Abstract
Susceptibility and carboxylesterase (CarE) activity to four selected acaricides (amitraz, propargite, azocyclotin, and diafenthiuron) were assayed for five field populations of Panonychus citri (McGregor). Mite populations were collected from Beibei, Zhongxian, Wanzhou, and Changshou counties of Chongqing municipality, and Nanchong county, Sichuan province, southwestern China, respectively. Among selected acaricides, all populations but Beibei seemed to be most sensitive to azocyclotin though the last population appeared to be least susceptible to the acaricide. The Wanzhou population expressed most sensitivity to all acaricides. For CarE activity assay, the Wanzhou population expressed the lowest general and specific enzymatic activity among the five populations. Kinetic analysis showed that the catalytic activities of CarE to the substrate α-naphthyl acetate in the other four relatively insensitive populations were higher, with the highest recorded in the Beibei population. Based on the detoxifying role of CarE, the higher activities of CarE in four other populations might have contributed to the previous toxicity assay results showing less sensitivity to four tested acaricides than the Wanzhou population. Subsequent in vitro inhibition assay showed that CarE of the Wanzhou population was more sensitive to all acaricides based on its lower I 50s (the acaricide concentration required to inhibit 50% of CarE activity). The current study suggested that CarE might be associated with lower sensitivity to acaricides.