Esterase‐mediated bifenthrin resistance in a multiresistant strain of the two‐spotted spider mite, Tetranychus urticae

A field‐collected multiresistant strain of Tetranychus urticae Koch exhibiting high resistance to bifenthrin was investigated in comparison with a susceptible laboratory strain. The esterase inhibitor S , S , S ‐tributyl‐phosphorotrithioate (DEF) was able strongly to synergise bifenthrin toxicity in the resistant strain. Optimal conditions for determining esterase activities in T. urticae were determined, and a higher esterase activity towards several artificial substrates was found in this resistant strain, which had a preference for hydrolysing 4‐nitrophenyl butyrate. Bifenthrin was able to bind the active centres of T. urticae esterases in vitro , as was determined after competition experiments by a Dixon plot, revealing a higher affinity of bifenthrin in the resistant strain. Bifenthrin‐hydrolysing activity in the resistant and susceptible strains was examined in vitro and quantified with gas chromatography. A 7.2‐fold higher metabolising rate was found in the resistant strain. Copyright © 2006 Society of Chemical Industry