Venom of parasitoid, Pteromalus puparum, suppresses host, Pieris rapae, immune promotion by decreasing host C-type lectin gene expression

An endoparasitoid uses its egg surface proteins to regulate its host immune response

With proteomic analysis, we identified 379 egg surface proteins from an endoparasitoid, Cotesia chilonis. Proteins containing conserved enzymatic domains constitute a large proportion of egg surface components. Some proteins, such as superoxidase dismutase, homolog of C. rubecula 32-kDa protein, and immunoevasive protein-2A, are classical parasitism factors that have known functions in host immunity regulation. Melanization assays revealed that a novel egg surface protein, C. chilonis egg surface serpin domain-containing protein had the same function as a C. chilonis venom serpin, as both suppressed host melanization in a dose-dependent manner. C. chilonis egg surface serpin domain-containing protein is mainly transcribed in C. chilonis oocytes with follicular cells, and it is located on both the anterior and posterior sides of the mature egg surface. Additionally, we used LC-MS/MS to identify 586 binding proteins sourced from C. suppressalis plasma located on the eggshell surface of C. chilonis, which included some immunity-related proteins. These results not only indicate that C. chilonis uses its egg surface proteins to reduce the immune response of its host but also imply that endoparasitoid egg surface proteins might be a new parasitism factor involved in host immune regulation.

Immulectin-2 from the ghost moth, Thitarodes xiaojinensis (Lepidoptera: Hepialidae), modulates cellular and humoral responses against fungal infection

C type-lectins constitute a large family of pattern recognition receptors, playing important roles in insect immune defenses. Thitarodes xiaojinensis larvae showed distinct immune features after Ophiocordyceps sinensis, Cordyceps militaris, or Beauveria bassiana infection. Based on transcriptome and immunoblot analysis, we found that immulectin-2 (IML2) was induced after T. xiaojinensis larvae were infected by C. militaris or B. bassiana but maintained at a low level after larvae injected with O. sinensis or Ringer's buffer. Recombinant IML2 (rIML2) could promote melanization, encapsulation, phagocytosis, and hemocyte aggregation in vitro. RNA interference with IML2 induced a significant reduction in the transcript levels of various antimicrobial peptides. Importantly, we found that the abundance of O. sinensis blastospores coated with rIML2 dramatically decreased in the host hemolymph. Overall, this study demonstrated that T. xiaojinensis IML2 modulates cellular and humoral responses to entomopathogenic fungi, broadening our view of the immune interaction between O. sinensis and its host.

CTL10 has multiple functions in the innate immune responses of the silkworm, Bombyx mori

Insect C-type lectins (CTLs) play crucial roles in modulating the humoral and cellular immune responses. In the domesticated silkworm Bombyx mori L., BmCTL10 gene encodes an immulectin containing two carbohydrate recognition domains (CRDs). The phylogenetic analysis showed that BmCTL10 didn't cluster with other immulectin homologs in B. mori. BmCTL10 was mainly expressed in second to fifth instar larvae, wandering stage larvae, prepupa, and adults. In naïve fifth instar larvae, BmCTL10 was predominantly expressed in the fat body and epidermis. In second instar larvae, the topical application of Beauveria bassiana by immersion caused down-regulation of BmCTL10. The intra-hemocoel injection of E. coli, S. aureus, B. bassiana, and 20-hydroxyecdysone in fifth instar larvae caused tissue and time-specific inductions. The recombinant protein (rBmCTL10) can bind to larval hemocytes and various pathogen-associated molecular patterns to enhance hemocyte-mediated nodulation, phagocytosis, and encapsulation. rBmCTL10 caused significant upregulation of most antimicrobial peptides and nitric oxide synthase 1 in hemocytes in vivo. Yeast two-hybrid demonstrated that integrin β3 and β4 subunits can interact with BmCTL10. Furthermore, only CRD2 can interact with the β3, while both CRD1 and CRD2 can interact with the β4. Taken together, this study showed that BmCTL10 has multiple functions in the innate immune responses of B. mori and two integrin β subunits are their potential receptors.

Haemocyte-mediated immunity in insects: Cells, processes and associated components in the fight against pathogens and parasites

The host defence of insects includes a combination of cellular and humoral responses. The cellular arm of the insect innate immune system includes mechanisms that are directly mediated by haemocytes (e.g., phagocytosis, nodulation and encapsulation). In addition, melanization accompanying coagulation, clot formation and wound healing, nodulation and encapsulation processes leads to the formation of cytotoxic redox-cycling melanin precursors and reactive oxygen and nitrogen species. However, demarcation between cellular and humoral immune reactions as two distinct categories is not straightforward. This is because many humoral factors affect haemocyte functions and haemocytes themselves are an important source of many humoral molecules. There is also a considerable overlap between cellular and humoral immune functions that span from recognition of foreign intruders to clot formation. Here, we review these immune reactions starting with the cellular mechanisms that limit haemolymph loss and participate in wound healing and clot formation and advancing to cellular functions that are critical in restricting pathogen movement and replication. This information is important because it highlights that insect cellular immunity is controlled by a multilayered system, different components of which are activated by different pathogens or during the different stages of the infection.

Venom composition of the endoparasitoid wasp Cotesia flavipes (Hymenoptera: Braconidae) and functional characterization of a major venom peptide

Endoparasitoid wasps use complex biochemical arsenals to suppress the normal humoral and cellular immune responses of their hosts in order to transform them into a suitable environment for development of their eggs and larvae. Venom injected during oviposition is a key component of this arsenal, but the functions of individual venom toxins are still poorly understood. Furthermore, there has been little investigation of the potential biotechnological use of these venom toxins, for example for control of agricultural pests. The endoparasitoid Cotesia flavipes (Hymenoptera: Braconidae) is a biocontrol agent reared in biofactories and released extensively in Brazil to control the sugarcane borer Diatraea saccharalis (Lepidoptera: Crambidae). The objectives of this work were to reveal venom components produced by C. flavipes and explore the function of a major venom peptide, Cf4. Using a combined proteomic/transcriptomic approach, we identified 38 putative venom toxins including both linear and disulfide-rich peptides, hydrolases, protease inhibitors, apolipophorins, lipid-binding proteins, and proteins of the odorant binding families. Because of its high abundance in the venom, we selected Cf4, a 33-residue peptide with three disulfide bonds, for synthesis and further characterization. We found that synthetic Cf4 reduced the capacity of D. saccharalis hemocytes to encapsulate foreign bodies without any effect on phenoloxidase activity, consistent with a role in disruption of the cellular host immune response. Feeding leaves coated with Cf4 to neonate D. saccharalis resulted in increased mortality and significantly reduced feeding compared to caterpillars fed untreated leaves, indicating that Cf4 is a potential candidate for insect pest control through ingestion. This study adds to our knowledge of endoparasitoid wasp venoms composition, host regulation mechanisms and their biotechnological potential for pest management.

