Efficacy of various concentrations of coumaphos to control adult, nymphal, and larval stages of an organophosphate-resistant strain of Boophilus microplus on infested cattle.
OBJECTIVE
To evaluate the efficacy of coumaphos, an organophosphate (OP) acaricide, at concentrations up to 2 times higher than the highest concentration required by the US Eradication Program against all stages of an OP-resistant strain of Boophilus microplus in experimentally infested cattle.


METHODS
16 tick-naïve 200-kg female Hereford calves.


METHODS
Four groups of cattle (4 calves/group) were all infested with Boophilus ticks 3 times before treatment. Each group was treated with coumaphos as follows: group 1, at 0.165% active ingredient (AI); group 2, at 0.299% AI; group 3, at 0.566% AI; and group 4, not treated. Following treatment, ticks were collected for 21 days. Ticks collected 1 to 7, 8 to 14, and 15 to 21 days after treatment were considered adults, nymphs, and larvae, respectively, at time of treatment.


RESULTS
Overall control at 0.165, 0.299, and 0.566% AI was 52.9, 75.8, and 89.7%, respectively. Control of adults ranged from 4.3% at 0.165% AI to 73.5% at 0.566% AI. Control of nymphs ranged from 60.6% at 0.165% AI to 97.3% at 0.566% AI. Control of larvae was > 98% at all coumaphos concentrations.


CONCLUSIONS
All coumaphos concentrations failed to provide acceptable control for use in the US Eradication Program against OP-resistant ticks. Treatment was least effective against adults and most effective against larvae. Even at 0.566% AI (2 times higher than required by the US Eradication Program), ticks were not eradicated, placing the United States at risk from dispersing cattle harboring viable ticks to uninfested areas.
Davey
Ronald B
RB
USDA, Agricultural Research Service, Cattle Fever Tick Research Lab, Rt 3 Box 1010, Edinburg, TX 78539, USA.
George
John E
JE
Miller
Robert J
RJ
D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000188:drug therapy / Q000469:parasitology*; D003372:Coumaphos / Q000008:administration & dosage* / Q000494:pharmacology* / Q000627:therapeutic use; D004305:Dose-Response Relationship, Drug; D005260:Female; D007305:Insecticide Resistance; D007306:Insecticides / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D007814:Larva / Q000187:drug effects*; D009758:Nymph / Q000187:drug effects*; D013983:Tick Control / Q000379:methods; D013984:Tick Infestations / Q000188:drug therapy / Q000469:parasitology; D013987:Ticks / Q000187:drug effects* / Q000254:growth & development
D007306:Insecticides; D003372:Coumaphos