Susceptibility to acaricides and detoxification enzyme activity of four field populations of Panonychus citri

The susceptibility of four Chongqing populations of the citrus red mite Panonychus citri(McGregor)to four commonly used acaricides,abamectin,azocyclotin,pyridaben and spirodiclofen,was investigated.The results show that all four populations were least sensitive to azocyclotin,with LC50 values ranging from 209.9 to 370.9 mg/L,relative to the other three acaricides.The Bishan population exhibited the highest level of sensitivity to abamectin;LC50 values of the Wulong and Zhongxian populations were 12-and 11-times higher than that of Bishan population.Although the Beibei population had significantly higher resistance to pyridaben,it had a low LC50value to spirodiclofen.Investigation of the activities of the main detoxification enzymes (cytochrome P450 momooxygenases,glutathione S-transferase,carboxylesterase) indicated that there was no significant correlation between resistance levels and detoxification enzyme activity.These could possibly be caused by different strategies of applying acaricides in the field,differences in mode of action between different acaricides and different resistance mechanisms in the four populations.