Ooencyrtus nezarae lshii (Hymenoptera: Encyrtidae) is a major egg parasitoid of Riptortus pedestris (F.) (Hemiptera: Alydidae). One of the components of the aggregation pheromone of R. pedestris, (E)-2-hexenyl (Z)-3-hexenoate (E2HZ3H), is known to attract O. nezarae female. Response of O. nezarae females to E2HZ3H and its isomers was studied using electro-antennogram (EAG) and field tests. O. nezarae females showed higher antennal response to E2HZ3H and Z2HE3H isomers than E2HE3H and Z2HZ3H. In field tests, O. nezarae females were attracted to E2HZ3H traps, but not to Z2E3 traps. Interestingly, the blend of E2HZ3H and Z2HE3H showed significant antagonistic activities to the attraction of O. nezarae females in the field. We conclude from this study that Z2HE3H is a potent antagonist to the behavioral response of O. nezarae.