Arthropod natural enemies and Melanaphis sorghi (Hemiptera: Aphididae) population dynamics in grain sorghum

The sorghum aphid, Melanaphis sorghi (Theobald) (Hemiptera: Aphididae), is an economically important pest of grain sorghum, Sorghum bicolor (L.), in the Southern and Central US Great Plains where biological control by natural enemies may be an important contributor to its management. We measured M. sorghi population growth rate (rt-to) on a M. sorghi susceptible (KS-585) and a resistant (DKS37-07) sorghum hybrid in replicated natural enemy exclusion cages during three growing seasons from 2019 to 2021. In a second experiment, we modeled rt-to against natural enemy population intensity data obtained from fields of KS-585 across 3 seasons 2021 to 2023. In the exclusion cage experiment, the rt-to was significantly greater on sorghum plants in complete exclusion cages than in partial exclusion cages and on uncaged plants in 2019 and 2021 but not in 2020. For the second experiment, linear regression models for groupings of natural enemies were not significant except the model for adult coccinellids, where the slope was -43.72, indicating a reduction in M. sorghi population growth rate with increasing adult coccinellid population intensity. Results are discussed in terms of mechanisms that might explain M. sorghi population suppression by natural enemies in grain sorghum.