Stereospecificity in toxicity of the optical isomers of EPN.

While the optical isomers of EPN were equally toxic to mice, (+)-EPN was 2.9 fold and 4.0 fold more toxic to houseflies and rice stem borer larvae, respectively, than the (-)-isomer. In addition, (-)-EPN produced paralysis of the legs in hens about 10 to 14 days after dosing, whereas (+)-EPN caused no paralytic effects. Thus, (+)-EPN appears to be a more appropriate insecticide than the racemic compound, since it combines high toxicity to insects and no delayed neruotoxicity in hens.