The nocturnal loreyi leafworm, Mythimna loreyi Duponchel, is one of the important economical pests to gramineous crops in Taiwan. How to investigate and prevent this pest out breaking is a very essential topic nowadays. We observed that females attracted males by releasing sex pheromone to mate during the scotophase. Also, the production of sex pheromone in the virgin females showed a diurnal periodicity, because the sex pheromone titer in pheromone gland on the scotophase was higher than on the photophase. Females started to synthesize sex pheromone in their first photophase and hit the maximal titer on the third day after adult emergence. In addition, we assumed that a PBAN-like peptide exists in M loreyi′s subesophageal ganglion (SOG) is to control females sex pheromone biosynthesis. Both SOG extracts and synthesized pyrokinins/myotropins were tested for pheromonotropic activity. Dose-response results of the synthesized pyrokinins/myotropins showed that Hez-PBAN, Lom-MT II, Lom-PK I, Lom-PK II, Lom-MT I, LPK, Pss-PT, and type Ib turn (cyclo) raised significantly in the sex pheromone titer. It might indicate that the peptide conformations of pyrokinins/myotropins would affect the pheromonotropic activity by binding to the PBAN receptor.