A viral histone H4 encoded by Cotesia plutellae bracovirus inhibits haemocyte-spreading behaviour of the diamondback moth, Plutella xylostella

Multiple, diverse endogenous giant virus elements within the genome of a brown alga

Endogenous viral elements (EVEs) have been found in diverse eukaryotic genomes. These elements are particularly frequent in the genomes of brown algae (Phaeophyceae) because these seaweeds are infected by viruses (Phaeovirus) of the phylum Nucleocytoviricota (NCV) that are capable of inserting into their host's genome as part of their infective cycle. A search for inserted viral sequences in the genome of the freshwater brown alga Porterinema fluviatile identified seven large EVEs, including four complete or near-complete proviruses. The EVEs, which all appear to have been derived from independent insertion events, correspond to phylogenetically diverse members of the Phaeovirus genus and include members of both the A and B subgroups of this genus. This latter observation is surprising because the two subgroups were thought to have different evolutionary strategies and were therefore not expected to be found in the same host. The EVEs contain a number of novel genes including a H4 histone-like sequence but only one of the EVEs possesses a full set of NCV core genes, indicating that the other six probably correspond to nonfunctional, degenerated viral genomes. The majority of the genes within the EVEs were transcriptionally silent and most of the small number of genes that showed some transcriptional activity were of unknown function. However, the existence of some transcriptionally active genes and several genes containing introns in some EVEs suggests that these elements may be undergoing some degree of endogenization within the host genome over time.

Transcriptional dynamics during Heliothis zea nudivirus 1 infection in an ovarian cell line from Helicoverpa zea

Nudiviruses (family Nudiviridae) are double-stranded DNA viruses that infect various insects and crustaceans. Among them, Heliothis zea nudivirus 1 (HzNV-1) represents the rare case of a lepidopteran nudivirus inducing a sexual pathology. Studies about molecular pathological dynamics of HzNV-1 or other nudiviruses are scarce. Hence, this study aims to provide a transcriptomic profile of HzNV-1 in an ovary-derived cell line of Helicoverpa zea (HZ-AM1), during early (3, 6 and 9 h post-infection) and advanced (12 and 24 h post-infection) stages of infection. Total RNA was extracted from both virus- and mock-infected cells, and RNA-seq analysis was performed to examine both virus and host transcriptional dynamics. Hierarchical clustering was used to categorize viral genes, while differential gene expression analysis was utilized to pinpoint host genes that are significantly affected by the infection. Hierarchical clustering classified the 154 HzNV-1 genes into four temporal phases, with early phases mainly involving transcription and replication genes and later phases including genes for virion assembly. In addition, a novel viral promoter motif was identified in the upstream region of early-expressed genes. Host gene analysis revealed significant upregulation of heat shock protein genes and downregulation of histone genes. The identification of temporal patterns in viral gene expression enhances the molecular understanding of nudivirus pathology, while the identified differentially expressed host genes highlight the key pathways most hijacked by HzNV-1 infection.

The caterpillar Manduca sexta brain shows changes in gene expression and protein abundance correlating with parasitic manipulation of behaviour

The parasitic wasp, Cotesia congregata, manipulates the behaviour of its host, the caterpillar Manduca sexta. The female wasp injects her eggs and a symbiotic virus (i.e. bracovirus, CcBV) into the body of its host. The host's behaviour remains unchanged until the wasps exit the caterpillar, and then the caterpillar becomes a non-feeding "bodyguard" for the wasp cocoons. Using proteomic, transcriptomic and qPCR studies, we discovered an increase in antimicrobial peptide gene expression and protein abundance in the host central nervous system at the time of wasp emergence, correlating with the change in host behaviour. These results support the hypothesis that the wasps hyperactivate an immune-neural connection to help create the change in behaviour. At the time of wasp emergence, there was also an increase in bracoviral gene expression and proteins in the host brain, suggesting that the bracovirus may also be involved in altering host behaviour. Other changes in gene expression and protein abundance suggest that synaptic transmission may be altered after wasp emergence, and a reduction in descending neural activity from the host's brain provides indirect support for this hypothesis.

Proteomic analyses of venom from a Spider Hawk, Pepsis decorata

Background

The composition of the venom from solitary wasps is poorly known, although these animals are considered sources of bioactive substances. Until the present moment, there is only one proteomic characterization of the venom of wasps of the family Pompilidae and this is the first proteomic characterization for the genus Pepsis.

Methods

To elucidate the components of Pepsis decorata venom, the present work sought to identify proteins using four different experimental conditions, namely: (A) crude venom; (B) reduced and alkylated venom; (C) trypsin-digested reduced and alkylated venom, and; (D) chymotrypsin-digested reduced and alkylated venom. Furthermore, three different mass spectrometers were used (Ion Trap-Time of Flight, Quadrupole-Time of Flight, and Linear Triple Quadruple).

Results

Proteomics analysis revealed the existence of different enzymes related to the insect's physiology in the venom composition. Besides toxins, angiotensin-converting enzyme (ACE), hyaluronidase, and Kunitz-type inhibitors were also identified.

Conclusion

The data showed that the venom of Pepsis decorata is mostly composed of proteins involved in the metabolism of arthropods, as occurs in parasitic wasps, although some classical toxins were recorded, and among them, for the first time, ACE was found in the venom of solitary wasps. This integrative approach expanded the range of compounds identified in protein analyses, proving to be efficient in the proteomic characterization of little-known species. It is our understanding that the current work will provide a solid base for future studies dealing with other Hymenoptera venoms.

Genomic Analysis of Amphioxus Reveals a Wide Range of Fragments Homologous to Viral Sequences

Amphioxus species are considered living fossils and are important in the evolutionary study of chordates and vertebrates. To explore viral homologous sequences, a high-quality annotated genome of the Beihai amphioxus (Branchiostoma belcheri beihai) was examined using virus sequence queries. In this study, 347 homologous fragments (HFs) of viruses were identified in the genome of B. belcheri beihai, of which most were observed on 21 genome assembly scaffolds. HFs were preferentially located within protein-coding genes, particularly in their CDS regions and promoters. A range of amphioxus genes with a high frequency of HFs is proposed, including histone-related genes that are homologous to the Histone H4 or Histone H2B domains of viruses. Together, this comprehensive analysis of viral HFs provides insights into the neglected role of viral integration in the evolution of amphioxus.

