The Effect Of Spodoptera Exigua Nuclear Polyhedrosis Virus (SeNPV) On The Growth And Development Of Microplitis Pallidipes Szepligeti And On The Endocrine Activity Of Host Larvae

Nuclear polyhedrosis virus (NPV) and Microplitis pallidipes Szepligeti are theimportant biogical agents for controling beet armyworm, Spodoptera exigua (Hubner).To discover the effects of these two agents on Spodoptera exigua, we took “M.pallidipes-NPV-S. exigua” as study system, and discussed the infection of NPV onthe growth and development of M. pallidipes and on the endocrine activity of hostlarvae. The main results were as follows:1. M. pallidipes egresses and cocoons on day7after the2nd-instar larvae S.exigua were parasitized, i.e the duration from egg to larva and then to cocoon wasabout7days in which the duration of embryonic development is about one day. Inorder to ensure the embryo develops rapidly, by virtue of egg shell the parasitoid eggabsorbs nutrients from the host hemolymph; the parasitoid is up to the larval period onday2after parasitization when the tail end occurs a cauda; on day3the amnioticmembrane attached to the body surface of larval parasitoids begins to be disintegrated;an day4the cauda dies away and trans-parent round bladder occurs; on day5digestive tract is bottle green, and the capsule is light yellow; on day6host body islight yellow, a little bit bent and starts spinning; on day7larval parasitoid begins tococoon, host larvae dies of body burnout.2. The infection of NPV affected the life parameters of M. pallidipes. The valuesof life parameters varied with the infection time and infection concentrations. Theparasitism rates of “virus infection for24h and then parasitization for24h” group,“combined virus infection and parasitization for24h” group and “parasitization for24h and3days later virus infection for24h” group were44.3-74.7,41.7-48.2and58.5-62.3%respectively, the percentage of cocoons were60.3-71.3,60.3-67.1and65.2-75.5%respectively, and the emergence rate were65.8-70.9%,64.1-65.5%, and73.1-80.6%respectively. Compared to that in control (parasitized) group, the values(the duration of egg and larvae, the duration of cocoon and the longevity of adultparasitoids) in the combination groups of parasitization and virus infection were allobviously shortened and this effect was increased with the increase of virusconcentrations.3. The parasitization of M. pallidipes affected the NPV proliferation in host larvae body. When the virus concentrations were5.7×103,5.7×104and5.7×105OB.ml-1, the most numbers of NPV particles in host body on day6after virus infectionwere all “parasitization for24h and3days later virus infection for24h” group,0.723×10~8,1.150×10~8, and1.000×10~8OB respectively which were2.24times,2.36times and1.24times of those in control (virus-infected) group. Compared to that incontrol group(0.323×10~8OB),“combined virus infection at5.7×103OB.ml-1andparasitization for24h” group and “virus infection at5.7×103OB.ml-1for24h and thenparasitization for24h” group increased by43.03and118.89%respectively while thenumbers of NPV particles in these two combination groups decreased with theincrease of virus concentration. When the virus concentrations were at5.7×104and5.7×105OB.ml-1, the number of NPV particles in “combined virus infection andparasitization for24h” group was0.240×10~8and0.292×10~8OB respectively,49.28%and36.18%of controls respectively, while that in “virus infection for24h and thenparasitization for24h” group was0.247×10~8and0.222×10~8OB respectively,50.72%and27.51%of controls respectively.4. The interactions of M. pallidipes and NPV affected the molting hormonecontent. Compared to that in virus-infected (5.7×103OB.ml-1) group, the moltinghormone content in “combined virus infection and parasitization for24h” groupsignificantly increased on days2and5but significantly decreased on days3and4after treatment, the one in “virus infection for24h and then parasitization for24h”group significantly increased on day2but significantly decreased on days3,4and6after treatment, and the one in “parasitization for24h and3days later virus infectionfor24h” group increased on day1but significantly decreased on days1,3and4aftertreatment. Compared to that in virus-infected (5.7×105OB.ml-1) group, the moltinghormone content in “combined virus infection and parasitization for24h” groupsignificantly rose up at the first two days but obviously dropped down on day3andthese differences were significant from day4after treatment, the one in “virusinfection for24h and then parasitization for24h” group significantly ascended on day3but significantly descended on days2,4and6, and the one in “parasitization for24hand3days later virus infection for24h” group significantly increased on days1,3and4but significantly decreased on any other days.5. The calyx fluid of M. pallidipes could restrain the melanization andphenoloxidase activity in the hemolymph of larval S. exigua. The percentage ofmelanization of4th-instar larvae began to gradually decrease from0.5h but increasedfrom12h after calyx fluid injection, and that the inhibitory effect of calyx fluid onmelanization gradually weakened with the passage of time after calyx fluid injection;within the24h-observation time, the percentage of melanization was consistentlylower in calyx fluid injection group than phosphate buffer injection group and thesedifferences were significant at the first16hours after injection; the inhibitory effect of calyx fluid on the phenoloxidase activity of the hemolymph of host4th-instar larvaegradually weakened with the increase of injection, and the phenoloxidase activity wasconsistently lower in calyx fluid injection group than phosphate buffer injection groupand these differences were significant at the first12hours after injection.