A super-clone of Rhopalosiphum padi is present in the central United States of America

Authors: HAYASHIDA, RAFAEL - Oklahoma State University; Harris-Shultz, Karen; Mornhinweg, Dolores; Elliott, Norman; HOBACK, WILLIAM - Oklahoma State University

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/2025
Publication Date: 11/19/2025
Citation: Hayashida, R., Harris-Shultz, K.R., Mornhinweg, D.W., Elliott, N.C., Hoback, W.W. 2025. A super-clone of Rhopalosiphum padi is present in the central United States of America. Southwestern Entomologist. 50(4):1495-1512. https://doi.org/10.3958/059.050.0420.
DOI: https://doi.org/10.3958/059.050.0420

Interpretive Summary: The bird cherry-oat aphid is a pest of wheat, oat, and barley worldwide and is often associated with economic losses. Little is known about the genetic diversity of the bird cherry-oat aphid in the U.S. which is important information for an understanding of its reproduction and its control. A collection trip was made in May and September of 2024 in Utah, Colorado, Wyoming, Nebraska, Kansas, New Mexico, and Oklahoma and bird cherry-oat aphid was present at 14 sampling sites in Colorado, Nebraska, Oklahoma and Wyoming. Genotyping and sequencing was used and all 63 samples collected in 2024 were the same genotype whereas a lab colony collected 25 years ago from Oklahoma was a different genotype. These results show the bird cherry-oat is spreading on grasses as a super-clone with no sexual reproduction. With no predators or parasitoids seen on these aphids in the sampled locations and the ability of these aphids to reproduce exponentially, control methods (plant resistance, pesticides with multiple modes of action) should be utilized to limit their spread.

Technical Abstract: The bird cherry-oat aphid, Rhopalosiphum padi (L.) (Hemiptera: Aphididae, BCOA), is a key pest of cereal crops worldwide, yet its genetic diversity in the United States remain poorly characterized. We surveyed BCOA populations across the central United States in 2024 and analyzed their genetic structure using microsatellite (SSR) markers and cytochrome oxidase I (COI) sequencing. BCOA was detected at 14 of 157 sampling sites, all on cultivated or volunteer wheat, with no parasitoids or predators observed. Eleven SSR markers amplified successfully, revealing low allelic diversity and the presence of only two multilocus genotypes (MLGs). Among 64 samples, 63 (98%) belonged to a single predominant genotype, while one laboratory colony represented a distinct genotype. COI sequencing confirmed clonal uniformity among most samples, with the lab colony (BCOAUSDA1) differing by a single SNP. These findings demonstrate that BCOA populations in the region are dominated by a super-clone maintained through obligate parthenogenesis, with very low genetic diversity. The clonal dominance and absence of natural enemies highlight the vulnerability of cereal agroecosystems to aphid outbreaks and underscore the need for integrated pest management strategies that reduce reliance on chemical insecticides.