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北硫黄島の昆虫は、2001、2003年の調査により50種が記録されたのみであったが、2019年6月の総合学術調査において124種が記録された。過去の標本も再調査し、総種数は141種となった。91種が同島新記録(49種は火山列島初、うち8種は小笠原諸島初、南硫黄島固有とされていた種も含む)で、同島の記録種数が火山列島で最大となった。南硫黄島で欠如する陸水環境等の存在によりトンボ目などが生息する一方、海鳥の絶滅により、死体に依存する昆虫は乏しい。硫黄島と共通のハチの外来種が確認されており、硫黄島の外来種の影響を受けている可能性が示唆される。小笠原群島に分布し火山列島から欠如する昆虫には、タマムシ類、ハナノミ類などが挙げられる。, Insect fauna on Kita-iwoto Island has been only recorded 50 species from short-term insect surveys conducted in 2001 and 2003. On the Kita-iwoto Island Scientific Research Project on June 18-23, 2019, the survey was conducted and attempted to identify the insect fauna on Kita-iwoto Island. In this survey, 124 species were recorded and 91 species were newly recorded in Kita-iwoto Island. Forty-nine species were recorded for the first time in the Volcano Islands, eight of which were first records on Ogasawara Islands. Among them, some species described as endemic to Minami-iwoto Island were included, and it was revealed that they were also distributed to Kita-iwoto Island. To summarize the all records, 141 species have been recorded on Kita-iwoto Island. It was the largest species record in Volcano Islands compared to Minami-iwoto Island, which has the similar altitude and cloud forest. Insect fauna on Kita-iwoto Island compared to Minami-iwoto Island has the following features. Odonata and some flesh water species inhabit inland water that does not exist in Minami-iwoto Island. On the other hand, seabirds that lived in high density on Minami-iwoto Island were extinct due to the predation by the rat, and a lot of insect species that depended on the carcass of seabirds could not be confirmed. As a distinct alien wasp species which has settled on Iwoto Island, has been recorded again since 2003. In addition, Buprestidae, Mordellidae, and Lucanidae are examples of taxa lacking as both Kita-iwoto Island and Minami-iwoto Island, although they are representative insects that are highly endemic in the Ogasawara Islands.

2019年6月に東京都の北硫黄島学術調査において陸産貝類の調査を実施した。本調査で初記録となる3種を含む5科9属11種が見出され、その内8種が在来種と判断された。前回の調査で記録のあったオガサワラノミガイとヒメベッコウマイマイ属の一種は本調査では確認されておらず、これまで北硫黄島で記録された種の総数は5科10属13種となる。10年前と比較して陸産貝類の生息状況に大きな変化は認められず、多くの種は一定の高度ないし特定の場所に限定した分布を示した。標高と種多様性の関係では、南硫黄島でみられたような特定の傾向は認められず、過去の人為的な影響を改めて示唆する結果となった。, In the expedition of Kita-iwoto Island, 11 specimens (5 families 9 genera) of land snails were collected and three species were newly recorded in this island. However, Lamellidea sp. corresponds to the Lamellidea nakadai which was obtained in the previous survey, and the identification error was revealed as a result of the subsequent classification. The other new records, Allopeas pyrgula and Geostilbia caledonica were considered to be alien species due to the distribution of around Kita-iwoto Island. Thus, 8 species, excluding 3 alien species, were native species among all 11 species. Lamellidea ogasawarana and Discoconulus sp. which were recorded in the previous survey were not confirmed this time. Taking together with previously reported data, the land snails of the island include 5 families 10 genera 13 species. There was no noticeable change in the habitat of land snails in these 10 years. Pacificella hataiana was dominant in low elevation area, while Lamprocystis kitaiwojimana was dominant in high elevation area, respectively. Many species were restricted to certain elevations or specific habitats, except for Tornatellides triyoni at almost all survey sites. The relationship between elevation and species diversity did not show a specific trend as seen in Minami-iwoto Island, suggesting a past anthropogenic impact.

