A new nucleopolyhedrovirus strain (LdMNPV-like virus) with a defective fp25 gene from Lymantria xylina (Lepidoptera: Lymantriidae) in Taiwan

Evaluation of the Potential Flight Ability of the Casuarina Moth, Lymantria xylina (Lepidoptera: Erebidae)

Lymantria xylina Swinhoe (Lepidoptera: Erebidae) is a potentially invasive pest, similar to Lymantria dispar asiatica Vnukovskij and Lymantria dispar japonica Motschulsky (Lepidoptera: Erebidae). To evaluate its potential for spread and flight distance related to egg deposition on vessels at ports, we employed a flight mill to assess the flight capabilities of its adults under varying conditions. Our findings revealed that females primarily flew short distances and ceased flying after 3:00 AM, whereas males covered much longer distances throughout the day. Sex, age, and flight duration significantly influenced flight ability. Females exhibited weaker flight capability than males, and their ability declined with increasing age or flight duration. Notably, 1-day-old moths displayed the strongest flight ability, with average flight distances of up to 3.975 km for females and 8.441 km for males. By the fifth day, females no longer flew, and males experienced reduced flight ability. After continuous hanging for 16 h, females lost most of their flight capacity, while males remained capable of flight even after 32 h. Additionally, female flight ability decreased significantly after mating, possibly due to factors such as egg-carrying capacity, weight, and load ratio. This study provides a foundation for assessing the risk of long-distance dispersal of L. xylina via ocean-going freighters, considering female moths' phototactic flight and oviposition.

The complete genome sequence of an alphabaculovirus from the brown tussock moth, Olene mendosa Hübner, expands our knowledge of lymantriine baculovirus diversity and evolution

The complete genome sequence was determined for an apparent alphabaculovirus isolated from larval cadavers of the brown tussock moth, Olene mendosa Hübner, collected during an epizootic in Coimbatore, India. The genome was determined to be a circular 142,291 bp molecule, and 147 ORFs and nine homologous regions were annotated for the sequence. Analysis of the sequence confirmed that this virus, Olene mendosa nucleopolyhedrovirus (OlmeNPV), was a member of genus Alphabaculovirus in family Baculoviridae. Phylogenies inferred from nucleotide and amino acid alignments indicated that OlmeNPV was part of a group of viruses that infect moths of genus Lymantria, suggesting that OlmeNPV may have shifted hosts from a Lymantria species to an ancestral Olene species at some point during its evolutionary history. OlmeNPV was most closely related to Lymantria xylina multiple nucleopolyhedrovirus isolate 5 (LyxyMNPV-5). The genomes of OlmeNPV and LyxyMNPV-5 were distinguished not only by differences in ORF content, but by a 27 kbp region of the genome that is inverted in LyxyMNPV-5 relative to OlmeNPV. Pairwise nucleotide distances between OlmeNPV and other Lymantria spp. alphabaculoviruses indicate that OlmeNPV represents a new baculovirus species.

Characterization and functional assay of apsup (Lyxy105) from Lymantria xylina multiple nucleopolyhedrovirus (LyxyMNPV)

