2. Solenopsis invicta Invasion Status in Japan Fig. 1 Number of Solenopsis invicta infestations in Japan from 2017 through September 2024. The bar chart shows the number of invasions in each year and the line graph shows the cumulative number of invasions. Y. HASHIMOTO et al. Japan’s disrupting ecosystems and undermining cultural traditions that celebrate and cherish the natural environment, such as cherry blossom viewing. Given these high risks, this article provides an overview of the current, pressing situation concerning S. invicta in Japan, where the risk of establishment is increasing with the continued incursions detected in recent years. Furthermore, to counter this growing threat, we have developed novel, effective techniques from entering containerized cargo and nesting in container yards, which are also discussed in this article (Hashimoto et al., 2024). 2.1 Ongoing S. invicta Invasion via Chinese Shipping Containers Since the first detection of S. invicta in Japan in 2017, between eight and 26 infestations have been detected each year, totaling 129 incursions as of September 2024 (Ministry of the Environment, 2024) (Fig. 1). Solenopsis invicta has been reported in 18 prefectures: Aichi, Chiba, Fukuoka, Hiroshima, Hokkaido, Hyogo, Ibaraki, Kanagawa, Kyoto, Mie, Oita, Okayama, Osaka, Saitama, Saga, Shizuoka, Tochigi and Tokyo. Among these prefectures, Tokyo recorded the highest number of detections (38 cases), followed by Kanagawa (23 cases), Aichi (18 cases) and Osaka (14 cases). Most of these detections occurred in cargo containers at devanning warehouses or container yards. However, in five cases, workers or a single queen were found on goods already delivered to customers inland. The origin of S. invicta introductions, i.e. the loading port of the cargo and the shipping route, has been confirmed in 47 cases (Fig. 2). Of these, 41 were introduced by sea containers from In Japan, S. invicta was first detected in a shipping container in Amagasaki, Hyogo Prefecture, on 26 May 2017. The container had originated from Nansha port in Guangzhou, China (Hashimoto et al., 2019). As of September 2024, no wild S. invicta populations have been confirmed in Japan; however, there have been 129 documented incursions, most of which were associated with containers from China (Ministry of the Environment, 2024; Fig.1). In China, S. invicta is now widespread, infesting 1 million hectares and affecting more than 250 counties across 12 provinces (Wang & Lu, 2017). Given that China is Japan’s largest trading partner, with over 1 million tons of containerized cargo shipped to Japan annually (JETRO, 2024), further S. invicta incursions via contaminated cargo are inevitable (Bertelsmeier et al., 2018). Furthermore, S. invicta nests from imported containers have consistently been found in pavement cracks at container yards across Japan, with some nests confirmed to contain winged queens (Ministry of the Environment, 2024). Given the proximity of container ports to urban areas, these findings further heighten the risk of S. invicta becoming established in Japan. If the ants became permanently established and spread throughout Japan, the economic impacts could be severe. Aoyama et al. (2020) estimated up to 43 billion JPY in damage would result if S. invicta were to invade Okinawa Prefecture, which has only 1.1% of Japan’s population. There is potential for even greater economic costs in densely populated regions like Tokyo. Beyond the economic damage, S. invicta poses a serious threat to rich biodiversity, to prevent S. potentially invicta 102 production (Segarra et al., 1999). Consequently, S. invicta incurs substantial damage and control costs in the areas it infests (Angulo et al., 2022): for example, approximately $6 billion in costs reported in the United States alone (Lard et al., 2006).
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