2019年9月、西之島において、初めて専門家による陸上節足動物の上陸調査が行われた。2013年より度重なる火山活動によってほぼすべての地域が溶岩に覆われた一方、一部草地が残された。定量調査と定性調査を並行して実施し、旧島部に残存する節足動物を確認するとともに、新たに形成された大地への進出状況を明らかにすることとした。4綱15目28科33種の陸上節足動物を確認した。うち21種は同島から初めて確認された。既存の記録を加えるとこれまでに西之島から確認された陸上節足動物は少なくとも44種となる。特に2013年噴火後に新たに形成された植生のない溶岩台地において海鳥の死体下よりトビムシ、ササラダニ等の土壌分解者が発見されたことは一次遷移の過程に関する新たな視座を提示するものである。一方、外来種であるワモンゴキブリが残存していることが確認され、対策の実施が望まれる。トラップを用いた定量調査も行われたことにより今後の継続的なモニタリングの基礎情報となる。, For the first time in Nishinoshima Island, terrestrial arthropods were surveyed by experts in September 2019. While some grassland remained, almost all areas were covered with lava due to repeated eruptions since 2013. Quantitative and qualitative surveys were conducted in parallel to confirm the remaining arthropods on the former island and to clarify the status of their entry onto the newly formed beach and plateau. Thirty-three terrestrial arthropods of 4 classes, 15 orders, and 28 families were identified. Of these, 21 species were recorded from the island for the first time. When these new records are added to existing records, it appears that a total of 44 terrestrial arthropods have been identified from Nishinoshima. The discovery of soil decomposers, such as Collembola and Oribatida, under a seabird carcass on the newly formed lava plateau after the 2013 eruption suggests a new hypothesis regarding the process of primary succession. On the other hand, the alien cockroach remains on the former island, and an investigation into cockroach control is desirable. The results of a quantitative survey using traps will provide a baseline for continuous monitoring in the future.

小笠原諸島の西之島は2013年からの噴火で島のほとんどが溶岩に覆われ、新たな陸地が生まれた。この島は太平洋上に孤立し、最寄の陸地から130kmも隔離された無人島であることから、海洋島における生態系の一次遷移を人為的影響のない状態で観察できる世界に例のない場所と言える。そこで、2019年9月、西之島の自然環境の現況を明らかにするため、初の総合学術調査が行われた。噴火直後に生物、地質及び火山活動における網羅的な分野の調査を実施することで、火山島の形成過程、噴火による生物相への影響、新たな遷移の開始時点の状況等を把握して、西之島の科学的価値を明らかにすることを目的とした。本調査は環境省とともに、東京大学及び日本放送協会の連携により実施され、鳥類、陸上節足動物、植物、潮間帯生物、地質、火山活動の各分野における専門家、及び調査研究に対するサポート隊を含め、計22名の調査隊が組織され、9月3日～5日に上陸して行った。調査の実施に当たっては、調査による人為的な影響を最小限に抑えるため、外来生物の侵入を防止するための検疫を実施した。また、火山活動や上陸時の安全管理にも十分に配慮した。, Nishinoshima Island in the Ogasawara Islands had erupted since 2013, and the island was broadly covered with lava, creating new land. The island lies in an isolated spot in the Pacific Ocean, 130 km away from the nearest land; therefore, it is one of the best places in the world to observe the primary succession of an ecosystem on an oceanic island without anthropogenic effects. In September 2019, the first comprehensive academic survey was conducted to record the current state of the island’s nature. Using a biological and geological approach, the aim was to investigate the changes that had occurred, such as the process of formation of volcanic islands, the impact on the biota due to the eruption, and the situation at the start of primary succession. This survey was conducted in cooperation with the Ministry of the Environment, the University of Tokyo, and the Japan Broadcasting Corporation. A total of 22 members, including experts in ornithology, entomology, soil zoology, botany, marine biology, geology and volcanology, and support squads, landed on September 3-5. During the survey, quarantine measures were implemented to prevent the invasion of alien organisms to Nishinoshima and minimize the human impact of the survey. Considerable attention was given to safety management during landing operations and minimizing risks from volcanic activity.

