Fig. 2 Percentage distribution of countries and ports of origin sending Solenopsis invicta infestations to Japan via container cargo, based on cases with confirmed voyage routes from 2017 through September 2024. Over 90% of the infestations originated from China, including cargo transshipped through China. 103 The battle against the fire ant in Japan mainland China. The remaining six were introduced by air cargo from the United States and by sea containers from Djibouti, France, Italy, Taiwan and Vietnam. However, it has been confirmed that the containers from Djibouti, Vietnam and Italy were transshipped in China, and the container from France was transshipped in Singapore before being transported to Japan. Consequently, 44 infestations of S. invicta were associated with containers from China, and the ports of origin included Shekou (13), Xiamen (8), Nansha (6), Zhongshan (4) and other ports (13). Items in containerized cargo with infestations varied, including machine parts, home appliances, miscellaneous goods, lumber, paving stones, blankets, drinking water and straw as livestock feed. This suggests that the invasion of S. invicta by sea container is not associated with particular commodity types that originate from China. As Japan’s supply chain is heavily dependent on China, it is inevitable that S. invicta will continue to enter Japan via infested marine containers from China. Notably, in 2017, the first human injury caused by S. invicta occurred in Fukuoka Prefecture, Japan. In this case, a worker who was unloading container cargo from China at a warehouse, was stung on his left arm. Subsequently, in 2018, two workers unloading container cargo from China were also stung in Osaka Prefecture. In addition, in 2019, another ant sting incident occurred at the Port of Tokyo. In this case, S. invicta was attached to a bundle of rice straw sitting in a container yard, which had likely fallen from a container, and a worker was stung while handling it. Since rice straw is currently imported to animal and plant exclusively from China due quarantine restrictions, it is reasonable to assume that the rice straw found in the container yard had originated from China. Fortunately, in these incidents, no fatalities have resulted from these stings. However, in response to the occurrence of health risks caused by the ants, the Ministry of the Environment and port administrations have instructed importers to take the utmost caution when handling marine containers from China (Ministry of the Environment, 2024). Additionally, importers have been affected financially by the need to treat contaminated container cargo. Contaminated cargo normally must be fumigated to exterminate the ants, with fumigation costs, in principle, being the responsibility of the importer. Furthermore, the fumigated cargo is typically discarded, increasing the importer’s disposal costs. Although the damage is still limited, continued invasion of S. invicta from China has already caused problems in container logistics that heavily support Japan’s economic activities. 2.2 Detection of S. invicta Nesting in Container Yards Following the first discovery of S. invicta in 2017, the Ministry of the Environment has conducted regular surveys twice a year at more than 60 major international trade ports in Japan. By September 2024, 11 of these port surveys had discovered 86 independent nests of S. invicta, including Hakata, Hiroshima, Kitakyushu, Kobe, Mizushima, Nagoya, Osaka, Shizuoka, Tokyo, Yokkaichi and Yokohama (Ministry of the Environment, 2024) (Fig. 3). Of these ports, Tokyo had the highest number of nests, with 26 cases, followed by Yokohama with 21, Nagoya with 16 and Osaka with eight. Large colonies with thousands of workers and multiple winged queens have been detected in Hakata, Nagoya, Osaka and Tokyo ports. Among all the discovered nests, three were found in the ground at a bonded warehouse, which serves as a storage facility for loaded containers in a port area. The remaining cases involved nests located in cracks in the container yard pavement. Container yards are typically paved with four centimeters of asphalt (Fig. 4A). Over time, the
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