Identification of a mutation in the para-sodium channel gene of the cattle tick Rhipicephalus microplus associated with resistance to flumethrin but not to cypermethrin

Abstract

A mutation in the domain II S4-5 linker region of the para-sodium channel gene has been associated previously with synthetic pyrethroid (SP) resistance in the cattle tick (Rhipicephalus microplus) in Australia. This is a C → A mutation at nucleotide position 190, which results in a leucine to isoleucine amino acid substitution (L64. I). In a survey of 15 cattle tick populations with known SP resistance status, sourced from Queensland and New South Wales in Australia, there was a strong relationship (r=0.98) between the proportion of ticks carrying the L64. I homozygous resistant genotype and the survival percentage after exposure to a discriminating concentration of cypermethrin in the bioassay, as expected. However, among populations resistant only to flumethrin, the L64. I homozygous genotype was not found. The sequence obtained for a 167. bp region including domain II S4-5 linker in flumethrin-resistant ticks identified a G → T non-synonymous mutation at nucleotide position 214 that results in a glycine to valine substitution (G72. V). The frequency of the G72. V homozygous genotype in each population was found to be moderately related to the survival percentage at the discriminating concentration of flumethrin in the larval packet test (r=0.74). However, a much stronger relationship between genotype and resistance to flumethrin was observed when the heterozygotes of L64. I and G72. V were added to the G72V homozygotes (r=0.93). These results suggest that there is an interaction between the two mutations in the same gene, such that flumethrin resistance might be conferred by either two copies of the G72. V mutation or by being a L64. I and G72. V heterozygote. © Australian Society for Parasitology Inc