An endoparasitoid wasp, Cotesia plutellae parasitized young larval of diamondback moth, Plutella xylostella. Parasitized larva exhibit significant immunosuppression and fail to metamorphose to pupal stage. Especially, during last instar of parasitized P. xylostella, massive nutrients divert from host to wasp development. HTIF (host translation inhibitory factor) encoded in C. Plutella bracovirus (CpBV) play a crucial role in suppressing host usage of amino acids. However, its inhibitory activity is selective by discriminating mRNAs based on their 5’UTR secondary structures. Our RT-PCR and proteomic analysis indicated that arginine kinase mRNA was inhibited by HTIF, but imaginal disc growth factor was not. Arginine kinase and IDGF were persistently expressed in parasitized P. .xylotella with the gradual decrease at the late parasitisation period. Expression of arginine kinase and IDGF were also tissue specific in the gut/epidermis and haemocyte but not in fat bodies. Subsequent analysis of these gene functions by RNA interference explained the benefit of parasitoid for the mRNA discrimination by HTIF.

A polydnavirus, Cotesia plutellae bracovirus (CpBV), possesses segmented genome located on chromosome(s) of an endoparasitoid wasp, C. plutellae. An episomal viral segment (CpBV-S3) consists of 11,017 bp encoding two putative open reading frames (ORFs). ORF301 shows amino acid sequence homologies (28~50%) with RNase T2s of various organisms. It also contains BEN domain in C-terminal region. ORF302 is a hypothetical gene, which is also found in other bracoviruses. Both genes were expressed in larvae of Plutella xylostella parasitized by C. plutellae. ORF301 and ORF302 were transiently expressed in hemocyte, fat body, gut, and epidermis of P. xylostella. To analyze effects of these genes on the parasitism, the segment of CpBV-S3 was injected to non parasitized larvae of P. xylostella, in which the two genes were expressed at least for four days post-injection. The P. xylostella larvae injected with CpBV-S3 exhibited significant immunosuppression, such as reduction in total hemocyte population, suppression of immune associated genes including cecropin, pro-phenoloxidase (PO) and serpin1, and impairment in nodule formation behavior of hemocytes in response to bacterial challenge. Each gene expression in the treated larvae was inhibited by co-injecting respective double strand RNA (dsRNA) specific to each ORF. Injection of dsRNA of ORF301 could rescue the immunosuppression by the viral segmenttreated larvae, but not by ORF302 specific dsRNA. The larval injected with CpBV-S3 exhibited an enhanced susceptibility to baculovirus infection. These results indicate that ORF301 of CpBV-S3, which containing BEN domain, suppresses both cellular and humoral immune responses in P. xylostella.

Upon oviposition, parasitoid wasps inject their eggs along with venom, teratocytes and polydnavirus (PDV) on the host. Among these parasitic factors, PDVs are known to suppress the host immune system and utilize the host translational mechanisms allowing the juvenile parasitoid to develop. Polydnavirusencoded genes can selectively inhibit host translation and still use the translation machinery of the host to synthesize their own proteins. In this study, we utilize a proteomic approach involving two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) that couples isoelectric focusing (IEF) and SDS-PAGE to resolve complex protein mixtures that results from the parastization of Cotesia plutellae on the lepidopteran host, Plutella xylostella. We specifically analyze the changes in protein synthesis using this technique after treatment of HTIFs that has been previously identified on C. plutellae. The difference in protein profile due to parasitization was confirmed by in vitro translation assay using rabbit reticulosyte lysate.

A cysteine- rich protein encoded by Cotesia plutellae bacovirus (CpBV) was identified in the parasitized Plutella xylostella. The gene, called CpBV-CRP, encodes 189 amino acids with a signal peptide of 20 residues at N-terminus determined by bioinformatic analysis, suggesting a secretory protein. High CpBV-CRP expression in the parasitized P. xylostella was observed at early days after parasitization and decreased with the course of parasitization. Expression of CpBV-CRP was tissue-specific in the fat body/epidermis, but not in hemocyte and gut. Its physiological function was analyzed by transient expression of a CpBV segment containing CpBV-CRP. The treated larvae underwent an immunosuppression in terms of hemocyte-spreading behavior. When the treated larvae were also co-injected with dsRNA against CpBV-CRP, the suppressed hemocyte behavior was significantly recovered. This study reports a cysteine-rich protein encoded in CpBV genome and its physiological function to be an immunosuppressant.

