Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 11, 2001
Publication Date: N/A
Interpretive Summary: The Cattle Fever Tick Eradication Program is charged with preventing the re-establishment of cattle fever ticks back into the United States. Presently the program relies exclusively on a single pesticide, coumaphos, for the treatment of all cattle to prevent the ingress of these ticks. The reliance on this single pesticide carries a high risk of causing failure in nthe program because of factors associated with environmental safety issues and the development of resistance to this material. Therefore, it is critical to the continued success of the program to evaluate the effectiveness of any new compounds that may have potential for use against cattle fever ticks. Spinosad, a new naturally derived fermentation product of actinomycete bacteria, was evaluated for effectiveness against the southern cattle tick. At the highest dose (0.15% active ingredient) we achieved 87.9% control of the ticks that were infested on cattle at the time treatment was applied. In addition, this concentration provided two weeks of complete protection against reinfestation by larval ticks following treatment. The results, while not providing the required 99% control necessary for use in the program, do suggest that spinosad may have potential for use in situations where multiple treatments of infested cattle could be made. These multiple treatments would have the cumulative effect of eliminating a tick population in the field over time. Thus, spinosad should be given consideration for use in the program.
Technical Abstract: Cattle infested with Boophilus microplus (Canestrini) were treated with a single whole-body spray of spinosad at three concentrations to determine the acute and residual activity of the compound. At 0.0167% active ingredient (AI) there was no difference in tick numbers or the index of fecundity (IF) of females as compared to untreated females. However, both the 0.05 and 0.15% AI concentrations produced fewer ticks per calf with lower IF values than either the untreated or 0.0167% AI treated groups. The percent control of ticks on the animals at the time of treatment (acute efficacy) was lower at 0.0167% AI (21.4%) than at 0.05 (86.3%) and 0.15% AI (87.9%). All spinosad treatments appeared to be more effective against immature ticks (nymphs and larvae) than against adult ticks on the calves at the time of treatment. The weight of females that survived was similar for both untreated and treated groups. However, weight of egg masses produced by females showed a dose related response, ranging from 155 mg fo untreated ticks down to 73 mg in ticks treated at 0.15% AI. The percent hatch of eggs derived from females also showed a dose related response, except at the two high doses, ranging from 93.4% for untreated ticks down to 53.9% in ticks treated at 0.15% AI spinosad. Residual efficacy of spinosad at 0.0167% AI was not effective for even 1 wk following treatment. However, the 0.15% concentration provided >99% protection against successful reinfestation for up to 2 wk following treatment.