The baculoviral anti-apoptotic genes, p35 and iap (inhibitor of apoptosis), play important roles in the initiation of viral infection. Recently, a new anti-apoptotic gene (apoptosis suppressor, apsup) was identified in Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV). An apsup homolog gene, Lyxy105 (ly-apsup), was also predicted in the Lymantria xylina multiple nucleopolyhedrovirus (LyxyMNPV) genome. In this study, we attempt to perform a gene expression analysis and a functional assay of ly-apsup to demonstrate its anti-apoptotic activity and identify the functional domain of this protein. The transcription of the ly-apsup gene region was detected from 12 h post-infection (hpi) and increased significantly after 24-72 hpi. Comparison of the putative amino acid sequences to those of 18 baculoviral homolog proteins showed high amino acid identity to the LdMNPV sequences. Moreover, five conserved protein domains (named as domains I-V) were found. Therefore, protein functional assays were conducted on full-length proteins and different truncation clones. The overexpression of each clone was confirmed by western blot analysis, and the data revealed that a cleavage of ~ 5 kDa at the N-terminal region of the full-length, domains I-IV (1-241) and I-III (1-178), proteins occurred. The results of the functional analysis showed that full-length Ly-apsup and Ly-apsup with domain I (1-70) could inhibit Drosophila-RPR protein (D-RPR)-induced and actinomycin D (ActD)-induced apoptoses. In addition, the domains I and I-II (1-126) regions showed higher anti-apoptotic activity than the other domains in both D-RPR-induced and ActD-induced cell apoptoses. In conclusion, domain I of Ly-apsup may play an important role in the anti-apoptotic activity of this protein; cleavage of the Ly-apsup N-terminus may lead to decreased anti-apoptotic activity.

Lymantria mathura nucleopolyhedrovirus: Identification, occurrence and genetic diversity in Iwate Prefecture, Japan

A high prevalence of nuclear polyhedrosis has been observed in larval outbreaks of Lymantria mathura in Iwate Prefecture, Japan. However, the virus responsible has not been identified. Here the virus was designated Lymantria mathura nucleopolyhedrovirus (LymaNPV), based on partial sequence results of the lef-8, lef-9, and polh genes and transmission electron microscopic observations. Diagnosis by polymerase chain reaction targeting of the partial polh gene and a subsequent restriction fragment length polymorphism (RFLP) analysis indicated that LymaNPV was an exclusive causative agent for the nuclear polyhedrosis of the L. mathura larvae. LymaNPV was also detected from a very small fraction of L. dispar larvae that co-occurred with L. mathura larvae where the prevalence of LymaNPV-caused disease was high. A bioassay using LymaNPV against L. dispar larvae produced infection with the inoculated virus. This finding was consistent with the results of the field sample analysis. LymaNPV contained six genome types in the L. mathura populations sampled, as determined by RFLP of LymaNPV genomic DNA and southern blot hybridization analyses. None of the genome types was unique to any sampling site, indicating that some flow had occurred among sites. However, genome-type composition seemed to differ among sites. This study provides basic information about the interaction between L. mathura and LymaNPV.

Classification, genetic variation and pathogenicity of Lymantria dispar nucleopolyhedrovirus isolates from Asia, Europe, and North America

Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV) has been formulated and applied to control outbreaks of the gypsy moth, L. dispar. To classify and determine the degree of genetic variation among isolates of L. dispar NPVs from different parts of the range of the gypsy moth, partial sequences of the lef-8, lef-9, and polh genes were determined for Lymantria spp. virus samples from host populations throughout the world. Sequence analysis confirmed that all L. dispar virus samples tested contained isolates of the species Lymantria dispar multiple nucleopolyhedrovirus (Baculoviridae: Alphabaculovirus). Phylogenetic inference based on the lef-8 sequences indicated that the LdMNPV isolates formed two groups, one consisting primarily of isolates from Asia, and one consisting primarily of isolates from Europe and North America. The complete genome sequence was determined for an isolate from the Asian group, LdMNPV-2161 (S. Korea). The LdMNPV-2161 genome was 163,138bp in length, 2092bp larger than the previously determined genome of LdMNPV isolate 5-6 (CT, USA). The two genome sequences were co-linear, with an overall nucleotide sequence identity of 97.5% and some differences in ORF content. In droplet-feeding bioassays against neonate L. dispar larvae, isolates LdMNPV-3029 (Virin-ENSh/Russia) and LdMNPV-Ab-a624 (MA, USA) killed neonate larvae with an LC50 values that were 1.8- to 3.2-fold lower than a sample of Gypchek® (CT, USA) and isolates LdMNPV-3041 (Japan) and LdMNPV-2161. This study expands our knowledge about genetic variation among LdMNPV isolates and provides novel information on the distinct groups in which these NPVs occur.