Identification of 35 C-Type Lectins in the Oriental Armyworm, Mythimna separata (Walker)

Simple Summary

The oriental armyworm Mythimna separata is a lepidopteral agricultural pest that causes serious damage to many crops, such as maize, wheat, and sorghum. To control this pest, it is advisable to take comprehensive measures, including the use of chemical pesticides, microbial pesticides, and cultural practices. However, microbial pesticides (entomopathogens) can be eliminated by the insect immune system. C-type lectins (CTLs) are a family of pattern-recognition receptors that recognize carbohydrates and mediate immune responses. C-type lectins in the oriental armyworm have not yet been identified and characterized. In this study, a transcriptome of M. separata larvae was constructed and a total of 35 CTLs containing single or dual carbohydrate-recognition domains (CRDs) were identified from unigenes. Phylogenetic analyses, sequence alignments and structural predictions were performed. Gene expression profiles in different developmental stages, naïve larval tissues, and bacteria/fungi-challenged larvae were analyzed. Overall, our findings indicate that most dual-CRD CTLs are expressed in mid-late-stage larvae, pupae, and adults. Bacterial and fungal challenges can stimulate the expression of many CTLs in larval hemocytes, fat body, and midgut. Our data suggest the importance of CTLs in immune responses of M. separata.

Abstract

Insect C-type lectins (CTLs) play vital roles in modulating humoral and cellular immune responses. The oriental armyworm, Mythimna separata (Walker) (Lepidoptera: Noctuidae) is a migratory pest that causes significant economic loss in agriculture. CTLs have not yet been systematically identified in M. separata. In this study, we first constructed a transcriptome of M. separata larvae, generating a total of 45,888 unigenes with an average length of 910 bp. Unigenes were functionally annotated in six databases: NR, GO, KEGG, Pfam, eggNOG, and Swiss-Prot. Unigenes were enriched in functional pathways, such as those of signal transduction, endocrine system, cellular community, and immune system. Thirty-five unigenes encoding C-type lectins were identified, including CTL-S1~CTL-S6 (single CRD) and IML-1~IML-29 (dual CRD). Phylogenetic analyses showed dramatic lineage-specific expansions of IMLs. Sequence alignment and structural modeling identified potential ligand-interacting residues. Real-time qPCR revealed that CTL-Ss mainly express in eggs and early stage larvae, while IMLs mainly express in mid-late-stage larvae, pupae, and adults. In naïve larvae, hemocytes, fat body, and epidermis are the major tissues that express CTLs. In larvae challenged by Escherichia coli, Staphylococcus aureus, or Beauveria bassiana, the expression of different CTLs was stimulated in hemocytes, fat body and midgut. The present study will help further explore functions of M. separata CTLs.

A chromosome-level genome assembly of the parasitoid wasp Pteromalus puparum

Parasitoid wasps represent a large proportion of hymenopteran species. They have complex evolutionary histories and are important biocontrol agents. To advance parasitoid research, a combination of Illumina short-read, PacBio long-read and Hi-C scaffolding technologies was used to develop a high-quality chromosome-level genome assembly for Pteromalus puparum, which is an important pupal endoparasitoid of caterpillar pests. The chromosome-level assembly has aided in studies of venom and detoxification genes. The assembled genome size is 338 Mb with a contig N50 of 38.7 kb and a scaffold N50 of 1.16 Mb. Hi-C analysis assembled scaffolds onto five chromosomes and raised the scaffold N50 to 65.8 Mb, with more than 96% of assembled bases located on chromosomes. Gene annotation was assisted by RNA sequencing for the two sexes and four different life stages. Analysis detected 98% of the BUSCO (Benchmarking Universal Single-Copy Orthologs) gene set, supporting a high-quality assembly and annotation. In total, 40.1% (135.6 Mb) of the assembly is composed of repetitive sequences, and 14,946 protein-coding genes were identified. Although venom genes play important roles in parasitoid biology, their spatial distribution on chromosomes was poorly understood. Mapping has revealed venom gene tandem arrays for serine proteases, pancreatic lipase-related proteins and kynurenine-oxoglutarate transaminases, which have amplified in the P. puparum lineage after divergence from its common ancestor with Nasonia vitripennis. In addition, there is a large expansion of P450 genes in P. puparum. These examples illustrate how chromosome-level genome assembly can provide a valuable resource for molecular, evolutionary and biocontrol studies of parasitoid wasps.

Pattern recognition receptors from lepidopteran insects and their biological functions

Lepidopteran insects have potent innate immunity to fight against the invading pathogens. As the initiation step, pattern recognition receptors (PRRs) recognize and bind microbial surface configurations known as pathogen-associated molecular patterns (PAMPs). Aftermath, they initiate both cellular and humoral immune responses, including phagocytosis, agglutination, nodulation, encapsulation, prophenoloxidase activation, and synthesis of antimicrobial peptides. In this review, we summarize the recent findings concerning PRRs in lepidoptaeran insects, mostly agriculture pests including Helicoverpa armigera, Plutella xylostella, and Spodoptera exigua. We mainly focus on the function and phylogeny of C-type lectins (CTLs), peptidoglycan recognition proteins (PGRPs), β-1,3-glucan recognition proteins (βGRPs), and galectins (GALEs). It enriches our understanding of the immune system of lepidopteran insects and provides directions in the future research.

Evidence of Leaf Consumption Rate Decrease in Fall Armyworm, Spodoptera frugiperda, Larvae Parasitized by Coccygidium luteum

Biological control is one of the best options for the sustainable management of the invasive maize pest Spodoptera frugiperda in Africa. However, there is limited knowledge of the efficacy of native natural enemies of S. frugiperda and their potential use in integrated pest management. The endoparasitoid wasp Coccygidium luteum is one of the natural enemies of S. frugiperda in Africa. This study assessed, under laboratory conditions, the effect of C. luteum on the leaf consumption rate of its host. Fifty first instar S. frugiperda larvae were exposed to C. luteum for oviposition and the maize leaf consumption rate of parasitized larvae was assessed and compared to 50 unparasitized larvae from the same cohort. Coccygidium luteum completed a generation, from egg to adult emergence, in 16.7 days. The leaf consumption rate of parasitized S. frugiperda larvae declined gradually compared to unparasitized larvae and the overall consumption reduction by parasitized S. frugiperda larvae was 89%. Our findings show that C. luteum could reduce damage caused by S. frugiperda to maize farms but, prior to its use in biological control programmes, further studies are needed to assess potential parasitism rates in field conditions and develop a cost-effective mass production system.

