| The sweet potato whitefly,Bemisia tabaci(Gennadius)has become one of the important worldwide pests in subtropical and tropical agriculture as well as in greenhouse production system.Both in the USA and the BRA,B.tabaci causes great losses in agricultural production.Since the 1990s,B.tabaci has invaded our country with huge economic losses.Biological control could be an attractive alternative management for whitefly.Encarsia sophia is a significant parasitic enemy of B.tabaci.E.sophia derived from India with a good application prospect in the prevention and treatment of B.tabaci.Though it has a distribution in our country,the wasp hasn't been researched deeply.To explore the mechanism of physiological and biochemical effects of its parasitization on B.tabacii,we examined the activities of three antioxidant-related enzymes and levels of trehalose in the nymphs of host Bemisia tabaci parasitized and unparasitized by Encarsia sophia.The main results are as following:(1)Compared with non-parasitized ones,the activity of SOD(Superoxide dismutase),CAT(Catalase)and POD(Peroxidase)changed obviously in three different instars of B.tabaci nymphs after parasitized by E.sophia.It increased to a peak,and then decreased to a stable level.Within 12 h,SOD activity of parasitized nymphs increased to a peak,and then decreased.SOD activity of 2nd and 3rd whitefly nymphs reached a peak at 6h after parasitized,and the activity of 4th whitefly nymphs reached a peak at 9h after parasitized.SOD activity of 3rd and 4trh whitefly nymphs changed obviously at 3h,6h and 12h after parasitized compared with non-parasitized ones.After parasitized within 12h,CAT activity of 2nd and 4th whitefly nymphs changed observably,but the activity of 3rd whitefly nymphs has very little change compared with that in control.CAT activity of 2nd and 3rd nymphs reached a peak after parasitized at 6h,while the activity of 4th nymphs reached the peak at 9h after parasitized.CAT activity of 2nd whitefly nymphs at 3h,6h,9h after parasitized was significantly higher than that of the control,and the activity of 4th whitefly nymphs at 3h,6h,9h and 12h after parasitized showed an observably change compared with that in control.Within 12h,POD activity increased to a peak,and then decreased to a stable level.POD activity of 3rd whitefly nymphs at 3h and 9h after parasitized was obvious higher than its control and the activity of 2nd and 4th nymphs at 3h,6h and 9h after parasitized showed an obvious level which was higher than the control.After 12h,the activities of three antioxidant-related enzymes has very few change compared with that in control with a gradual decrease.(2)4th whitefly nymphs was chosen as the host of E.sophia.ln three different temperature treatments,trehalose content of whitefly nymphs parasitized by E.sophia increased to a peak,and then decreased to a stable level.Within 9h,trehalose content reached the maximum.With the treatments of 15°C and 33 ?,trehalose content of 4thwhitefly nymphs at 9h after parasitized showed an observably change compared with that in control.With the treatment of 28?,trehalose content of the nymphs at 9h after parasitized was significantly higher than its control,while its trehalose content at 6h and 24h after parasitized showed an observably level which was lower than that in control.Within 3h and 6h,trehalose content increased with the rising of temperature.Within 9h,12h and 24h,trehalose content of the treatment of 28? showed lower than it of the treatment of 15? and 3 3?.The results suggest that the activities of three antioxidant-related enzymes changed observably compared with that in control except CAT activity of 3rd whitefly nymphs.These results indicated that E.Sophia infection caused the rejection of whitefly nymphs with the increasing free radical,and the higher activity of three antioxidant-related enzymes would help parasitoids eliminate excess ROS and keep the balance of the ROS.The experimental results show that E.Sophia can regulate the physiology environment of its host to provide a suitable setting for its progenies.In different temperature,parasitism by E.Sophia would induce higher trehalose content than that in normal.While whitefly nymphs were treated by the stress temperatures,trehalose content showed an observably change compared with that in control.It indicated that this phenomenon was caused by that the saccharides entered into hemolymph due to organization hydrolase derived from some factors(PDV or venom)destroying organs and tissues of the host. |
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