A new cell line (NTU-SE) from pupal tissues of the beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae), is highly susceptible to S. exigua multiple nucleopolyhedrovirus (SeMNPV) and Autographa californica MNPV (AcMNPV)

A new continuous cell line, NTU-SE, was established from the pupal tissues of an economically important pest, the beet armyworm Spodoptera exigua (Lepidoptera: Noctuidae). This cell line contains four major morphologic types: round, polymorphic, spindle-shaped, and comma-shaped cells. The population doubling time of this new line in TNM-FH medium supplemented with 8% fetal bovine serum (FBS) at 28°C is 35.5h. The chromosomal spread from NTU-SE cells is typical to the chromosomal morphology of lepidopteran cell lines. Confidently, NTU-SE cell line is a new cell line that exhibits distinct isozyme patterns of esterase, lactate dehydrogenase (LDH), and malate dehydrogenase (MDH) from those of the other insect cell lines. In addition, the DNA sequence of the nuclear ribosomal internal transcribed spacer (ITS) region of NTU-SE cells is above 96% identical to that sequence of S. exigua larvae, as compared to only 66% identical to that of S. litura larvae. The NTU-SE cell line is highly susceptible to S. exigua multiple nucleopolyhedrovirus (SeMNPV) and Autographa californica MNPV (AcMNPV). Therefore, a highly virulent SeMNPV strain, SeMNPV-1, had been successfully isolated and propagated in NTU-SE cells. We conclude that the NTU-SE cell line will be a useful tool for the selection and mass production of highly virulent SeMNPV strains for the S. exigua biocontrol and the baculovirus based recombinant protein expression systems.

Genomic sequencing and analyses of Lymantria xylina multiple nucleopolyhedrovirus

BACKGROUND

Outbreaks of the casuarina moth, Lymantria xylina Swinehoe (Lepidoptera: Lymantriidae), which is a very important forest pest in Taiwan, have occurred every five to 10 years. This moth has expanded its range of host plants to include more than 65 species of broadleaf trees. LyxyMNPV (L. xylina multiple nucleopolyhedrovirus) is highly virulent to the casuarina moth and has been investigated as a possible biopesticide for controlling this moth. LdMNPV-like virus has also been isolated from Lymantria xylina larvae but LyxyMNPV was more virulent than LdMNPV-like virus both in NTU-LY and IPLB-LD-652Y cell lines. To better understand LyxyMNPV, the nucleotide sequence of the LyxyMNPV DNA genome was determined and analysed.

RESULTS

The genome of LyxyMNPV consists of 156,344 bases, has a G+C content of 53.4% and contains 157 putative open reading frames (ORFs). The gene content and gene order of LyxyMNPV were similar to those of LdMNPV, with 151 ORFs identified as homologous to those reported in the LdMNPV genome. Two genes (Lyxy49 and Lyxy123) were homologous to other baculoviruses, and four unique LyxyMNPV ORFs (Lyxy11, Lyxy19, Lyxy130 and Lyxy131) were identified in the LyxyMNPV genome, including a gag-like gene that was not reported in baculoviruses. LdMNPV contains 23 ORFs that are absent in LyxyMNPV. Readily identifiable homologues of the gene host range factor-1 (hrf-1), which appears to be involved in the susceptibility of L. dispar to NPV infection, were not present in LyxyMNPV. Additionally, two putative odv-e27 homologues were identified in LyxyMNPV. The LyxyMNPV genome encoded 14 bro genes compared with 16 in LdMNPV, which occupied more than 8% of the LyxyMNPV genome. Thirteen homologous regions (hrs) were identified containing 48 repeated sequences composed of 30-bp imperfect palindromes. However, they differed in the relative positions, number of repeats and orientation in the genome compared to LdMNPV.

CONCLUSION

The gene parity plot analysis, percent identity of the gene homologues and a phylogenetic analysis suggested that LyxyMNPV is a Group II NPV that is most closely related to LdMNPV but with a highly distinct genomic organisation.