筆者らは2017年6月14日-26日の期間に南硫黄島の学術調査隊に参加する機会を得て、昆虫類の調査を行なった。得られた試料は現在も各専門家による解析中であるが、これまでに10目68科116種を確認しており、うち36種(カジリムシ目1、カメムシ目7、コウチュウ目9、ハチ目4、ハエ目9、チョウ目6)は南硫黄島初記録、うち8種は小笠原諸島初記録であった。ミナミイオウスジヒメカタゾウムシは1981年以来36年ぶりに2例目の確認となったほか、コケムシ亜科の1種など未記載種の発見もあり、今後の解析結果が期待される。3回の総合学術調査で識別された計184種を整理すると、南硫黄島の昆虫相の偏りが明確となった。若く険しく厳しい島の環境への定着の困難さからか、多くの分類群が欠落する。捕食者、花粉媒介者、分解者、寄生者等、様々な生態的地位において特殊な状況が見られ、一部はニッチの置き換わりが起きていることも示唆された。また、南硫黄島固有の昆虫類に注目すると、ミナミイオウヒメカタゾウムシでは標高に応じて生息密度が急激に変化していたり、ミナミイオウムネボソアリでは翅を持たないオスが発見されたりするなど、他の地域では見られない変化を生じていることも明らかとなってきた。アカカミアリ等、隣接する硫黄島からの侵略的外来昆虫の侵入は今回も確認されず、、南硫黄島の昆虫相は健全な状態であることを確認した。一方で、複数の目立ちやすい広域分布種について、新たに確認されたり、再び確認されなくなったりすることから、この島では数十年間のうちにも昆虫類の侵入と絶滅が繰り返されていることが示唆された。10年ぶりに同様のルート、同一調査者が調査を行ったことは、小面積の海洋島における昆虫群集の遷移の検討にもつながっている。上記のような視点から、「本来」の自然が保存された南硫黄島における昆虫類は、海洋島における生態系、進化の形成過程を考察するための良好なモデルとなるであろう。, We surveyed insect fauna on Minami-Iwo-To Island from June 14 to 27, 2017. While expert identification of specimens is ongoing, we have already confirmed 116 species from 10 orders and 68 families, of which 36 species were recorded on Minami-Iwo-To Island for the first time and eight were the first records in the Ogasawara Islands. The endemic weevil Torishimazo minamiiwoensis has been confirmed for the first time in 36 years (since 1981), and we discovered some new species, including a new scydmaenine beetle. Over the three most recent surveys, a total of 184 insect species have been recorded. There is a clear bias in the composition of insect fauna on this island. The extreme habitats on the young island seem to cause the "anharmonic" taxa, which affects the ecological niches of insect species such as predators, pollinators, decomposers, and parasites. In some cases, species may occupy replacement niches. We found several notable features relating to the island’s endemic insects. There were drastic changes in the population density of the flightless weevil Satozo minamiiwoensis along an altitudinal gradient. In the endemic ant Temnothorax mekira, males (which usually have to fly to mate) were wingless. Surveys conducted by the same research team along the same route at a 10-year interval enabled the monitoring of transitional changes in insect communities on this small oceanic island. Fortunately, we discovered no invasive alien species which spread in neighboring island, such as the tropical fire ant Solenopsis geminata. On the other hand, the establishment of new records and the absence of conspicuous species from earlier surveys suggests that migration and extinction of insects have occurred repeatedly on this island during the past several decades. The insect fauna on Minami-Iwo-To Island would provide a good model for investigating ecosystems and the processes of evolution on oceanic islands.