A Polydnavirus Protein Tyrosine Phosphatase Negatively Regulates the Host Phenoloxidase Pathway

Polydnavirus (PDV) is a parasitic factor of endoparasitic wasps and contributes greatly to overcoming the immune response of parasitized hosts. Protein tyrosine phosphatases (PTPs) regulate a wide variety of biological processes at the post-transcriptional level in mammals, but knowledge of PDV PTP action during a parasitoid−host interaction is limited. In this study, we characterized a PTP gene, CvBV_12-6, derived from Cotesia vestalis bracovirus (CvBV), and explored its possible regulatory role in the immune response of the host Plutella xylostella. Our results from qPCR show that CvBV_12-6 was highly expressed in hemocytes at an early stage of parasitization. To explore CvBV_12-6 function, we specifically expressed CvBV_12-6 in Drosophila melanogaster hemocytes. The results show that Hml-Gal4 > CvBV_12-6 suppressed the phenoloxidase activity of hemolymph in D. melanogaster, but exerted no effect on the total count or the viability of the hemocytes. In addition, the Hml-Gal4 > CvBV_12-6 flies exhibited decreased antibacterial abilities against Staphylococcus aureus. Similarly, we found that CvBV_12-6 significantly suppressed the melanization of the host P. xylostella 24 h post parasitization and reduced the viability, but not the number, of hemocytes. In conclusion, CvBV_12-6 negatively regulated both cellular and humoral immunity in P. xylostella, and the related molecular mechanism may be universal to insects.

Viral histones: pickpocket's prize or primordial progenitor?

The common histones H2A, H2B, H3, and H4 are the characteristic components of eukaryotic nucleosomes, which function to wrap DNA and compact the genome as well as to regulate access to DNA for transcription and replication in all eukaryotes. In the past two decades, histones have also been found to be encoded in some DNA viruses, where their functions and properties are largely unknown, though recently histones from two related viruses have been shown to form nucleosome-like structures in vitro. Viral histones can be highly similar to eukaryotic histones in primary sequence, suggesting they have been recently picked up from eukaryotic hosts, or they can be radically divergent in primary sequence and may occur as conjoined histone doublets, triplets, or quadruplets, suggesting ancient origins prior to the divergence of modern eukaryotes. Here, we review what is known of viral histones and discuss their possible origins and functions. We consider how the viral life cycle may affect their properties and histories, and reflect on the possible roles of viruses in the origin of the nucleus of modern eukaryotic cells.

Sophora subprostrate polysaccharide regulates histone acetylation to inhibit inflammation in PCV2-infected murine splenic lymphocytes in vitro and in vivo

Porcine circovirus type 2 (PCV2) has caused large economic losses in the swine industry worldwide; therefore, research on relevant therapeutic medicines is still urgently needed. To define the relationship between histone acetylation and inflammation induced by PCV2, we investigated whether traditional Chinese medicinal polysaccharides could alleviate viral infection by regulating histone acetylation. In this study, Sophora subprostrate polysaccharide (SSP)-treated PCV2-infected murine splenic lymphocytes in vitro and murine spleen in vivo were used to explore the regulatory effects of SSP on inflammation and histone acetylation caused by PCV2. SSP at different concentrations significantly reduced the secretion levels of the proinflammatory cytokines TNF-α and IL-6, the activity of COX-2, the mRNA expression levels of TNF-α, IL-6, iNOS and COX-2 and the protein expression levels of iNOS and COX-2 but promoted the secretion and mRNA expression levels of IL-10. Furthermore, the different concentrations of SSP significantly regulated the activity of histone acetylase (HAT) and the mRNA expression of HAT1, increased the activity of histone deacetylase (HDAC) and the mRNA expression of HDAC1 and reduced the protein expression levels of Ac-H3 and Ac-H4. Overall, SSP inhibited inflammation in PCV2-infected murine splenic lymphocytes by regulating histone acetylation in vitro and in vivo, thus playing an important role in PCV2 infection.

Polydnavirus Innexins Disrupt Host Cellular Encapsulation and Larval Maturation

Polydnaviruses are dsDNA viruses associated with endoparasitoid wasps. Delivery of the virus during parasitization of a caterpillar and subsequent virus gene expression is required for production of an amenable environment for parasitoid offspring development. Consequently, understanding of Polydnavirus gene function provides insight into mechanisms of host susceptibility and parasitoid wasp host range. Polydnavirus genes predominantly are arranged in multimember gene families, one of which is the vinnexins, which are virus homologues of insect gap junction genes, the innexins. Previous studies of Campoletis sonorensis Ichnovirus Vinnexins using various heterologous systems have suggested the four encoded members may provide different functionality in the infected caterpillar host. Here, we expressed two of the members, vnxG and vnxQ2, using recombinant baculoviruses in susceptible host, the caterpillar Heliothis virescens. Following intrahemocoelic injections, we observed that >90% of hemocytes (blood cells) were infected, producing recombinant protein. Larvae infected with a vinnexin-recombinant baculovirus exhibited significantly reduced molting rates relative to larvae infected with a control recombinant baculovirus and mock-infected larvae. Similarly, larvae infected with vinnexin-recombinant baculoviruses were less likely to survive relative to controls and showed reduced ability to encapsulate chromatography beads in an immune assay. In most assays, the VnxG protein was associated with more severe pathology than VnxQ2. Our findings support a role for Vinnexins in CsIV and more broadly Ichnovirus pathology in infected lepidopteran hosts, particularly in disrupting multicellular developmental and immune physiology.

