Chemical control of the cattle tick Boophilus microplus (Can.)

The effectiveness of ten acaricides against Boophilus microplus (Can.) on cattle in southern Queensland, Australia, was investigated in 1960–63. Of infested cattle dipped in or sprayed with each acaricide, some were kept in stalls so that observations on ticks that survived treatment could be made, and others were grazed in tick-infested pastures in order to find the period of protection against reinvasion by larvae. Untreated cattle were also kept in the stalls to indicate the numbers of ticks occurring in the absence of treatment. The reproductive capacity, in terms of eggs and larvae produced, of ticks surviving treatment was compared with that of untreated ticks, and, for aldrin, dieldrin and the last four compounds mentioned below, the protective period in the field was compared with deposits of acaricide on the hair of the cattle as indicated by chemical and biological tests. For the last four acaricides, the effect on toxicity of artificially fouling the dip fluid was investigated, and also the relative toxicity of clean and artificially fouled fluids to ticks dipped in them under laboratory conditions. The acaricides tested, and (in brackets) the concentrations used, were aldrin (0·05 & 0·1%), dieldrin (0·1%), carbaryl (0·2%), Boots' ED 12308 (0·2%), ethion (0·1%), Ciodrin (0·1%), coumaphos (0·02%), diazinon (0·05%), carbophenothion (0·086%) and dioxathion (0·075%). All were emulsion formulations except carbaryl and diazinon, which were used in wettable-powder form. Daily collections of engorged adult ticks that fell from the stalled cattle provided clear-cut, though not quantitative, assessments of the effects of the acaricides. All the compounds tested gave a very high level of control, the only exception being the lower concentration of aldrin, and the reproductive capacity of ticks that survived treatment was negligible. With some of the acaricides, large numbers of surviving ticks fell in the first day or two after treatment, and some laid eggs; but the viability of the latter was invariably low. These observations emphasise the need to consider the reproductive capacity as well as the direct kill of parasitic ticks when assessing the value of acaricides. At the concentrations tested, nearly all the compounds allowed a few ticks to survive that were in the engorged-nymph stage at the time of treatment; these dropped off the cattle from the tenth day onwards and laid viable eggs. The mean protective periods of the chlorinated hydrocarbons and organophosphorus compounds ranged from three to six days, but on individual animals periods from three to eight days were recorded. Amongst the carbamates, a mean protective period of seven days was recorded for carbaryl in summer, whereas the mean protective period of RD12308 in winter, when such periods are longer, was 12 days. In come cases, protection appeared to continue when deposits of the original acaricide could no longer be detected on hair samples, and reasons for this are discussed. The influence of various factors, other than concentration, on the effectiveness of acaricidal fluids and on the results of tests was examined. Chemical and biological tests of hair samples showed that the acaricides persisted longer on stalled than on pastured cattle. Formulations affected the amount of toxicant deposited on the hair, and there was an indication that fouling of the dip fluid with soil and dung may, under certain circumstances, increase the amount of toxicant deposited.