Synergism Studies with Binary Mixtures of Permethrin plus Methyl Parathion, Chlorpyrifos, and Malathion on European Corn Borer Larvae12

Binary mixtures of permethrin with methyl parathion, chlorpyrifos, and malathion, respectively, in ratios of 9:1, 4:1, 2.3:1, and 1.5:1 insecticide: permethrin were tested for synergistic activity against larvae of Ostrinia nubilalis (Hubner). Statistically significant ( P = 0.05) synergistic activity was exhibited by all tested mixtures of methyl parathion + permethrin and chlorpyrifos + permethrin. On the basis of LD50 values, mixtures of methyl parathion + permethrin were ca. 14- to 89-fold more toxic to the larvae than methyl parathion and ca. 5- to 34-fold more toxic than permethrin. Mixtures of chlorpyrifos + permethrin were ca. 25- to 29-fold more toxic than chlorpyrifos and ca. 5-fold more toxic than permethrin. Synergism was not exhibited by the mixtures of malathion + permethrin.