Detection and characterisation of three novel species of reovirus (Reoviridae), isolated from geographically separate populations of the winter moth Operophtera brumata (Lepidoptera: Geometridae) on Orkney

Biological and genomic characterization of a cypovirus isolated from golden muga silkworm, Antheraea assamensis Helfer (Lepidoptera: Saturniidae)

A potential viral pathogen, cypovirus causing cytoplasmic polyhedrosis in the Indian golden muga silkworm, Antheraea assamensis Helfer, was isolated and characterized. Electron microscopy analysis confirmed the presence of typical occlusion bodies with icosahedral virions embedded in polyhedral matrices. The viral genome was dsRNA totaling approximately 24.9 kb in size, divided into 10 discrete segments containing one single open reading frame (ORF) each. Genomic analysis revealed conserved non-coding sequences such as 'AGUAAU' and 'AUAGAGC' at 5' and 3' termini, respectively. Functional annotation identified the presence of structural proteins, such as major and minor capsid proteins, as well as enzymatic proteins, including RNA-dependent RNA polymerase (RdRp). Phylogenetic analysis using deduced amino acid sequences of viral RdRp gene indicated a close evolutionary relationship between the cypovirus isolated from Antheraea assamensis and Antheraea mylitta cypovirus 4 (AmCPV4), thus we named the Indian golden muga silkworm cypovirus as Antheraea assamensis cypovirus 4 (AaCPV4). Nevertheless, AaCPV4 does not have a genomic segment 11 which was earlier reported in AmCPV4. Bioassay studies demonstrated high virulence, with 100 % larval mortality observed within 12 days of infection due to cytoplasmic polyhedrosis. Tissue tropism studies revealed significant viral replication in the midgut, hemolymph, and malpighian tubules, with the midgut exhibiting the highest viral load (9.65 log copy number of RdRp gene/µg of RNA). Cross-transmission experiments demonstrated AaCPV4 host specificity, infecting only in Antheraea species (A. mylitta and A. assamensis), while other lepidopteran insects including silkworms Bombyx mori, and Samia ricini were not susceptible to AaCPV4 infection. According to morphological, genetic, and biological characteristics, we suggest that AaCPV4 is an isolate of the species Cypovirus antheraeae (family Spinareoviridae).

Linc20486 promotes BmCPV replication through inhibiting the transcription of AGO2 and Dicers

The silkworm holds pivotal economic importance, serving not only as a primary source of silk but also as a prominent model organism in scientific research. Nonetheless, silkworm farming remains vulnerable to diverse factors, with viral infections posing the gravest threat to the sericulture industry. Among these, the Bombyx mori cytoplasmic polyhedrosis virus (BmCPV), a member of the Reoviridae family and the cytoplasmic polyhedrosis virus genus, emerges as a significant pathogen in silkworm production. BmCPV infection primarily induces midgut sepsis in silkworms, spreads rapidly, and can inflict substantial economic losses on sericulture production. Presently, effective strategies for preventing and treating BmCPV infections are lacking. Long non-coding RNA (lncRNA) constitutes a class of RNA molecules with transcripts exceeding 200 nt, playing a crucial role in mediating the interplay between pathogens and host cells. Investigation through high-throughput technology has unveiled that BmCPV infection markedly upregulates the expression of Linc20486. This observation suggests potential involvement of Linc20486 in regulating virus replication. Indeed, as anticipated, knockdown of Linc20486 in cells profoundly impedes BmCPV replication, whereas overexpression significantly enhances virus propagation. To probe into the mechanism underlying Linc20486's impact on virus replication, its effects on autophagy, innate immunity, and RNAi-related pathways were scrutinized. The findings revealed that Linc20486 exerts significant influence on the expression of RNAi pathway-related genes, such as Dicer1, Dicer2 and AGO2. This discovery holds promise for unveiling novel avenues to comprehend and combat BmCPV infections in silkworms.