Medusavirus, a Novel Large DNA Virus Discovered from Hot Spring Water

Recent discoveries of new large DNA viruses reveal high diversity in their morphologies, genetic repertoires, and replication strategies. Here, we report the novel features of medusavirus, a large DNA virus newly isolated from hot spring water in Japan. Medusavirus, with a diameter of 260 nm, shows a T=277 icosahedral capsid with unique spherical-headed spikes on its surface. It has a 381-kb genome encoding 461 putative proteins, 86 of which have their closest homologs in Acanthamoeba, whereas 279 (61%) are orphan genes. The virus lacks the genes encoding DNA topoisomerase II and RNA polymerase, showing that DNA replication takes place in the host nucleus, whereas the progeny virions are assembled in the cytoplasm. Furthermore, the medusavirus genome harbored genes for all five types of histones (H1, H2A, H2B, H3, and H4) and one DNA polymerase, which are phylogenetically placed at the root of the eukaryotic clades. In contrast, the host amoeba encoded many medusavirus homologs, including the major capsid protein. These facts strongly suggested that amoebae are indeed the most promising natural hosts of medusavirus, and that lateral gene transfers have taken place repeatedly and bidirectionally between the virus and its host since the early stage of their coevolution. Medusavirus reflects the traces of direct evolutionary interactions between the virus and eukaryotic hosts, which may be caused by sharing the DNA replication compartment and by evolutionarily long lasting virus-host relationships. Based on its unique morphological characteristics and phylogenomic relationships with other known large DNA viruses, we propose that medusavirus represents a new family, Medusaviridae IMPORTANCE We have isolated a new nucleocytoplasmic large DNA virus (NCLDV) from hot spring water in Japan, named medusavirus. This new NCLDV is phylogenetically placed at the root of the eukaryotic clades based on the phylogenies of several key genes, including that encoding DNA polymerase, and its genome surprisingly encodes the full set of histone homologs. Furthermore, its laboratory host, Acanthamoeba castellanii, encodes many medusavirus homologs in its genome, including the major capsid protein, suggesting that the amoeba is the genuine natural host from ancient times of this newly described virus and that lateral gene transfers have repeatedly occurred between the virus and amoeba. These results suggest that medusavirus is a unique NCLDV preserving ancient footprints of evolutionary interactions with its hosts, thus providing clues to elucidate the evolution of NCLDVs, eukaryotes, and virus-host interaction. Based on the dissimilarities with other known NCLDVs, we propose that medusavirus represents a new viral family, Medusaviridae.

The genome of a prasinoviruses-related freshwater virus reveals unusual diversity of phycodnaviruses

Background

Phycodnaviruses are widespread algae-infecting large dsDNA viruses and presently contain six genera: Chlorovirus, Prasinovirus, Prymnesiovirus, Phaeovirus, Coccolithovirus and Raphidovirus. The members in Prasinovirus are identified as marine viruses due to their marine algal hosts, while prasinovirus freshwater relatives remain rarely reported.

Results

Here we present the complete genomic sequence of a novel phycodnavirus, Dishui Lake Phycodnavirus 1 (DSLPV1), which was assembled from Dishui Lake metagenomic datasets. DSLPV1 harbors a linear genome of 181,035 bp in length (G + C content: 52.7%), with 227 predicted genes and 2 tRNA encoding regions. Both comparative genomic and phylogenetic analyses indicate that the freshwater algal virus DSLPV1 is closely related to the members in Prasinovirus, a group of marine algae infecting viruses. In addition, a complete eukaryotic histone H3 variant was identified in the genome of DSLPV1, which is firstly detected in phycodnaviruses and contributes to understand the interaction between algal virus and its eukaryotic hosts.

Conclusion

It is in a freshwater ecosystem that a novel Prasinovirus-related viral complete genomic sequence is discovered, which sheds new light on the evolution and diversity of the algae infecting Phycodnaviridae.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4432-4) contains supplementary material, which is available to authorized users.

Genomic exploration of individual giant ocean viruses

Viruses are major pathogens in all biological systems. Virus propagation and downstream analysis remains a challenge, particularly in the ocean where the majority of their microbial hosts remain recalcitrant to current culturing techniques. We used a cultivation-independent approach to isolate and sequence individual viruses. The protocol uses high-speed fluorescence-activated virus sorting flow cytometry, multiple displacement amplification (MDA), and downstream genomic sequencing. We focused on 'giant viruses' that are readily distinguishable by flow cytometry. From a single-milliliter sample of seawater collected from off the dock at Boothbay Harbor, ME, USA, we sorted almost 700 single virus particles, and subsequently focused on a detailed genome analysis of 12. A wide diversity of viruses was identified that included Iridoviridae, extended Mimiviridae and even a taxonomically novel (unresolved) giant virus. We discovered a viral metacaspase homolog in one of our sorted virus particles and discussed its implications in rewiring host metabolism to enhance infection. In addition, we demonstrated that viral metacaspases are widespread in the ocean. We also discovered a virus that contains both a reverse transcriptase and a transposase; although highly speculative, we suggest such a genetic complement would potentially allow this virus to exploit a latency propagation mechanism. Application of single virus genomics provides a powerful opportunity to circumvent cultivation of viruses, moving directly to genomic investigation of naturally occurring viruses, with the assurance that the sequence data is virus-specific, non-chimeric and contains no cellular contamination.

Characterization of joining sites of a viral histone H4 on host insect chromosomes

A viral histone H4 (CpBV-H4) is encoded in a polydnavirus, Cotesia plutellae bracovirus (CpBV). It plays a crucial role in parasitism of an endoparasitoid wasp, C. plutellae, against diamondback moth, Plutella xylostella, by altering host gene expression in an epigenetic mode by its N-terminal tail after joining host nucleosomes. Comparative transcriptomic analysis between parasitized and nonparasitized P. xylostella by RNA-Seq indicated that 1,858 genes were altered at more than two folds in expression levels at late parasitic stage, including 877 up-regulated genes and 981 down-regulated genes. Among parasitic factors altering host gene expression, CpBV-H4 alone explained 16.3% of these expressional changes. To characterize the joining sites of CpBV-H4 on host chromosomes, ChIP-Seq (chromatin immunoprecipitation followed by deep sequencing) was applied to chromatins extracted from parasitized larvae. It identified specific 538 ChIP targets. Joining sites were rich (60.2%) in AT sequence. Almost 40% of ChIP targets included short nucleotide repeat sequences presumably recognizable by transcriptional factors and chromatin remodeling factors. To further validate these CpBV-H4 targets, CpBV-H4 was transiently expressed in nonparasitized host at late larval stage and subjected to ChIP-Seq. Two kinds of ChIP-Seqs shared 51 core joining sites. Common targets were close (within 1 kb) to genes regulated at expression levels by CpBV-H4. However, other host genes not close to CpBV-H4 joining sites were also regulated by CpBV-H4. These results indicate that CpBV-H4 joins specific chromatin regions of P. xylostella and controls about one sixth of the total host genes that were regulated by C. plutellae parasitism in an epigenetic mode.

