Tetranychus urticae was collected from greenhouse roses to monitor the development of acaricide resistance. Dose-mortality lines were estimated on 16 regional populations with 13 acaricides. For each acaricide, LC50s of the populations were plotted to check normality. LC50s of eight acaricides showed normal distribution and five others did not. An index of Ln (recommended dose/LC50 for each acaricide) checked the development of resistance to populations. The index is based upon recommended dose to control a pest stage and empirical LC50 got from serial dilution range for each pesticide. We tried to categorize acaricides by index due levels of effectiveness to mites: tebufenpyrad, fenpyroximate, bifenthrin, and fenbutatin oxide as non-effective acaricides with less than index 1.0, chlorpyrifor+bifenthrin and milbemectin as alert level placed between 1.0 and 2.0, acequincyl as caution between 2.0 and 3.0, and abamectin, cyflumetofen, bifenazate, chlorfenapyr+fulacrypyrim and propargite as effective over 3.0. We also tested the similarity of acaricide actions for choosing effective acaricides against resistant mites and of populations for resistance management. We could make several acaricides groups: group1 including abamectin, cyflumetofen, and bifenazate group 2 propargite and chlorpyrifos+bifenthrin group 3 chlorfenapyr and acequinocy and group 4 mibemectin, fenyroximate, and bifenthrin, by which we can suggest not to use acaricide within the same group to avoid the resistance development. Populations grouping would imply similar practices of acaricide use, so we can manage pesticide usage, effectively. Group A includes Gimhae 2, 3, 4, 5, Jincheon2, and Taean, and Group B includes Goyang, Gangjin1, Paju, Gangin2 and Namwon.

• Bu-Keun Chung(Div. of Plant Environment, Gyeongnam ARES)
• Si-Woo Lee(Crop Protection Div., NAAS, RDA)