BmCPV replication is suppressed by the activation of the NF-κB/autophagy pathway through the interaction of vsp21 translated by vcircRNA_000048 with ubiquitin carboxyl-terminal hydrolase

Bombyx mori cypovirus (BmCPV), a typical double-stranded RNA virus, was demonstrated to generate a viral circRNA, vcircRNA_000048, which encodes a vsp21 with 21 amino acid residues to suppress viral replication. However, the regulatory mechanism of vsp21 on virus infection remained unclear. This study discovered that vsp21 induces reactive oxygen species (ROS) generation, activates autophagy, and attenuates virus replication by inducing autophagy. Then we confirmed that the effect of vsp21-induced autophagy on viral replication was attributed to the activation of the NF-κB signaling pathway. Furthermore, we clarified that vsp21 interacted with ubiquitin carboxyl-terminal hydrolase (UCH) and that ubiquitination and degradation of phospho-IκB-α were enhanced by vsp21 via competitive binding to UCH. Finally, we validated that vsp21 activates the NF-κB/autophagy pathway to suppress viral replication by interacting with UCH. These findings provided new insights into regulating viral multiplication and reovirus-host interaction.

Faecal virome of the Australian grey-headed flying fox from urban/suburban environments contains novel coronaviruses, retroviruses and sapoviruses

Bats are important reservoirs for viruses of public health and veterinary concern. Virus studies in Australian bats usually target the families Paramyxoviridae, Coronaviridae and Rhabdoviridae, with little known about their overall virome composition. We used metatranscriptomic sequencing to characterise the faecal virome of grey-headed flying foxes from three colonies in urban/suburban locations from two Australian states. We identified viruses from three mammalian-infecting (Coronaviridae, Caliciviridae, Retroviridae) and one possible mammalian-infecting (Birnaviridae) family. Of particular interest were a novel bat betacoronavirus (subgenus Nobecovirus) and a novel bat sapovirus (Caliciviridae), the first identified in Australian bats, as well as a potentially exogenous retrovirus. The novel betacoronavirus was detected in two sampling locations 1375 km apart and falls in a viral lineage likely with a long association with bats. This study highlights the utility of unbiased sequencing of faecal samples for identifying novel viruses and revealing broad-scale patterns of virus ecology and evolution.

Tight junction protein claudin-2 promotes cell entry of Bombyx mori cypovirus

Claudin-2 is a major component of tight junctions (TJs), which play an important role in reovirus entry into host cells. The Bombyx mori cytoplasmic polyhedosis virus (BmCPV) relates to the cypovirus strain of the reovirus family. So far, the role of claudin-2 in the process of BmCPV infection is not known. In the present study, it was observed that increasing expression of the claudin-2 gene (CLDN2) may concomitantly elevate BmCPV infection. Contrarily, knockdown of CLDN2 expression by siRNAs can reduce BmCPV infection. Similarly, antibody-based blockage of claudin-2 could also decrease BmCPV cell entry. These results suggest that claudin-2 can promote BmCPV infection in vitro. Moreover, immunofluorescence (IF) assays showed that claudin-2 can interact with BmCPV during viral infection. Specifically, co-immunoprecipitation experiments indicated that claudin-2 binds the BmCPV VP7 (instead of VP3 proteins). The interaction between VP7 and claudin-2 was further confirmed by bimolecular fluorescence complementation (BIFC). Altogether, our results suggest that BmCPV cell entry can be promoted upon interaction of VP7 with claudin-2. These findings provide new mechanistic insights related to BmCPV infection. KEY POINTS: •Claudin-2 could promote BmCPV infection of cells. •Claudin-2 interacted with BmCPV during BmCPV infection. •Claudin-2 could interact with BmCPV VP7 protein, but not with VP3 proteins.

Exploration of the Ixodes ricinus virosphere unveils an extensive virus diversity including novel coltiviruses and other reoviruses

Recent metagenomics studies have revealed several tick species to host a variety of previously undiscovered RNA viruses. Ixodes ricinus, which is known to be a vector for many viral, bacterial, and protozoan pathogens, is the most prevalent tick species in Europe. For this study, we decided to investigate the virosphere of Belgian I. ricinus ticks. High-throughput sequencing of tick pools collected from six different sampling sites revealed the presence of viruses belonging to many different viral orders and families, including Mononegavirales, Bunyavirales, Partitiviridae, and Reoviridae. Of particular interest was the detection of several new reoviruses, two of which cluster together with members of the genus Coltivirus. This includes a new strain of Eyach virus, a known causative agent of tick-borne encephalitis. All genome segments of this new strain are highly similar to those of previously published Eyach virus genomes, except for the fourth segment, encoding VP4, which is markedly more dissimilar, potentially indicating the occurrence of a genetic reassortment. Further polymerase chain reaction-based screening of over 230 tick pools for 14 selected viruses showed that most viruses could be found in all six sampling sites, indicating the wide spread of these viruses throughout the Belgian tick population. Taken together, these results illustrate the role of ticks as important virus reservoirs, highlighting the need for adequate tick control measures.

