Table 1.
Two acaricide resistance mechanisms with the respective acaricide classes and their targets.
Fig 1.
Heatmap indicating the resistance factors of 37 selected isolates for the five different acaricide classes [21].
The gray blocks (NA) indicate that no data are available for that sample.
Fig 2.
Schematic representation of the R. microplus VGSC highlighting pyrethroid resistance conferring target-site mutations.
The topology of the VGSC shows amino acid substitutions and their positions relative to the five transmembrane domains, each containing six membrane-spanning segments. The membrane-spanning segments are colour-coded: blue for the voltage-sensing modules and green for the pore modules. All residue numbers correspond to positions in the house fly VGSC (GenBank accession: X96668).
Fig 3.
Multiple sequence alignment of amino acid substitutions in the VGSC gene in R. microplus isolates.
The isolates are ordered by their synthetic pyrethroid resistance factor (RF) (deltamethrin; alpha-cypermethrin), with isolates having the lowest RF at the top and the highest RF at the bottom. Isolates Rm_BRA_962, Rm_BRA_963, and Rm_MX_ElZamora, which did not have exact RF values, are labelled RF > 26, as they were confirmed to be phenotypically resistant to SP. The ‘X’ at position 655 in the Rm_MX_ElZamora isolate indicates high variability, leading to more than two possible amino acids at that position. All other ’X’ amino acids indicate a lack of sequence data at those positions. *Denotes previously reported mutations.
Fig 4.
3D structure of R. microplus VGSC with key mutations and deltamethrin binding.
SwissModel 3D structure of the R. microplus VGSC protein with amino acid substitution sites (as listed in Fig 3), mapped in blue. The PyR1 binding site and the amino acid substitutions known to be associated with R. microplus pyrethroid resistance (Fig 2; mapped in red in Fig 4) are located inside the orange rectangle. All residue numbers correspond to the position of the house fly sodium channel (GenBank accession: X96668).
Table 2.
Targets implicated in tick acaricide resistance.