Immune Regulation Of Plutella Xylostella (Lepidoptera: Plutellidae) By Venom And Calyx Fluid From Cotesia Vestalis (Hymenoptera: Braconidae)

The immune regulation of Plutella xylostella (Lepidoptera: Pluttelidae) by the venom, calyx fluid or the mixture from Cotesia vestalis (Hymenoptera: Braconidae) were studied. The results are summarized as follows:1. Determination of the effective concentration of venom and/or calyx fluid from C. vestalis for injection into the host P. xylostella larvaeWhen fourth instar P. xylostella larvae were injected with 0.01 E/μl or 0.03 E/μl venom from C. vestalis, total hemocyte counts (THCs) indicated that there was no significant difference in the number of hemocytes per milliliter of hemolymph as compared to values obtained from the PBS-injected control larvae examined at 1, 4,12, 24, 36, 48h time points; when injected with 0.05E/μl venom, THCs reduced significantly at 1-4h, but not after 4h as compared to the control. However, when injected with 0.01 E/μl, 0.03 E/μl, and 0.05 E/μl calyx fluid or the mixture (V_venom: V_{calyx fluid}=1:1), THCs decreased significantly at all time points except those at 1h after injection of 0.01 E/μl and 0.03 E/μl calyx fluid or the mixture, and the mixture exhibited significantly higher efficiency than calyx fluid along in the reduction of THCs.The effective concentration of venom was up to 0.05 E/μl, thus, we chose this concentration for venom, calyx fluid and the mixture (venom plus with calyx fluid) injection all through this study.2. Effects of venom/calyx fluid from C. vestalis on encapsulation of Sephadex A-50 beads and eggs of C. vestalis in vitroHemocytes incubated with venom in vitro could not form a melanized coat around the Sephadex A-50 beads at first, but their capbility of encapsulation recovered after lh. Moreover, hemocytes in the incubation with calyx fluid or the mixture exhibited significant depression in encapsulation of such beads.However, hemocytes in all incubation experiments could not encapsulate egg of C. vestalis in vitro.3. Effects of venom/calyx fluid from C. vestalis on hemocyte spreading ability of P. xylostella larvaeAfter injection with venom from C. vestalis, hemocyte spreading ability of P. xylostella larvae was depressed at first but recovered after 4h, while calyx fluid or the mixture had significant inhibitor}' effects on the spreading ability of hemocytes at all examined time points. Such an observation of depression in the incubation with the mixture exhibited even more significant inhibiton, which showed that venom could synergize the effect of calyx fluid or polydnavirus.4. Effects of venom/calyx fluid from C. vestalis on hemolymph melanization and the phenoloxidase activity in the hemolymph of P. xylostella larvae after injectionHemolymph collected from normal P. xylostella larvae could be melanized in vitro. However, hemolymph collected from the venom-injected host larvae could not be melanized within 4h after injection, but after that up to 48h hemolymph could be melanized as same to the control. In contrast, injection of calyx fluid could significantly inhibit melanization of hemolymph at all examined time points, and this effect was enhancen by the mixture of venom.Compared to the PBS-injected control, phenoloxidase (PO) activities in cell debris and hemocyte lysate of P. xylostella larvae were significantly decreased after injection of calyx fluid or the mixture, while there were no significant changes of PO activities in the larvae injected with venom.5. Effects of venom/calyx fluid from C. vastalis on activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and H₂O₂ concentration in its host P. xylostellaCompared to the PBS-injected control, H₂O₂ concentration in the host larvae increased significantly after injected with venom, calyx fluid or the mixture from C. vestalis at all examined time points, and increased more obviously in the larvae injected with the mixture, where the H₂O₂ concentration at 48h was 1.2-3.0 times higher than those at other time points. POD activity did not significantly change after injection of venom, calyx fluid or the mixture; and SOD activity increased significantly; CAT activity in the larvae injected with venom or calyx fluid was not altered, however, that in the larvae injected with the mixture was increased significantly.6. Effects of venom/calyx fluid from C. vastalis on activities of mixed function oxidases (MFOs) and acetylcholinesterase (AchE) of P. xylostella larvae after injectionAfter injected with venom, calyx fluid or the mixture from C. vestalis, no signicant difference in the activity of MFOs was observed compared to the PBS-injected control. The same result was obtained in the activity of AchE during 1-24h after injection, but during 36-48h this enzyme activity increased gradually and remained at a high level, and moreover, the effect of the mixture was higher than those of venom or calyx fluid along, but there was no difference between the effects of venom and calyx fluid.