Direct Toxicity and Repellent Activity of Pyrethroids Against Tetranychus urticae (Acari: Tetranychidae)

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Abstract
Direct toxicity and repellency of various technical-grade and formulated pyrethroid insecticides were tested against the twospotted spider mite, Tetranychus urticae Koch, in the laboratory. Direct toxicity (LC50)was measured by slide-dip tests while repellent activity was measured by mite dispersal (runoff50) from residues on broad bean, Vicia faba L., leaf disks. Technical-grade chemicals generally showed greater activity than formulated products. Comparison of activity among formulated pyrethroids showed that, for direct toxicity, deltamethrin 2.5 emulsifiable concentrate (EC) > cypermethrin 10 EC > flucythrinate 100 microemulsion > fenpropathrin 10 EC > fenvalerate 10 EC > fluvalinate 23.3 Aquaflow. For runoff, deltamethrin > fluvalinate > fenpropathrin > cypermethrin > f1ucythrinate > fenvalerate. The relative contribution of direct toxicity or runoff to any overall measure of acaricidal activity required the use of a suitable index. Therefore, we propose the ratio of LC50/runoff50 as an index of activity. This index gives an order of activity of fluvalinate > fenpropathrin > flucythrinate > cypermethrin > fenvalerate > deltamethrin.