Spatial and temporal dynamics of egg parasitism in the fields where aggregation pheromone traps of Riptortus clavatus (Hemiptera: Alydidae) were installed with refrigerated host eggs

Riptortus clavatus Thunberg (Hemiptera: Alydidae) causes losses in several crops including soybean, sweet persimmon, and apple in Korea and Japan. Though chemical spray is a common control method against the pest, aggregation pheromone traps are widely used in fields. Aggregation pheromone of R. clavatus is known to attract its egg parasitoids as well as conspecific individuals. Spatial and temporal dynamics of egg parasitism was investigated in the fields where aggregation pheromone traps were installed with refrigerated eggs of R. clavatus. Refrigerated eggs of R. clavatus (which become non-viable) have been successfully used to enhance egg parasitism in fields. Three traps containing refrigerated eggs were installed in the center of a barley field allowing parasitoids attracted to reproduce from the refrigerated eggs. Parasitism was assessed after collecting refrigerated eggs released at distance of eight, 16, 24, and 32 m from the trap location. We found higher parasitism by Gryon japonicum Ashmead (Hymenoptera: Scelionidae) whereas parasitism by Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) was very low. There was no statistical difference in parasitism among the eggs collected in the location of eight to 32 m from the traps, but the parasitism increased significantly from 6-30% to 34-82% after two weeks from the installation of the traps.