Questions on unusual Mimivirus-like structures observed in human cells

Background: Mimiviruses or giant viruses that infect amoebas have the ability to retain the Gram stain, which is usually used to colour bacteria. There is some evidence suggesting that Mimiviruses can also infect human cells. Guided by these premises, we performed a routine Gram stain on a variety of human specimens to see if we could detect the same Gram positive blue granules that identify Mimiviruses in the amoebas.  Methods: We analysed 24 different human specimens (liver, brain, kidney, lymph node and ovary) using Gram stain histochemistry, electron microscopy immunogold, high resolution mass spectrometry and protein identification.  Results: We detected in the human cells Gram positive granules that were distinct from bacteria. The fine blue granules displayed the same pattern of the Gram positive granules that diagnose Mimiviruses in the cytoplasm of the amoebas. Electron microscopy confirmed the presence of human Mimiviruses-like structures and mass spectrometry identified histone H4 peptides, which had the same footprints as giant viruses. However, some differences were noted: the Mimivirus-like structures identified in the human cells were ubiquitous and manifested a distinct mammalian retroviral antigenicity.  Conclusions: Our main hypotheses are that the structures could be either giant viruses having a retroviral antigenicity or ancestral cellular components having a viral origin. However, other possible alternatives have been proposed to explain the nature and function of the newly identified structures.

An endoparasitoid wasp influences host DNA methylation

Parasitism by endoparasitoid wasps changes the expression of various host genes, and alters host immune and developmental processes. However, it is not clearly understood how parasitism changes host gene expression in a whole genome scale. This study focused on an epigenetic control of Cotesia plutellae, an endoparasitoid wasp, against its host, Plutella xylostella. Two DNA methyltransferases (DNMT-1 and DNMT-2) are encoded in the genome of P. xylostella. In addition, methyl-binding domain proteins (MBDs) and DNA demethylation factor, ten-eleven translation protein (TET) are encoded. DNA methylation of P. xylostella genomic DNA was confirmed by restriction digestion with Gla I specific to 5-methylcytosine. DNA methylation intensity in parasitized (P) larvae was decreased compared to that in nonparasitized (NP) larvae, especially at late parasitic stage, at which expression levels of both DNMT-1 and DNMT-2 were also decreased. DNA demethylation of P. xylostella was confirmed in both NP and P larvae by restriction digestion with PvuRts1I recognizing 5-hydroxymethyl cytosine. Parasitism also suppressed expression levels of TET and MBDs. Treatment of 5-aza-2′-deoxycytidine (AZA) reduced DNA methylation intensity of NP larvae, causing suppression of hemocyte-spreading behavior and delay of immature development. RNA interference of DNMT-1 or DNMT-2 mimicked the adverse effects of AZA.

A viral histone H4 suppresses insect insulin signal and delays host development

Parasitization by an endoparasitoid wasp, Cotesia plutellae, alters host development of Plutella xylostella by extending larval period and preventing metamorphosis. Insulin signal plays a crucial role in mediating insect development and controlling blood sugar level in insects. In this study, three insulin-like peptide genes (PxILP1-3) were predicted from the genome of P. xylostella. However, only PxILP1 was confirmed to be expressed in P. xylostella. Starvation suppressed the expression level of PxILP1 and up-regulated plasma trehalose level. RNA interference against PxILP1 mimicked starvation effect and extended the larval period of P. xylostella. Parasitized larvae exhibited significantly lower levels of PxILP1 expression compared to nonparasitized larvae. Injection of wasp-symbiotic polydnavirus C. plutellae bracovirus (CpBV) also suppressed PxILP1 expression and extended the larval period. Injection of a viral segment (CpBV-S30) containing a viral histone H4 (CpBV-H4) also suppressed PxILP1 expression. Co-injection of CpBV-S30 and double-stranded RNA (dsCpBV-H4) specific to CpBV-H4 rescued the suppression of PxILP1 expression. Injection of CpBV-S30 significantly extended larval development. Co-injection of CpBV-S30 with dsCpBV-H4 rescued the delay of larval development. Injection of a bovine insulin to parasitized larvae prevented parasitoid development. These results indicate that parasitism of C. plutellae can down-regulate host insulin signaling with the help of parasitic factor CpBV-H4.

Suppressive activity of a viral histone H4 against two host chromatin remodelling factors: lysine demethylase and SWI/SNF

Histone H4, a nucleosome subunit in eukaryotes, plays crucial roles in DNA package and regulation of gene expression through covalent modification. A viral histone H4 encoded in Cotesia plutellae bracovirus (CpBV), a polydnavirus, is called CpBV-H4. It is highly homologous to other histone H4 proteins excepting 38 extra amino acid residues in the N terminus. CpBV-H4 can form octamer with other histone subunits and alter host gene expression. In this study, CpBV-H4 was transiently expressed in a natural host (Plutella xylostella) and its suppressive activity on host gene expression was evaluated by the suppressive subtractive hybridization (SSH) technique. The SSH targets down-regulated by CpBV-H4 were read with the 454 pyrosequencing platform and annotated using the genome of P. xylostella. The down-regulated genes (610 contigs) were annotated in most functional categories based on gene ontology. Among these SSH targets, 115 genes were functionally distinct, including two chromatin remodelling factors: a lysine-specific demethylase (Px-KDM) and a chromatin remodelling complex [Px-SWI/SNF (SWItch/Sucrose Non-Fermentable)]. Px-KDM was highly expressed in all tested tissues during the entire larval period. Suppression of Px-KDM expression by specific RNA interference (RNAi) significantly (P<0.05) reduced haemocyte nodule formation in response to immune challenge and impaired both larval and pupal development. Px-SWI/SNF was expressed in all developmental stages. Suppression of Px-SWI/SNF expression by RNAi reduced cellular immune response and interfered with adult metamorphosis. These results suggest that CpBV-H4 can alter host gene expression by interfering with chromatin modification and remodelling factors in addition to its direct epigenetic control activity.

Ongoing ecological speciation in Cotesia sesamiae, a biological control agent of cereal stem borers

To develop efficient and safe biological control, we need to reliably identify natural enemy species, determine their host range, and understand the mechanisms that drive host range evolution. We investigated these points in Cotesia sesamiae, an African parasitic wasp of cereal stem borers. Phylogenetic analyses of 74 individual wasps, based on six mitochondrial and nuclear genes, revealed three lineages. We then investigated the ecological status (host plant and host insect ranges in the field, and host insect suitability tests) and the biological status (cross-mating tests) of the three lineages. We found that one highly supported lineage showed all the hallmarks of a cryptic species. It is associated with one host insect, Sesamia nonagrioides, and is reproductively isolated from the other two lineages by pre- and postmating barriers. The other two lineages had a more variable phylogenetic support, depending on the set of genes; they exhibited an overlapping and diversified range of host species and are not reproductively isolated from one another. We discuss the ecological conditions and mechanisms that likely generated this ongoing speciation and the relevance of this new specialist taxon in the genus Cotesia for biological control.

