Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 22, 2009
Publication Date: April 1, 2009
Citation: Lohmeyer, K.H., Miller, J.A., Pound, J.M., Oehler, D.D. 2009. Efficacy of Eprinomectin and Doramectin against Amblyomma americanum (Acari:Ixodidae)on cattle. Journal of Economic Entomology. 102(2):809-814. Interpretive Summary: The avermectins, a class of endectocides that includes ivermectin, doramectin, and eprinomectin have proven to be an important new class of compounds for control and management of arthropod pests of livestock. Ivermectin, the first of this class to be introduced has been shown to control a variety of tick species. In this study conducted at the Knipling-Bushland U.S. Livestock Insects Laboratory, Kerrville, TX, we determined the efficacy of doramectin and eprinomectin applied orally against lone star ticks on cattle. In each trial nine Hereford steers were divided into 3 groups and treated by oral capsule for 28 consecutive days at a dosage of either 200 µg/kg or 50 µg/kg or without the drug. The concentration of the drug in the serum of the steers treated at either dose and with either drug provided 100% control throughout the treatment period. When the treatment was terminated on the 28th day, the efficacy declined in a pattern consistent with the decline of drug in the serum. The decline in efficacy and in serum concentration was more rapid in steers treated with eprinomectin than in those treated with doramectin. Both of these compounds have potential for control of ticks on cattle, deer and other wild ungulates with appropriate oral delivery systems.
Technical Abstract: Hereford steers were treated with either doramectin or eprinomectin by daily oral capsule for 28 consecutive days. The level of doramectin in the serum of steers treated at 200 µg/kg/da reached a maximum of 104.0 ± 22.1 ppb at Day 21 and steadily declined from 93.3 ± 20.5 ppb on the final day of treatment (Day 28) to below detectable on Day 56. For steers treated at 50 µg/kg/d, the serum level of doramectin reached a maximum of 24.7 ± 1.2 ppb on Day 21 and declined from 24.7 ± 0.6 ppb on the final day of treatment to less than detectable on Day 42. Both treatments provided 100% control of estimated larvae (EL) of the lone star tick, Amblyomma americanum throughout the 28 day treatment period. The daily oral treatment at a dosage of 200 µg/kg for 28 consecutive days produced a maximum concentration of eprinomectin in the serum of 41.6 ± 11.0 ppb at Day 14 and declined from 38.3 ± 5.9 ppb on the final day of treatment (Day 28) to below detectable on Day 35. For those steer treated at 50 µg/kg/d, the serum level of eprinomectin reached a maximum of 10.0 ± 3.0 ppb on Day 28 and declined from to less than detectable on Day 35. At both of these dosages, eprinomectin provide complete control of EL of lone star ticks during the treatment period. Because eprinomectin is efficacious against lone star ticks at lower levels in the serum of cattle and is eliminated from the serum at a more rapid rate than either doramectin or ivermectin, it provides distinct advantages for use in applications such as the medicated bait for control of ticks on white-tailed deer and should have potential for use in the Cattle Fever Tick Eradication Program.