Stability of Cyhexatin Resistance in Field Populations of European Red Mite (Acari: Tetranychidae)

Abstract

Two field populations of European red mite, Panonychus ulmi (Koch), that were resistant to cyhexatin were exposed for 2 yr to three different levels of selection pressure by cyhexatin to determine whether resistance was stable under field conditions. Populations of European red mites from field plots where pressure with cyhexatin was intensive, limited, or absent were periodically tested for susceptibility to cyhexatin residues with a 24-h leafless bioassay technique. By late in the second year, mites from the plot where no cyhexatin had been applied were as susceptible to cyhexatin in bioassay as mites from the intensively treated plot. After at least 10 generations without selection pressure, the frequency of mites that were phenotypically resistant to cyhexatin appeared to be stable in these populations.