New methods of applying drugs for the control of ectoparasites.

A brief history of the development of methods used to apply drugs (commonly called insecticides or acaricides) to domesticated animals for the control of ectoparasites is presented. The focus is on methods used in the United States for treating cattle, sheep and goats, and swine. Details of the evolution of treatment methods are presented for lice, flies, cattle grubs, keds, ticks, and other arthropods. In general, treatment methods have undergone some change over the years; while, in contrast, treatment materials have changed considerably. Three trends in treatment methods become obvious - (1) Gradual reduction in the amount of treatment material applied dermally from spray or dip to pouron, to spoton, and to insecticide-impregnated ear tags, (2) Increasingly wider use of animal systemic insecticides administered orally or percutaneously to control a variety of ectoparasites, and (3) The development of new methods (sustained release devices) to lengthen the residual effectiveness of treatments. Unfortunately, lengthened residual effectiveness may lead to resistance of important ectoparasites to the treatment materials.