DNA in the eukaryotic nucleus is packaged into highly organized chromatin. The basic structural unit of chromatin is the nucleosome, which consists of approximately 146 base pairs of DNA wrapped around a histone octamer core containing two molecules each of core histones H2A, H2B, H3, and H4. Histone covalent modification at the protruding N-terminal region from the nucleosomal core can change the chromatin conformation in order to regulate gene expression. A viral H4 was found in the genome of Cotesia plutellae bracovirus (CpBV). The obligate host of the virus is an endoparasitoid wasp, C. plutellae, which parasitizes the diamondback moth, Plutella xylostella, and interrupts host development and immune reactions. CpBV-H4 has been regarded as an immunosuppressive gene. Its extended N-terminal region contains nine lysine residues which are the target for modification. Previous report showed that CpBV-H4 inhibited hemocyte-spreading after transient expression. Here, transient expression of truncated CpBV-H4 (without N-terminal region) did not show high inhibitory effects on hemocyte-spreading. Moreover, the truncated CpBV-H4 induced acetylation of nucleus histone H4. Host H4 was found to be decreased in transcription after parasitization compared to nonparasitized larvae. Atransient expression of CpBV-H4 significantly inhibited host H4 transcription, suggesting a role of CpBV-H4 in controlling gene expression. Point mutagenesis study showed that two lysines (K6 and K16) of CpBV-H4 were found to have high inhibitory effects on hemocyte spreading. These results indicate the importance of CpBV-H4 and its N-terminal region to control gene expression and suppress host immunity.

For the development of integrated pest management system by harmonizing biological and chemical control, some experiments were carried out to select low toxic pesticides against natural enemies, and their residual toxicity were evaluated. Leaf dipping method, body dipping method, and diet treatment method were set up for the toxicity evaluation against Cotesia glomerata adults. We had tested 46 different pesticides (31 insecticides, 11 fungicides, 4 herbicides) at recommending concentration commonly used to control diamond back moth, disease and up-land weeds in chinese cabbage field. Twenty three insecticides, eleven fungicides, and four herbicides were shown to be low toxic to C. glomerata adults in the treatment of body dipping. After insecticide spraying at recommending dose on the chinese cabbage, we examined residual effect of insecticides by introducing natural enemies on different days. Safety interval for the introduction of C. glomerata adults was established according to the residual toxicity of pesticides. Safe insecticides for the introduction of C. glomerata adults at one day after treatment (DAT) were thiacloprid, acephate, chlorfenapyr, clothianidin and at 3 DAT were imidacloprid, deltamethrin, thiamethoxam, dimethylvinphos, emamectin benzoate.

Reproductive incompatibility is an important factor to select a specific biological control agent for successful augmentation of the corresponding endogenous population. An endoparasitoid, Cotesia plutellae (Kurdjumov), is an effective control agent to diamondback moth, Plutella xylostella (L.) and has been known to be classified into two groups in terms of reproductive incompatibility. This study analyzed an Korean population of C. plutellae in terms of morphological characters and mitochondrial DNA marker, which did not match with either of two reproductive incompatibility groups. These results suggest that a Korean population of C. plutellae can be involved in a novel reproductive group. For any augmentation program of C. plutellae in Korea, reproductive incompatibility should be seriously considered to select a particular exotic population.

A solitary endoparasitoid, Cotesia plutellae, parasitizes diamondback moth, Plutellae xylostella. It bas been suggested that its antennae are a major sensory organ to search host and recognize host developmental and other physiological condition during parasitization. This research was performed to understand the parasitic behavior of C. plutellae by analyzing sensory types and their numbers on the antennae using scanning electron microscope. There was no significant difference in antennal length in both male and female C. plutellae, in which both sexes had 16 flagellomeres. Three different types of sensilla (trichoid, seta, and placodea sensilla) were located mostly on flagella and analyzed in their density on the different antennomeres. Trichoid sensillum was the major sensory type and showed about 87% density among all sensilla. Both trichoid and placodea types of sensilla exhibited even numbers on all flagellomeres with some decrease at terminal segments. In contrast, seta form of sensilla showed drastic increase in its density at distal part after 9th flagellomere. When distal half of flagellomeres were cut off, the C. plutellae could not parasitize host larvae. Even when only four distal flagellorneres were removed, the parasitism showed only 30%. These results indicate that C. plutellae antennae are required for parasitism and suggest that seta form of sensilla may play significant roles in recognizing host for parasitization.

Inhibitor <SUB>K</SUB>B (I<SUB>K</SUB>B)-like gene has been found ill the genome of Cotesia plutellae bracovirus (CpBV), which is the obligatory symbiont of an endoparsitoid wasp, C. plutellae. The open reading frame of CpBV-I<SUB>K</SUB>B was 417 bp and encoded 138 amino acids. Four ankyrin repeat domains were found in CpBV-I<SUB>K</SUB>B, which shared high homology with other known polydnavirus I<SUB>K</SUB>Bs. Considering a presumptive cellular I<SUB>K</SUB>B based on Drosophila Cactus, CpBV-I<SUB>K</SUB>B exhibited a truncated structure with deletion of signal-receiving domains, which suggested its irreversible inhibitory role in NF<SUB>K</SUB>B signal transduction pathway of the parasitized host in response to the wasp parasitization. CpBV-I<SUB>K</SUB>B was expressed only in the parasitized diamondback moth, Plutella xylostella. Its expression was estimated by quantitative RT-PCR during parasitization period, showing a constitutive expression pattern from the first day of parasitization. An indirect functional analysis of CpBV-I<SUB>K</SUB>B was conducted and suggested a hypothesis of host antivirus inhibition.