Physiological Regulation Mechanisms Of The Cooperation Of SeNPV And Microplitis Pallidipes Szepligeti On The Spodoptera Exigua

Both Nuclear polyhedrosis virus （NPV） and Microplitis pallidipes Szepligeti arethe important regulators to the beet armyworm, S. exigua （Lepidoptera: Noctuidae） inthe fields, which paly a key role in sustainable control of S. exigua. In this study wetook the dominant species M. pallidipes （Hymenoptera: Braconidae） and SeNPV as objects,and S. exigua as a target. Meanwhile, the combined effect of SeNPV and M.pallidipes on host growth development, immunodepression and physiologicalmetabolism was summarized as follows:1. The infected larvae grow more slowly, prolonged their4th instar duration, and1.8days were delayed than nonparasitized host larvae; the length of body, width ofbody and width of the head capsule all significantly shortened, and the weight of bodysignificantly decreased; the length of body, width of body, width of the head capsuleand the weight of body of all treatment combinations gradually increased with theprolong of the virus inoculation.2. Biochemical mechanism of S. exigua was affected by the combination ofSeNPV and M. Pallidipes. SeNPV affected the synthesis of protein in the hemolymphin which the content of total protein was just1.95mg/ml at first day after virusinoculation, while up to12.17mg/ml at the fifth day after virus inoculation; the proteincontents of the larvae which were firstly infected and then were parasitized, were allhigher than that of CK during the inoculation time except the first day after virusinoculation; the lowest total carbohydrate content in the hemolymph is just0.14mg/mat the first day after the larvae is parasitized, the total carbohydrate contents in thehemolymph for treatments of parasitization after virus inoculation and inoculationafter parasitization, were all lower than CK except the second day after virusinoculation when the total carbohydrate content was slightly higher than CK. The lipidcontents of treatments of parasitization after virus inoculation and inoculation afterparasitization at the first day after virus inoculation were all lower than CK, but thelipid content of treatment of only virus inoculation has no significantly difference than that of CK.3. Through observation of phase contrast microscopy, five types of hemocyteswere determined in the hemolymph of S. exigua larvae, namely Granulocytes,Plasmatocytes, Oenocytoids, Prohemocytes and Coagulocytes. When Sephadex G-50beads were injected into the larvae, they were soon encapsulated by the hemocytes, thecyst rate of later5th instar was93.3%,4th instar was90%, early5th instar was80%.67%of the beads were encapsulated at the1sthours after injection, the cyst rateincreased gradually with the prolong of injection time, up to97%at the9th hours afterinjection.The total hemocytes of the treatment group were increased first and thendecreased and subsequently increased compared with the control. The Number ofGranulocytes and Plasmatocytes involved in immune response have also changed.4. Humoral immunity in S. exigua is affected by the combination of SeNPV and M.pallidipes. The melanization reaction of the host was inhibited in each group. ThePhenoloxidase activity and LSZ activity of the infected group was decreased first andthen increased and subsequently decreased. The Phenoloxidase activity of treatmentsof parasitization after virus inoculation and inoculation after parasitization maintain alower level, which indicated that the Phenoloxidase activity is inhibited. The LSZactivities of treatment of parasitization after virus inoculation were all lower than thatof CK, but slightly higher than that of CK at the4th day after virus inoculation, andthere were significant difference at the2nd and4th day.5. The host protective enzymes were affected by virus inoculation. The value ofSOD activity of the infected larvae was up to the highest1,2.39U/mg, whereasgradually declined at the2nd day after virus inoculation. This indicated that theincrease of O₂consumption led to the substantial increase of O₂^-and HO· in larvaebody, and further led to the obvious increases of SOD activity, so as to removeextensive free radicals. The CAT activity of the infected group was up to the largest16.78U/mg at the1st day after virus inoculation, whereas next gradually decreased.The POD activity of the infected group was significantly higher than that of CK at the1st and2nd day after virus inoculation. This indicated that virus infection led to theincrease of POD activity as well.