Biochemical mechanisms of resistance to chlorpyrifos and dichlorvos in field populations of Bemisia tabaci (Gennadius) B-biotype

Biochemical mechanisms of resistance to chlorpyrifos and dichlorvos were investigated in six field populations of Bemisia tabaci collected from Fujian Province of China with synergist bioassay and biochemical analysis. Compared with the susceptible SUD-S strain, the six field populations showed 54.53-78.43 and 6.23-11.25-fold resistance to chlorpyrifos and dichlorvos, respectively. TPP, PBO and DEF had 3.61-24.94, 1.14-1.76, and 1.04-fold synergistic effect on chlorpyrifos, and 1.67-2.64, 1.33-1.65 and 1.09-fold synergistic effect on dichlorvos, respectively, suggesting that carboxylesterase (CarE)-based detoxification could be an important resistance mechanism to chlorpyrifos in B. tabaci. K_m and V_ max of acetylcholinesterase (AChE) of the six field resistant populations were 1.83-4.0 and 0.34-0.62 times those of the SUD-S strain. Activity of AChE was inhibited both in the SUD-S strain and the resistant field populations when their subtrate concentrations were higher than 1.0 mmol/L and 16.0 mmol/L, respectively. AChE of the six field resistant populations was 119.92-161.33 and 10.11-14.24-fold less sensitive to chlorpyrifos and dichlorvos than that of the SUS-S strain, respectively. The results suggest that both insensitive AChE and increased CarE are the major mechanisms conferring chlorpyrifos resistance in B. tabaci, and only insensitive AChE is important for dichlorvos resistance.