Detachment of Four Species of Ticks Exposed to Selected Formamidine Compounds12

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Abstract
Detachment time from guinea pigs and dosage-detachment relationships were determined for adults of the lone star tick, Amblyomma americanum (L.), the Cayenne tick, A. cajennense (F.) , the American dog tick, Dermacentor variabilis (Say), and the brown dog tick, Rhipicephalus sanguineus (Latreille), after topical treatment (0.125–1.0 μ/tick) in 0.5 μl acetone of 3 formamidine compounds, chlordimeform amitraz ( N ′-(2, 4-dimethylphenyl)- N -[[(2,4-dimethylphenyl)imino]methyl]- N -methylmethanimidamide), and Upjohn U-42,564 ( N -[[(2,4-dimethylphenyl)imino]methyl- N -methylbenzenesulfenamide). At the median detachment time (DT50) and with dosages of 0.5 μg/tick, Upjohn U-42,564 was 11,3,9.1, and 18.3 times and amitraz was 2, 1.4, 2, and 10.2 times as effective as chlordimeform against R. sanguineus, D. variabilis, A. american , and A. cajennense , respectively. The order of effectiveness of the compounds was U-42,564, amitraz, and chlordimeform. There was a clear distinction in the resistance to detachment between the 2 Amblyomma species (long hypostomes) and the Dermacentor and Rhipicephalus species (short hypostomes): A. americanum and A. cajennense took longer to detach and higher doses were required to provide > 90% detachment. Within all species, there were no significant differences between the sexes in susceptibility to detachment.

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