A novel cypovirus found in a betabaculovirus co-infection context contains a poxvirus immune nuclease (poxin)-related gene

The cassava hornworm Erinnyis ello ello (Lepidoptera: Sphingidae) is an important pest in Brazil. This insect feeds on host plants of several species, especially Manihot esculenta (cassava) and Hevia brasiliensis (rubber tree). Cassava hornworm outbreaks are quite common in Brazil and can cause great impact over crop production. Granulare and polyhedral-shaped occlusion bodies (OBs) were observed in extracts of dead E. ello larvae from rubber-tree plantations by light and scanning electron microscopy (SEM), suggesting a mixed infection. The polyhedral-shaped OB surface revealed indentations that resemble those found in cypovirus polyhedra. After OB nucleic acid extraction followed by cDNA production and Illumina deep-sequencing analysis, the results confirmed for the presence of a putative novel cypovirus that carries ten segments and also a betabaculovirus (Erinnyis ello granulovirus, ErelGV). Phylogenetic analysis of the predicted segment 1-enconded RdRP showed that the new cypovirus isolate is closely related to a member of species Cypovirus 2, which was isolated from Inachis io (Lepidoptera: Nymphalidae). Therefore, we named this new isolate Erinnyis ello cypovirus 2 (ErelCPV-2). Genome in silico analyses showed that ErelCPV-2 segment 8 (S8) has a predicted amino acid identity of 35.82 % to a hypothetical protein of betabaculoviruses. This putative protein has a cGAMP-specific nuclease domain related to the poxvirus immune nucleases (poxins) from the 2',3'-cGAMP-degrading enzyme family.

Bombyx mori cypovirus encoded small peptide inhibits viral multiplication

Bombyx mori cypovirus (BmCPV) is one of the most infectious pathogen in sericulture and a member of the family Reoviridae. It specifically infects the midgut of silkworm. The BmCPV genome consists of 10 dsRNAs segments (S1-S10), which have generally been assumed to be monocistronic. In this study, a small open reading frame encoding the peptide S5-sORF, containing 27 amino acid residues, was predicted in a region of the negative (-) strand of BmCPV segment S5. An immunofluorescence assay detected S5-sORF in the cytoplasm and nuclei of BmCPV-infected cells, and it was also detected in the virion with western blotting, suggesting that S5-sORF may be assembled into the BmCPV virion. Viral gene expression was inhibited by overexpressed S5-sORF, and viral multiplication was dose-dependently suppressed by the S5-sORF peptide. A viable recombinant virus, BmCPV-S5-sORF^mut, in which the start codon (ATG) of S5-sORF was mutated to a stop codon (TGA), was generated with reverse genetics. The proliferation of BmCPV was increased by the abolition of S5-sORF expression. Furthermore, the RNA transcript of S5-sORF and small peptide of S5-sORF were involved in BmCPV replication. The expression of genes related to the innate immune pathways and apoptosis in the silkworm were not significantly affected by S5-sORF overexpression. Our results suggest that a viral nucleotide sequence is utilized by the host to generate an antiviral peptide, which may be a novel strategy protecting the host from viral infection.

Clathrin-mediated endocytosis is a candidate entry sorting mechanism for Bombyx mori cypovirus

Bombyx mori cypovirus (BmCPV), a member of the Reoviridae, specifically infects silkworms and causes extensive economic losses to the sericulture industry. To date, the entry mechanism of BmCPV into cells is unclear. Here we used electron microscopy to study the route of entry of BmCPV into cells, and the results demonstrated that the entry of BmCPV into BmN cells was mediated by endocytosis. Blocking the entry pathway with four endocytosis inhibitors, including dansylcadaverine, chlorpromazine, genistein, and PP2, significantly decreased the infectivity of BmCPV. This indicates that BmCPV enters BmN cells via endocytosis, and that clathrin-mediated sorting is the predominant entry method. After the relative expression levels of clathrin heavy chain (clathrin, GenBank accession No. NM_001142971.1) and the adaptor protein complex-1 gamma subunit AP-1 (AP-1, GenBank accession No. JQ824201.1), which are involved in clathrin-mediated endocytosis, were inhibited by RNA interference or abolishing the functions of clathrin and AP-1 with their corresponding antibodies, the infectivity of BmCPV was reduced significantly, which suggests that clathrin-mediated endocytosis contributed to the entry of BmCPV into cells. Our findings suggest that the clathrin-mediated endocytosis pathway is a candidate for the development of therapeutics for silkworm cytoplasmic polyhedrosis.

The virome of Drosophila suzukii, an invasive pest of soft fruit

Drosophila suzukii (Matsumura) is one of the most damaging and costly pests to invade temperate horticultural regions in recent history. Conventional control of this pest is challenging, and an environmentally benign microbial biopesticide is highly desirable. A thorough exploration of the pathogens infecting this pest is not only the first step on the road to the development of an effective biopesticide, but also provides a valuable comparative dataset for the study of viruses in the model family Drosophilidae. Here we use a metatransciptomic approach to identify viruses infecting this fly in both its native (Japanese) and invasive (British and French) ranges. We describe eighteen new RNA viruses, including members of the Picornavirales, Mononegavirales, Bunyavirales, Chuviruses, Nodaviridae, Tombusviridae, Reoviridae, and Nidovirales, and discuss their phylogenetic relationships with previously known viruses. We also detect 18 previously described viruses of other Drosophila species that appear to be associated with D. suzukii in the wild.

The Operophtera brumata Nucleopolyhedrovirus (OpbuNPV) Represents an Early, Divergent Lineage within Genus Alphabaculovirus

Operophtera brumata nucleopolyhedrovirus (OpbuNPV) infects the larvae of the winter moth, Operophtera brumata. As part of an effort to explore the pesticidal potential of OpbuNPV, an isolate of this virus from Massachusetts (USA)-OpbuNPV-MA-was characterized by electron microscopy of OpbuNPV occlusion bodies (OBs) and by sequencing of the viral genome. The OBs of OpbuNPV-MA consisted of irregular polyhedra and contained virions consisting of a single rod-shaped nucleocapsid within each envelope. Presumptive cypovirus OBs were also detected in sections of the OB preparation. The OpbuNPV-MA genome assembly yielded a circular contig of 119,054 bp and was found to contain little genetic variation, with most polymorphisms occurring at a frequency of < 6%. A total of 130 open reading frames (ORFs) were annotated, including the 38 core genes of Baculoviridae, along with five homologous repeat (hr) regions. The results of BLASTp and phylogenetic analysis with selected ORFs indicated that OpbuNPV-MA is not closely related to other alphabaculoviruses. Phylogenies based on concatenated core gene amino acid sequence alignments placed OpbuNPV-MA on a basal branch lying outside other alphabaculovirus clades. These results indicate that OpbuNPV-MA represents a divergent baculovirus lineage that appeared early during the diversification of genus Alphabaculovirus.

Genomes of viral isolates derived from different mosquitos species

Eleven viral isolates derived mostly in albopictus C6/36 cells from mosquito pools collected in Southeast Asia and the Americas between 1966 and 2014 contained particles with electron microscopy morphology typical of reoviruses. Metagenomics analysis yielded the near complete genomes of three novel reoviruses, Big Cypress orbivirus, Ninarumi virus, and High Island virus and a new tetravirus, Sarawak virus. Strains of previously characterized Sathuvarachi, Yunnan, Banna and Parry's Lagoon viruses (Reoviridae), Bontang virus (Mesoniviridae), and Culex theileri flavivirus (Flaviviridae) were also characterized. The availability of these mosquito virus genomes will facilitate their detection by metagenomics or PCR to better determine their geographic range, extent of host tropism, and possible association with arthropod or vertebrate disease.

The gene expression profile of resistant and susceptible Bombyx mori strains reveals cypovirus-associated variations in host gene transcript levels