Regulation of the Larval Transcriptome of Diatraea saccharalis (Lepidoptera: Crambidae) by Maternal and Other Factors of the Parasitoid Cotesia flavipes (Hymenoptera: Braconidae)

Koinobiont endoparasitoid wasps regulate the host's physiology to their own benefit during their growth and development, using maternal, immature and/or derived-tissue weaponry. The tools used to subdue the wasps' hosts interfere directly with host transcription activity. The broad range of host tissues and pathways affected impedes our overall understanding of the host-regulation process during parasitoid development. Next-generation sequencing and de novo transcriptomes are helpful approaches to broad questions, including in non-model organisms. In the present study, we used Illumina sequencing to assemble a de novo reference transcriptome of the sugarcane borer Diatraea saccharalis, to investigate the regulation of host gene expression by the larval endoparasitoid Cotesia flavipes. We obtained 174,809,358 reads and assembled 144,116 transcripts, of which 44,325 were putatively identified as lepidopteran genes and represented a substantial number of pathways that are well described in other lepidopteran species. Comparative transcriptome analyses of unparasitized versus parasitized larvae identified 1,432 transcripts of D. saccharalis that were up-regulated under parasitization by C. flavipes, while 1,027 transcripts were down-regulated. Comparison of the transcriptomes of unparasitized and pseudoparasitized D. saccharalis larvae led to the identification of 1,253 up-regulated transcripts and 972 down-regulated transcripts in the pseudoparasitized larvae. Analysis of the differentially expressed transcripts showed that C. flavipes regulated several pathways, including the Ca+2 transduction signaling pathway, glycolysis/gluconeogenesis, chitin metabolism, and hormone biosynthesis and degradation, as well as the immune system, allowing us to identify key target genes involved in the metabolism and development of D. saccharalis.

Alteration of the phagocytosis and antimicrobial defense of Octodonta nipae (Coleoptera: Chrysomelidae) pupae to Escherichia coli following parasitism by Tetrastichus brontispae (Hymenoptera: Eulophidae)

Although parasites and microbial pathogens are both detrimental to insects, little information is currently available on the mechanism involved in how parasitized hosts balance their immune responses to defend against microbial infections. We addressed this in the present study by comparing the immune response between unparasitized and parasitized pupae of the chrysomelid beetle, Octodonta nipae (Maulik), to Escherichia coli invasion. In an in vivo survival assay, a markedly reduced number of E. coli colony-forming units per microliter was detected in parasitized pupae at 12 and 24 h post-parasitism, together with decreased phagocytosis and enhanced bactericidal activity at 12 h post-parasitism. The effects that parasitism had on the mRNA expression level of selected antimicrobial peptides (AMPs) of O. nipae pupae showed that nearly all transcripts of AMPs examined were highly upregulated during the early and late parasitism stages except defensin 2B, whose mRNA expression level was downregulated at 24 h post-parasitism. Further elucidation on the main maternal fluids responsible for alteration of the primary immune response against E. coli showed that ovarian fluid increased phagocytosis at 48 h post-injection. These results indicated that the enhanced degradation of E. coli in parasitized pupae resulted mainly from the elevated bactericidal activity without observing the increased transcripts of target AMPs. This study contributes to a better understanding of the mechanisms involved in the immune responses of a parasitized host to bacterial infections.

Analysis of the Gynaephora qinghaiensis pupae immune transcriptome in response to parasitization by Thektogaster sp

As a pest on the Qinghai-Tibet Plateau, Gynaephora qinghaiensis causes severe damage to grassland vegetation and its pupae are also natural hosts of Thektogaster sp. To successfully parasitize, endoparasitoids generally introduce or secrete multiple parasitic factors into the host body during the spawning stage to suppress the host immune response. To study the parasitic effects of Thektogaster sp. on G. qinghaiensis, a transcriptome analysis of immune-related genes in parasitized and nonparasitized G. qinghaiensis pupae was performed. A total of 371,260,704 clean reads were assembled into 118,144 unigenes with an average length of 884.33 base pairs. Of these, 23,660 unigenes were annotated in at least one database and 94,484 unigenes were not annotated in any databases. These findings indicated that the majority of the genetic resources (79.97% of all unigenes) in Gynaephora should be further explored. Parasitization significantly affected the transcriptional profile of G. qinghaiensis pupae. The present study identified 12,322 differentially expressed genes and 57 immune-related genes were identified in parasitized G. qinghaiensis pupae. Most immune-related genes were downregulated, potentially resulting from the inhibitory effect of Thektogaster sp. on G. qinghaiensis pupae after parasitization. Overall, the transcriptome analysis sheds valuable light on the molecular mechanisms of G. qinghaiensis parasitization by Thektogaster sp. and promotes the development of novel biocontrol strategies for Gynaephora based on immune defense.

Molecular characterization of immune responses of Helicoverpa armigera to infection with the mermithid nematode Ovomermis sinensis

Background

Mermithid nematodes, such as Ovomermis sinensis, display a broad host range including some lepidopteran pests. Infective juveniles penetrate their host through the cuticle, complete their growth within the hemocoel and eventually kill the host upon their emergence. Hence, mermithid nematodes are considered potential biological control agents of insect pests. Our previous data indicate that the infection rate of O. sinensis on cotton bollworm (Helicoverpa armigera) is low, which may be largely due to the strong immune system of the host. However, current knowledge on the interactions of mermithid nematodes with their hosts and the mechanisms employed by hosts to defend themselves against mermithid nematodes is limited.