Transcriptome analysis of an endoparasitoid wasp Cotesia chilonis (Hymenoptera: Braconidae) reveals genes involved in successful parasitism

For successful parasitization, parasitiods usually depend on the chemosensory cues for the selection of hosts, as well as a variety of virulence factors introduced into their hosts to overcome host immunity and prevent rejection of progeny development. In bracovirus-carrying wasps, the symbiotic polydnaviruses act in manipulating development and immunity of hosts. The endoparasitoid Cotesia chilonis carrying bracovirus as a key host immunosuppressive factor is a superior endoparasitoid of rice stem borer, Chilo suppressalis. So far, genomic information for C. chilonis is not available and transcriptomic data may provide valuable resources for global studying on physiological processes of C. chilonis, including chemosensation and parasitism at molecular level. Here, we performed RNA-seq to characterize the transcriptome of C. chilonis adults. We obtained 27,717,892 reads, assembled into 38,318 unigenes with a mean size of 690 bp. Approximately, 62.1% of the unigenes were annotated using NCBI databases. A large number of chemoreception-related genes encoding proteins including odorant receptors, gustatory receptors, odorant-binding proteins, chemosensory proteins, transient receptor potential ion channels, and sensory neuron membrane proteins were identified in silico. Totally, 72 transcripts possessing high identities with the bracovirus-related genes were identified. We investigated the mRNA expression levels of several transcripts at different developmental stages (including egg, larva, pupae, and adult) by quantitative real-time PCR analysis. The results revealed that some genes had adult-specific expression, indicating their potential significance for mating and parasitism. Overall, these results provide comprehensive insights into transcriptomic data of a polydnavirus-carrying parasitoid of a rice pest.

Antiviral activity of the inducible humoral immunity and its suppression by eleven BEN family members encoded in Cotesia plutellae bracovirus

Upon parasitization by some endoparasitoids, polydnaviruses (PDVs) play a crucial role in inducing host immunosuppression. This study reports a novel immunosuppressive activity against humoral immune responses by BEN family genes encoded in Cotesia plutellae bracovirus (CpBV). A total of 11 BEN family members are encoded in 10 different CpBV DNA segments. When the CpBV segments were individually injected, specific BEN genes were expressed and suppressed the expression of antimicrobial peptide (AMP) and prophenoloxidase genes following bacterial challenge. The suppressive activities of the BEN genes were reversed by injection of the double-stranded RNA (dsRNA) specific to each BEN gene. The suppression of the AMP gene expressions by the BEN genes was also confirmed using an inhibition zone assay against Gram-positive and Gram-negative bacterial growth. The significance of the suppressive activity of BEN genes against humoral immune responses was analyzed in terms of suppression of antiviral activity by the host humoral immunity. When CpBV was incubated with the plasma obtained from the larvae challenged with bacteria, the immunized plasma severely impaired the expression activity of the viral genes. However, an expression of BEN gene significantly rescued the viral gene expression by suppressing humoral immune response. These results suggest that BEN family genes of CpBV play a crucial role in defending the antiviral response of the parasitized Plutella xylostella by inhibiting humoral immune responses.

Environmental responses mediated by histone variants

Fluctuations in the ambient environment can trigger chromatin disruptions, involving replacement of nucleosomes or exchange of their histone subunits. Unlike canonical histones, which are available only during S-phase, replication-independent histone variants are present throughout the cell cycle and are adapted for chromatin repair. The H2A.Z variant mediates responses to environmental perturbations including fluctuations in temperature and seasonal variation. Phosphorylation of histone H2A.X rapidly marks double-strand DNA breaks for chromatin repair, which is mediated by both H2A and H3 histone variants. Other histones are used as weapons in conflicts between parasites and their hosts, which suggests broad involvement of histone variants in environmental responses beyond chromatin repair.

A viral histone h4 joins to eukaryotic nucleosomes and alters host gene expression

A viral histone H4 (CpBV-H4) is encoded in a polydnavirus, Cotesia plutellae bracovirus. Its predicted amino acid sequence is highly homologous to that of host insect histone H4 except for an extended N-terminal tail containing 38 amino acids with nine lysine residues. Its expression induces an immunosuppression of target insects by suppressing immune-associated genes, presumably through an epigenetic control. This study analyzed its molecular interaction with eukaryotic host nucleosomes and subsequent regulation of host gene expression. Purified recombinant CpBV-H4 could associate with nucleosomal components (H2A, H2B, H3, and H4) and form an octamer. Transient expression of CpBV-H4 in an insect, Tribolium castaneum, was performed by microinjection of a recombinant expression vector and confirmed by both reverse transcriptase PCR (RT-PCR) and immunoblotting assays. Under this transient expression condition, total RNAs were extracted and read by a deep-sequencing technique. Annotated transcripts were classified into different gene ontology (GO) categories and compared with those of control insects injected with a truncated CpBV-H4. Target genes manipulated by CpBV-H4 expression showing significant differences (fold changes > 10(9)) included all GO categories, including development and immune-associated genes. When the target genes were physically mapped, they were found to be scattered on entire chromosomes of T. castaneum. In addition, chromatin immunoprecipitation against CpBV-H4 determined 16 nucleosome sites (P < 10(-5)) of the viral histone incorporation, which were noncoding regions near DNA-binding and inducible genes. These findings suggest that the viral histone H4 alters host gene expression by a direct molecular interaction with insect nucleosomes.

