Novel iflavirus species discovered through virome analysis of cotton field-collected aphids

Insect-associated viruses (viromes) shape insect biology and agroecosystems, yet aphid viromes remain undercharacterized. The cotton aphid, Aphis gossypii, is a globally distributed pest with a broad plant host range and demonstrated virus-vector competence, making it well suited for investigating virome composition at the plant-insect-virus interface. In this study, we profiled the virome of field-collected aphid alates, which were dominated by A. gossypii but included additional aphid species in some samples, across 15 cotton fields in Alabama, USA, to assess taxonomic diversity, relative viral abundance, and focal aphid-associated viruses.

Metatranscriptomic sequencing of aphid alates revealed differences in taxonomic composition among county-level libraries, including viruses and diverse prokaryotic and eukaryotic taxa. Fifty-eight viral contigs > 1 kb were assembled, of which 20 were assigned to seven families: Dicistroviridae, Iflaviridae, Mitoviridae, Nudiviridae, Partitiviridae, Phasmaviridae, and Solemoviridae. Representative contigs from six families (all except Phasmaviridae) and five additional family-unassigned viruses were validated by PCR and Sanger sequencing. Three iflaviruses (RrIV, AgIV1, and AgIV2), positive-sense single-stranded RNA viruses, were discovered, including one associated with Rhopalosiphum rufiabdominale and two with A. gossypii. Their complete genomes were determined using PCR-based resequencing and 5'/3' RACE, each comprising a single open reading frame that encodes a polyprotein. Sequence identity and phylogenetic analyses indicate that the newly identified viruses are putative new species and form a distinct clade together with previously reported aphid iflaviruses within Iflaviridae. AgIV1 and AgIV2, despite being associated with the same host species, were not monophyletic within this clade, consistent with cross-species transmission among aphid hosts. Strand-specific RT-PCR detected negative-strand RNA for AgIV1 and AgIV2, suggesting replication in aphids. Given their low field prevalence, we propose the names Iflavirus furtiva (RrIV), Iflavirus obscurata (AgIV1), and Iflavirus rarivira (AgIV2).

The aphid virome is taxonomically diverse and shows county-level differences in relative viral contig abundance. We identified seven viral families and three complete iflavirus genomes, providing a foundation for further investigating their host range, transmission, and potential impacts on aphid biology and cotton production.