Physiological Regulation Of Diamondback Moth, Plutella Xylostella (Linnaeus) (Lepidoptera: Plutellidae) By Diadromus Collaris (Gravenhorst) (Hymenoptera: Ichneumonidae)

Diadromus collaris (Gravenhorst) is one of the preponderant parasitoid of the pupae of diamondback moth (DBM), Plutella xylostella (Linnaeus), an important insect pest of crucifer vegetable crops. The characterization and physiological effects of parasitism, pseudoparasitism and venom were studied in this paper. The major results are summarized as follows:1 Observation on reproductive system and ultrastructure of venom apparatus of Diadromus collarisThe results of dissection and TEM revealed that the ovary of Diadromus collaris did not contain calyx region and polydnavirus. Two gland tubules and a common bladder-like reservoir form the gland part, and the free gland tubules arelocated on the top of the reservoir. A ductus venatus joins the reservoir with the sting apparatus, by which the venom of reservoir enters the ovipositor.A series of secretory units line around the two free tubules, each secretory unit consists of a secretory cell and a duct cell. An axial symmetry end apparatus and a cuticular ductule exists in the secretory cell, they connect the secretory cell with the collecting duct within the center of each of both the free tubules and the reservoir. Many member-bounded vesicles are present in the cytoplasm, they were secreted to collecting duct by end apparatus and a cuticular ductile. Secretory cell was well developed on about 7th day after eclosion and declined later.Cells of the reservoir wall were devided into two types with different morphology and function: one belongs to secretory unit including a secretory cell and a duct cell, and the other is the epithelial cell. The secretory unit of the revervoir is similar to that of the free tubules of venom gland, but is simpler than the later. A thin muscle layer, in which many mitochondria exist, surrounds the secretory unit to separate the latter from the haemolymph space. Cells in the reservoir wall are changed as well as the cells in venom gland.2 Biochemical properties and antimicrobial activity against E. coli of Diadromus collaris venomEach venom reservoir contains about 0.4μg proteins. There are 9 kinds of proteins or peptides in the venom in total, of which the peptides of 32.5 , 28.2 , 25.1 and 9kDa are the most abundant. There are denier glycoprotein in venom by glycoprotein stain, which MW is 75kDaand content is 0.1 ug in the band as compared to the maker that is 0.25ug in the band.Venom has the antimicrobial activity against E. coli shown by the plate and liquid growth assay. When incubated in plate no inhibition of E. coli growth occurred when treated by 2 venom reservoir equation, partial inhibition observed when treated by 10 venom reservoir equation while the bacterial growth were alomost all inhibited when treated by 20 venom reservoir equation. The MIC (minimal inhibition concentration) of the venom is 0.2-0.8ug/ul.3 Effects of parasitism and pesudoparasitism of Diadromus collaris on immune factors of DBM pupaeThe numbers of total haemocytes, plasmatocytes and granular cell increased in the parasitized host pupae, which is 3-6 times greater than those in the unparasitized pupae. The spreading behaviour of plasmatocytes and granular cells and the activity of phenoloxidase in the hemolymph of the parasitized pupae was inhibited. The inhibition of phenoloxidase activity and ability to encapsulate the Sephadex G-100 of DBM pupae hemolymph was found after pseudoparasitism. The DMB pupae showed an increased susceptibility to the entomopathogen Metarhizium anisopliae after pseudoparasitized.4 Effects of Diadromus collaris venom on immune factors of DBM larvaeWhen both the larval hemocytes and venom (0.04VRE/ul) were added to TC-100 medium simultaneously, both of plasmatocytes and granular cells were not adhesive and did not spread in certain extend. After 3h incubation with venom, the percentage of granular cells and plasmatocytes spreading is 50±3% and 5%, respectively. When the larval hemocytes were incubated in vitro for 3h at 27"C in TC-100 medium prior to addition of wasp venom, plasmatocytes and granular cell lysed in the presence of venom.The viability of granular cells is 5O±3% and the plasmatocytes is 20±l% after 3h incubation with venom. When incubated with venom for 3.5h, the vacuoles appeared in haemocytes. Venom also inhibite the melanism of L-DOPA when add to the hemolymph of DBM larvae.Venom afTect the phagocytosis of larval hemolymph to Eschechia coli in vitro. When the bacteria were resuspended in TBS containing 400, 80 or 4 ng/ul venom and then incubated with the hemocytes, the phagocytosis caused by haemocytes reduced by 75±5%, 30±8% and 10±2%, respectively. When the larval haemocytes were incubated with 400ng/ul venom for lh, later venom washed off, and the bacteria were added, the phagocytosis caused by haemocytes reduced by 62±3%. When bacteria were incubated with 400ng/ul venom for lh,later venom washed off, and then haemocytes were added, no significant reduction of phagocytosis by haemocytes occurred.5 Effect of Diadromus collaris venom on immune factors of factitious hostThe spreading behavior and adhesion of plasmatocytes and granular cells of Pieris rapae and Ostrinia furnacalis lavae were not affected when incubated with venom (0.04VRE/ul) for 3h. But the viability of haemocytes of Pieris rapae larvae was affected, the viability of plasmatocytes and granular cells was 73±4% and 65±2%, respectively, where the viability of both haemocytes of Ostrinia furnacalis lavae were identical to the control. PO activity of Pieris rapae but not Ostrinia furnacalis were slightly suppressed.6 Effect of parasitism and pseudoparasitism of Diadromus collaris on nutrition state of host pupaeLipid titre and protein concentration in fat body were reduced in parasitized and pseudoparasitized host pupae, and with the help of feeding by wasp larvae the reduction is more remarkable in parasitized ones from 1.5th day after parasitism. Lipid titre and protein concentration in hemolymph showed some increase after parasitism and pseudoparasitism. However, it decreased in parasitized pupae from 2th day due to the feeding by wasp larvae as comparaed to nonparasitized ones.The lipid titre of parasitoid larvae was low when they hatched from egg shortly, and after then increased gradually, and increased rapidly from 2.5th to 3.5th day and from 4.5th to 5.5th day after parasitization.7 Effect of parasitism and pseudoparasitism of Diadromus collaris on structure of fat body of DBM pupaeObservation on the morphology of fat body under light microscope revealed that the cells of fat body became loose from outer side in parasitized and pseudoparasitized pupae. The semi-thin slices dyeing with methylene blue indicated that the inclusion in cells were absent and some vacuole appeared in cells. The ultrastructure of fat body cell of parasitized and pseudoparasitized pupae showed that protein and lipid particles were decomposed with the action of autophagosome. Cells were divided each other and some cells lysed, substance embedded in cells were released to the hemocole. The variations of the structure of fat body in parasitized pupae are more obviously than that in pseudoparasitized ones. The acticity ofPLA2 and PLB in venom were detected and their functions discussed.8 Effect of parasitism and pseudoparasitism of Diadromus collaris on behavior and development of DBM pupaeEclosion of the DBM pupae was inhibited when pseudoparasitized by Diadromus collaris. The parasitoid venom could cause a transitory paralysis on parasitized and pseudoparasitized pupae. The paralysis influence is evident in 0.5h after parasitism, but disappeared in 7h after parasitism.