Abstract
The spider mite, Tetranychus urticae Koch is a serious pest of economically important plants in closed and open area worldwide. The spider mite resistance to acaricide plays a major role in the failure of the chemical control method. Thus, the aim of the current study was to evaluate the efficacy of two acaricides, abamectin and propargite, against two populations (strains) of the spider mite. Results showed that LC50s of the abamectin against susceptible and resistant strains of the spider mite were 0.1 and 2730 ppm, respectively. Whilst LC50s of the propargite against susceptible and resistant strains of the spider mite were 55 and 7199 ppm, respectively. Resistance ratio (RR) calculated as the ratio of resistance LC50/susceptible LC50 showed that RR for abamectin and propargite was 20285 and 130, respectively. The enzyme assay results showed that three mechanisms of MFO, GST and EST are involved in the abamectin resistance of the spider mite. In gel assays, when α-naphthyl acetate was used as substrate, three bands appeared in the gel in which bands E2 and E3 were major bands and E1 was a minor band confirming that α-naphthyl acetate was a better substrate for general esterase activity in the spider mite whereas β-acetate when used for esterase activity, only two faint bands (E1 and E2) were observed. The order of their involvement in the abamectin resistance is EST > MFO > GST.
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