Recruitment of natural enemies of the invasive sugarcane aphid vary spatially and temporally in sorghum fields in the southern Great Plains of the USA

Authors: Elliott, Norman - Norm; GILES, KRISTOPHER - Oklahoma State University; BREWER, MICHAEL - Texas A&M University; SZCZEPANIEC, ADRIANA - Texas A&M University; KNUTSON, ALLEN - Texas A&M Agrilife; MICHAUD, JOHN - Kansas State University; JESSIE, CASI - Oregon State University; FARIS, ASHLEIGH - Texas A&M University; ELKINS, BLAKE - Texas A&M University; WANG, HSIAO-HSUAN - Texas A&M University; KORALEWSKI, TOMASZ - Texas A&M University; GRANT, WILLIAM - Texas A&M University

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2021
Publication Date: 6/29/2021
Citation: Elliott, N., Giles, K., Brewer, M., Szczepaniec, A., Knutson, A., Michaud, J.P., Jessie, C., Faris, A., Elkins, B., Wang, H., Koralewski, T., Grant, W. 2021. Recruitment of natural enemies of the invasive sugarcane aphid vary spatially and temporally in sorghum fields in the southern Great Plains of the USA. Southwestern Entomologist. 46(2):357-372. https://doi.org/10.3958/059.046.0207.
DOI: https://doi.org/10.3958/059.046.0207

Interpretive Summary: Sorghum is an important summer grain crop in the U.S. Great Plains because it is one of the few crops that consistently produces acceptable yields in the harsh and unpredictable summer weather that characterizes the region. Damaging infestations of the sugarcane aphid, Melanaphis sacchari (Zehntner), occur commonly in sorghum throughout Texas and Oklahoma, two of the leading sorghum producing states. Geographically separated locations in Texas and Oklahoma were targeted for sampling during 2017 and 2018. Natural enemies samples were grouped into categories that could be reliably identified by individuals in the field. A natural enemy importance index for predation on sugarcane aphid was developed that incorporated cumulative degree days of first occurrence of a natural enemy category in a field, the average density of the natural enemy in a field, and natural enemy voracity. Across all locations in Texas and Oklahoma larval coccinellids had the greatest importance for controlling sugarcane aphid and Orius sp, had the least. Among locations, natural enemies had the greatest importance in the Texas Coastal Plains and the least in the Oklahoma Panhandle. Results indicate that there are differences among species of natural enemy in their potential to exert biological control of sugarcane aphid, and there are also differences among geographic locations in potential for effective biological control. The importance of the results are that efforts to use natural enemy conservation methods should focus on those natural enemies with greatest potential to exert effective biological control, and that potential for biological control will be greater in some locations, particularly southern Texas, than in others.

Technical Abstract: Sorghum (Sorghum bicolor (L.) Moench) is an important summer grain crop in the U.S. Southern Great Plains because it is one of the few crops that consistently produces acceptable yields in the harsh summer weather that characterizes the region. Damaging infestations of the sugarcane aphid, Melanaphis sacchari (Zehntner), occur commonly in sorghum throughout Texas and Oklahoma, two of the leading sorghum producing states. Grain sorghum fields were sampled at two locations in Texas and three locations in Oklahoma. Fields were sampled approximately weekly by examining two leaves on each of 54 plants and counting all sugarcane aphids and aphid natural enemies on each leaf. Sampling began at an early growth stage and continued until the crop either matured or was treated with insecticide to suppress the sugarcane aphid infestation. For a total of 123 fields in 2017 and 2018, aphids, Aphelinus nigritus Howard mummies, adult coccinellids, larval coccinellids, larval lacewings, and larval dipterans were counted, and relative density estimates were determined. When natural enemy and sugarcane aphid count data were aggregated at the scale of geographic locations and multiple years, there was no evidence for a numerical response by natural enemies to sugarcane aphid density. When fields were compared within locations, a numerical response was consistently observed. A natural enemy importance index was developed that incorporated cumulative degree days of first occurrence of a natural enemy taxa in a field, the average density of the natural enemy in a field, and natural enemy voracity. Factorial analyses of variance indicated that cumulative degree days at first occurrence and average relative density differed significantly among natural enemy taxa and locations, as did natural enemy importance. Averaged across locations larval coccinellids had the largest importance index, I = 1.47, and A. nigritus had the smallest, I = 0.61. Among locations, the Texas Coastal Plains had the largest importance index, I = 1.27 whereas the Oklahoma Panhandle had the smallest, I = 1.02. Results suggest that differences occur in the biological control contributions of various natural enemies and in biological control efficacy among locations.