Soybean aphid, Aphis glycines Matsumura, remains the most economically damaging arthropod pest of soybean in the midwestern United States and southern Canada. Foliar applications of a limited number of insecticide modes of action have been the primary management tactic, and pyrethroid resistance was documented recently with full concentration-response leaf-dip and glass-vial bioassays. Full concentration-response bioassays can be cumbersome, and a more efficient assessment tool was needed. In this study, we implemented a diagnostic-concentration glass-vial bioassay using bifenthrin and λ-cyhalothrin. Bioassays were conducted with field-collected soybean aphid populations to assess the geographic extent and severity of resistance to pyrethroids. In 2017, 10 of 18 and 11 of 21 field populations tested with bifenthrin and λ-cyhalothrin, respectively, had mean proportion mortalities less than the susceptible laboratory population. In 2018, 17 of 23 and 13 of 23 field populations tested with bifenthrin and λ-cyhalothrin, respectively, had mean proportion mortalities less than the susceptible laboratory population. Populations collected after reported field failures of a pyrethroid insecticide generally had mean proportion mortalities less than the susceptible laboratory population. In both years, there was a strong correlation between chemistries, which suggests cross-resistance between these insecticides. The diagnostic-concentration glass-vial bioassays reported here will provide the foundation for an insecticide resistance monitoring program with the ability to determine practical levels and geographic extent of insecticide resistance.
Bibliographical noteFunding Information:
We thank Natalie Eisner, Lesley Lubenow, Samantha Lahman, Josephine Dillon, Travis Prochaska, and the numerous crop consultants, extension and research staff, and undergraduate and graduate students who aided in the location and collection of aphid field populations and the conducting of bioassays. Funding was provided by the Minnesota Soybean Research and Promotion Council, North Dakota Soybean Council, South Dakota Research and Promotion Council, Iowa Soybean Association, and Syngenta.
© 2020 The Author(s) 2020. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved.