Identification and genomic sequence analysis of a new Spodoptera exigua multiple nucleopolyhedrovirus, SeMNPV-QD, isolated from Qingdao, China

Whole genome analysis of a novel Spodoptera exigua nucleopolyhedrovirus isolate (SeMNPV-IR) to Iran

Baculoviruses are successful microbial control agents used in the biological control of agricultural pest species, especially in the order Lepidoptera. The beet armyworm, Spodoptera exigua is a popular agricultural pest in the world. S exigua larvae, which are active in the all-summer period, cause economic losses by damaging many crops in agricultural production areas. This article aims to analyze the full genome of Spodoptera exigua multiple nucleopolyhedroviruses from Iran (SeMNPV-IR) and to determine the geographical difference between the strains at the genomic level. The full genome of SeMNPV-IR is 135.764 base pairs in length that contained 136 open reading frames (ORFs), and 43.92% G + C content. The seven homologous repeated (hr) regions were identified. In the results of genome-wide phylogenetic analysis, it was determined that the SeMNPV-IR genome isolated from Iran was interestingly close to the genome of the US and Korea isolates. However, there are significant differences in the two hypothetical (Orf 83 and Orf 104) genes. The SeMNPV-IR has a unique homolog repeat region (hr1, 96 bp) that is not found in other SeMNPV genomes, and it also differs in terms of the hr2 region. In silico restriction endonuclease analysis by StuI and SacII enzymes show that there were significant differences between all geographic isolates of SeMNPV.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11756-023-01399-2.

Antiviral Treatment Reveals a Cooperative Pathogenicity of Baculovirus and Iflavirus in Spodoptera exigua, a Lepidopteran Insect

NPVThe beet armyworm, Spodoptera exigua, is a serious insect pest infesting various vegetable crops. Two infectious insect viruses, baculovirus and iflavirus, are known to induce epizootics in S. exigua populations. Indeed, some laboratory colonies have appeared to be covertly infected by these viruses. Diagnostic PCR tests detected two different viruses: Spodoptera exigua multiple nucleopolyhedrosis virus (SeMNPV) and iflaviruses (SeIfV1 and SeIfV2). Viral extract from dead larvae of S. exigua could infect Sf9 cells and produce occlusion bodies (OBs). Feeding OBs to asymptomatic larvae of S. exigua caused significant viral disease. Interestingly, both SeIfV1 and SeIfV2 increased their titers at late larval stages. Sterilization of laid eggs with 1% sodium hypochloride significantly reduced SeMNPV titers and increased larval survival rate. Doublestranded RNA (dsRNA) specific to SeIfV1 or SeIfV2 significantly reduced viral titers and increased larval survival rate. To continuously feed dsRNA, a recombinant Escherichia coli HT115 expressing SeIfV1-dsRNA was constructed with an L4440 expression vector. Adding this recombinant E. coli to the artificial diet significantly reduced the SeIfV1 titer and increased larval survival. These results indicate that laboratory colony collapse of S. exigua is induced by multiple viral infections. In addition, either suppression of SeMNPV or SeIfV infection significantly increased larval survival, suggesting a cooperative pathogenicity between baculovirus and iflavirus against S. exigua.

Appearances are deceptive: Three RNA viruses co-infected with the nucleopolyhedrovirus in host Lymantria dispar

The virus infection, which visually looks like typical monoinfection, in fact may hide a great complex of different species. Without detailed analysis, we may miss the important interaction between pathogens, including new species. In the current study, we found the new species inside the mix of cubic and polyhedral occlusion bodies (OBs) isolated from the gypsy moth, Lymantria dispar L. (Ld). Transmission electron microscopy (TEM) revealed that into the one cadaver were OBs which belonged to baculovirus and cypoviruses. The baculovirus produced polyhedral OBs, while cypoviruses produced polyhedral and cubic OBs. Genomic analysis detected the multiple Ld nucleopolyhedroviruses, and cypoviruses were Hubei lepidoptera virus 3 and Dendrolimus punctatus cypovirus 1. This represents the first isolation of the Hubei lepidoptera virus 3 from the gypsy moth, proposed as "Lymantria dispar cypovirus 3". The RNAseq analysis also revealed the presence of Lymantria dispar iflavirus 1. The insecticidal activity of the mixed infection was comparable to that of typical baculovirus monoinfection. Thus, we demonstrate that i) the shape of OBs identified by light microscopy cannot be a robust indicator of viral species infecting the host; ii) only specific analysis may reveal the true composition of viral infection.