The invention describes a method for inhibiting the growth of pests comprising applying thereto a pesticidal amount of a compound of the formula ##STR1## wherein R.sub.1, and R.sub.2 are independently hydrogen, substituted or unsubstituted lower alkyl, cycloalkyl, phenyl, or alkenyl, and halogen, amino or hydroxy groups, R.sub.3 and R.sub.4 are independently hydrogen or substituted or unsubstituted lower alkyl, R.sub.5 is hydrogen, substituted or unsubstituted lower alkyl, cycloalkyl or phenyl, and naphthyl groups; pesticidal compositions containing at least one of said compounds; and novel thiohydantoin compounds having pesticidal activity.