Melanaphis sorghi, colonization and population growth in grain sorghum and johnson grass in Oklahoma

Authors: Elliott, Norman - Norm; GILES, KRISTOPHER - Oklahoma State University; MUYOMBO-DIBUE, EPHRAIM - Oklahoma State University; LOFTON, JOSH - Oklahoma State University

Submitted to: International Journal of Ecology and Environmental Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2024
Publication Date: 2/14/2024
Citation: Elliott, N.C., Giles, K.L., Muyombo-Dibue, E.M., Lofton, J. 2024. Melanaphis sorghi, colonization and population growth in grain sorghum and johnson grass in Oklahoma. Journal of Economic Entomology. 1(5).

Interpretive Summary: Grain sorghum is an important rainfed crop in Oklahoma because it produces adequate and relatively consistent yields in the typically hot and dry Oklahoma summers. The sorghum aphid, Melanaphis sorghi, is a severe insect pest throughout Oklahoma. In addition to sorghum, the sorghum aphid survives and reproduces on johnsongrass. The role of johnsongrass in causing or contributing to sorghum aphid infestations of sorghum in Oklahoma has not been studied. This study had two objectives. First to determine if sorghum aphid occurred on johnsongrass in Oklahoma at an earlier calendar date than on sorghum. Second to determine if the population growth rate of sorghum aphid differed between johnsongrass and sorghum. To accomplish these objectives, we sampled fields of sorghum and nearby johnsongrass stands in Oklahoma weekly to bi-weekly during the growing seasons of 2019, 2020, and 2021. The average number of sorghum aphids per per leaf during the three-year study was roughly 10 times greater on sorghum than on johnsongrass. M. sorghi was first detected on johnsongrass a few days later than in sorghum in. The population growth rate was greater in sorghum than in johnsongrass, varying from four to 500 times greater. Results indicate that johnsongrass is usually not an important alternate host for sorghum aphid in Oklahoma from which to disperse to infest sorghum or increase the severity of infestations in sorghum.

Technical Abstract: Grain sorghum, Sorghum bicolor (L.), is an important rainfed crop in Oklahoma because it produces adequate and relatively consistent yields in the typically hot and dry Oklahoma summers. The sorghum aphid, Melanaphis sorghi (Theobald 1904), was first found in Oklahoma late in the 2013 sorghum growing season and by 2015 was a severe pest of sorghum throughout Oklahoma. In addition to sorghum, M. sorghi survives and reproduces on johnsongrass, Sorghum halepense (L.). The role of johnsongrass in the infestation dynamics of M. sorghi in sorghum in Oklahoma has not been studied. This study had two objectives. First to determine if M. sorghi was present on johnsongrass in Oklahoma at an earlier calendar date than on sorghum. And second to determine if the population growth rate of M. sorghi differed between johnsongrass and sorghum. To accomplish these objectives, we sampled fields of sorghum and nearby johnsongrass stands in Oklahoma weekly to bi-weekly during the growing seasons of 2019, 2020, and 2021. The average number of M. sorghi per leaf during the three-year study was roughly 10 times greater on sorghum than on johnsongrass. M. sorghi was first detected on johnsongrass an average of 2.8, 8.7, and 3.4 days later than in sorghum in 2019, 2020, and 2021, respectively. The population growth rate averaged over all sampling dates for each field and across fields for a particular year was greater in sorghum than in johnsongrass in each of the three years, varying from a low of four times greater in 2021 to a high of approximately 500 times greater in 2019, and differed significantly among the two plant species. Results are discussed in terms of local and landscape perspectives of the role of johnsongrass in the infestation dynamics of grain sorghum fields in Oklahoma.