Laboratory selection for spirodiclofen resistance and cross-resistance in Panonychus citri

Selection for spirodiclofen resistance was done in the laboratory with a susceptible strain of the citrus red mite, Panonychus citri (McGregor). Successive selections for spirodiclofen resistance through 42 generations resulted in a high level of resistance and the resistance ratio at LC50 was 103 compared with that of the original susceptible strain. In the selected strain, the level of resistance to spirodiclofen was high at all developmental stages except eggs and P. citri adult infertility caused by spirodiclofen was decreased. Cross-resistance to spirotetramat was detected but not to 10 other acaricides. Synergist experiments indicated that, piperonyl butoxide (PBO), S,S,S-tributyl-phosphorotrithioate (DEF) and diethyl maleate (DEM) synergized the toxicity of spirodiclofen in the selected strain by 3.3, 2.3 and 1.6 fold and the resistance ratio decreased from 103 to 38, 45 and 65, respectively, but no synergism was found in the susceptible strain.