Adaptive selection on bracovirus genomes drives the specialization of Cotesia parasitoid wasps

The geographic mosaic of coevolution predicts parasite virulence should be locally adapted to the host community. Cotesia parasitoid wasps adapt to local lepidopteran species possibly through their symbiotic bracovirus. The virus, essential for the parasitism success, is at the heart of the complex coevolutionary relationship linking the wasps and their hosts. The large segmented genome contained in the virus particles encodes virulence genes involved in host immune and developmental suppression. Coevolutionary arms race should result in the positive selection of particular beneficial alleles. To understand the global role of bracoviruses in the local adaptation or specialization of parasitoid wasps to their hosts, we studied the molecular evolution of four bracoviruses associated with wasps of the genus Cotesia, including C congregata, C vestalis and new data and annotation on two ecologically differentiated populations of C sesamie, Kitale and Mombasa. Paired orthologs analyses revealed more genes under positive selection when comparing the two C sesamiae bracoviruses belonging to the same species, and more genes under strong evolutionary constraint between species. Furthermore branch-site evolutionary models showed that 17 genes, out of the 54 currently available shared by the four bracoviruses, harboured sites under positive selection including: the histone H4-like, a C-type lectin, two ep1-like, ep2, a viral ankyrin, CrV1, a ben-domain, a Serine-rich, and eight unknown genes. Lastly the phylogenetic analyses of the histone, ep2 and CrV1 genes in different African C sesamiae populations showed that each gene described differently the individual relationships. In particular we found recombination had happened between the ep2 and CrV1 genes, which are localized 37.5 kb apart on the wasp chromosomes. Involved in multidirectional coevolutionary interactions, C sesamiae wasps rely on different bracovirus mediated molecular pathways to overcome local host resistance.

Lateral gene exchanges shape the genomes of amoeba-resisting microorganisms

Based on Darwin's concept of the tree of life, vertical inheritance was thought to be dominant, and mutations, deletions, and duplication were streaming the genomes of living organisms. In the current genomic era, increasing data indicated that both vertical and lateral gene inheritance interact in space and time to trigger genome evolution, particularly among microorganisms sharing a given ecological niche. As a paradigm to their diversity and their survival in a variety of cell types, intracellular microorganisms, and notably intracellular bacteria, were considered as less prone to lateral genetic exchanges. Such specialized microorganisms generally have a smaller gene repertoire because they do rely on their host's factors for some basic regulatory and metabolic functions. Here we review events of lateral gene transfer (LGT) that illustrate the genetic exchanges among intra-amoebal microorganisms or between the microorganism and its amoebal host. We tentatively investigate the functions of laterally transferred genes in the light of the interaction with their host as they should confer a selective advantage and success to the amoeba-resisting microorganisms (ARMs).

In vivo transient expression for the functional analysis of polydnaviral genes

Transient expression of a foreign gene in an organism is useful to determine its physiological function. This study introduces an efficient expression technique in the insect system using a recombinant eukaryotic expression vector. A recombinant construct expressing an enhanced green fluorescence protein (EGFP) gene under an immediately early promoter was injected into the larval hemocoel of Spodoptera exigua along with a cell transfection reagent. The expression of EGFP occurred earlier, and persisted for longer period with increasing injection dose. However, there was significant variation in expression efficiency among different cell transfection reagents. In addition, the transfection efficiency measured by RT-PCR varied among tissues with high expression of EGFP in hemocytes and fat body, but not in epidermis, gut, and nerve tissues. Two functional genes (CpBV15α and CpBV15β) derived from a polydnavirus were inserted into the eukaryotic expression vector and injected into S. exigua larvae. Expression levels in hemocytes and fat body were measured by RT-PCR and immunofluorescence assay. Both mRNAs and proteins were detected in the two tissues, in which expression signals depended on the amount of injected DNA. These immunosuppressive factors significantly inhibited hemocyte behavior, such as hemocyte-spreading, nodule formation, and phagocytosis. These results demonstrate the use of in vivo transient expression of polydnaviral genes for direct analysis of biological function in the host insect.

Transient expression of a viral histone H4 inhibits expression of cellular and humoral immune-associated genes in Tribolium castaneum

A viral histone H4 is encoded in a polydnavirus called Cotesia plutellae bracovirus (CpBV), which is symbiotic to an endoparasitoid wasp, C. plutellae. Compared to general histone H4s, the viral H4 possesses an extra N-terminal tail containing 38 amino acid residues, which has been presumed to control host gene expression in an epigenetic mode. To analyze the epigenetic control activity of CpBV-H4 on expression of immune-associated genes, it was transiently expressed in larvae of Tribolium castaneum that had been annotated in the immune genes from a full genome sequence. Subsequent alteration of gene expression pattern was compared with that of its mutant form deleting N-terminal tail (truncated CpBV-H4). In response to bacterial challenge, T. castaneum induces expression of 13 antimicrobial peptide (AMP) genes. When CpBV-H4 was expressed, the larvae failed to express 12 inducible AMP genes. By contrast, when truncated CpBV-H4 was transiently expressed, all AMP genes were expressed. Hemocyte nodule formation was significantly impaired by expression of CpBV-H4, in which expressions of tyrosine hydroxylase and dihydroxyphenylalanine decarboxylase were suppressed. However, expression of truncated CpBV-H4 did not give any significant adverse effect on the cellular immunity. The immunosuppression of CpBV-H4 was further supported by its activity of enhancing bacterial pathogenicity of an entomopathogenic bacterium, Xenorhabdus nematophila, against larvae transiently expressing CpBV-H4. These results suggest that CpBV-H4 suppresses both humoral and cellular immune responses of T. castaneum by altering a normal epigenetic control of immune-associated gene expression.

Apolipophorin III and transmission electron microscopy as toxicity indicators for harmaline and tea saponin in Spodoptera exigua (Noctuidae: Lepidoptera)

Apolipophorin III, traditionally known for lipid transport in insects is fairly established as toxicity indicator against harmaline and tea saponin during this study. Apolipophorin III expressed in the hemolymph and midgut tissues of 3rd, 4th, 5th larval instars and pupae of Spodoptera exigua. Apolipophorin III presence was further confirmed by achieving its partial cDNA (Genbank accession no. FJ606822) of 448bp. qRT PCR revealed that tea saponin resulted in significant reduction of gene expression in 3rd and 4th larval instars but increased in 5th instar as compared to control. Harmaline caused gradual increase of gene expression in 3rd, 4th and 5th instars after feeding on the treated diet. Fifth instar larvae synonymously resulted in the highest gene expressions against both the biochemicals. After the injection of harmaline and tea saponin abrupt increase in gene expression of 4th, 5th larval instar and pupae was observed as compared to control treatment. Transmission electron microscopy of midgut epithelium after being fed with harmaline and tea saponin depicted certain cytological changes. Harmaline treatment lead to cytoplasm vacuolization, mitochondrial disruption, spherocrystals with concentric layers, irregular nucleus and floating nuclei in cytoplasm. Tea saponin treatment resulted in denser cytoplasm, higher intracellular osmotic concentration and reduced complement of apical microvilli. Cells were found to have only a few mitochondria and glycogen deposits in comparison to control treatment.

