ubstituted phenyl group, R3 is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkenyl or alkinyl group each having 2 to 4 carbon atoms, the optional substituents on the phenyl group of R1 and/or R2 being selected from the group consisting of halogen, alkyl having 1 to 4 carbon atoms, alkoxy or alkylthio each having 1 or 2 carbon atoms, and halogenoalkyl having 1 or 2 carbon atom