Frequency distribution of residual acetylcholinesterase activity in presence of inhibitor and its relationship with insecticide resistance in different populations of Bemisia tabaci (Gennadius) (Homoptera:Aleyrodidae)

To study the difference in sensitivity of acetylcholinesterase (AChE) from individual adult female and its relationship with insecticide resistance in different populations of Bemisia tabaci, the response of AChE to inhibition by dichlorvos and the frequency distribution of residual activity in presence of inhibitor in the susceptible SUD-S strain and six field resistant populations of B. tabaci were measured by microtiter plate kinetic assay. The results showed that dichlorvos at 300 μmol/L completely inhibited AChE activity of the SUD-S strain, and clearly distinguished the SUD-S from the six resistant populations. Significant differences were observed in frequency distribution of the residual AChE activity in adult female individuals in the six field populations of B. tabaci in presence of 2 000 μmol/L dichlorvos. The frequency distribution patterns of the residual AChE activity in ZZ-R and ZZ-R populations were similar, and most of the residual activity in adult female individuals ranged from 1.00 to 1.80 mOD/min. SM-R and ND-R populations also had similar frequency distribution patterns of the residual AChE activity, and most of their residual activity in adult female individuals ranged from 0.40 to 1.00 mOD/min; whereas in LY-R and NP-R populations, most of the residual AChE activity in adult female individuals ranged from 1.00 to 1.80 mOD/min and 0.80 to 1.20 mOD/min, respectively. The correlation coefficient between the high residual AChE activity (higher than 1.00 mOD/min) and the resistant level to dichlorvos was 0.86 (P0.05). Since the insensitivity of AChE to inhibitor is one of the mechanisms of resistance to organophosphorus and carbamate insecticides in some insects, we suggest that the sensitivity of AChE to dichlorvos be used as a reference index for the biochemical detection of insecticide resistance in B. tabaci.