Results

Here, we investigated the response of H. armigera to O. sinensis infection. Parasitism by O. sinensis caused a sharp decline in the survival rate of H. armigera. The hemocytic phagocytosis ability, antibacterial activity, and phenoloxidase (PO) activity in plasma of H. armigera increased at 1 d post parasitism (dpp) but decreased at 3 dpp. Further, we investigated gene expression in the fat body of parasitized and non-parasitized H. armigera larvae at 1, 3, and 5 dpp using a digital gene expression system. In total, 41, 60 and 68 immune-related differentially expressed genes were identified at 1, 3, and 5 dpp, respectively. These genes encoded pattern recognition receptors (PRRs), antimicrobial peptides (AMPs), serine proteases (SPs), SP inhibitors, mucins and other immune-related proteins. The expression of most PRRs, AMPs, SPs, and mucins was upregulated in the fat body of larvae at 1 dpp, downregulated at 3 dpp, and then again upregulated at 5 dpp by O. sinensis. The increased expression of SP inhibitors may contribute to the inhibited PO activity at 5 dpp.

Conclusions

This study demonstrates that parasitism by O. sinensis modulates the immune reaction of the host H. armigera by altering the expression of immune-related genes. Our data provide a basis for future investigation of the molecular mechanisms employed by the mermithid nematode O. sinensis to modulate the immunity of the host H. armigera. These data will also likely facilitate the improvement of success in parasitism of H. armigera by O. sinensis.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5544-1) contains supplementary material, which is available to authorized users.

Insect C-type lectins in innate immunity

C-type lectins (CTLs) are a family of proteins that contain characteristic modules of carbohydrate-recognition domains (CRDs) and they possess the binding activity to ligands in a calcium-dependent manner. CTLs play important roles in animal immune responses, and in insects, they are involved in opsonization, nodule formation, agglutination, encapsulation, melanization, and prophenoloxidase activation, as well as in maintaining gut microbiome homeostasis. In this review, we will summarize insect CTLs, compare the properties of insect CTLs with vertebrate CTLs, and focus mainly on the domain organization and functions of insect CTLs in innate immunity.

Oxidative stress and cytotoxicity elicited lipid peroxidation in hemocytes of Bombyx mori larva infested with dipteran parasitoid, Exorista bombycis

Parasitization of silkworm, Bombyx mori by invasive larva of dipteran parasitoid Exorista bombycis caused upto 20% revenue loss in sericulture. The parasitism was successful by suppressing host immune system however mechanism of immune suppression induced by E. bombycis is unknown which is unravelled here. The infestation induced cytotoxic symptoms in host hemocytes, such as vacuolated cytoplasm, porous plasma membrane, indented nuclei with condensed chromatin and dilated RER. One of the markers of necrosis is cell permeabilization, which can be measured as released lactate dehydrogenase (LDH). LDH level showed significantly (P<0.01) high release into extracellular medium in vitro after exposure of hemocytes to parasitoid larval tissue protein compared with control revealing membrane permeability and loss of cell integrity. At five minutes after exposure, cytotoxicity was 43% and was increased to 99% at 3h. The cytotoxicity is signalled by increased content of hydrogen peroxide (H2O2) causing lipid peroxidation followed by porosity in plasma membrane. A test for lipid peroxidation by measurement of lipid peroxidation breakdown product, malondialdehyde (MDA) revealed significant increase in peroxidation from one to 24 h post-invasion, with maximum at 12 h (P<0.008). Level of reactive oxygen species measured as H2O2 production increased from 6 to 12 h post-invasion and continued to increase significantly (P<0.03) reaching maximum at 48 h. These observations reveal that dipteran endoparasitoid invasion induced H2O2 production in the hemocytes causing cytotoxicity, lipid peroxidation and membrane porosity that suppressed both humoral- and cell-mediated immune responses of hemocytes in B. mori.

The genomic and transcriptomic analyses of serine proteases and their homologs in an endoparasitoid, Pteromalus puparum

In insects, serine proteases (SPs) and serine protease homologs (SPHs) constitute a large family of proteins involved in multiple physiological processes such as digestion, development, and immunity. Here we identified 145 SPs and 38 SPHs in the genome of an endoparasitoid, Pteromalus puparum. Gene duplication and tandem repeats were observed in this large SPs/SPHs family. We then analyzed the expression profiles of SP/SPH genes in response to different microbial infections (Gram-positive bacterium Micrococcus luteus, Gram-negative bacterium Escherichia coli, and entomopathogenic fungus Beauveria bassiana), as well as in different developmental stages and tissues. Some SPs/SPHs also displayed distinct expression patterns in venom gland, suggesting their specific physiological functions as venom proteins. Our finding lays groundwork for further research of SPs and SPHs expressed in the venom glands.

A novel negative-stranded RNA virus mediates sex ratio in its parasitoid host

Parasitoid wasps are important natural enemies of arthropod hosts in natural and agricultural ecosystems and are often associated with viruses or virion-like particles. Here, we report a novel negative-stranded RNA virus from a parasitoid wasp (Pteromalus puparum). The complete viral genome is 12,230 nucleotides in length, containing five non-overlapping, linearly arranged open reading frames. Phylogenetically, the virus clusters with and is a novel member of the mononegaviral family Nyamiviridae, here designated as Pteromalus puparum negative-strand RNA virus 1 (PpNSRV-1). PpNSRV-1 is present in various tissues and life stages of the parasitoid wasp, and is transmitted vertically through infected females and males. Virus infections in field populations of P. puparum wasps ranged from 16.7 to 37.5%, without linearly correlating with temperature. PpNSRV-1 increased adult longevity and impaired several fitness parameters of the wasp, but had no influence on successful parasitism. Strikingly, PpNSRV-1 mediated the offspring sex ratio by decreasing female offspring numbers. RNA interference knockdown of virus open reading frame I eliminated these PpNSRV-1-induced effects. Thus, we infer that PpNSRV-1 has complex effects on its insect host including sex ratio distortion towards males, as well as possible mutualistic benefits through increasing wasp longevity.

Although a few viruses with RNA genomes have been discovered in parasitoid wasps, their numbers are limited and their effects on the wasps have rarely been determined. Unambiguous negative-sense, single-stranded RNA [(-)ssRNA] viruses in parasitoids wasps have not been described. In this report, we identify a novel (-)ssRNA virus from a parasitoid wasp, verify the presence of virion-like particles in various wasp tissues, and characterize the viral genomic structure, transcription strategy, phylogenetic relationship, transmission strategy, and biological impacts on its host. Most importantly, we reveal that this novel virus mediates secondary sex ratio of its host by decreasing female offspring numbers, and can be transmitted both by male and female to offspring. Decrease in female offspring could be due to increased female mortality or to alterations in the primary sex ratio. The reduced female offspring number per female could therefore be a fecundity cost or a tradeoff for increased longevity of the wasp. However, it remains to be determined whether increased longevity under laboratory conditions translates into increased lifetime fecundity for the wasp in nature. Increased longevity could be beneficial to the virus by promoting its transmission to more hosts. The secondary sex-ratio distortion induced by the virus may also increase its transmission in host populations, because males transmit the virus to their offspring and can mate with multiple females, thus further spreading the virus.

