Measuring the frequency of mutations associated with pyrethroid resistance in Aphis glycines

Soybean aphid (Aphis glycines; Hemiptera: Aphididae) is becoming a more challenging pest to manage. Sub-populations are resistant to pyrethroids, an affordable insecticide used in the North Central region of the US. Molecular markers have been developed to detect point mutations within the voltage-gated sodium channel (vgsc) of soybean aphids that are associated with pyrethroid resistance. During the summer of 2021, the frequency of four vgsc mutations within A. glycines found in commercial soybean fields were determined using genetic markers. Aphids were sampled from fields before and after a foliar application of a pyrethroid insecticide. We hypothesized the frequency of aphids with vgsc mutations would increase in the post-application sampling. We collected and are analyzing 791 aphids from eight fields. Preliminary analysis indicates one mutation (L1014F) was present in all fields prior to spraying. The frequency of this mutation increased by an average of 4% after treatment with a pyrethroid, with 79% of all aphids sampled having this mutation. Prior to treatment with a pyrethroid, 21% of aphids had no vgsc mutations and 10% had none after treatment. We will repeat this survey during the summer of 2022 and survey the presence of and monitor changes in pyrethroid resistance in Iowa. We will discuss the potential for genetic markers to aid farmers in making timely management decisions by detecting resistance in soybean fields.