Toxicity and persistence of six insecticides, including three pyrethroids and three organophosphorus insecticides, against Euxoa messoria (Harris) larvae were evaluated. These insecticides were applied to winter rye or tobacco seedlings in the field, and the residues on the foliage were bioassayed in the laboratory. The pyrethroids, cypermethrin, fenvalerate and permethrin, were more effective and persistent, and killed the larvae more rapidly than the organophosphorus insecticides, sulfopros, chlorpyrifos and trichlorfon. The higher rate of cypermethrin and fenvalerate gave a longer period of protection than the lower rate of the same materials and both materials were persistent longer than permethrin. No visible phytotoxicity was found on the tobacco plants treated directly with sulfopros, trichlorfon, cypermethrin, fenvalerate, and permethrin in the 3 years of tests.