Assessment of pyrethroid susceptibility, parasitism, and biotype variation in alfalfa weevil populations in Nebraska

Alfalfa (Medicago Sativa L.) is a key agricultural forage crop of the western United States, and the alfalfa weevil (Hypera Postica) is a major pest that poses a significant threat to alfalfa forage quality and productivity. Although various management strategies exist, including cultural practices (i.e., early harvest and grazing), biological control, and host plant resistance, the alfalfa weevil remains a persistent pest heavily relied on insecticides to control. Resistance to pyrethroids has been recently reported in western states; however, whether alfalfa weevil populations in the central Midwest have developed resistance is unknown. The aim of this study is to assess alfalfa weevil larvae susceptibility to two pyrethroids: lambda-cyhalothrin (type II) and permethrin (type I) in Nebraska. Alfalfa weevil larvae were collected from farm locations across Nebraska for vial bioassays to calculate median lethal concentrations (LC50) at 24 and 48 hours. Parasitism rates were also recorded for all populations. Because alfalfa weevil biotype composition differs across regions, this study also determines weevil biotypes and investigates if biotypes influence pyrethroid susceptibility. We anticipate that the susceptibility to pyrethroid and parasitism rate varies among alfalfa weevil populations in Nebraska, and biotype composition would affect pyrethroid susceptibility.