High-throughput paired-end RNA sequencing (RNA-Seq) was performed to investigate the gene expression profile of a susceptible Bombyx mori strain, Lan5, and a resistant B. mori strain, Ou17, which were both orally infected with B. mori cypovirus (BmCPV) in the midgut. There were 330 and 218 up-regulated genes, while there were 147 and 260 down-regulated genes in the Lan5 and Ou17 strains, respectively. Gene ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment for differentially expressed genes (DEGs) were carried out. Moreover, gene interaction network (STRING) analyses were performed to analyze the relationships among the shared DEGs. Some of these genes were related and formed a large network, in which the genes for B. mori cuticular protein RR-2 motif 123 (BmCPR123) and the gene for B. mori DNA replication licensing factor Mcm2-like (BmMCM2) were key genes among the common up-regulated DEGs, whereas the gene for B. mori heat shock protein 20.1 (Bmhsp20.1) was the central gene among the shared down-regulated DEGs between Lan5 vs Lan5-CPV and Ou17 vs Ou17-CPV. These findings established a comprehensive database of genes that are differentially expressed in response to BmCPV infection between silkworm strains that differed in resistance to BmCPV and implied that these DEGs might be involved in B. mori immune responses against BmCPV infection.

Involvement of microRNAs in infection of silkworm with bombyx mori cytoplasmic polyhedrosis virus (BmCPV)

Bombyx mori cytoplasmic polyhedrosis virus (BmCPV) is one of the most important pathogens of silkworm. MicroRNAs (miRNAs) have been demonstrated to play key roles in regulating host-pathogen interaction. However, there are limited reports on the miRNAs expression profiles during insect pathogen challenges. In this study, four small RNA libraries from BmCPV-infected midgut of silkworm at 72 h post-inoculation and 96 h post-inoculation and their corresponding control midguts were constructed and deep sequenced. A total of 316 known miRNAs (including miRNA*) and 90 novel miRNAs were identified. Fifty-eight miRNAs displayed significant differential expression between the infected and normal midgut (P value < = 0.01 and fold change > = 2.0 or < = 0.5), among which ten differentially expressed miRNA were validated by qRT-PCR method. Further bioinformatics analysis of predicted target genes of differentially expressed miRNAs showed that the miRNA targets were involved in stimulus and immune system process in silkworm.

RNA Viruses in Parasitoid Wasps

This chapter describes the different RNA viruses that have been detected at least once in parasitoid wasps. It could be wondered whether the other families of parasitoids are really absent, or if this is due to the fact that inadequate techniques were used to detect viruses. In fact, several different methods have been used: TEM of the venom glands of females, extraction of nucleic acids, followed by DNAse digestion to eliminate the polydnavirus or ascovirus genome, RT-PCR with primers specific of RdRp or data mining in an EST library. To resolve this problem of detecting RNA viruses, a systematic search for viruses in parasitoids should be carried out using a combination of these different methods. Only a few hymenopteran species are known to be infected by RNA viruses, although thousands of species are known to carry polydnaviruses or VLPs. This could suggest that the presence of polydnaviruses or VLPs may block infections with other viruses.

Molecular detection, penetrance, and transmission of an inherited virus responsible for behavioral manipulation of an insect parasitoid

For insects, the prevalence of numerous vertically transmitted viruses can be high in their host populations. These viruses often have few, if any, pathological effects on their hosts, and consequently, many of them can remain unnoticed for long periods, despite their potential role in the evolution of the host phenotype. Some females of Leptopilina boulardi, a solitary parasitoid of Drosophila larvae, are infected by an inherited virus (LbFV) that manipulates the behavior of the wasp by increasing its tendency to lay eggs in a host that is already parasitized (superparasitism). This behavioral alteration allows horizontal transmission of the virus within superparasitized Drosophila larvae. Using suppressive subtractive hybridization with infected and uninfected lines, we identified one putative viral sequence. Based on this sequence, we developed a simple PCR test. We tested the correlation between the superparasitism phenotype and PCR amplification of the putative viral marker using several experimental conditions (including horizontal transfers) and several parasitoid genotypes. All of the results revealed that there was a perfect match between the superparasitism phenotype and the amplification profile, which validated use of the molecular marker as a tool to track the presence of the virus and provided the first genomic data for this fascinating virus. The results also show that there was very efficient horizontal and vertical transmission of LbFV, which probably explains its high prevalence in the French populations that we sampled (67 and 70% of infected females). This manipulative virus is likely to play a major role in the ecology and evolution of its parasitoid host.

Molecular characterisation of a cypovirus isolated from the western spruce budworm Choristoneura occidentalis

A novel cypovirus, assigned CoCPV, was isolated from natural populations of the western spruce budworm, Choristoneura occidentalis. The complete nucleotide sequences of genomic segments S2-S5 and S7-S10 were determined. Each segment contained a single open reading frame. Conserved motifs 5' (AGUUU......UUUGUGC) 3' were found at the ends of each segment. Analysis of S2, which encoded a putative RNA-dependent RNA polymerase protein, confirmed CoCPV belonged to the genus Cypovirus within the family Reoviridae. Further phylogenetic analysis using S10 (the polyhedrin gene) aligned this virus with species type-16, closely related to a cypovirus isolated from C. fumiferana.

