Spatial and temporal insecticide resistance in onion thrips (Thrips tabaci) populations in onions

Onion thrips are becoming an increasingly difficult pest to control on onions in the Great Lakes region of the United States. One potential factor for this occurrence is insecticide resistance. Using a treated vial assay, within 24 hours we could rapidly determine whether field collected populations of onion thrips were resistant to insecticides. Our initial surveys in New York during 2002-3 indicated there were large spatial variations in susceptibility to lambda cyhalothrin across onion-growing regions, with even thrips populations from nearby fields varying greatly in susceptibility. Furthermore, changes in susceptibility occurred both within and between seasons. These results and conversations with growers suggested that individual grower practices were likely responsible for such differences. Additional studies in 2002-2 indicated that methomyl was effective, but that genes for resistance were present. Other insecticide products with novel modes of action have since been registered, but past experience warns us that they must be introduced within an insecticide resistance management framework. Current recommendations involve using a series of products with specific thresholds in a “window strategy” for managing thrips on onions.