Differential responses of Helicoverpa armigera C-type immunlectin genes to the endoparasitoid Campoletis chlorideae

The C-type lectins mediate nonself recognition in insects. The previous studies focused on host immunlectin response to bacterial infection; however, the molecular basis of immunlectin reactions to endoparasitoids has not been elucidated. The present study investigated the effect of parasitization by Campoletis chlorideae on hemagglutination activity (HA; defined as the ability of lectin to agglutinate erythrocytes or other cells), and transcriptional expression of C-type immunlectin genes in the larval host, Helicoverpa armigera. Parasitization induced four- to eightfold higher HA in the parasitized larvae, compared to nonparasitized larvae at days 2 and 6 postparasitization (PP), however inhibited HA at other days PP. Eight C-type lectins were differentially expressed in different host developmental stages, from feeding to wandering stage. The mRNA levels of HaCTL1, HaCTL3, HaCTL4, and HaCTL5 were upregulated and HaCTL2 and HaCTL7 were downregulated. Tissue analysis showed that HaCTLs were mainly expressed in fat body or hemocytes, while HaCTL5 was highly expressed in testes. The effects of parasitization on the lectin expression patterns differed. Lectins except HaCTL6 or HaCTL5 were significantly down- or upregulated in parasitized larvae at day 4 or 6 PP compared with that of nonparasitized larvae. We infer from our results that C-type immunlectins are involved in host-parasitoid interactions, and parasitization alter host immunlectin levels both in inhibiting and promoting host immune defenses to endoparasitoids. These immunlectin genes indicated an altered physiological status of the host insect, depending on developmental stage, tissue, and parasitization.

A Venom Serpin Splicing Isoform of the Endoparasitoid Wasp Pteromalus puparum Suppresses Host Prophenoloxidase Cascade by Forming Complexes with Host Hemolymph Proteinases

To ensure successful parasitism, parasitoid wasps inject venom along with their eggs into their hosts. The venom serves to suppress host immune responses, including melanization. Venom from Pteromalus puparum, a pupal endoparasitoid, inhibits melanization of host hemolymph in vitro in a dose-dependent manner. Using assay-guided fractionation, a serpin splicing isoform with phenoloxidase inhibitory activity was identified as P puparum serpin-1, venom isoform (PpS1V). This serpin gene has 16 predicted splicing isoforms that differ only in the C-terminal region. RT-PCR results show that the specific serpin isoform is differentially expressed in the venom gland. Recombinant PpS1V (rPpS1V) suppresses host prophenoloxidase (PPO) activation rather than inhibiting the phenoloxidase directly. Pulldown assays show that PpS1V forms complexes with two host hemolymph proteins, here named Pieris rapae hemolymph proteinase 8 (PrHP8) and P. rapae prophenoloxidase-activating proteinase 1 (PrPAP1), based on gene sequence blasting and phylogenetic analysis. The role of rPrPAP1 in the PPO activation cascade and its interaction with rPpS1V were confirmed. The stoichiometry of inhibition of PrPAP1 by PpS1V is 2.3. PpS1V also inhibits PPO activation in a non-natural host, Ostrinia furnacalis, through forming a complex with O. furnacalis serine protease 13 (OfSP13), an ortholog to PrPAP1. Our results identify a venom-enriched serpin isoform in P. puparum that inhibits host PPO activation, probably by forming a complex with host hemolymph proteinase PrPAP1.

De novo sequencing and transcriptome analysis of venom glands of endoparasitoid Aenasius arizonensis (Girault) (=Aenasius bambawalei Hayat) (Hymenoptera, Encyrtidae)

Aenasius bambawalei Hayat (Encyrtidae: Hymenoptera) has been synonymized with Aenasius arizonensis (Girault) is a small, newly discovered endoparasitoid of the cotton mealybug Phenacoccuss solenopsis Tinsley (Pseudococcidae: Hemiptera), which completes its life cycle inside the body of its host and it is a potential insect control tool. Despite the acquired knowledge regarding host-parasitoid interaction, little information is available on the factors of parasitoid origin able to modulate mealybug physiology. The components of A. arizonensis venom have not been well studied but venom from other parasitoids and wasps contain biologically active proteins that have potential applications in pest management or may be of medicinal importance. To provide an insight into the transcripts expressed in the venom gland of A. arizonensis, a transcriptomic database was developed utilizing high throughput RNA sequencing approaches to analyze the genes expressed in venom glands of this endoparasitic wasp. The resulting A. arizonensis RNA sequences were assembled de-novo with contigs then blasted against the NCBI non-redundant sequence database. Contigs which matched database sequences were mostly homologous to genes from hymenopteran parasitoids such as Nasonia vitripennis, Copidosoma floridanum, Fopius arsenus and Pteromalas puparium. Further analysis of the A. arizonensis database was then performed which focused on selected genes encoding proteins potentially involved in host developmental arrest, disrupting the host immune system, host paralysis, and transcripts that support these functions. Sequenced mRNAS predicted to encode full length ORFs of Calreticulin, Serine Protease Precursor and Arginine kinase proteins were identified and the tissue specific expression of these putative venom genes was analyzed by RT-PCR. In addition, results also demonstrate that de novo transcriptome assembly allows useful venom gene expression analysis in a species lacking a genome sequence database and may provide useful information for devising control tools for insect pests and other applications.

De novo sequencing and transcriptome analysis of female venom glands of ectoparasitoid Bracon hebetor (Say.) (Hymenoptera: Braconidae)

Venom is a key-factor in the regulation of host physiology by parasitic Hymenoptera and a potentially rich source of novel bioactive substances for biotechnological applications. The limited study of venom from the ectoparasitoid Bracon hebetor, a tiny wasp that attacks larval pest insects of field and stored products and is thus a potential insect control agent, has not described the full complement and composition of these biomolecules. To have a comprehensive picture of genes expressed in the venom glands of B. hebetor, a venom gland transcriptome was assembled by using next generation sequencing technologies followed by de novo assemblies of the 10.81 M sequence reads yielded 22,425 contigs, of which 10,581 had significant BLASTx hits to know genes. The majority of hits were to Diachasma alloeum, an ectoparasitoid from same taxonomic family, as well as other wasps. Gene ontology grouped the sequences into molecular functions in which catalytic activity with 42.2% was maximum, cellular components in which cells with 33.8% and biological processes among which metabolic process with 30% had the most representatives. In this study, we highlight the most abundant sequences, and those that are likely to be functional components of the venom for parasitization. Full length ORFs of Calreticulin, Venom Acid Phosphatase Acph-1 like protein and arginine kinase proteins were isolated and their tissue specific expression was studied by RT-PCR. Our report is the first to characterize components of the B. hebetor venom glands that may be useful for developing control tools for insect pests and other applications.