Sequence analysis of a reovirus isolated from the winter moth Operophtera brumata (Lepidoptera: Geometridae) and its parasitoid wasp Phobocampe tempestiva (Hymenoptera: Ichneumonidae)

A reovirus was isolated from Operophtera brumata (ObRV) and its parasitoid wasp Phobocampe tempestiva. Each of the 10 dsRNA genome segments of ObRV was sequenced and shown to contain a single open reading frame (ORF). Conserved motifs ([+ve] 5'-AAATAAA ...(G)/(T)AGGTT-3') were found at the termini of each segment, with the exception of Seg-6 and Seg-8, where the 5' termini were 5'-AACAAA...-3'. The putative proteins encoded by each segment were compared with those of other members of the family Reoviridae. Phylogenetic comparisons to published sequences for the RNA-dependent RNA polymerase genes from other reoviruses indicated that ObRV is most closely related to members of the genus Cypovirus. However, unlike the cypoviruses, ObRV has a double-layered capsid structure. When the protein encoded by ObRV Seg-10 was expressed (by inserting the open reading frame into a baculovirus expression vector) no 'occlusion bodies' were observed in the recombinant baculovirus infected insect cell cultures. This suggests that unlike the cypoviruses, Seg-10 of ObRV does not contain a polyhedrin gene. Further phylogenetic comparisons also identified relationships between Seg-2 and Seg-10 of ObRV, and genes of Diadromus pulchellus Idnoreovirus 1 (DpIRV1), suggesting that ObRV represents a new species from the genus Idnoreovirus.

Occurrence, function and evolutionary origins of '2A-like' sequences in virus genomes

2A is an oligopeptide sequence mediating a ribosome ‘skipping’ effect, producing an apparent ‘cleavage’ of polyproteins. First identified and characterized in picornaviruses, ‘2A-like’ sequences are found in other mammalian viruses and a wide range of insect viruses. Databases were analysed using a motif conserved amongst 2A/2A-like sequences. The newly identified 2A-like sequences (30 aa) were inserted into a reporter polyprotein to determine their cleavage activity. Our analyses showed that these sequences fall into two categories. The majority mediated very high (complete) cleavage to separate proteins and a few sequences mediated cleavage with lower efficiency, generating appreciable levels of the uncleaved form. Phylogenetic analyses of 2A-like sequences and RNA-dependent RNA polymerases (RdRps) indicated multiple, independent, acquisitions of these sequences at different stages during virus evolution. Within a virus family, 2A sequences are (probably) homologous, but diverge due to other evolutionary pressures. Amongst different families, however, 2A/2A-like sequences appear to be homoplasic.

The complete nucleotide sequence of the type 5 Helicoverpa armigera cytoplasmic polyhedrosis virus genome

The S1-6, S8, and S9 segments of the type 5 Helicoverpa armigera cytoplasmic polyhedrosis virus (HaCPV-5, Chinese strain) were cloned and sequenced, completing the HaCPV-5 genome. We found that each HaCPV-5 segment exhibits the conserved terminal sequences AGUU and UUGC located at the 5' and 3' ends, respectively. We also analyzed the translation initiation codon of the HaCPV-5 genome and compared it with the available cypovirus sequences in GenBank. We postulated that the conserved purine at the -3 position in relation to the AUG codon is probably the most important nucleotide for efficient translation initiation in cypovirus. Although the nucleotide sequences of the HaCPV-5 segments S1-10 exhibit no significant similarity to other viruses, blast searches did reveal some similarities between predicted HaCPV-5 amino acid sequences and those of other viruses.

