Cyhexatin Resistance in New York Populations of European Red Mite (acari: Tetranychidae)

Populations of the European red mite (ERM), Panonychus ulmi (Koch), from apple orchards throughout New York State were evaluated by laboratory bioassays to assess range of susceptibility to cyhexatin. As an indicator of cyhexatin susceptibility of adult ERM, a 72-h open-leaf residual bioassay was more sensitive than a 24-h slide-dip bioassay. At 100 ppm, a 12-fold difference in susceptibility to cyhexatin residues was found between a resistant ERM population from a commercial orchard and a susceptible field population. The difference between the same populations by slide-dip bioassay at 75 ppm cyhexatin was only 3-fold. The resistant population was substantially more heterogeneous in response to cyhexatin than was the susceptible population. Field trials in five commercial orchards in which cyhexatin control failures had been reported in previous years showed that levels of resistance evident in laboratory bioassays were associated with failure of cyhexatin to provide adequate control of ERM when applied in orchards at the standard rate. Mite populations collected from representative commercial orchards had 0–65% survival in residual bioassays at 316 ppm cyhexatin, compared with 76–88% survival of mites from five problem orchards. These results show that resistance to cyhexatin is not present at uniformly high levels in ERM populations in New York orchards.