Altered immune function of Octodonta nipae (Maulik) to its pupal endoparasitoid, Tetrastichus brontispae Ferrière

Most studies on the contribution of the altered immune response by endoparasitoid have been restricted to the interactions between Ichneumonoidea and their hosts, while effects of parasitism by Chalcidoidea on the hosts have rarely been characterized except some wasps such as Pteromalidae. Endoparasitoid Tetrastichus brontispae Ferrière, belonging to Eulophidae (Hymenoptera), has a great potential to control some Coleopteran beetles such as Octodonta nipae, one invasive species in southern China. However, the physiological mechanism underlying the escape from the melanotic encapsulation in O. nipae pupae has not been demonstrated. In the present study, effects of parasitism on the immune function of its pupal host O. nipae were investigated. The combining results that granulocytes and plasmatocytes could phagocytize bacteria from 2 to 48h and granulocytes, plasmatocytes and oenocytoids were prophenoloxidase/phenoloxidase positive hemocytes indicated that granulocytes, plasmatocytes and oenocytoids were the main immunocompetent hemocytes in O. nipae pupae. Parasitism by T. brontispae resulted in a significant increase in the percentage of hemocytes viability and spreading at 96h, growing percentage of granulocytes at 24h but no effects on the total hemocyte counts, and an enhanced phenoloxidase activity only at 12 and 72h while a significantly longer melanization time of the hemolymph at 96h following parasitism. These results indicate that mixtures of systemic active and local active regulation are used for T. brontispae to escape host encapsulation in O. nipae pupae. The present study contributes to the understanding of the diversity of virulence strategies used by parasitoids.

Venom of Parasitoid Pteromalus puparum Impairs Host Humoral Antimicrobial Activity by Decreasing Host Cecropin and Lysozyme Gene Expression

Insect host/parasitoid interactions are co-evolved systems in which host defenses are balanced by parasitoid mechanisms to disable or hide from host immune effectors. Here, we report that Pteromalus puparum venom impairs the antimicrobial activity of its host Pieris rapae. Inhibition zone results showed that bead injection induced the antimicrobial activity of the host hemolymph but that venom inhibited it. The cDNAs encoding cecropin and lysozyme were screened. Relative quantitative PCR results indicated that all of the microorganisms and bead injections up-regulated the transcript levels of the two genes but that venom down-regulated them. At 8 h post bead challenge, there was a peak in the transcript level of the cecropin gene, whereas the peak of lysozyme gene occurred at 24 h. The transcripts levels of the two genes were higher in the granulocytes and fat body than in other tissues. RNA interference decreased the transcript levels of the two genes and the antimicrobial activity of the pupal hemolymph. Venom injections similarly silenced the expression of the two genes during the first 8 h post-treatment in time- and dose-dependent manners, after which the silence effects abated. Additionally, recombinant cecropin and lysozyme had no significant effect on the emergence rate of pupae that were parasitized by P. puparum females. These findings suggest one mechanism of impairing host antimicrobial activity by parasitoid venom.

Effects of the endoparasitoid Cotesia chilonis (Hymenoptera: Braconidae) parasitism, venom, and calyx fluid on cellular and humoral immunity of its host Chilo suppressalis (Lepidoptera: Crambidae) larvae

The larval endoparasitoid Cotesia chilonis injects venom and bracoviruses into its host Chilo suppressalis during oviposition. Here we study the effects of the polydnavirus (PDV)-carrying endoparasitoid C. chilonis (Hymenoptera: Braconidae) parasitism, venom and calyx fluid on host cellular and humoral immunity, specifically hemocyte composition, cellular spreading, encapsulation and melanization. Total hemocyte counts (THCs) were higher in parasitized larvae than in unparasitized larvae in the late stages following parasitization. While both plasmatocyte and granulocyte fractions and hemocyte mortality did not differ between parasitized and unparasitized hosts, in vitro spreading behavior of hemocytes was inhibited significantly by parasitism throughout the course of parasitoid development. C. chilonis parasitism suppressed the encapsulation response and melanization in the early stages. Venom alone did not alter cellular immune responses, including effects on THCs, mortality, hemocyte composition, cell spreading and encapsulation, but venom did inhibit humoral immunity by reducing melanization within 6h after injection. In contrast to venom, calyx fluid had a significant effect on cell spreading, encapsulation and melanization from 6h after injection. Dose-response injection studies indicated the effects of venom and calyx fluid synergized, showing a stronger and more persistent reduction in immune system responses than the effect of either injected alone.

Insights into the venom composition and evolution of an endoparasitoid wasp by combining proteomic and transcriptomic analyses

Parasitoid wasps are abundant and diverse hymenopteran insects that lay their eggs into the internal body (endoparasitoid) or on the external surface (ectoparasitoid) of their hosts. To make a more conducive environment for the wasps’ young, both ecto- and endoparasitoids inject venoms into the host to modulate host immunity, metabolism and development. Endoparasitoids have evolved from ectoparasitoids independently in different hymenopteran lineages. Pteromalus puparum, a pupal endoparasitoid of various butterflies, represents a relatively recent evolution of endoparasitism within pteromalids. Using a combination of transcriptomic and proteomic approaches, we have identified 70 putative venom proteins in P. puparum. Most of them show higher similarity to venom proteins from the related ectoparasitoid Nasonia vitripennis than from other more distantly related endoparasitoids. In addition, 13 venom proteins are similar to venoms of distantly related endoparasitoids but have no detectable venom matches in Nasonia. These venom proteins may have a role in adaptation to endoparasitism. Overall, these results lay the groundwork for more detailed studies of venom function and adaptation to the endoparasitic lifestyle.

