The relevance of different test methods for the evaluation of tick controlling substances

Results of comparative investigations of different in vitro and in vivo procedures are reported. The aim of the investigations was to determine which of the test methods gives the best estimate of the activity against ticks under field conditions when used for active ingredients of varying chemical constitutions and different types of action. The data obtained indicate that results of in vitro test methods using tick larvae differ with the test procedure employed and the chemical class of the active ingredient. Therefore, in many instances these test methods do not allow extrapolation to practical conditions. In vitro tests employing engorged female ticks are much more reliable for most classes of compounds. However, there still are groups of compounds for which this test furnishes incorrect predictions. A better indication of the potency of a compound is therefore obtainable using in vivo test procedures. An economic and reliable method for the selection of prospective active ingredients is the mini-dip method using the specific host animal. This method provides not only an indication of the future concentration to be recommended but also provides information on the different types of activity of compounds active against ticks, i.e. tickicidal effect, paralysis, detachment, inhibition of development. Such observations are difficult or even impossible when in vitro methods are employed. The predictive value of the mini-dip method has been established for tick controlling substances of widely varying chemical constitution like organophosphorus compounds, carbamates, thioureas, diamidides, thiazolines and synthetic pyrethroids.