Relationship between High Esterase Activity and In Vitro Degradation of 14C-Malathion by Organophosphate-Resistant and Susceptible Strains of the Kanazawa Spider Mite, Tetranychus kanzawai KISHIDA (Acarina : Tetranychidae), and Their Inhibition with Specific Synergists

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Abstract
The relationship between the enzymes which catalyze hydrolysis of β-naphthyl acetate and degradation of malathion was studied in resistant and susceptible strains of the Kanazawa spider mite, Tetranychus kanzawai KISHIDA.The homogenate of resistant mites exhibited higher activity in the degradation of malathion in vitro than that of susceptible mites, but such activity was remarkably inhibited by the compound K-1, which also manifested a prominent synergism with malathion to resistant mites. Six esterase bands and three peaks of malathion degradation were resolved by agar-gel electrophoresis. Resistance to malathion was associated with increased esterase activity at E3 and E4 bands on which the main peak of malathion degradation was detected. The compound K-1 selectively inhibited the esterase and degradation activities. Compounds K-9 and IBP, on the other hand, selectively inhibited E1 and E2 bands which overlapped with the minor peaks of malathion degradation.