A method of and a composition for treating a parasitic infestation in an animal and/or its environment is provided. The method includes providing an ectoparasitcidal formulation which comprises two or more IGRs, in which the IGRs may be selected from the same IGR class or from different IGR classes (excluding two or more juvenile hormone mimic IGRs selected from S-methoprene, hydroprene and pyriproxyfen) and regardless of whether each IGR is mobile or non-mobile or is capable or incapable of translocation in the environment.
