Effects Of Parasitization By The Endoparasitic Wasp Pteromalus Puparum (Hymenoptera: Ptermalidae) On Host Cellular Immune Responses And Physiological Metabolism

Pteromalus puparum is a key important pupal-specific endoparasitoid of Pieris rapae,which has evolved a unique means to suppress the host's immune system, as no otherparasitoid-associated virulence factors other than venom is found in the femalereproductive organ. The effects of parasitization by P. puparum on host cellular immuneresponses and physiological metabolism were studied. The results were summarized asfollows:1. Hemocytes characterization of P. rapae parasitized by P.puparumThe hemocytes morphology of P. rupae responed to parasitization by P. puparumwas investigated using light microscope and transmission electron microscope. Underlight microscope, the main influence of parasitization was observed on granulocytes andplasmatocytes. Light microscope showed that most of the granulocytes andplasmatocytes turned rounded, and their adhesion and spreading behavior was inhibited,while other types of hemocytes remained unaffected. Under transmission electronmicroscope, parasitization had a differential effect on host hemocytes. Prohemocytes,granulocytes, plasmatocytes and oenocytoids were all damaged to various extents.However, no changing was observed in coagulocytes.2. The effeets of venom on the encapsulation and phagoeytie reactionsin P. rapaeUsing monolayers of plasmatocytes and granulocytes prepared from P. rapae pupaehaemolymph by lylon wool cell fractionation method, we investigated the venom on thekey process of capsule formation and phagocytic reactions of plasmatocytes andgranulocytes in vitro in P. rapae. The results showed that both hemocyte number andvenom concentration affected the encapsulation index. In this study, Although venom reduced the number of granulocytes attached to sephadex A-50 beads, it could notinhibited the first step process that granulocytes attached to beads. However, venominhibited the attachment of multiple layers of plasmatocytes, which led to thetermination of capsule formation could not occured. In the present study wedemonstrated that in vitro, both granular cells and plasmatocytes are involved inphagocytic reaction. However, granulocytes were the main phagocytic hemocytes.Venom inhibited both plasmatocytes and granulocytes phagocytic ability, and thisinhibition showed a positive correlation with venom concentration.3 The effects of parasitization by P. puparum on the carbohydratemetabolism in hemolymph and fat body of P. rapaeEffects of parasitization on the carbohydrate metabolism of hemolymph and fat bodyof P. rapae pupae on hours 24, 36, 48, 60 and 72 were investigated. The results showedthat pyruvate level and lactate dehydrogenase activity decreased with elevated lactatelevels, indicating reduced mobilization of pyruvate into the Krebs cycle. Enzymes ofKrebs cycle, namely succinate dehydrogenase and malate dehydrogenase, weresignificantly lowered, suggesting a decrease in respiration rate at the tissue level. Theseresults suggest that parasitization affect the carbohydrate metabolism in P. rapae andconsequently alter their metabolic functions to meet the required energy demands underthe parasitized stress conditions.4 The effects of parasitization by P. puparum on the activity ofantioxidant enzymes and levels of antioxidant in P. rapaeParasitization causes oxidative stress by the release of reactive oxygen species (ROS)that are toxic to the cells. The antioxidant enzymes associated with oxidative stressduring the process of parasitization in hemolymph and fat body of P. rapae werequantitatively determined at different time intervals post parasitization (24, 36, 48, 60and 72 h after parasitization). The activities of superoxide dismutase in fat body,catalase in hemolymph and glutathione-S-transferase both in hemolymph and fat body,showed significant reductions compared to the control ones. These results showed thatthe venom injected into P. rapae followed parasitization together with ROS released by P. rapae inactivated the antioxidant enzymes. While glutathione reductase and reducedglutathione showed no differences to the controls indicated that parasitization did notinduce glutathione reductase and reduced glutathione to defend against parasitization.5 The effects of parasitization by P. puparum on activities of membranebound phosphatases and transaminases in P. rapaeThe activities of membrane bound phosphatases and transaminases were analyzed inhemolymph and fat body of P. rapae parasitized by P. puparum at different timeintervals post parasitization (24, 36, 48, 60 and 72 h after parasitization). Our resultsshowed that the activities of membrane bound phosphatases (Na⁺ K⁺ ATPase,C^a2+ATPase, Mg²⁺ ATPase and Total ATPase) in P. rapae parasitized by P. puparumsignificantly reduced compared to these control ones, which indicated that parasitizationcauses the decrease of membrane fluidity of host hemocytes and fat body cells. Theactivities of transaminases (alanine transaminase (ALT) and aspartate transaminase(AST)) were significantly elevated. This may be due to the tissues were large rangedamaged.