methods and formulations for treating animal ectoparasites , effective against parasites such as fleas and ticks are provided . the methods comprise topically co - administering a non - mobile insect growth regulator and a mobile insect growth regulator to the animal . parasiticidal formulations for treating animal ectoparasites are also provided , which can be safe to use and avoid the many common deleterious side effects of conventional topical formulations . the topical formulations comprise a combination of two insect growth regulators , a non - mobile insect growth regulator and a mobile insect growth regulator . the topical formulation can be packaged with the two insect growth regulators together or packaged to prevent mixing of the two insect growth regulators prior to administering the topical insecticide formulation to the animal .