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Released eggs of Riptortus pedestris (Hemiptera: Alydidae) enhances parasitism in Agakong field
Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) causes losses in several crops in Korea. Release of non-viable refrigerated eggs of R. pedestris is known to enhance natural parasitism by Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) and Gryon japonicum (Ashmead) (Hymenoptera: Scelionidae) in soybean fields. In this study, we conducted an experiment of cage-exclusion design to verify the former results in more manipulative approach in a soybean field. Agakong field (45×26 m2) located at Songcheon, Andong was divided into 15 plots (10×6 m2) with each experimental arena of 3×2 m2 in the center. There were three treatments: (1) release of refrigerated eggs of R. pedestris, (2) release of refrigerated eggs with one time spray of thiamethoxam, and (3) untreated control. A fine mesh cloth with iron poles was used to encircle the arenas. Refrigerated eggs of R. pedestris were released (100/arena) twice before sampling. One-day old eggs of R. pedestris were released (60/arena) in all the experimental arenas at an interval of 6 days, and 30 eggs from each were collected to record parasitism. We found no significant difference in the eggs and nymphs population of R. pedestris among the treatments. However, adult density was significantly reduced in the treated plots during final two sampling days compared to the control. We found significantly higher parasitism by G. japonicum on the eggs collected from treated plots (9-25%) compared to the control plots (1-9%). It is verified that releasing non-viable eggs of R. pedestris help to enhance natural parasitism in soybean field.
