Increase in importance of Aphelinus nigritus (Howard) on winter crops in Oklahoma coincides with invasion of sugarcane aphid on sorghum in Oklahoma

Authors: GILES, KRIS - Oklahoma State University; Elliott, Norman - Norm; BUTLER, HAYLEY - Oklahoma State University; BAUM, KRISTEN - Oklahoma State University; BACKOULOU, GEORGES - Oklahoma State University

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2021
Publication Date: 3/25/2021
Citation: Giles, K.L., Elliott, N.C., Butler, H.E., Baum, K.A., Backoulou, G.F. 2021. Increase in importance of Aphelinus nigritus (Howard) on winter crops in Oklahoma coincides with invasion of sugarcane aphid on sorghum in Oklahoma. Southwestern Entomologist. 46(1):59-68. https://doi.org/10.3958/059.046.0105.
DOI: https://doi.org/10.3958/059.046.0105

Interpretive Summary: Parasitoids of aphids in the Southern Great Plains provide important pest suppression services in summer and winter crops. The main parasitoid species, Lysiphlebus testaceipes (Cresson), Aphelinus nigritus (Howard), and Diaretiella rapae (McIntosh), that prey on aphid pests on multiple crops in he Southern Plains. Historically, L. testaceipes has been the most abundant and arguably most important parasitoid species. However, following the introduction of the sugarcane aphid (Melanaphis sacchari Zehntner) on sorghum in the Southern Plains, A. nigritus increased in abundance and impact in this summer crop. We hypothesized that A. nigritus populations would also be more abundant in winter wheat and winter canola fields in the region following the invasion of the sugarcane aphid. We documented aphid parasitoid abundance and percent parasitism in Oklahoma winter wheat and canola crops during the late fall and early spring using a standardized sentinel aphid deployment retrieval and rearing approach. Interestingly, A. nigritus was found at relatively high levels in winter wheat fields and at extremely low levels in winter canola fields, but its abundance and impact declined during the study. Our results suggest that A. nigritus populations mirrored those of the sugarcane aphid in the region, and the temporary presence of this parasitoid in winter crops reflects dynamics at a landscape level. The study highlights the importance of focusing on the landscape as a whole when attempting to assess the biological control potential of parasitoids in insect pest management in a crop, rather than focusing solely on the target crop.

Technical Abstract: Aphid parasitoids in the Southern Great Plains provide important pest suppression services in summer and winter crops. The primary parasitoids Lysiphlebus testaceipes (Cresson), Aphelinus nigritus (Howard), and Diaretiella rapae (McIntosh) utilize multiple aphid host species on multiple crops in agricultural landscapes and historically, L. testaceipes has been the most abundant and arguably most important. However, following the introduction of the sugarcane aphid (Melanaphis sacchari Zehntner) on sorghum in the Southern Plains, A. nigritus increased in abundance and impact in this summer crop. We hypothesized that A. nigritus populations would also be more abundant in winter wheat and winter canola fields in the region following the invasion of the sugarcane aphid. From 2016-2019 we documented aphid parasitoid abundance and percent parasitism in Oklahoma winter crops during the late fall and early spring using a standardized sentinel aphid deployment retrieval and rearing approach. Interestingly, A. nigritus was found at relatively high levels in winter wheat fields and at extremely low levels in winter canola fields, but its abundance and impact declined during the study. Our results suggest that A. nigritus populations mirrored those of the sugarcane aphid in the region, and the temporary presence of this parasitoid in winter crops reflects dynamics at a landscape level.