Abstract: The effects of quercetin,2-tridecanone and cucurbitacin B on the specific activity of carboxylesterase (CarE) in the tobacco whitefly,Bemisia tabaci (Gennadius) type B were investigated by feeding on artificial diet.The sensitivities of CarE to dichlorvos,methomyl,dimethoate,omethoate and S,S,S-tributyl phosphorotrithioate(DEF),an inhibitor of CarE,were also determined.After treated with quercetin ranged from 0.01 mg/mL to 1.0 mg/mL for 24 h,the specific activity of CarE increased obviously and the highest was 4.32-fold higher than the control. The specific activity of CarE was partially inhibited by 22% and 58%,respectively in the 0.1 and 0.5 mg/mL 2-tridecanone treatments. The cucurbitacin B ranged from 0.75 to 30.0 mg/L inhibited activity of CarE obviously.The I50 values of dichlorvos and DEF to the CarE from B.tabaci treated with 1.0 mg/L quercetin were respectively 20.05- and 3.16-fold higher than the control. When treated with 3.75 mg/L of cucurbitacin B for 24 h,the I50 values of dichlorvos and methomyl to the CarE were 25.94- and 2.45- fold higher than the control, respectively.While when treated with 1.0 mg/mL 2-tridecanone for 24 h,the I50 values of dichlorvos,DEF and dimethoate to the CarE were decreased by 89% ,83% and 90% ,respectively.