Assessment of the efficiency of acaricides and their mode of application against the cattle tick (Boophilus microplus)

Abstract

A method for assessing the effect of acaricides on B. microplus is described based on counts of female ticks 4.5–8 mm in length on treated and untreated groups of naturally infested cattle. Ticks of this size engorge during the next night and drop from cattle the following morning. The counting method was used to compare the efficiency of different ways of applying acaricides. In comparison with untreated cattle, 0.025% coumaphos applied in summer by hand-spraying, plunge-dipping, or commercial spray race was estimated to kill respectively 99.5, 98, and 95% of female ticks which would have been present on days 1–21 after treatment. The lower efficiency of the spray races was due principally to survival of ticks on the ears and neck and most survivors were found 9–15 days after treatment. Cattle of all treated groups became reinfested with larvae 2–3 days after treatment.

The relative inefficiency of spray race treatment was confirmed by spraying and plunge-dipping cattle in 0.075% ethion in early winter, when the mortality on days 1-21 after treatment was estimated to be respectively 90 and 98.5%. In the same experiment the counting method was compared with the stalling of cattle to collect engorged females after treatment with 0.025% coumaphos: estimates of 98.5 and 99.1% mortality were obtained by the counting and stalling methods respectively. The relative efficiency of different acaricides was also compared: coumaphos and ethion in plunge dips were estimated to kill 98.5%; chlorxylam, ethion, and DDT applied by spray race were estimated to kill 99.2, 90, and 88.2% respectively on days 1–21 after treatment. The number of days during which cattle were protected from infestation with larvae could not be determined precisely, but was about 8–9 days after treatment with coumaphos and 10–12 days after treatment with ethion, DDT, and chlorxylam.

No difference was found in the effect of coumaphos against ticks on Hereford, Shorthorn, and Zebu x British cattle. In trials with the candidate acaricides chlorxylam, Dursban, bromophos ethyl, and SD8447 applied at a range of concentrations, distinct differences in the mortality of ticks 9–15 days after treatment were recorded at the different concentrations with most candidate acaricides, and their efficacy could be compared readily with a reference commercial acaricide.