Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2023
Publication Date: 5/15/2023
Citation: Sparks, M., Wang, Y., Shi, J., Harrison, R.L. 2023. Lymantria dispar iflavirus 1 RNA comprises a large proportion of RNA in adult L. dispar moths. Insects. https://doi.org/10.3390/insects14050466.
DOI: https://doi.org/10.3390/insects14050466

Interpretive Summary: Spongy moth (formerly known as European gypsy moth) is an invasive forest pest in the United States and is under quarantine in the Eastern part of the country. The flighted spongy moth complex, a group of related spongy moths formerly known as Asian gypsy moth, are exotic pests that are not currently present in the United States. While spongy moth females in the United States are flightless, flighted spongy moth females are very flightworthy. As a consequence, it is expected that an invasion of North America by the flighted spongy moth would result in damage to forests over a wider geographic area. As part of research to characterize spongy moth pathogens for potential insecticidal use against spongy moth, we determined the genome sequences and relative amounts of genomes of an iflavirus, an RNA-based virus, from spongy moths in two locations in the USA and flighted spongy moths in two locations in China. The iflaviruses from the USA and China spongy moths could be distinguished from each other on the basis of their genome sequences. Also, iflavirus genome levels in all moth samples were very high, but these high genome levels were not associated with any obvious disease symptoms. The information in this study contributes to progress towards developing bio-insecticides for use against the spongy moth, and will be of interest to those in academia, government, and industry who work with spongy moths and other invasive forest pests.

Technical Abstract: The spongy moth virus Lymantria dispar iflavirus 1 (LdIV1), originally identified from a Lymantria dispar cell line, was detected in 24 RNA samples from female moths of four popula-tions from the USA and China. Genome-length contigs were assembled for each population and compared with the reference genomes of the first reported LdIV1 genome (Ames strain) and two unpublished LdIV1 sequences available in GenBank originating from Novosibirsk, Russian Federation. A whole-genome phylogeny was generated for these sequences, indicating that LdIV1 viruses observed in North American (flightless) and Asian (flighted) spongy moth line-ages indeed partition into clades as would be expected per their host’s geographic origin and bi-otype. A comprehensive listing of synonymous and non-synonymous mutations, as well as in-dels, among the polyprotein coding sequences of these seven LdIV1 variants was compiled, and a codon-level phylogram computed using polyprotein sequences of these viruses and 50 addi-tional iflaviruses placed LdIV1 in a large clade consisting mostly of iflaviruses from other spe-cies of Lepidoptera. Of special note, LdIV1 RNA was present at very high levels in all samples, with LdIV1 reads accounting for a mean average of 36.41% (ranging from 1.84% to 68.75%) of to-tal sequenced volume.