Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2003
Publication Date: 5/10/2004
Citation: Davey, R.B., George, J.E., Miller, R.J. 2004. Control of an organophosphate-resistant strain of Boophilus microplus (Acari: Ixodidae) infested on cattle following a series of dips in coumaphos applied at different treatment intervals. Journal of Medical Entomology. 41(3):524-528.
Interpretive Summary: The presence of organophosphate (OP)-resistant Boophilus microplus ticks on cattle presented for import to the United States from Mexico poses an enormous risk to the U.S. Cattle Fever Tick Eradication Program (CFTEP) of dispersing viable ticks into the country. Studies have shown that a single dip in coumaphos (OP) against an OP-resistant strain of cattle fever ticks will not eradicate the ticks on the cattle, even at a dose that is two times higher than is presently required in the program (0.6% active ingredient). In this study cattle infested with OP-resistant ticks were dipped up to 3 times at either 7 or 10 day intervals at 0.3% active ingredient coumaphos to determine whether the ticks could be eliminated. Results showed that a single dip at either 7 or 10 days apart would provide only 46.8 and 65.6% control, respectively. The application of either 2 or 3 dip treatments at both intervals provided similar levels of control (>90%), but only the application of 3 separate dip treatments at either interval provided the level of control necessary for use in the eradication program (>99%). Thus, results of this study demonstrate that the application of 3 separate dips at either 7 or 10 days apart is the only treatment regime that will virtually eliminate the risk of dispersing OP-resistant ticks into uninfested areas of the United States.
Technical Abstract: Efficacy of multiple dipping treatments (up to 3 dips) in coumaphos at 0.3% active ingredient (AI) applied at either 7 or 10 d intervals was determined against organophosphate (OP)-resistant Boophilus microplus (Canestrini). The percentage reduction in the number of females per calf (24.8%) and the percentage control of the index of fecundity (IF) (46.8%) for treated cattle in the 7 d following a single treatment were lower than all other treatments. Similarly, the percentage reduction in the number of ticks per calf (47.1%) and the control of the IF (65.6%) of treated cattle in the 10 d following a single treatment were lower than all multiple dip treatments. Application of 2 or 3 coumaphos treatments at both 7 and 10 d intervals produced similar reductions in the number of females per calf (range; 80.2 to 88.8%), as well as in the level of control of the IF(range; 92.9 to >99.9%). While the level of control obtained following 2 or 3 dip treatments at either 7 or 10 d intervals was similar, only the application of 3 treatments provided high enough control (>99%) to be considered for use in the U.S. Boophilus eradication program, regardless of the treatment interval. Thus, only the use of 3 dip treatments applied at 7 or 10 d apart would virtually eliminate the risk of dispersing viable ticks to uninfested areas of the United States, even against OP-resistant ticks.