Quantification of biological effectiveness for pesticides against Tetranychus urticae (Acari: Tetranychidae)

A comprehensive method for evaluating direct and indirect mortality of acaricides to spider mites is presented. Technical improvements include use of lauryl sulfate as a surfactant, leaf disks of uniform size and quality, and a new method of assessing effectiveness of the acaricide that permits quantification of irritability. Uniform distribution of acaricide was assumed. Results using four contact acaricides on three strains of twospotted spider mites, Tetranychus urticae Koch, demonstrated significant differences in quantification of effects in 25% of cases when irritability was included in analysis. Quantitative evaluation of the nature of observed irritability (i.e., threshold or dose/response) was also performed.