Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2002
Publication Date: 7/17/2002
Citation: DAVEY, R.B., GEORGE, J.E. EFFICACY OF MACROCYCLIC LACTONE ENDECTOCIDES AGAINST BOOPHILUS MICROPLUS(ACARI: IXODIDAE INFESTED ON CATTLE USING DIFFERENT POUR-ON APPLICATION TREATMENT REGIMES. JOURNAL OF MEDICAL ENTOMOLOGY. 2002. v. 39. p. 763-769. Interpretive Summary: Presently the U.S. Cattle Fever Tick Eradication program relies exclusively on the systematic dipping of all livestock in the organophosphorus chemical, coumaphos, to eliminate tick infestations on cattle. This reliance on a single acaricide points out the critical need for the evaluation of alternative chemicals and treatment methods that may show promise for potential use in the eradication program. A study was conducted to determine the efficacy of pour-on formulations of three macrocyclic lactone endectocides (moxidectin, ivermectin, and eprinomectin) against Boophilus microplus ticks using two different treatment regimes. A single application treatment regime with each compound produced similar levels of control against ticks, with moxidectin being least effective and eprinomectin being most effective, although none of the treatments produced a high enough level of control to be considered for use in the eradication program. However, when a double application treatment regime with a 4 d interval between treatments was evaluated, the eprinomectin treatment provided 99.7% control, a level that would be suitable for use in the eradication program. In addition, eprinomectin was also shown to be the only chemical that was equally effective against both young adult ticks and adult ticks that were in the final stages of engorgement. Thus, a double application treatment regime with eprinomectin may provide a viable alternative to presently used treatments with coumaphos.
Technical Abstract: Efficacy of moxidectin, ivermectin, and eprinomectin was evaluated against Boophilus microplus using two different treatment regimes. A single application treatment regime with each endectocide produced similar levels of control (range; 78.7-87.7%). Moxidectin treated females weighed more than ivermectin or eprinomectin treated females. The egg masses of moxidectin treated females weighed more than eggs of eprinomectin treated females, while ivermectin treated females produced egg masses that were of intermediate weight. In the double application treatment regime with a 4 d interval between treatments, control with moxidectin (90.3) was lower than ivermectin (98.9%) or eprinomectin (99.7%). Mean female and egg mass weights of the moxidectin treated group were greater than the other two treated groups. A single application treatment against 18-d-old and 20-d-old adult ticks provided different results with each endectocide. Control with moxidectin was the same against both age classes, but mean female and egg mass weights of 20-d-old adults were greater than that of 18-d-old adults. With ivermectin, female and egg mass weights were similar in the two age classes, but the level of control against 20-d-old adults was lower than that of 18-d-old adults. Thus, moxidectin and ivermectin were less effective against ticks in the final stages of engorgement. In contrast, eprinomectin was the only endectocide tested that was equally effective against both age classes of ticks.