Baseline susceptibility to afidopyropen of soybean aphid (Hemiptera: Aphididae) from the north central United States

Afidopyropen, a novel Group 9D insecticide, has proven effective for management of soybean aphid, Aphis glycines (Hemiptera: Aphididae). However, to ensure continued efficacy of this insecticide, insecticide resistance management programs are needed. The goal of this study was to evaluate baseline susceptibility of several populations of soybean aphid to afidopyropen using leaf-dip bioassays in 2017 and 2018. Overall, mortality of adult soybean aphid varied among populations. Lethal concentrations necessary to kill 50% of a population (LC50) for adults ranged from 0.0013 to 0.40 mg a.i. per liter of afidopyropen. Lethal concentrations necessary to kill 70% of a population (LC70) of adults ranged from 0.136 to 13.1 mg a.i. per liter of afidopyropen. Afidopyropen was effective against populations resistant to pyrethroid insecticides, suggesting a lack of cross-resistance between afidopyropen and pyrethroids. Furthermore, afidopyropen was effective against nymphs of soybean aphid with concentrations ranging from 0.0285 to 54.45 mg a.i. per liter of afidopyropen causing 100% mortality by 6 days after exposure. The results reported here can be used for establishment of programs to monitor for development of resistance to this insecticide by soybean aphid.