Submitted to: Resistance Pest Management Newsletter
Publication Type: Review article
Publication Acceptance Date: 3/30/2004
Publication Date: 6/7/2004
Citation: Li, A.Y. 2004. Status of resistance of acaricides in mexican strains of the southern cattle tick boophilus microplus (acari: ixodidae). Resistance Pest Management Newsletter. 13(2):7-12. Available: http://whalonlab.msu.edu/rpmnews/vol.13_no.2/printable/rpm_printable.htm. Interpretive Summary: The southern cattle tick is an economically damaging pest of cattle, and more importantly a vector of the disease agents that cause cattle fever disease. The USDA's Cattle Fever Tick Eradication Program (CFTEP) has successfully prevented this pest from re-infesting the U.S. via cattle importation from Mexico. The core of this program is the dipping treatment of all cattle for importation from Mexico in dipping vats charged with 0.3% coumaphos, an organophosphate acaricide. Such treatment eliminates any tick larva that may have escaped inspections USDA's tick inspectors at the ports of entry. However, the cattle tick populations in Mexico have developed resistance to a variety of acaricides in Mexico as a result of intense acaricide use over the past decades. The emergence of tick resistance to acaricides, particularly to coumaphos, in Mexico endangers the continued success of the CFTEP as resistant ticks may survive the dipping treatment of cattle. The focus of research at USDA, ARS, Kinpling-Bushland Livestock Insects Research Laboratory during has been on elucidation of resistance mechanisms and development of molecular and biochemical diagnostic techniques that allow accurate and rapid detection of resistance. This paper gives a brief account on the history of tick control and acaricide resistance in Mexico, and summarize the recent progresses made on research of acaricide resistance mechanisms and resistance detection techniques.
Technical Abstract: This paper reviews the current status and mechanisms of resistance to commonly used acaricides in Mexican strains of the southern cattle tick, Boophilus microplus (Canestrini). Resistance to organophosphates (OPs) and pyrethroids was measured using the FAO Laval Packet Test (LPT), and a modification of the FAO-LPT was used to measure amitraz resistance. The resistance ratios to pyrethroids range from 10 to >1000, depending on the mechanisms involved. The highest resistance ratios to organophosphate acaricides coumaphos and diazinon were 10 and 35, respectively. A survey of 15 field strains of B. microplus from Mexico revealed low levels of resistance to amitraz, with resistance ratios ranging from 2 to 5. Many tick populations in Mexico demonstrated multiple resistance to all three classes of acaricides. Resistance to pyrethroids was conferred by either a sodium channel mutation or enhanced activity of a carboxyesterase, CzEst9. Resistance to organophosphate acaricides was found to be conferred by insensitive AChE and/or enhanced activity of mixed function oxidases. Resistance to amitraz is considered to be mainly by target site insensitivity, although there was also evidence for the involvement of metabolic enzymes.