Seasonal occurrence of Riptortus pedestris (Hemiptera: Alydidae) and its egg parasitism

Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) is one of the major pests of soybean in Korea. Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) and Gryon japonicum (Ashmead) (Hymenoptera: Scelionidae), two important egg parasitoids of R. pedestris may play an important role in controlling the pest. R. pedestris is mobile stink bug which colonize various crops, but seasonal occurrence of R. pedestris as well as the parasitoids is poorly known. Understanding seasonal occurrence and movement of R. pedestris and its parasitoids is important to develop biological control program against the stink bug. We placed aggregation pheromone traps added with R. pedestris eggs in a field where a series of crops including barley, sesame, and soybean were cultivated and in an apple orchard in Andong, Korea to record seasonal occurrence of R. pedestris and its egg parasitism from March to December in 2009. In the field crops R. pedestris appeared from second week of April in barley and peaked during third and last week of August in soybean whereas in the apple orchard it appeared in May and peaked during August. G. japonicum started to appear in May and was dominant until the first week of August in the field crops. However, from the beginning of August and September O. nezarae became dominant in apple and soybean, respectively. These results suggest that R. pedestris population occurs from April in barley and reach highest in August in soybean. G. japonicum is dominant in spring while O. nezarae is more common in the fall.