Host translational control of a polydnavirus, Cotesia plutellae bracovirus, by sequestering host eIF4A to prevent formation of a translation initiation complex

Host translational control is a viral strategy to exploit host cellular resources. Parasitization by some endoparasitoids containing polydnaviruses inhibits the synthesis of specific host proteins at post-transcriptional level. Two host translation inhibitory factors (HTIFs) have been proposed in Cotesia plutellae bracovirus (CpBV). Parasitization by C. plutellae inhibited storage protein 1 (SP1) synthesis of Plutella xylostella at post-transcriptional level. One HTIF, CpBV15β, inhibited the translation of SP1 mRNA in an in vitro translation assay using rabbit reticulocyte lysate, but did not inhibit its own mRNA. To further analyse the discrimination of target and nontarget mRNAs of the inhibitory effect of HTIF, 5' untranslated regions (UTRs) of SP1 and CpBV15β mRNA were reciprocally exchanged. In the presence of HTIFs, the chimeric CpBV15β mRNA that contained SP1 5' UTR was not translated, whereas the chimeric SP1 mRNA that contained CpBV15β 5' UTR was translated. There was a difference in the 5' UTR secondary structures between target (SP1) and nontarget (CpBV15α and CpBV15β) mRNAs in terms of thermal stability. Different mutant 5' UTRs of SP1 mRNA were prepared by point mutations to modify their secondary structures. The constructs containing 5' UTRs of high thermal stability in their secondary structures were inhibited by HTIF, but those of low thermal stability were not. Immunoprecipitation with CpBV15β antibody coprecipitated eIF4A, which would be required for unwinding the secondary structure of the 5' UTR. These results indicate that the viral HTIF discriminates between host mRNAs according to their dependency on eIF4A to form a functional initiation complex for translation.

Identification of an in vitro interaction between an insect immune suppressor protein (CrV2) and G alpha proteins

The protein CrV2 is encoded by a polydnavirus integrated into the genome of the endoparasitoid Cotesia rubecula (Hymenoptera:Braconidae:Microgastrinae) and is expressed in host larvae with other gene products of the polydnavirus to allow successful development of the parasitoid. CrV2 expression has previously been associated with immune suppression, although the molecular basis for this was not known. Here, we have used time-resolved Förster resonance energy transfer (TR-FRET) to demonstrate high affinity binding of CrV2 to Gα subunits (but not the Gβγ dimer) of heterotrimeric G-proteins. Signals up to 5-fold above background were generated, and an apparent dissociation constant of 6.2 nm was calculated. Protease treatment abolished the TR-FRET signal, and the presence of unlabeled CrV2 or Gα proteins also reduced the TR-FRET signal. The activation state of the Gα subunit was altered with aluminum fluoride, and this decreased the affinity of the interaction with CrV2. It was also demonstrated that CrV2 preferentially bound to Drosophila Gα(o) compared with rat Gα(i1). In addition, three CrV2 homologs were detected in sequences derived from polydnaviruses from Cotesia plutellae and Cotesia congregata (including the immune-related early expressed transcript, EP2). These data suggest a potential mode-of-action of immune suppressors not previously reported, which in addition to furthering our understanding of insect immunity may have practical benefits such as facilitating development of novel controls for pest insect species.

Immunosuppression induced by entomopathogens is rescued by addition of apolipophorin III in the diamondback moth, Plutella xylostella

Apolipophorin III (ApoLpIII) has been known to play critical roles in lipid transport and immune activation in insects. This study reports a partial ApoLpIII gene cloned from the diamondback moth, Plutella xylostella. It showed that the gene was expressed in all developmental stages of P. xylostella. In larval stage, it was expressed in all tested tissues of hemocyte, fat body, gut, and epidermis. In response to bacterial challenge, the larvae showed an enhanced level of ApoLpIII expression by a quantitative real-time RT-PCR. RNA interference of ApoLpIII by its specific double stranded RNA (dsRNA) caused significant knockdown of its expression level and resulted in significant suppression in hemocyte nodule formation in response to bacterial challenge. However, larvae treated with the dsRNA exhibited a significant recovery in the cellular immune response by addition of a recombinant ApoLpIII. Parasitization by an endoparasitoid wasp, Cotesia plutellae, suppressed expression of ApoLpIII and resulted in a significant suppression in the hemocyte nodule formation. The addition of the recombinant ApoLpIII to the parasitized larvae significantly restored the hemocyte activity. Infection of an entomopathogenic bacterium, Xenorhabdus nematophila, caused potent pathogenicity of P. xylostella. However, the addition of the recombinant ApoLpIII to the infected larvae significantly prevented the lethal pathogenicity. This study suggests that ApoLpIII limits pathogenicity induced by parasitization or bacterial infection in P. xylostella.

A viral histone H4 suppresses expression of a transferrin that plays a role in the immune response of the diamondback moth, Plutella xylostella

A transferrin (Tf) gene has been predicted from an expressed sequence tag of the diamondback moth, Plutella xylostella. It encodes 681 amino acid residues that share 80-90% sequence homologies with other lepidopteran Tfs. The gene was constitutively expressed in all developmental stages of P. xylostella. Double-stranded RNA (dsRNA) specific to the Tf gene was prepared and microinjected into the larvae. We hypothesize that the dsRNA treatment suppressed the Tf gene expression level and it significantly inhibited haemocyte nodule formation in response to bacterial challenge. The larvae treated with dsRNA also showed a significantly enhanced susceptibility to an entomopathogenic bacterium, Bacillus thuringiensis. An endoparasitoid wasp, Cotesia plutellae, parasitized the larvae of P. xylostella, which showed significant reduction of Tf expression. The suppression of Tf expression was mimicked by transient expression of a viral gene CpBV-H4, encoded in the symbiotic virus of C. plutellae. A truncated form of CpBV-H4 prepared by deleting an extended N-terminal 38 amino acid residue lost its inhibitory activity against the Tf gene expression. These results suggest that Tf of P. xylostella plays an immunological role in P. xylostella and that the suppression of its expression in the parasitized larvae is caused by a viral histone H4 in an epigenetic mode.

