Abstract: This invention relates to a stable pesticidal microemulsion formulation comprising from about 0.01 to about 25% by weight of an insect growth regulator, for example methoprene, S-methoprene, hydroprene and/or S-hydroprene, and from about 0.1 to about 5.0% by weight of an active ingredient, for example pyrethroids or permethrins, and from about 3 to 50% by weight of one or more surfactants with a hydrophile-lipophile balance value of 6 or higher, and from about 25 to 98% by weight of water wherein the insect growth regulator and active ingredient are dispersed in the surfactant(s) forming an oil phase which is in turn dispersed in water and forms discrete micelles in the range of about 0.001 to about 0.5 micrometers. This invention also teaches a method of applying the stable pesticidal microemulsion on animals to control ticks and fleas.