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| The toxicological and biochemical characteristics of acetylcholinesterase (AChE) in two field and one laboratory populations of Tribolium castaneum larvae were investigated. The two field populations HSTC-R (higher level resistance) and HYTC-R (lower level resistance) were both resistant to phosphine as well as organophosphorus insecticides such as dichlorvos and malathion. Compared with the laboratory population (ABTC-S), the activities per insect and specific activities of AChE in HSTC-R and HYTC-R were significantly lower. The apparent Michaelis–Menten constant value (Km) for acetylthiocholine iodide (ATChI) was obviously lower in ABTC-S than that in HSTC-R, indicating a higher affinity to the substrate ATChI in the laboratory population. The affinity for the substrate ATChI in HYTC-R and ABTC-S were not significantly different. The Vmax value of the HSTC-R was significantly greater compared to the Vmax for the ABTC-S suggesting a possible over expression of AChE in this field population. The inhibition study of AChE to insecticide exposure in vitro revealed that all the inhibitors possessed excellent effect. For the efficiencies of the tested inhibitors, the rank order from the most sensitive to the least was eserine, followed by malaoxon, paraoxon-ethyl, carbaryl, and demeton-S-methyl. Based on the I50s, AChE of the ABTC-S were more sensitive to all the inhibitors than those of HSTC-R. The statistical analysis of the bimolecular rate constants (ki) was consistent with the above situation. It is concluded that the insensitive AChEs were probably involved in the resistance of T. castaneum against insecticides observed in the field populations. |
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| Keywords:Tribolium castaneum;acetylcholinesterase;biochemistry;resistance |
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