A SERI technique reveals an immunosuppressive activity of a serine-rich protein encoded in Cotesia plutellae bracovirus

Polydnavirus genome is segmented and dispersed on host wasp chromosome. After replication, the segments form double- stranded circular DNAs and embedded in viral coat proteins. These viral particles are delivered into a parasitized host along with parasitoid eggs. A serine-rich protein (SRP) is predicted in a polydnavirus, Cotesia plutellae bracovirus (CpBV), genome in its segment no. 33 (CpBV-S33), creating CpBVSRP1. This study explored its expression and physiological function in the diamondback moth, Plutella xylostella, larvae parasitized by C. plutellae. CpBV-SRP1 encodes 122 amino acids with 26 serines and several predicted phosphorylation sites. It is persistently expressed in all tested tissues of parasitized P. xylostella including hemocyte, fat body, and gut. Its physiological function was analyzed by injecting CpBV-S33 and inducing its expression in nonparasitized P. xylostella by a technique called SERI (segment expression and RNA interference). The expression of CpBV-SRP1 significantly impaired the spreading behavior and total cell count of hemocytes of treated larvae. Subsequent RNA interference of CpBV-SRP1 rescued the immunosuppressive response. This study reports the persistent expression of CpBV-SRP1 in a parasitized host and its parasitic role in suppressing the host immune response by altering hemocyte behavior and survival.

Analysis of promoter activity of selected Cotesia plutellae bracovirus genes

In a previous study, we cloned 27 discrete genome segments of Cotesia plutellae bracovirus (CpBV) and provided the complete nucleotide sequences and annotation. Seven putative coding regions were predicted from one of the largest segments, CpBV-S30. The activity of promoters associated with six predicted ORFs from this segment were investigated using both transient and baculovirus expression assays with enhanced green fluorescent protein as a reporter gene. CpBV promoters showed activity earlier than the polyhedrin promoter and the activity of some of these promoters was superior to that of the Autographa californica multiple nucleopolyhedrovirus (AcMNPV) ie-1 promoter in the baculovirus expression assays. The promoter of ORF3004 showed the highest level of activity in insect cells, exhibiting 24 % of the activity obtained with the AcMNPV polyhedrin promoter in Sf9 cells. In Spodoptera exigua larvae, the ORF3006 promoter showed the highest activity, with about 35 % of the activity measured with the polyhedrin promoter. In addition, analysis of the ORF3006 promoter revealed that the region between -382 and -422 from the translation start point was critical for activity of this promoter. These results suggest that the CpBV-S30 promoters characterized here could be useful tools in a variety of biotechnological applications, such as gene expression analyses and insecticide development.

N-terminal tail of a viral histone H4 encoded in Cotesia plutellae bracovirus is essential to suppress gene expression of host histone H4

An endoparasitoid wasp, Cotesia plutellae, possesses a symbiotic bracovirus (CpBV), which facilitates parasitism of a specific host, such as larvae of the diamondback moth, Plutella xylostella. A viral histone H4 (CpBV-H4) has been found in the CpBV genome and its gene product plays a role in impairing the host insect cellular immune response. Based on its high similarity to histone H4 of P. xylostella apart from its extended N-terminal tail, it has been suspected to alter host gene expression. Histone subunits were purified from parasitized P. xylostella larvae and found to contain both host and viral H4s, confirming a previous report of a possible epigenetic mode of action. Moreover, this study showed that the host H4 levels in the parasitized larvae clearly decreased during the parasitization period, whereas CpBV-H4 levels maintained a significant level without significant changes. To understand the decrease of host H4 levels, transcription levels of host H4 were monitored by quantitative reverse-transcriptase PCR (RT-PCR) and showed a significant decrease in parasitized P. xylostella larvae, whereas no significant change of the mRNA level was detected in nonparasitized larvae. This transcriptional control of host H4 expression was also observed by inducing transient expression of CpBV-H4 in nonparasitized P. xylostella. Moreover, co-injection of CpBV-H4 and its specific double-stranded RNA recovered the host H4 expression level. To identify a functional domain of CpBV-H4 involved in the transcriptional control, the extended N-terminal tail of CpBV-H4 was removed by preparing a truncated viral H4 construct in an expression vector by deleting the N-terminal tail of 38 amino acid residues and inducing its expression in nonparasitized P. xylostella larvae. The truncated CpBV-H4 clearly lost its inhibitory effects on host H4 transcription. Moreover, the presence of CpBV-H4 affects the spreading of host haemocytes by an epigenetic effect, which is at least partly restored in larvae expressing the truncated version of CpBV-H4. This study suggests that the viral H4 encoded in CpBV can alter host gene expression with its extended N-terminal tail.

Immunoevasive property of a polydnaviral product, CpBV-lectin, protects the parasitoid egg from hemocytic encapsulation of Plutella xylostella (Lepidoptera: Yponomeutidae)

Immunosuppression is the main pathological symptom of the diamondback moth, Plutella xylostella (Lepidoptera: Yponomeutidae), parasitized by an endoparasitoid wasp, Cotesia plutellae (vestalis, Hymenoptera: Braconidae). C. plutellae bracovirus (CpBV), which is a symbiotic virus of C. plutellae, has been known to be the main parasitic factor in the host-parasitoid interaction. CpBV-lectin, encoded in the viral genome and expressed in P. xylostella during early parasitization stage, was suspected to play a role in immunoevasion of defense response. Here we expressed CpBV-lectin in Sf9 cells using a recombinant baculovirus for subsequent functional assays. The recombinant CpBV-lectin exhibited hemagglutination against vertebrate erythrocytes. Its hemagglutinating activity increased with calcium, but inhibited by adding EDTA, indicating its C-type lectin property. CpBV-lectin showed specific carbohydrate-binding affinity against N-acetyl glucosamine and N-acetyl neuraminic acid. The role of this CpBV-lectin in immunosuppression was analyzed by exposing hemocytes of nonparasitized P. xylostella to rat erythrocytes or FITC-labeled bacteria pretreated with recombinant CpBV-lectin, which resulted in significant reduction in adhesion or phagocytosis, respectively. The immunosuppressive activity of CpBV-lectin was further analyzed under in vitro encapsulation response of hemocytes against parasitoid eggs collected at 1- or 24-h post-parasitization. Hemocytic encapsulation was observed against 1-h eggs but not against 24-h eggs. When the 1-h eggs were pretreated with the recombinant CpBV-lectin, encapsulation response was completely inhibited, where CpBV-lectin bound to the parasitoid eggs, but not to hemocytes. These results suggest that CpBV-lectin interferes with hemocyte recognition by masking hemocyte-binding sites on the parasitoid eggs.