Characterisation and partial sequence analysis of two novel cypoviruses isolated from the winter moth Operophtera brumata (Lepidoptera: Geometridae)

The complete nucleotide sequences of genomic segments S5 to S10 from Operophtera brumata cypovirus 18 (OpbuCPV18), and the complete nucleotide sequences of genomic segments S2, S5, S9 and S10 from Operophtera brumata cypovirus 19 (OpbuCPV19) have been determined. Each genome segment contained a single open reading frame (ORF). Conserved motifs 5' (AGUAAA....GUUAGCU) 3' were found at the ends of each segment of OpbuCPV18, whilst conserved motifs 5' (AACAAA....UUUGC) 3' were found at each segment terminus of OpbuCPV19. The putative proteins were compared with those of other members of the Reoviridae family. Phylogenetic analysis using the polyhedrin gene (S10) indicated that OpbuCPV18 was most closely related to Dendrolimus punctatus cypovirus 1, whilst OpbuCPV19 was most closely related to Trichoplusia ni cypovirus 15. In addition, analysis of S2, which encoded a putative RNA-dependant RNA polymerase gene, confirmed OpbuCPV19 belonged to the genus Cypovirus. Following the expression of the ORF from OpbuCPV19 S10, using a baculovirus expression vector, occlusion bodies were observed in insect cell culture. This demonstrated that segment 10 coded for the polyhedrin gene, capable of forming a polyhedral crystalline matrix.

Biological and molecular studies of a cypovirus from the black fly Simulium ubiquitum (Diptera: Simuliidae)

A cypovirus from the black fly Simulium ubiquitum (SuCPV) was isolated and examined using biological and molecular techniques. SuCPV produces small (typically 0.25mum), polyhedral shaped inclusion bodies (polyhedra), in which the virus particles become multiply embedded. SuCPV is the third cypovirus isolated from Diptera, but the first from Simuliidae that has been characterized using molecular analyses. SuCPV has a genome composed of 10 segments of dsRNA, with an electrophoretic migration pattern that is different from those of recent UsCPV-17 and CrCPV-17 isolates from the mosquitoes Uranotaenia sapphirina and Culex restuans, respectively. The SuCPV electropherotype appears to show significant differences from those of the previously characterized lepidopteran cypoviruses. Sequence analysis of SuCPV segment 10 shows that it is unrelated to either of the two CPV isolates from Diptera or to the CPV species for which Seg-10 has been previously characterized from Lepidoptera. A comparison of the terminal regions of SuCPV genome segments to those of CPV-1, 2, 4, 5 14, 15, 16, 17, 18, and 19 also revealed only low levels of conservation. We therefore, propose that SuCPV is classified within a new Cypovirus species, which we have tentatively identified as Cypovirus-20. We have therefore referred to this virus isolate as S. ubiquitum CPV-20 (SuCPV-20).

Phylogenetic analysis of Heliothis armigera cytoplasmic polyhedrosis virus type 14 and a series of dwarf segments found in the genome

Full-length nucleotide sequences for the genome segments (S1-S6) of Heliothis armigera cytoplasmic polyhedrosis virus type 14 (HaCPV-14) have been characterized. Each segment consists of a single open reading frame with conserved motifs AGAA and AGCU at the 5' and 3' ends, respectively. Comparison of the proteins of HaCPV-14 with those of other members of the family Reoviridae suggests that S1 encodes an RNA-dependent RNA polymerase (RdRp), whilst S2 encodes a major capsid protein of the virus. Phylogenetic analysis of RdRps from 16 viruses in the family Reoviridae reveals that the genera Cypovirus and Oryzavirus may have originated from a common insect virus ancestor. A series of viable dwarf segments originating from S5 of HaCPV-14 has been identified. Analysis of the predicted secondary structures for these dwarf segments suggests that the signals essential for replication and packaging are located within the terminal sequences of these segments.

Interference and the persistence of vertically transmitted parasites

Given their ubiquity in nature, understanding the factors that allow the persistence of multiple enemies and in particular vertically transmitted parasites (VTPs) is of considerable importance. Here a model that allows a virulent VTP to be maintained in a system containing a host and a horizontally transmitted parasite (HTP) is analysed. The method of persistence relies on the VTP offering the host a level of protection from the HTP. The VTP is assumed to reduce the HTPs ability to transmit to the host through ecological interference. We show that VTPs are more likely to persist with HTPs that prevent host reproduction than with those that allow it. The VTP persists more easily in r-selected hosts and with highly transmittable HTPs. As the level of protection through interference increases the densities of the host also increase. We also show that VTPs when they do persist tend to stabilise the host population cycles produced by free-living HTPs. The study raised questions about persistence of diseases through interactions with others, and also the stabilising effects of VTPs on dynamical systems in a biological control context.