| The sweet potato whitefly, Bemisia tabaci (Gennadius) was described over100years ago and has become one of the most important pests in subtropical and tropical agriculture as well as in greenhouse production systems. Biological control could be an attractive alternative management for whiteflies. Encarsia sophia (Girault&Dodd) is one of the most important parasitoid species parasitizing B. tabaci. To explore the mechanism of physiological and biochemical effects of wasp parasitization on its hosts, activities of three Antioxidant-Related Enzymes’ and levels of three nutrition in the nymphs of host Bemisia tabaci parasitized and unparasitized by Encarsia sophia were examined. The main results are as following.(1) According to a pin hole left on B. tabaci after host detection or oviposition by E. sophia, we can determine whether E. sophia really oviposited host through observing the pin hole. We can quickly make sure B. tabaci was parasitized by this method.(2) Changes of POD (Peroxidase) and SOD (Superoxide dismutase) activity showed similar tendencies in two different instars of B. tabaci nymphs after parasitized by En. sophia. It increased to a peak, and then decreased to a stable level. CAT (Catalase) activity in parasitized nymphs changed very few compared with that in control. Within12h, POD activity of parasitized nymphs increased to a peak, and then decreased. POD activity of3rd whitefly nymphs at3h and9h after parasitized were as2.53times and1.63times, respectively, as that in non-parasitized ones. POD activity of4th whitefly nymphs at6h and9h after parasitization were as2.39and1.78times, respectively, as that in non-parasitized ones. POD activities begun to decrease until24h post-parasitization and then kept at a stable level for3rd nymphs parasitized at12,24,48and72h. While the POD activity of the4th instar nymphs parasitized at24h and48h were significantly lower than those in non-parasitized ones. After being parasitized, SOD activity increased to a peak at24h, and then decreased and kept at stable level. SOD activity of3rd whitefly nymphs at3,6,9and 12h after parasitized were as1.48times.1.67times.1.68times and1.31times, respectively, as those of non-parasitized ones. SOD activity of4th whitefly nymphs at6,9and12h after parasitized were as1.50times,1.49times and1.60times, respectively, as that of non-parasitized ones at corresponding times. SOD activities of parasitized3rd and4th instar nymphs at24,48and72h were not significantly different from that in control group.(3) Comparison of nutrition content was carried out among the three instars of B. tabaci nymphs, we find that3rd instar B. tabaci had the highest glycogen content and4th instar had highest lipid and protein content. All these three nutrition contents in2nd instar B. tabaci nymphs were the slightest, which were significantly lower than that in3rd and4th instars. At72h after being parasitized the content of glycogen in3rd and4th instars of B. tabaci were12.08μg/individual,10.72μg/individual, respectively, and were significantly higher than that in unparasitized hosts (10.02μg/individual,9.39μg/individual). The contents of lipid and protein of parasitized B. tabaci were decreased. At72h after being parasitized, the content of protein in4th instar B. tabaci decreased19.54%, and was significantly lower than that in unparasitized ones. The content of protein for2nd and3rd instars was not significantly different between parasitized and unparasitized nymphs of B. tabaci. The content of lipid in3rd and4th instars B. tabaci began to decrease after parasitized for48h. At72h after parasitized, the content of lipid in3rd and4th instar B. tabaci nymphs were significantly lower than that in unparasitized ones. The content of lipid in2nd instar B. tabaci nymphs decreased after parasitized for72h.The results suggest that the POD and SOD activities of3rd and4th instar nymphs increased to a top and then decreased after E. sophia parasitized within24hours, and CAT activity changed little. These results indicated that ROS may be involved in whitefly nymphs’defense responses to E. Sophia infection. The higher POD and SOD activities would help parasitoids degrade excess ROS and maintain the ROS balance. Then the enzymes activities almost decreased to the normal ones. It seems that the physiology environment of the host was suitable for the offspring of the parasitoid.The content of glycogen was higher and the content of lipid and protein were lower in the B. tabaci parasitized by E. sophia. That3rd and4th instars have more abundant nutrition is one of the possible reasons that E. sophia prefers parasitize the3rd and4th instars to2nd ones. |
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