Impact of foliar insecticide sprays on Melanaphis sacchari (Hemiptera: Aphididae) and natural enemy populations in grain sorghum

Abstract The sugarcane aphid, Melanaphis sacchari is an important pest of grain sorghum (Sorghum bicolor) in the United States. Current M. sacchari management programs aim to control M. sacchari with insecticides while minimizing impacts on natural enemies that contribute to biological control of aphid populations. As a result, balancing both insecticide efficacy on the target pest and preservation of biological control agents remains an important step toward sustainable management of M. sacchari in grain sorghum. To document tradeoffs between M. sacchari control and non-target impacts, we evaluated three common aphicides (afidopyropen, flupyradifurone, and sulfoxaflor) for M. sacchari control and natural enemy safety. Treatments were paired with surfactants when recommended. Insect abundance was measured before and after foliar insecticide application using randomized complete clock design small plot studies during the 2019 and 2020 field seasons. All plots were harvested at maturity to document the relationship between in-season aphid abundance and grain yield. In this two year study, the average aphid abundance three days after insecticide application was lower in some but not all insecticidal treatments when compared to the untreated control, suggesting some insecticides had limited aphid suppression capabilities. Mean cumulative aphid days were lower in all treated plots compared to the untreated control with the exception of Sefina (afidopyropen). Twenty-eight days after foliar insecticide application, there were no differences in total natural enemy abundance in any of the treatments including the untreated control, suggesting that while M. sacchari populations were reduced by foliar insecticide treatments, the insecticides did not have clear adverse effects to natural enemy populations.