Dose Responses of Field Populations of Alfalfa Weevil from Various Western States to Lambda-Cyhalothrin® Using a Feeding and Contacting Assay

Formulated insecticide, lambda-cyhalothrin, was diluted with water to form a series of desired concentrations to examine a dose response by field populations of alfalfa weevil using feeding assays. Alfalfa weevil larvae were collected from 14 different locations in seven different states during 2019. Results showed responses of alfalfa weevil larvae to different doses of lambda-cyhalothrin. Mortality rates ranged from 88-100% for the higher two doses in all locations. Weaker responses to lower doses have been detected in populations from northern CA and TX in this assay. Further investigation is planned for the 2020 season, including testing a wider range of lower doses.