Venom gland components of the ectoparasitoid wasp, Anisopteromalus calandrae

The wasp Anisopteromalus calandrae is a small ectoparasitoid that attacks stored product pest beetle larvae that develop inside grain kernels, and is thus a potential insect control tool. The components of A. calandrae venom have not been studied, but venom from other organisms contains proteins with potential applications, such as pest management tools and treatments for human diseases. We dissected female A. calandrae and collected venom and associated glands. Using high throughput sequencing, a venom gland transcriptome was assembled that contained 45,432 contigs, 25,726 of which had BLASTx hits. The majority of hits were to Nasonia vitripennis, an ectoparasitoid from the same taxonomic family, as well as other bees, wasps, and ants. Gene ontology grouped sequences into eleven molecular functions, among which binding and catalytic activity had the most representatives. In this study, we highlighted the most abundant sequences, including those that are likely the functional components of the venom. Specifically, we focused on genes encoding proteins potentially involved in host developmental arrest, disrupting the host immune system, host paralysis, and transcripts that support these functions. Our report is the first to characterize components of the A. calandrae venom gland that may be useful as control tools for insect pests and other applications.

THE ENDOPARASITOID Pteromalus puparum INFLUENCES HOST GENE EXPRESSION WITHIN FIRST HOUR OF PARASITIZATION

The small cabbage butterfly, Pieris rapae, is an important pest of cruciferous corps, and Pteromalus puparum is a predominant pupal endoparasitoid wasp of this butterfly. For successful development of parasitoid offspring, female parasitoids usually introduce one or several kinds of maternal factors into the hemocoels during oviposition to suppress host immunity. To investigate the early changes in host immune-related genes following parasitization, we analyzed transcriptomes of parasitized and unparasitized, control, host pupae. Approximately 17.7 and 19.3 million paired-end reads were generated from nonparasitized and parasitized host pupae, and assembled de novo into 45,639 transcripts and 27,659 nonredundant unigenes. The average unigene length was 790 bp. A total 18,377 of 27,659 unigenes were annotated and we identified 557 differentially expressed unigenes in host pupae at 1 h after parasitization, of which 21 were immune-related. Parasitization led to downregulation of most pattern recognition receptors and upregulation of all serine protease inhibitors. The transcirptomic profile of P. rapae is considerably affected by parasitization. This study provides valuable sources for future investigations of the molecular interaction between P. puparum and its host P. rapae.

Venom Proteins from Parasitoid Wasps and Their Biological Functions

Parasitoid wasps are valuable biological control agents that suppress their host populations. Factors introduced by the female wasp at parasitization play significant roles in facilitating successful development of the parasitoid larva either inside (endoparasitoid) or outside (ectoparasitoid) the host. Wasp venoms consist of a complex cocktail of proteinacious and non-proteinacious components that may offer agrichemicals as well as pharmaceutical components to improve pest management or health related disorders. Undesirably, the constituents of only a small number of wasp venoms are known. In this article, we review the latest research on venom from parasitoid wasps with an emphasis on their biological function, applications and new approaches used in venom studies.

Evidence of a Genetic Basis for Differences in Parasitization Success between Strains of Avetianella longoi (Siscaro)

When the cerambycid, Phoracantha recurva, invaded California in the mid 1990’s a parasitoid wasp was imported from its native range in Australia as part of a biological control program. The wasp was later identified to be Avetianella longoi, which had already been released years earlier to control the congener longhorned beetle, Phoracantha semipunctata. Despite being recognized as the same species, the two wasps exhibited differential success on P. recurva eggs, indicating the presence of two separate strains. Here we determine if the differentiating factor between the two strains of A. longoi is a heritable genetic trait. All four pairings between the two strains were conducted, resulting in two homogenous and two heterogeneous crosses. All crosses except one produced viable F1 female offspring. F1 females were allowed to oviposit on P. recurva eggs and the survival of their offspring was compared to determine if survival can be affected by paternal contributions. The result was that the offspring of females with fathers from the second introduced strain showed significantly increased survival compared to F1 females with parents from the first introduced strain. This increased survival demonstrated that there is a heritable dominant trait that is associated with increased survival on P. recurva host eggs.

Functions of Armigeres subalbatus C-type lectins in innate immunity

C-type lectins (CTLs) are a superfamily of calcium-dependent carbohydrate binding proteins containing at least one carbohydrate-recognition domain (CRD) and they are present in almost all metazoans. Insect CTLs may function as pattern-recognition receptors and play important roles in innate immunity. In this study, we selected five AsCTLs from the mosquito Armigeres subalbatus, a natural vector of filarial nematodes, and performed both in vitro and in vivo studies to elucidate their functions in innate immunity. AsCTLMA15, AsCTLGA5 and AsCTL15 were mainly expressed in hemocytes, AsCTL16 was expressed in fat body, while AsCTLMA11 was expressed in both hemocytes and fat body, and only AsCTLMA11 and AsCTL16 were expressed at high levels in adult females. In vitro binding assays showed that all five recombinant AsCTLs could bind to different microbial cell wall components, including lipopolysaccharide (LPS), lipid A, peptidoglycan (PG), lipoteichoic acid (LTA), zymosan and laminarin (beta-1,3-glucan). Recombinant AsCTLs also bound to several Gram-negative and Gram-positive bacteria, and could agglutinate bacterial cells. Injection of double-stranded RNAs (dsRNAs) could significantly reduce expression of the five AsCTL mRNAs, and the survival of mosquitoes treated with dsRNA to AsCTLGA5 was significantly decreased after Escherichia coli infection, but did not change significantly after Micrococcus luteus infection compared to the control groups, suggesting that Ar. subalbatus AsCTLGA5 may participate in innate immunity against E. coli.

Transcriptome immune analysis of the invasive beetle Octodonta nipae (Maulik) (Coleoptera: Chrysomelidae) parasitized by Tetrastichus brontispae Ferrière (Hymenoptera: Eulophidae)

The beetle Octodonta nipae (Maulik) (Coleoptera: Chrysomelidae) is a serious invasive insect pest of palm plants in southern China, and the endoparasitoid Tetrastichus brontispae Ferrière (Hymenoptera: Eulophidae) is a natural enemy of this pest that exhibits great ability in the biocontrol of O. nipae. For successful parasitism, endoparasitoids often introduce or secrete various virulence factors to suppress host immunity. To investigate the effects of parasitization by T. brontispae on the O. nipae immune system, the transcriptome of O. nipae pupae was analyzed with a focus on immune-related genes through Illumina sequencing. De novo assembly generated 49,919 unigenes with a mean length of 598 bp. Of these genes, 27,490 unigenes (55.1% of all unigenes) exhibited clear homology to known genes in the NCBI nr database. Parasitization had significant effects on the transcriptome profile of O. nipae pupae, and most of these differentially expressed genes were down-regulated. Importantly, the expression profiles of immune-related genes were significantly regulated after parasitization. Taken together, these transcriptome sequencing efforts shed valuable light on the host (O. nipae) manipulation mechanisms induced by T. brontispae, which will pave the way for the development of novel immune defense-based management strategies of O. nipae, and provide a springboard for further molecular analyses, particularly of O. nipae invasion.

