Laboratory Studies on Effects of Three Permethrin Formulations on Mortality, Fecundity, Feeding, and Repellency of the Twospotted Spider Mite (Acari: Tetranychidae)

A monosize droplet generator was used to apply discrete amounts of three permethrin formulations (Ambush, TF2465, and D325) to bean leaf disks. After treatment, five adult female Tetranychus ulrticae Koch were placed on the disks. Fecundity, mortality, feeding rate, and repellency were detennined 24 and 48 h later. For each formulation, six droplet densities were used with five replicate leaf disks per droplet density. Results indicated that the effects of permethrin on T. urticae varied with both formulation and droplet density. With Ambush and TF2465, significant reductions in feeding and oviposition were recorded concomitantly with a significant increase in repellency. All of these effects were significantly correlated with droplet density. With D325, no significant treatment effects were observed. If the typical irritant effect of pyrethroids is partially responsible for the resurgence of mite populations within apple orchards, use of formulations that do not elicit this effect (i.e., D325) may allow these pesticides to be applied safely for control of other target species.