Monitoring of resistance or susceptibility of Amblyomma mixtum (Acari: Ixodidae) to synthetic acaricides from Mexico

Abstract

In Mexico, a substantial challenge within cattle industry pertains to the widespread occurrence of Rhipicephalus microplus and Amblyomma mixtum infestation. Various acaricides compounds have been developed to manage these ticks infestation; however, their improper and frequent application has contributed to the emergence of resistant tick strains. However, there is a paucity of data specifically regarding the acaricide resistance status of A. mixtum. For this reason, the aim of this study was to monitor the susceptibility or resistance of A. mixtum to principal synthetic chemical acaricides used in control programme of A.mixtum and identify potential risk factors associated with A. mixtum resistant to ixodicides. Fully engorged adult female A. mixtum ticks were collected from cattle in twenty ranches. Larval packet test (LPT) and larval immersion test (LIT) were performed using discriminating doses (d.d) of ixodicides. The formulations tested were a Phenylpyrazole (fipronil), Organophosphates (coumaphos), Formamidine (amitraz) Synthetic Pyrethroids (cypermethrin) and Macrocyclic Lactones (ivermectin). The resulting phenotype was categorized as either resistant, probable resistant, or susceptible. A strain of A. mixtum collected from a cattle farm in the municipality of Las Choapas exhibited resistance to multiple acaricides, demonstrating diverse mortality levels at the d.d: fipronil (65.3 %), coumaphos (54.3 %), amitraz (52.4 %), and cypermethrin (35.5 %); except for ivermectin, where probable resistance was observed (90.8 %). A total of 50 % (10/20) of A. mixtum strains collected were resistant at least one acaricide evaluated. Furthermore, the strains of A. mixtum evaluated showed a higher frequency of resistance to amitraz. Also, only three strains assessed were susceptible to all acaricides tested. This crucial information will refine strategies for the effective control of ectoparasites.