Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 3, 1999
Publication Date: N/A
Interpretive Summary: In the United States, the eradication campaign against Boophilus ticks has been among the most successful programs ever undertaken. Within the permanent quarantine zone and at all U.S. ports-of-entry the success of the program has been largely due to the systematic dipping of all livestock in the organophosphorus (OP) acaricide, coumaphos. However, during the past 15 years the development and spread of OP resistance in Boophilus populations in Mexico has caused great concern because of the question of whether the coumaphos concentrations used in the program are high enough to eliminate OP resistant ticks on cattle. Thus, coumaphos was tested to compare its efficacy against OP-resistant and OP- susceptible strains of B. microplus by dipping tick-infested groups of cattle in one of four different concentrations of the acaricide. At the highest dose (0.279% active ingredient (AI) coumaphos) the control achieved was only 86.3%. Likewise, the level of control obtained at 0.160 and 0.083% AI was similar to the highest treatment level (87.4 and 76.6%, respectively). Thus, the control obtained at these treatment levels was well below the standard of 99% level of control required by the program. This study indicates that the presence of OP resistant ticks at U.S. ports-of-entry could undermine the continued success of the eradication program, and it points out the critical need for alternative chemical agents for use.
An efficacy study was conducted on cattle infested with a strain of Boophilus microplus (Canestrini) that was 9.5 times more resistant to coumaphos, an organophosphorus (OP) acaricide, than a known susceptible strain by dipping animals at four different concentrations (0.031, 0.083, 0.160, and 0.279% active ingredient). At 0.031% active ingredient (AI) control (26.8%) was lower (P<0.05) than the other treatments, and there was no difference (P>0.05) in any measured biological parameter as compared to the untreated control group. At the two high doses (0.160 and 0.279% AI), there was no difference (P>0.05) in the level of control (87.4 and 86.3%, respectively) or any other biologically measured parameter, but both concentrations produced significant (P<0.05) adverse effects on ticks as compared to the 0.031% AI treatment and the untreated control group. At the 0.083% AI treatment most measured biological parameters were intermediate between the lower and higher treatment levels, but there was no difference (P>0.05)in the control (76.6%) as compared to the two higher concentrations. None of the treatments provided protection against larval re-infestation for even 1 wk following treatment. Thus, results indicated that the presence of OP resistant ticks at U.S. ports-of-entry could jeopardize the success of the Boophilus eradication program.