Toxicological and biochemical characterizations of GSTs in <i>Liposcelis bostrychophila</i> Badonnel (Psocop., Liposcelididae)

Abstract

Abstract: The toxicological and biochemical characteristics of glutathione S‐transferases (GSTs) in the resistant and susceptible strains of Liposcelis bostrychophila were investigated. The two resistant strains were the dichlorvos‐resistant strain (DDVP‐R) and PH 3 ‐resistant strain (PH 3 ‐R), and the resistance factors were 22.36 and 4.51, respectively. Compared with their susceptible counterparts, the activities per insect and specific activities of GSTs in DDVP‐R and PH 3 ‐R were significantly higher. The apparent Michaelis–Menten constant values ( K m ) for 1‐chloro‐2,4‐dinitrobenzene (CDNB) were obviously lower in DDVP‐R and PH 3 ‐R (i.e. lower K m values, 1.5625 m m for DDVP‐R and 0.6230 m m for PH 3 ‐R) when compared with their susceptible counterpart ( K m = 3.5520), indicating a higher affinity to the substrate CDNB in resistant strains. In contrast, the catalytic activity of GSTs towards CDNB in the susceptible strain was significantly higher than those in resistant strains. It was noticeable that when reduced glutathione (GSH) was used as substrate, GSTs from resistant strains both indicated a significantly declined affinity. For the catalytic activity of GSTs towards GSH, only the V max value in DDVP‐R increased significantly compared with that from the susceptible strain, suggesting an overexpression of GST in this resistant strain. The inhibition kinetics of insecticides to GSTs in vitro revealed that dichlorvos and paraoxon possessed excellent inhibition effects on GSTs. The susceptible strain showed higher sensitivity ( I 50 = 0.9004 m m ) to dichlorvos than DDVP‐R and PH 3 ‐R (higher I 50 s, 8.0955 m m for DDVP‐R and 9.3346 m m for PH 3 ‐R). As for paraoxon, there was a similar situation. The resistant strains both suggested a higher I 50 (1.8735 m m for DDVP‐R, and 0.4291 m m for PH 3 ‐R) compared with the susceptible strain (0.2943 m m ). These suggested that an elevated detoxification ability of GSTs developed in the resistant strains.