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Mosquitoes (Diptera: Culicidae) are primary vectors of arthropod-borne viruses (arboviruses) that pose significant public health threats. Recent advances in sequencing technology emphasize the importance of understanding the arboviruses and insect-specific viruses (ISVs) hosted by mosquitoes, collectively called the "virome". Colombia, a tropical country with favorable conditions for the development and adaptation of multiple species of Culicidae, offers a favorable scenario for the transmission of epidemiologically important arboviruses. However, entomovirological surveillance studies are scarce in rural areas of the country, where humans, mosquitoes, and animals (both domestic and wild) coexist, leading to a higher risk of transmission of zoonotic diseases to humans. Thus, our study aimed to perform a preliminary metagenomic analysis of the mosquitoes of special relevance to public health belonging to the genera Ochlerotatus, Culex, Limatus, Mansonia, Psorophora, and Sabethes, within a rural savanna ecosystem in the Colombian Orinoco. We employed third-generation sequencing technology (Oxford Nanopore Technologies; ONT) to describe the virome of mosquitoes samples. Our results revealed that the virome was primarily shaped by insect-specific viruses (ISVs), with the Iflaviridae family being the most prevalent across all mosquito samples. Furthermore, we identified a group of ISVs that were common in all mosquito species tested, displaying the highest relative abundance concerning other groups of viruses. Notably, Hanko iflavirus-1 was especially prevalent in Culex eknomios (88.4%) and Ochlerotatus serratus (88.0%). Additionally, other ISVs, such as Guadalupe mosquito virus (GMV), Hubei mosquito virus1 (HMV1), Uxmal virus, Tanay virus, Cordoba virus, and Castlerea virus (all belonging to the Negevirus genus), were found as common viral species among the mosquitoes, although in lower proportions. These initial findings contribute to our understanding of ISVs within mosquito vectors of the Culicidae family in the Eastern Plains of Colombia. We recommend that future research explore deeper into ISV species shared among diverse vector species, and their potential interactions with arboviruses. In addition, we also showed the need for a thorough exploration of the influence of local rural habitat conditions on the shape of the virome in mosquito vectors., (© 2023. The Author(s).)

What affects the ability of a virus to adapt and specialize to its hosts? To answer this question, Visher et al. (2022) performed experimental evolution on a virus-insect system and showed that the virus specializes in its hosts through the evolution of its ability to infect or replicate. Genomic analysis of adapted lines of viruses in different host genotypes suggests that viral specialization is influenced by a complicated and polygenic mechanism., (© The Author(s) 2022. Published by Oxford University Press on behalf of The Society for the Study of Evolution (SSE). All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Mosquitoes not only transmit human and veterinary pathogens called arboviruses (arthropod-borne viruses) but also harbor mosquito-associated insect-specific viruses (mosquito viruses) that cannot infect vertebrates. In the past, studies investigating mosquito viruses mainly focused on highly pathogenic interactions that were easier to detect than those without visible symptoms. However, the recent advances in viral metagenomics have highlighted the abundance and diversity of viruses which do not generate mass mortality in host populations. Over the last decade, this has facilitated the rapid growth of virus discovery in mosquitoes. The circumstances around the discovery of mosquito viruses greatly affected how they have been studied so far. While earlier research mainly focused on the pathogenesis caused by DNA and some double-stranded RNA viruses during larval stages, more recently discovered single-stranded RNA mosquito viruses were heavily studied for their putative interference with arboviruses in female adults. Thus, many aspects of mosquito virus interactions with their hosts and host-microbiota are still unknown. In this context, considering mosquito viruses as endosymbionts can help to identify novel research areas, in particular in relation to their long-term interactions with their hosts (e.g. relationships during all life stages, the stability of the associations at evolutionary scales, transmission routes and virulence evolution) and the possible context-dependent range of interactions (i.e. beneficial to antagonistic). Here, we review the symbiotic interactions of mosquito viruses considering different aspects of their ecology, such as transmission, host specificity, host immune system and interactions with other symbionts within the host cellular arena. Finally, we highlight related research gaps in mosquito virus research., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Altinli, Schnettler and Sicard.)

When the Drosophila cells were infected with the mixo- and arboviruses, in case of influenza A/WSN virus a rise in the titre and slight cytopathogenic effect with the subsequent decrease in the titre was observed. Since the decrease in the virus titer was not observed when actinomycin D was added, it was supposed that interferonlike inhibitor may be produced by the infected cells. Vacuolization and increase in the size of the infected cells were caused by all the nuclear polyhedrosis viruses tested. The number of the infected cells depended on the virus type and multiplicity of the infection.

