Ooencyrtus nezarae Ishii and Gryon japonicum (Ashmead), egg parasitoids of Riptortus pedestris (Fabricius), coexist despite direct competition for host eggs. As asymmetrical pattern of seasonal occurrence, i.e., more G. japonicum during spring-summer and more O. nezarae during summer-fall, has been reported, host resource partitioning may occur in temporal scales. To test this hypothesis, we demonstrated the interspecific competition between the two species by measuring parasitism in nine combinations of host densities and exposure times. To reflect gregarious-solitary dichotomy, three O. nezarae and one G. japonicum mated females were used in each experiment. O. nezarae was better competitor when exposure time was longer than 1 day irrespective of host densities. Parasitism rate and progeny emergence of O. nezarae was 1.6-2.8 and 4.7-7.3 times higher than G. japonicum. O. nezarae has higher potential rate of increase than G. japonicum due to gregariousness, and be more successful in larval competition inside multiparasitized host egg as it acts as a facultative hyperparasitoid. Although G. japonicum was more effective in host finding (as they showed relatively higher per capita parasitism and progeny emergence), their progeny suffered high mortality from the larval competition with O. nezarae. These results may explain the asymmetrical occurrence pattern in the field.

• Un Taek Lim(Department of Bioresource Sciences, Andong National University)
• Bishwo P. Mainali(Department of Bioresource Sciences, Andong National University)
• Jaegeun Kim(Department of Bioresource Sciences, Andong National University)