Parasitization by Cotesia chilonis influences gene expression in fatbody and hemocytes of Chilo suppressalis

Background

During oviposition many parasitoid wasps inject various factors, such as polydnaviruses (PDVs), along with eggs that manipulate the physiology and development of their hosts. These manipulations are thought to benefit the parasites. However, the detailed mechanisms of insect host-parasitoid interactions are not fully understood at the molecular level. Based on recent findings that some parasitoids influence gene expression in their hosts, we posed the hypothesis that parasitization by a braconid wasp, Cotesia chilonis, influences the expression of genes responsible for development, metabolism and immune functions in the fatbody and hemocytes of its host, Chilo suppressalis.

Methodology/Principal Findings

We obtained 39,344,452 reads, which were assembled into 146,770 scaffolds, and 76,016 unigenes. Parasitization impacted gene expression in fatbody and hemocytes. Of these, 8096 fatbody or 5743 hemocyte unigenes were down-regulated, and 2572 fatbody or 1452 hemocyte unigenes were up-regulated. Gene ontology data showed that the majority of the differentially expressed genes are involved in enzyme-regulated activity, binding, transcription regulator activity and catalytic activity. qPCR results show that most anti-microbial peptide transcription levels were up-regulated after parasitization. Expression of bracovirus genes was detected in parasitized larvae with 19 unique sequences identified from six PDV gene families including ankyrin, CrV1 protein, cystatin, early-expressed (EP) proteins, lectin, and protein tyrosine phosphatase.

Conclusions

The current study supports our hypothesis that parasitization influences the expression of fatbody and hemocyte genes in the host, C. suppressalis. The general view is that manipulation of host metabolism and immunity benefits the development and emergence of the parasitoid offsprings. The accepted beneficial mechanisms include the direct impact of parasitoid-associated virulence factors such as venom and polydnavirus on host tissues (such as cell damage) and, more deeply, the ability of these factors to influence gene expression. We infer that insect parasitoids generally manipulate their environments, the internal milieu of their hosts.

"It stings a bit but it cleans well": venoms of Hymenoptera and their antimicrobial potential

Venoms from Hymenoptera display a wide range of functions and biological roles. These notably include manipulation of the host, capture of prey and defense against competitors and predators thanks to endocrine and immune systems disruptors, neurotoxic, cytolytic and pain-inducing venom components. Recent works indicate that many hymenopteran species, whatever their life style, have also evolved a venom with properties which enable it to regulate microbial infections, both in stinging and stung animals. In contrast to biting insects and their salivary glands, stinging Hymenoptera seem to constitute an under-exploited ecological niche for agents of vector-borne disease. Few parasitic or mutualistic microorganisms have been reported to be hosted by venom-producing organs or to be transmitted to stung animals. This may result from the presence of potent antimicrobial molecules in venoms, histological features of venom apparatuses and selective effects of venoms on immune defenses of targeted organisms. The present paper reviews for the first time the venom antimicrobial potential of solitary and social Hymenoptera in molecular, ecological, and evolutionary perspectives.

Transcriptomic immune response of Tenebrio molitor pupae to parasitization by Scleroderma guani

BACKGROUND

Host and parasitoid interaction is one of the most fascinating relationships of insects, which is currently receiving an increasing interest. Understanding the mechanisms evolved by the parasitoids to evade or suppress the host immune system is important for dissecting this interaction, while it was still poorly known. In order to gain insight into the immune response of Tenebrio molitor to parasitization by Scleroderma guani, the transcriptome of T. molitor pupae was sequenced with focus on immune-related gene, and the non-parasitized and parasitized T. molitor pupae were analyzed by digital gene expression (DGE) analysis with special emphasis on parasitoid-induced immune-related genes using Illumina sequencing.

METHODOLOGY/PRINCIPAL FINDINGS

In a single run, 264,698 raw reads were obtained. De novo assembly generated 71,514 unigenes with mean length of 424 bp. Of those unigenes, 37,373 (52.26%) showed similarity to the known proteins in the NCBI nr database. Via analysis of the transcriptome data in depth, 430 unigenes related to immunity were identified. DGE analysis revealed that parasitization by S. guani had considerable impacts on the transcriptome profile of T. molitor pupae, as indicated by the significant up- or down-regulation of 3,431 parasitism-responsive transcripts. The expression of a total of 74 unigenes involved in immune response of T. molitor was significantly altered after parasitization.

CONCLUSIONS/SIGNIFICANCE

obtained T. molitor transcriptome, in addition to establishing a fundamental resource for further research on functional genomics, has allowed the discovery of a large group of immune genes that might provide a meaningful framework to better understand the immune response in this species and other beetles. The DGE profiling data provides comprehensive T. molitor immune gene expression information at the transcriptional level following parasitization, and sheds valuable light on the molecular understanding of the host-parasitoid interaction.

Suppression of scavenger receptors transcription by parasitoid factors

Scavenger receptors (SR) are a group of membrane proteins that play central roles in various functions, such as immune responses in insects. Members of different SR classes were identified from Plutella xylostella larval transcriptome. SR B1 and B3 were found to be differentially expressed in larvae and pupae. Expression of P. xylostella SR genes was significantly altered during immune challenge induced in P. xylostella cells (Px) and parasitized larvae. Maternal factors injected into the larvae by the endoparasitoid wasp Diadegma semiclausum at oviposition include venom and ichnovirus (DsIV) genes to suppress the host immune system. Transient expression of two DsIV genes, Vankyrin1 and Repeat element 4 (Rep4), in Px cells led to significant down-regulation of both SR B1 and B3 transcript levels, while DsIV Rep4 expression did not change the relative transcription levels of SR B3. In conclusion, it appears that the two members of the SR family play important roles in innate immune responses in P. xylostella and that each member of this group may play different roles in the host-parasitoid interaction.