OCCASIONAL INTERSPECIFIC COMPETITION AND WITHIN-PLANT MICROHABITAT PREFERENCE IN EGG PARASITOIDS OF THE BEAN BUG, RIPTORTUS-CLAVATUS (HEMIPTERA, ALYDIDAE) IN SOYBEAN

We examined the occurrence of interspecific competition among egg para sitoids of Riptortus clavatus (Thunberg) (Hemiptera: Alydidae) in with in-plant microhabitats of soybean fields in Fukuoka during the plantin g seasons from 1985 to 1987. R. clavatus eggs were found mainly on lea ves and pods, and rarely on stems of soybean plants. They were parasit ized by Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae), Gryon japo nicum (Ashmead) and G. nigricorne (Dodd) (Hymenoptera: Scelionidae). D uring three planting seasons, O. nezarae was more abundant than Gryon spp. O. nezarae parasitized more than 70% of hosts on leaves but less than 50% of those on stems and pods. Gryon spp., especially, G. nigric orne, parasitized more hosts on pods than on leaves or stems. Multipar asitism by O. nezarae and Gryon spp. rarely occurred in hosts from all three parts of the plant. Exploitation competition was more likely to occur in the early part of the season during 1985 and 1986 when overe xploitation by O. nezarae was likely to reduce reproduction of Gryon s pp. in soybean. Since interspecific competition was infrequent, the di fferent parasitism patterns by O. nezarae and Gryon spp. on various pl ant parts were probably due to their differences in microhabitat prefe rence.