THIN SECTIONS HAVE BEEN CUT OF THE VIRUS PARTICLES FROM FOUR TYPES OF INSECT VIRUS DISEASES: cytoplasmic polyhedroses of lepidopterous larvae, a nuclear polyhedrosis of Tipula paludosa (Diptera), a granulosis from Melanchra persicariae (Lepidoptera), and a new virus disease without polyhedra from T. paludosa. The cytoplasmic polyhedral viruses are thought to have composite particles in some cases. The shape and enveloping membranes of the different virus particles are compared. In the new virus disease of T. paludosa some of the virus particles appear to be empty; inclusion bodies surrounded by complicated membranes are also demonstrated.

Purine and pyrimidine bases have been estimated from the desoxyribonucleic acids of eleven insect viruses. Their proportions vary in the different species in a balanced way so that the molar ratios adenine:thymine and guanine:cytosine are constant and close to unity, whereas adenine + thymine:guanine + cytosine ranges from 0.71 to 1.87. This ratio is identical for some biologically dissimilar viruses, and no general parallelism is evident between DNA composition and biological relationship. Two different viruses from one host have distinct DNA's.

Drosophila remains a pre-eminent insect model system for host–virus interaction, but the host range and fitness consequences of the drosophilid virome are poorly understood. Metagenomic studies have reported approximately 200 viruses associated with Drosophilidae, but few isolates are available to characterize the Drosophila immune response, and most characterization has relied on injection and systemic infection. Here, we use a more natural infection route to characterize the fitness effects of infection and to study a wider range of viruses. We exposed laboratory Drosophila melanogaster to 23 naturally occurring viruses from wild-collected drosophilids. We recorded transmission rates along with two components of female fitness: survival and the lifetime number of adult offspring produced. Nine different viruses transmitted during contact with laboratory D. melanogaster, although for the majority, rates of transmission were less than 20%. Five virus infections led to a significant decrease in lifespan (D. melanogaster Nora virus, D. immigrans Nora virus, Muthill virus, galbut virus and Prestney Burn virus), and three led to a reduction in the total number of offspring. Our findings demonstrate the utility of the Drosophila model for community-level studies of host–virus interactions, and suggest that viral infection could be a substantial fitness burden on wild flies. [ABSTRACT FROM AUTHOR]

BACKGROUND: The general principle of using microbes from one species to manage a different pest species has a clear precedent in the large‐scale release of mosquitoes carrying a Wolbachia bacterium derived from Drosophila flies. New technologies will facilitate the discovery of microbes that can be used in a similar way. Previously, we found three novel partiti‐like viruses in the African armyworm (Spodoptera exempta). To investigate further the utility and consistency of host shift of insect viruses as a potential pest management tool, we tested the interaction between the partiti‐like viruses and another novel host, the Egyptian cotton leafworm (Spodoptera littoralis). RESULT: We found that all three partiti‐like viruses appeared to be harmful to the novel host S. littoralis, by causing increased larval and pupal mortality. No effect was observed on host fecundity, and partiti‐like virus infection did not impact host susceptibility when challenged with another pathogen, the baculovirus SpliNPV. Transcriptome analysis of partiti‐like virus‐infected and noninfected S. littoralis indicated that the viruses could impact host gene‐expression profiles of S. littoralis, but they impact different pathways to the two other Spodoptera species through effects on pathways related to immunity (Jak–STAT/Toll and Imd) and reproduction (insulin signaling/insect hormones). CONCLUSION: Taken together with the previous findings in the novel host S. frugiperda, these results indicate a parasitic relationship between the partiti‐like viruses and novel insect hosts, suggesting a possible use and novel pest management strategy through the artificial host shift of novel viruses. © 2021 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Virus maturation is found in all animal viruses and dsDNA bacteriophages that have been studied. It is a programmed process, cued by cellular environmental factors, that transitions a noninfectious, initial assembly product (provirus) to an infectious particle (virion). Nudaurelia capensis omega virus (NωV) is an ssRNA insect virus with T=4 quasi-symmetry. Over the last 20 years, NωV virus-like particles (VLPs) have been an attractive model for the detailed study of maturation. The novel feature of the system is the progressive transition from procapsid to capsid controlled by pH. Homogeneous populations of maturation intermediates can be readily produced at arbitrary intervals by adjusting the pH between 7.6 and 5.0. These intermediates were investigated using biochemical and biophysical methods to create a stop-frame transition series of this complex process. The studies reviewed here characterized the large-scale subunit reorganization during maturation (the particle changes size from 48 nm to 41 nm) as well as the mechanism of a maturation cleavage, a time-resolved study of cleavage site formation, and specific roles of quasi-equivalent subunits in the release of membrane lytic peptides required for cellular entry. [ABSTRACT FROM AUTHOR]

