A survey of Rhipicephalus microplus populations for mutations associated with pyrethroid resistance.

Mutations associated with pyrethroid resistance were found in Mexican strains of Rhipicephalus microplus (Canestrini). A mutation in the sodium channel gene was reported in strains highly resistant to permethrin and another mutation in an esterase gene in a strain that shows moderate resistance to the same pesticide. Methods based on the melting temperature difference of amplified allele-specific DNA fragments were developed that can detect these mutations rapidly in individual larvae. When these methods were applied to ticks from various strains of R. microplus from Australia, neither of these mutations could be demonstrated. Different resistance mechanisms have apparently developed independently between Australian and Mexican strains of R. microplus.