Methyl Parathion (Synonyms: BAY 11405)

Methyl parathion is an organophosphate insecticide.¹ It is converted into an oxon-containing metabolite in vivo, similar to other organophosphate pesticides, that inhibits acetylcholinesterase. Methyl parathion is lethal to lab strains and field isolates of tobacco budworm larvae (LD₅₀s = 7 and 81.8-128.3 μg/g, respectively).² It reduces the number of stink bugs (C. sayi) caught per 100 net sweeps when applied to alfalfa fields at a concentration of 0.4 pounds per acre.³ Methyl parathion increases sister chromatid exchange (SCE) in a concentration-dependent manner and induces cell cycle arrest at the M₁ phase in V79 cells at a concentration of 40 μg/ml.⁴ It is toxic to rats (LD₅₀ = 14 mg/kg).¹

1.Guo, J.-X., Wu, J.J.-Q., Wight, J.B., et al.Mechanistic insight into acetylcholinesterase inhibition and acute toxicity of organophosphorus compounds: A molecular modeling studyChem. Res. Toxicol.19(2)209-216(2006) 2.Martinez-Carrillo, J.L., and Reynolds, H.T.Dosage-mortality studies with pyrethroids and other insecticides on the tobacco budworm (Lepidoptera: Noctuidae) from the Imperial Valley, CaliforniaJ. Econ. Entomol.76(5)983-986(1983) 3.Reynolds, H.T., Stern, V.M., Fukoto, T.R., et al.Potential use of dylox and other insecticides in a control program for field crop pests in CaliforniaJ. Econ. Entomol.53(1)72-78(1960) 4.Chen, H.H., Hsueh, J.L., Sirianni, S.R., et al.Induction of sister-chromatid exchanges and cell cycle delay in cultured mammalian cells treated with eight organophosphorus pesticidesMutat. Res.88(3)307-316(1981)