Characteristics Of Prepupal Diapause Of Chrysopa Pallens (Rambur)

The lacewing, Chrysopa pallens(Rambur), is an important natural enemy attacking agricultural and forestry pests like aphids, mites and eggs, young larvae of lepidopterous insects, and is a good biological control agent. It overwinters as diapausing prepupae. This paper mainly dealt in details with the characteristics of prepupal diapause of Ch. pallens. The main results were summarized as follows.1 The characteristics of diapause induction of Chrysopa pallensThe results showed that prepupal diapause of Ch. pallens was induced by the short-day photoperiods, prepupae developed without diapause under long-day conditions and entered diapause under short-day conditions. The second instar larvae was the uppermost sensitive stage for prepupal diapause induction, prepupae could go into diapause only when the second instar larvae stage was under diapause-inducing short-day photoperiods. Diapause incidence became higher when the first and third instar larvae also experienced the short-day conditions. The critical photoperiods for its diapause induction at 18℃,20℃and 22℃were between 12L﹣12D and 13.5L﹣10.5D,between 11L﹣13D and 12L﹣12D,between 10.5L﹣13.5D and 11L﹣13D, respectively.Photoperiod and temperature were main factors that affected the prepupal diapause of Ch. pallens, and the photoperiod was the key factor and temperature could modify the diapause -inducing effects of photoperiod. Effects of the different photoperiods on the larval duration and prepual weight of Ch. pallens were also investigated. The results showed that the second instar larvae stage was extended under the short-day photoperiods. The weight of diapause prepupae developed under the diapause-inducing short-day conditions was significantly higher than that of the non-diapause prepupae under the long-day or short-day conditions. The significant differences in the prepupal weight and diapause rate after the larvae reared with different aphids species indicated that the food quality eaten in the larval stage also could regulate the prepupal diapause.2 The characteristics of diapause development of Chrysopa pallens Temperature was the important factor that regulated the diapause development and there was a linear relation between the diapause developmental rate and the temperature during the prepupal diapause periods. The termination of prepupal diapause didn't need the activation of the low temperature, but the treatment of different low temperature had significant effects on the lacewing diapause development and the diapause developmental rate was the fastest at the temperature of 10℃compared with the temperature of 0℃, 5℃, 15℃. Photoperiod had no significant effect on diapause development during the diapause periods.The different short photoperiods inducing diapause had different effects on the prepupal diapause intensity, and the diapause intensity induced by the photoperiods near the critical photoperiod were weaker than that induced by the shorter photoperiods. Temperature that the larvae experienced also had obvious effects on the diapause development. Low temperature could make the prepupal diapause much more intensity and the development rate slower than high temperature.3 The adult biological characteristics after the end of diapause development of Chrysopa pallensTemperture was also the main regulator of the development after the end of diapause development of Chrysopa pallens. The longevity of the adults and the daily egg production at the high temperature were significantly longer and more than that at the low temperature. However the temperature had no effects on the total egg production. There were not obvious effects of photoperiod on the adult biology after the end of the diapause development.Diapause duration under the different temperatures had significant effects on the adult biology. There were no significant effects on the fecundity and longevity of the adults when the diapause duration were 150d and 170d compared with that of non-diapause duration experience. The fecundity and longevity were the lowest and shortest when the diapause duration was about 210d.4 The cold-hardiness of the diapause prepupae of Chrysopa pallensThe supercooling point(SCP) and freezing point(FP)of the different developmental stages of Chrysopa pallens were investigated. The results indicated that the SCP and FP of prepupae was the lowest, which were -11.54±1.95℃and -5.31±1.35℃, and the SCP and FP of adults was the highest, which were -9.45±1.93℃and -3.87±1.73℃. Compared cold-hardiness ability between diapausing prepupae and non-diapausing prepupae of Ch. pallens showed that the cold hardiness ability of diapausing prepupae was significantly higher than that of non-diapausing prepupae.Experiments were conducted to examine the water, the supercooling point (SCP)and freezing point(FP), and the total fat content of the diapausing prepupae. Results showed that the cold hardiness of the diapausing prepupae gradually strengthened during the pre-diapausing development and weakened during the late diapausing development.