Late male-killing, a male-specific death after hatching, is a unique phenotype found in Homona magnanima , oriental tea tortrix. The male-killing agent was suspected to be an RNA virus, but details were unknown. We herein successfully isolated and identified the putative male-killing virus as Osugoroshi viruses (OGVs). The three RNA-dependent RNA polymerase genes detected were phylogenetically related to Partitiviridae, a group of segmented double-stranded RNA viruses. Purified dsRNA from a late male-killing strain of H. magnanima revealed 24 segments, in addition to the RdRps, with consensus terminal sequences. These segments included the previously found male-killing agents MK1068 (herein OGV-related RNA16) and MK1241 (OGV-related RNA7) RNAs. Ultramicroscopic observation of purified virions, which induced late male-killing in the progeny of injected moths, showed sizes typical of Partitiviridae. Mathematical modeling showed the importance of late male-killing in facilitating horizontal transmission of OGVs in an H. magnanima population. This study is the first report on the isolation of partiti-like virus from insects, and one thought to be associated with late male-killing, although the viral genomic contents and combinations in each virus are still unknown. [ABSTRACT FROM AUTHOR]

As an overarching immune mechanism, RNA interference (RNAi) displays pathogen specificity and memory via different pathways. The small interfering RNA (siRNA) pathway is the primary antiviral defense mechanism against RNA viruses of insects and plays a lesser role in defense against DNA viruses. Reflecting the pivotal role of the siRNA pathway in virus selection, different virus families have independently evolved unique strategies to counter this host response, including protein-mediated, decoy RNA–based, and microRNA-based strategies. In this review, we outline the interplay between insect viruses and the different pathways of the RNAi antiviral response; describe practical application of these interactions for improved expression systems and for pest and disease management; and highlight research avenues for advancement of the field. [ABSTRACT FROM AUTHOR]

Recent advances in next generation sequencing (NGS) (e.g. metagenomic and transcriptomic sequencing) have facilitated the discovery of a large number of new insect viruses, but the characterization of these viruses is still in its infancy. Here, we report the discovery, using RNA-seq, of three new partiti-like viruses from African armyworm, Spodoptera exempta (Lepidoptera: Noctuidae), which are all vertically-transmitted transovarially from mother to offspring with high efficiency. Experimental studies show that the viruses reduce their host's growth rate and reproduction, but enhance their resistance to a nucleopolyhedrovirus (NPV). Via microinjection, these partiti-like viruses were transinfected into a novel host, a newly-invasive crop pest in sub-Saharan Africa (SSA), the Fall armyworm, S. frugiperda. This revealed that in this new host, these viruses appear to be deleterious without any detectable benefit; reducing their new host's reproductive rate and increasing their susceptibility to NPV. Thus, the partiti-like viruses appear to be conditional mutualistic symbionts in their normal host, S. exempta, but parasitic in the novel host, S. frugiperda. Transcriptome analysis of S. exempta and S. frugiperda infected, or not, with the partiti-like viruses indicates that the viruses may regulate pathways related to immunity and reproduction. These findings suggest a possible pest management strategy via the artificial host-shift of novel viruses discovered by NGS. Author summary: Modern molecular approaches allow the discovery of new viruses that do not present obvious symptoms of disease in their hosts. Using these methods, we discovered three new partiti-like viruses in a major crop pest, the African armyworm, Spodoptera exempta, which are naturally transmitted vertically from adult females to their offspring in her eggs. We discovered that these viruses decrease their host's growth rate and reproduction, but they may also help their insect host by protecting them from other lethal viruses, specifically the baculoviruses that are often used as biological pesticides. We transferred these partiti-like viruses into a novel host, the Fall armyworm, S. frugiperda, by microinjection and found that they also decrease S. frugiperda's growth rate and reproduction. Interestingly, however, it appears that the partiti-like viruses make S. frugiperda more susceptible to baculovirus, potentially making it more vulnerable to control using biopesticides. Our results suggest a possible novel pest management strategy via artificial host-shift of viruses discovered using molecular approaches and offers new insights into host-virus-virus interactions. [ABSTRACT FROM AUTHOR]

