Abstract: A novel heterocyclic compound represented by the following formula (I): ##STR1## wherein X represents an oxygen atom or sulfur atom; R.sup.1 represents a hydrogen atom or halogen atom; R.sup.2 represents a C.sub.4 -C.sub.6 alkyl group, C.sub.2 -C.sub.10 alkoxyalkyl group, C.sub.3 -C.sub.15 alkenyl group, C.sub.7 -C.sub.12 aralkyl group, C.sub.8 -C.sub.18 aralkyloxyalkyl group, C.sub.7 -C.sub.12 aryloxyalkyl group, C.sub.3 -C.sub.10 alkynyl group, C.sub.4 -C.sub.12 alkadienyl group, C.sub.6 -C.sub.18 alkatrienyl group, C.sub.6 -C.sub.12 alkadiynyl group, or C.sub.6 -C.sub.12 alkatriynyl group, said aryloxyalkyl group, alkynyl group, alkadienyl group, alkatrienyl group, alkadiynyl group and alkatriynyl group being capable of having at least one substituent selected from the group consisting of halogen atoms, C.sub.1 -C.sub.4 alkyl group, C.sub.1 -C.sub.4 halogenated alkyl group, phenyl group, hydroxyl group and C.sub.1 -C.sub.4 alkoxy group; and each of R.sup.3 and R.sup.