Efficacy of a single doramectin injection against adult female Boophilus microplus (Acari: Ixodidae) in the final stages of engorgement before detachment.
The efficacy of injectable doramectin applied at 200 microg/kg was evaluated against adult female Boophilus microplus (Canestrini) (Acari: Ixodidae) in the later stages of engorgement before detachment. Lethal levels of doramectin in the serum of treated cattle (9.7-36.6 ppb) were reached and sustained within 24 h after treatment. However, treatment at 19 or 20 d postinfestation allowed greater tick survival and reproductive capability (IF) than at 18 d postinfestation, indicating that a significant portion of the ticks were able to engorge and detach before obtaining a lethal dose of doramectin. Thus, treatment at 18 d after infestation provided significantly higher overall control (99.5%) than treatment at 19 or 20 d postinfestation (95.8 and 89.1%, respectively). Analysis of control on a daily basis demonstrated that treatment at 18 d postinfestation provided > 99% on each day of the evaluation. Conversely, treatment at 19 or 20 d postinfestation produced levels of control ranging from 22.6 to 85.6% during the first 2 d of female detachment, and > or = 99% control was not achieved until after the fourth day of female detachment, where it remained throughout the study. Therefore, application of injectable doramectin at < or = 18 d after tick infestation was the only treatment regime considered acceptable for use in the U.S. Boophilus Eradication Program. Treatment intervals > 18 d postinfestation could pose a substantial risk of dispersing viable ticks to tick-free areas outside the permanent quarantine zone that has been established along the Texas-Mexico border.
Davey
Ronald B
RB
USDA-ARS, Southern Plains Area, Cattle Fever Tick Research Laboratory, Moore Air Base, Bldg. 6419, 22675 North Moorefield Rd., Edinburg, TX 78541, USA. ronald.davey@ars.usda.gov
Miller
J Allen
JA
George
John E
JE
Klavons
Jerome A
JA
D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000188:drug therapy* / Q000469:parasitology / Q000517:prevention & control; D005260:Female; D007279:Injections, Subcutaneous / Q000662:veterinary; D007306:Insecticides / Q000008:administration & dosage* / Q000097:blood / Q000494:pharmacology; D007559:Ivermectin / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000097:blood / Q000494:pharmacology; D026863:Ixodidae / Q000187:drug effects*; D011897:Random Allocation; D013984:Tick Infestations / Q000188:drug therapy / Q000517:prevention & control / Q000662:veterinary*; D013997:Time Factors
D007306:Insecticides; D007559:Ivermectin; C084101:doramectin