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Overwintering aggregations of Halyomorpha halys (Hemiptera: Pentatomidae) in human-made structures cause nuisance problems and enable this pest to invade new countries. Therefore, understanding the overwintering aggregation behaviors of H. halys would serve as a basis to mitigate these pest problems. In this study, we induced adult H. halys to exhibit overwintering behaviors in laboratory conditions and assessed how this pest responded to a potential overwintering structure and settled in the structure over 24 hours. A potential overwintering micro-habitat was provided to H. halys in reproductive diapause by establishing a 5-mm gap between two acrylic panels facing each other. This experimental arena was kept in a cage at 11°C, 12:12 (L:D), and 30% relative humidity (RH). A total of 50 adults (sex ratio = 1:1) was released into the cage for each replication. First, more females than males crawled into the 5-mm gap and settled in the experimental arena: the proportion of females having settled in the arena was 68.64 ± 3.03%. Second, when H. halys were settling in the arena, they did not significantly synchronize their dorsal or ventral side directions with other individuals. Third, H. halys tended to settle in the lower section of the experimental arena. Finally, 69.1 ± 3.9% of overwintering H. halys were found to settle solitarily, not touching other individuals in the experimental arena. Further studies are warranted to validate our results in semi-field conditions in which more H. halys are released and monitored for longer times.

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Halyomorpha halys (Hemiptera: Pentatomidae), an important agricultural and nuisance pest, is highly invasive with peculiar hiding behavior in human-made structures for overwintering. To evaluate the contamination risk of overwintering H. halys in non-agricultural export goods, we conducted a two-year field survey in Republic of Korea to locate overwintering H. halys in two major ports of export, Ulsan and Pyeongtaek ports, and monitored both active and overwintering H. halys population levels with varying distances from the ports ranging from 1 km to 48 km. First, we deployed wooden shelters in the two ports to catch dispersing H. halys for overwintering and conducted visual inspections for human-made structures in the ports to locate overwintering H. halys. In addition, we sampled dead trees to find overwintering H. halys in wooded areas. Second, we monitored active H. halys populations using pheromone traps with varying distances from the ports. From the survey of overwintering populations, no H. halys was collected from wooden shelters deployed in the two ports. However, we found four adults overwintering in human-made structures in Pyeongtaek port in the first year of survey. One dead adult was also found from a dead tree located in a wooded area adjacent to Pyeongtaek port in the second year. For active populations, results of pheromone trapping indicated that H. halys populations were present during autumn dispersal period not only in agricultural areas, but also in wooded areas adjacent to the two ports. This study reports for the first time that overwintering H. halys were found from the inside the port of export in its native areas with a low density. The results were discussed for evaluating contamination risk of overwintering H. halys in export goods shipping from the Republic of Korea.