Aggregation pheromone traps installed with refrigerated eggs of Riptortus clavatus (Hemiptera: Alydidae) increase egg parasitism in soybean fields

Riptortus clavatus Thunberg (Hemiptera: Alydidae) is a key pest of soybean in Korea and Japan. Aggregation pheromone traps are commonly used to control the stink bug. The aggregation pheromone produced by male R. clavatus is also known to attract egg parasitoids, Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) and Gryon japonicum Ashmead (Hymenoptera: Scelionidae). As a new method of pest management, we are suggesting to use the aggregation pheromone trap and host eggs together for dual control actions, i.e., the trapping of stink bugs attracted to the trap and the propagation of natural parasitoids on the eggs attached to the trap. Totals of 10,257-10,326 refrigerated host eggs (which become non-viable) were installed outside of the pheromone traps in three soybean fields (1,677-2,844 m²). Significantly higher parasitism rates on both natural (78-91%) and refrigerated eggs (36-59%) were found during the second half of the study period at the sites where refrigerated eggs were provided in the pheromone traps. In control sites where pheromone traps were installed without host eggs, parasitism was 0-62% and 16-34% on natural and refrigerated eggs, respectively. The proportion of bean pods with stylet sheaths as an index of crop damage was also significantly reduced by 47% in the treatment sites. However, no statistical difference in R. clavatus density was found between the treatment and control sites.