Effect of posttreatment temperature on the toxicity of five synthetic pyrethroids toTetranychus urticae Koch (Acari: Tetranychidae)

The synthetic pyrethroids bioallethrin,d-phenothrin, and fenvalerate, when tested by the slidedip technique, were more toxic to female two-spotted spider mites,Tetranychus urticae Koch, at 30°C than at 20°C. LC₅₀ values differed by 1.7-, 3.8-, and 5.3-fold, respectively. Two other synthetic pyrethroids, flucythrinate and cyfluthrin, gave similar toxicity values at these two temperatures. The greater sensitivity ofT. urticae at a warmer temperature to the first three pyrethroids differs from insect toxicity studies, which often show negative temperature relationships.University of Minnesota Scientific Journal Series No. 14954