Mutations in the mitochondrial cytochrome b of Tetranychus urticae Koch (Acari: Tetranychidae) confer cross-resistance between bifenazate and acequinocyl.
BACKGROUND
Resistance of Tetranychus urticae Koch to bifenazate was recently linked with mutations in the mitochondrial cytochrome b Q(o) pocket, suggesting that bifenazate acts as a Q(o) inhibitor (Q(o)I). Since these mutations might cause cross-resistance to the known acaricidal Q(o)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(o) pocket.


RESULTS
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 b Q(o) 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 b genotype and fluacrypyrim resistance.


CONCLUSIONS
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(o) site.
Van Nieuwenhuyse
Pieter
P
Laboratory of Agrozoology, Department of Crop Protection, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, B9000 Ghent, Belgium.
Van Leeuwen
Thomas
T
Khajehali
Jahangir
J
Vanholme
Bartel
B
Tirry
Luc
L
D000085:Acetates / Q000494:pharmacology*; D000818:Animals; D002219:Carbamates / Q000494:pharmacology*; D045303:Cytochromes b / Q000235:genetics*; D006834:Hydrazines / Q000494:pharmacology*; D007305:Insecticide Resistance / Q000235:genetics; D007306:Insecticides / Q000494:pharmacology; D008928:Mitochondria / Q000201:enzymology*; D009154:Mutation; D009281:Naphthalenes / Q000494:pharmacology*; D040102:Tetranychidae / Q000187:drug effects* / Q000235:genetics* / Q000378:metabolism
D000085:Acetates; D002219:Carbamates; D006834:Hydrazines; D007306:Insecticides; D009281:Naphthalenes; C508134:bifenazate; D045303:Cytochromes b; C493666:acequinocyl