Insecticide resistance in California populations of alfalfa weevil (Hypera postica)

Insecticide resistance is a serious concern for growers, particularly in cases where there are few management options. The main pest of California’s most valuable field crop, alfalfa, is Hypera postica, or the alfalfa weevil. Control options for alfalfa weevil in California are effectively limited to chemical control. Recently, growers in isolated areas of California and throughout the western United States have reported field control failures with pyrethroid insecticides. It is imperative that resistance levels are monitored in these regions to preserve the limited control options available. As part of an ongoing project, I collected weevils from known resistant and susceptible populations and conducted dose-response lab assays. The assays used lambda-cyhalothrin, a widely used pyrethroid. I present results showing levels of resistance to pyrethroids in California populations of alfalfa weevil. These results are important for addressing current resistance issues, making recommendations to farmers, and expanding our understanding of resistance.