Mutations in the mitochondrial cytochrome <i>b</i> of <i>Tetranychus urticae</i> Koch (Acari: Tetranychidae) confer cross‐resistance between bifenazate and acequinocyl

<jats:title>Abstract</jats:title><jats:p><jats:bold>BACKGROUND:</jats:bold> Resistance of <jats:italic>Tetranychus urticae</jats:italic> Koch to bifenazate was recently linked with mutations in the mitochondrial cytochrome <jats:italic>b</jats:italic> Q<jats:sub>o</jats:sub> pocket, suggesting that bifenazate acts as a Q<jats:sub>o</jats:sub> inhibitor (Q<jats:sub>o</jats:sub>I). Since these mutations might cause cross‐resistance to the known acaricidal Q<jats:sub>o</jats:sub>I acequinocyl and fluacrypyrim, resistance levels and inheritance patterns were investigated in several bifenazate‐susceptible and bifenazate‐resistant strains with different mutations in the cd1 and ef helices aligning the Q<jats:sub>o</jats:sub> pocket.</jats:p><jats:p><jats:bold>RESULTS:</jats:bold> Cross‐resistance to acequinocyl in two bifenazate‐resistant strains was shown to be maternally inherited and caused by the combination of two specific mutations in the cytochrome <jats:italic>b</jats:italic> Q<jats:sub>o</jats:sub> pocket. Although most investigated strains were resistant to fluacrypyrim, resistance was not inherited maternally, but as a monogenic autosomal highly dominant trait. As a consequence, there was no correlation between cytochrome <jats:italic>b</jats:italic> genotype and fluacrypyrim resistance.</jats:p><jats:p><jats:bold>CONCLUSIONS:</jats:bold> Although there is no absolute cross‐resistance between bifenazate, acequinocyl and fluacrypyrim, some bifenazate resistance mutations confer cross‐resistance to acequinocyl. In the light of resistance development and management, high prudence is called for when alternating bifenazate and acequinocyl in the same crop. Maternally inherited cross‐resistance between bifenazate and acequinocyl reinforces the likelihood of bifenazate acting as a mitochondrial complex III inhibitor at the Q<jats:sub>o</jats:sub> site. Copyright © 2009 Society of Chemical Industry</jats:p>