Toxicological and biochemical characterizations of AChE in Liposcelis bostrychophila Badonnel (Psocoptera: Liposcelididae)

Abstract

The toxicological and biochemical characteristics of acetylcholinesterases (AChE) in the resistant and susceptible strains (SS) of Liposcelis bostrychophila were investigated. The two resistant strains were the dichlorvos-resistant strain (DDVP-R) and the phosphine-resistant strain (PH 3-R) with resistance ratios of 22.36 and 4.51, respectively. Compared to their susceptible counterpart, the AChE activity per insect and the specific activity of AChE in DDVP-R and PH 3-R were significantly higher. There were also significant kinetic differences between DDVP-R and PH 3-R. The apparent Michaelis–Menten constant ( K m) for acetylthiocholine iodide (ATChI) was obviously lower in SS than that in PH 3-R, indicating a higher affinity to the substrate ATChI in the susceptible strains. The affinity for the substrate ATChI in DDVP-R and SS were not significantly different. The V max value of the PH 3-R was significantly greater when compared to the V max for the SS suggesting a possible over expression of AChE in this resistant strain. The inhibition of AChE to insecticide exposure in vitro revealed that all six insecticides were inhibitory for the extracted AChE’s. Based on the I 50 values, AChE of the SS were more sensitive to dichlorvos, paraoxon-ethyl, malaoxon and demeton- S-methyl than those of the two resistant strains. As for carbaryl and eserine, the PH 3-R suggested a significantly higher I 50s compared to the susceptible strain, while, no significant differences were found between SS and DDVP-R.