Effects Of Exogenous Hydrogen Peroxide On Antioxidant And Diapause Of Cotesia Vestalis

Diamondback moth (DBM), Plutella xylostella (Linnaeus)(Lepidoptera: Plutellidae) is one of the most serious cruciferous vegetable pests, causing huge economic losses. The control of diamondback moth has relied on chemical pesticides for a long time. But recently, the safe and effective prevention and control measures-biological control takes people’s more attention, due to gradually increased resistance of DBM to insecticide, coupled with environmental destruction and pollution and some other side effects on creatures because of the use of insecticide.Cotesia vestalis (Haliday)(Hymenoptera:Braconidae) is an important parasitoid wasp of DBM larva. This parasitoid has a strong advantage in the natural conditions, with a high rate of parasitism and widely distributed in China. Thus it has a good prospect in the integrated pest management (IPM) of the diamondback moth. However, the storage duration of the wasp cocoons at room temperature is very short, while cold storage for a long time will reduce the rate of adult emergence. Fortunately, the parasitoid would be induced to enter diapause under certain conditions. The storage period of the diapause prepupae in the cocoon prolonged significantly at a low temperature, with a high emergence rate. Thus, research on the mechanism of diapause would help solve the problem of the storage and utilization of this wasp, which benefits biological control of DBM.As we know, a series of physiological and biochemical changes would take place in the body to accommodate this particular developmental process after the wasps entered diapause, including the process of hydrogen peroxide metabolism. It had been reported that, the diapause incidence of their progeny decreased as the photoperiod maternal generation experienced prolonged. The content of H2O2in prepupae reared under a short photoperiod was significant higher than that reared under a long photoperiod, but had an opposite case in the eggs producted by the adult femals. Obviously, H2O2played an important role in the processes of C. vestalis diapause induction and maintenance. In order to further explore the roles of hydrogen peroxide during the diapause process, we used the method of treating the maternal generation with extrogenous hydrogen perioxide in this thesis, and then compared hydrogen peroxide contents, protective enzymes activities and offspring diapause incidence changes. The major results were summarized as follows.When the prepupae were treated with exogenous H2O2, the diapause incidence of their progeny declined when they were reared under a short photoperiod at13degree. The diapause incidence in the progeny generation reduced from83.76%in the control group to35.22%in the group treated with1.6mol/L exogenous H2O2, close to the diapause incidence (12.24%) of their progeny whose maternal generation reared under a long photoperiod.The content of H2O2in the prepupae increased with the increasing concentration of exogenous H2O2applied on them, like with prolonging photoperiod uesed to reared them; while the activities of SOD decreased and the activities of CAT in the prepupae increased with the increasing concentration of exogenous H2O2, just opposite to the variation trends with increasing photoperiod uesed to reared them. The POD activity showed no significant difference between the exogenous H2O2treated prepupae and the control ones when the prepupae were treated at a low concentration (0.2mol/L). However, when the prepupae were treated at a high concentration (1.6mol/L), the POD activity was the same as or even lower than the control ones at4h, but much higher at20h after treatment.When the female wasps were treated with exogenous H2O2, the diapause incidence of their progeny declined, but had no significant relationships with the treated concentration. The H2O2content increased after the wasps were treated12-14hours, while the CAT activities had no significant difference between the treated groups and the control ones. On the other hand, the activities of SOD and POD in the wasps decreased after the treatment. The H2O2content and activities of CAT and POD in the progeny prepupae at13℃showed no significant differences in the treated groups with the control ones, except SOD.The results above indicated that exogenous H2O2treatment played a similar role to the long photoperiod in the process of diapause induction of C. vestalis, preventing diapause occurring. That the effection of prepupae treatment was more appreciable than adult treatment may due to a more absorption of H2O2and different ways in the effects on various antioxidant enzymes.