.Basalis.The developmental rate of eggs and the first instar larvae of D.hespera showed no differences at different photoperiod,and the developmental duration of the 2^nd instar larvae to pupae increased progressively with the decrease of light.The survival rate of D.hespera in different developmental stages maintained above 90%,the ratio of male to female adults was close to 1:1.The shortened day light treatment?such as8L:16D?could significantly prolong the preoviposition period,while reducing the fecundity of female adults.2.Effects of the constant photoperiod on diapause induction of Mallada basalis and Dichochrysa hesperaUnder the five constant photoperiods,each developmental stage of M.basalis showed no significant diapause characteristics.The eggs,larvae and pupae of D.Hespera had no diapause phenomenon,but the development of ovarian of some female adults delayed in each treatment?adult diapause characteristics?,and the diapause rate of female adults increased with the decreasing day light gradually.The diapause rates of female adults were17.91%,12.12%,27.03%,46.97%and 54.17%at the photoperiod 16L:8D?14L:10D?12L:12D?10L:14D and 8L:16D?temperature 25??respectively,the diapause rates was lower at of the long day light photoperiod,and higher at the short day light photoperiod.The ovarian development was associative to the photoperiod,and changed from long day light photoperiod 16L:8D to short day light photoperiod 8L:16D regularly.The proportion of the ovarian grade??ovarian shrinked?and grade II?littler egg yolk accumulated in ovarian?increased with the decreasing day light gradully,while the ovarian grade III?mature eggs were observed in the ovarian,but female adults did not lay eggs?and grade IV?mature eggs were observed in the ovarian,and female adults lay eggs normally?decreased.The critical photoperiod that induced diapause of D.Hespera was between photoperiod10L:14D and 8L:16D,and close to photoperiod 8L:16D.3.Diapause induction of Mallada basalis and Dichochrysa hespera through transfering photoperiod and temperatureM.basalis didn't show any diapause characteristics under two representative photoperiods?long day light 16L:8D and short day light 10L:14D?at 20?.Even when M.basalis individuals were transferred from photoperiod 16L:8D to 10L:14D at the 3^rd instar larave and fresh female adults at the same temperature 25?,or transferred from photoperiod 16L:8D at 25?to 10L:14D at 20?,M.basalis also could not be induced into diapause..While the diapause rate of D.hespera female adults could be improved through transferring the photoperiod.The diapause rate of D.hespera female adults was 49.35%under the photoperiod 10L:14D at 25?,however,its diapause rate was raised to 70.59%when D.hespera individuals were transferred from photoperiod 16L:8D to 10L:14D at the3^rd instar larave at the same temperature 25?.Diapause rate of D.hespera was not changed much when transferring the photoperiod and temperature at the same time compared to only changing the pho toperiod.The different development stage had the different sensibility to the change of photoperiod,the 3^rd instar larave were more sensitive to the photoperiod variation than the newly emerged adults.