Introduction: Emerging viral diseases, most of which are zoonotic, pose a significant threat to global health. There is a critical need to identify potential new viral pathogens and the challenge is to identify the reservoirs from which these viruses might emerge. Deep sequencing of invertebrate transcriptomes has revealed a plethora of viruses, many of which represent novel lineages representing both plant and animal viruses and little is known about the potential threat that these viruses pose. Methods: Providence virus, an insect virus, was used to establish a productive infection in Vigna unguiculata (cowpea) plants. Providence virus particles purified from these cowpea plants were used to infect two mammalian cell lines. Findings: Here, we present evidence that Providence virus, a non-enveloped insect RNA virus, isolated from a lepidopteran midgut cell line can establish a productive infection in plants as well as in animal cells. The observation that Providence virus can readily infect both plants and mammalian cell culture lines demonstrates the ability of an insect RNA virus to establish productive infections across two kingdoms, in plants and invertebrate and vertebrate animal cell lines. Conclusions: The study highlights the potential of phytophagous insects as reservoirs for viral re-assortment and that plants should be considered as reservoirs for emerging viruses that may be potentially pathogenic to humans. [ABSTRACT FROM AUTHOR]

Many mRNA-based vaccines have been investigated for their specific potential to activate dendritic cells (DCs), the highly-specialized antigen-presenting cells of the immune system that play a key role in inducing effective CD4+ and CD8+ T-cell responses. In this paper we report a new vaccine/gene delivery platform that demonstrates the benefits of using a self-amplifying (“replicon”) mRNA that is protected in a viral-protein capsid. Purified capsid protein from the plant virus Cowpea Chlorotic Mottle Virus (CCMV) is used to in vitro assemble monodisperse virus-like particles (VLPs) containing reporter proteins (e.g., Luciferase or eYFP) or the tandem-repeat model antigen SIINFEKL in RNA gene form, coupled to the RNA-dependent RNA polymerase from the Nodamura insect virus. Incubation of immature DCs with these VLPs results in increased activation of maturation markers – CD80, CD86 and MHC-II – and enhanced RNA replication levels, relative to incubation with unpackaged replicon mRNA. Higher RNA uptake/replication and enhanced DC activation were detected in a dose-dependent manner when the CCMV-VLPs were pre-incubated with anti-CCMV antibodies. In all experiments the expression of maturation markers correlates with the RNA levels of the DCs. Overall, these studies demonstrate that: VLP protection enhances mRNA uptake by DCs; coupling replicons to the gene of interest increases RNA and protein levels in the cell; and the presence of anti-VLP antibodies enhances mRNA levels and activation of DCs in vitro. Finally, preliminary in vivo experiments involving mouse vaccinations with SIINFEKL-replicon VLPs indicate a small but significant increase in antigen-specific T cells that are doubly positive for IFN and TFN induction. [ABSTRACT FROM AUTHOR]

Insects constitute the largest and most diverse group of animals on Earth with an equally diverse virome. The main antiviral immune system of these animals is the post-transcriptional gene-silencing mechanism known as RNA(i) interference. Furthermore, this process can be artificially triggered via delivery of gene-specific double-stranded RNA molecules, leading to specific endogenous gene silencing. This is called RNAi technology and has important applications in several fields. In this paper, we review RNAi mechanisms in insects as well as the potential of RNAi technology to contribute to species-specific insecticidal strategies. Regarding this aspect, we cover the range of strategies considered and investigated so far, as well as their limitations and the most promising approaches to overcome them. Additionally, we discuss patterns of viral infection, specifically persistent and acute insect viral infections. In the latter case, we focus on infections affecting economically relevant species. Within this scope, we review the use of insect-specific viruses as bio-insecticides. Last, we discuss RNAi-based strategies to protect beneficial insects from harmful viral infections and their potential practical application. As a whole, this manuscript stresses the impact of insect viruses and RNAi technology in human life, highlighting clear lines of investigation within an exciting and promising field of research. [ABSTRACT FROM AUTHOR]