This study was conducted to clear the regional difference in the resistance development of the spirodiclofen 36% WP, an acaricide of tetronic acid class, against two-spotted spider mite, Tetranychus urticae occurred in apple orchard since 2007. Two-spotted spider mite was collected from eight regions in the Chungnam, Chungbuk and Gyeongbuk that were major apple cultivation in Korea. An bioassay was investigated the ovicidal activity to compare with the degree of resistance development of this pest. The managed orchard in Sancheok-myeon, Myeongseo-ri, Chungju was controlled by several different acaricides from 2001 to 2008, and spirodiclofen WP was used for the last seven years. LC50 of spirodiclofen WP was estimated as 19.4 ppm in managed orchard, it showed as high as 2.6-fold (resistance ratio) comparing to those of susceptible strain showed as 7.5 ppm. LC50 of spirodiclofen WP against etoxazole-resistant two-spotted spider mite, gained from Chungbuk National University, was proved in 8.1 ppm. This observation indicates that spirodiclofen WP did not occurred in cross resistance with etoxazole SC. Other two regions in Chungju, the resistance ratio against spirodiclofen WP showed as 2.5- and 2.3-fold, respectively. In Chungnam, Gyeongbuk, it has been limited the resistance ratio under 3-fold, respectively.

This study was conducted to investigate the regional difference in the degree of resistance development of the spirodiclofen 36% WP, an acaricide of tetronic acid class, against two-spotted spider mite, Tetranychus urticae occurred in apple orchard. Two-spotted spider mite was collected from every three regions in the Chungbuk and Gyeongbuk. To compare with the degree of resistance development, this pest was focused on the ovicidal activity (when treated acaricide). The managed orchard in Sancheok-myeon, Myeongseo-ri, Chungju was controlled by several different acaricides from 2001 to 2007, and spirodiclofen WP was used for the last six years. In case of managed orchard, LC50 of spirodiclofen WP was 14.0 ppm, it showed 1.6 fold (resistance ratio) that was estimated as considerably low level resistance ratio comparing to the those of susceptible strain showed in 8.7 ppm. LC50 of spirodiclofen WP against etoxazole-resistant two-spotted spider mite, gained from Chungbuk National University, was investigated in 7.5 ppm. This observation indicates that spirodiclofen WP did not occurred in cross resistance with etoxazole SC. At other regions in Chungju, the resistance ratio against spirodiclofen WP showed as 1.0 and 1.4 fold, respectively. In Gyeongbuk, one region of Yecheon and two regions of Yeongju, it showed as 0.7, 0.8 and 0.9 fold, respectively.