The present invention relates to an active composition for controlling oreradicating Phthiraptera, Siphonaptera and Acarina Pests, typically indomestic animals, comprising a synergistic combination of at least one A83543compound and at least one macrocyclic lactone. The invention also relates tothe use of the active composition in pesticidal formulations, the formulationsthemselves and to the various applications of those formulations aspesticides, specifically in controlling all species of Phthiraptera,Siphonaptera and Acarina pests, typically in domestic animals. Suchapplications include the control of such external Phthiraptera, Siphonapteraand Acarina pests in domestic animals including but not limited to sheep,cattle, poultry, pigs, goats, camelids, horses, dogs and cats.
