Unveiling the occurrence of Melanaphis sorghi in Argentina following a major aphid outbreak

Abstract

Severe aphid outbreaks were recorded on sorghum (Sorghum bicolor (L.) Moench) and Johnson grass (Sorghum halepense (L.) Pers.) during the 2020/2021 and 2021/2022 cropping seasons in Argentina. The general aspect of the aphids resembled that of Melanaphis sacchari (Zehntner, 1897), a sugarcane pest occasionally attacking sorghum, reported in the country almost forty years ago. However, its rapid spread and extraordinary abundance on Sorghum spp. raised doubts about the species identity. To address this issue, aphids were sampled from heavily infested sorghum crops and volunteer Johnson grass plants throughout northern and central Argentina and subjected to direct partial sequencing of cytochrome c oxidase subunit I (COI) and elongation factor 1 alpha (EF1-α) genes. Sequence analyses provided evidence that the species causing the outbreaks on Sorghum spp. was, in fact, the closely related Melanaphis sorghi (Theobald, 1904), which had not been previously recorded in Argentina. The lack of genetic variability among the newly obtained sequences suggests the presence of a predominant clonal lineage. A broader population genetics study including further molecular markers, and the evaluation of pest management practices deserve future research.