Detection and characterization of amitraz resistance in the southern cattle tick, Boophilus microplus (Acari: Ixodidae)

Amitraz, a formamidine acaricide, plays an important role in the control of the southern cattle tick, Boophilus microplus (Canestrini), and other tick species that infest cattle, dogs, and wild animals. Although resistance to amitraz ill B. microplus was previously reported ill several countries, the actual measurement of the level of amitraz resistance ill ticks has been difficult to determine due to the lack of I proper bioassay technique. We conducted a survey, by using a newly reported technique that was a modification of the standard Food and Agriculture Organization larval packet test, to measure the levels of resistance (1.68- to 4.58-fold) was detected in 11 of those strains. Our laboratory selection Using amitraz oil larvae of the Santa Luiza strain, Which originated from Brazil, achieved a resistance ratio of 153.93 at F-6, indicating the potential for high resistance to this acaricide in B. microplus. Both triphenylphosphate and piperonyl butoxide significantly synergized amitraz toxicity in one resistant strains. Target site insensitivity, instead of metabolic detoxification mechanisms, might be responsible for amitraz resistance observed in the Santa Luiza strain and possibly ill other amitraz resistant B. microplus ticks from Mexico. The Santa Luiza strain also demonstrated high resistance to pyrethroids mid moderate resistance to organophosphates. Multiple resistance shown in this strain and other B. microplus strains from Mexico poses I significant challenge to the management of B. microplus resistance to at acaricides ill Mexico.