The Insect database in Dokdo, Korea: An updated version in 2020

Abstract Background Dokdo, a group of islands near the East Coast of South Korea, comprises 89 small islands. These volcanic islands were created by an eruption that also led to the formation of the Ulleungdo Islands (located in the East Sea), which are approximately 87.525 km away from Dokdo. Dokdo is important for geopolitical reasons; however, because of certain barriers to investigation, such as weather and time constraints, knowledge of its insect fauna is limited compared to that of Ulleungdo. Until 2017, insect fauna on Dokdo included 10 orders, 74 families, 165 species and 23 undetermined species; subsequently, from 2018 to 2019, we discovered 23 previously unrecorded species and three undetermined species via an insect survey. New information As per our recent study, the database of insect species on Dokdo has been expanded to 10 orders, 81 families, 188 species and 23 undetermined species. This database has been registered in the Global Biodiversity Information Facility (GBIF; www.GBIF.org) and is the first record for insect fauna on Dokdo.


Introduction
Islands are known for their ecologically-and biologically-important ecosystems. Due to geographical isolation, the movement of organisms is limited (Franks 2009) and island-like areas have low potential for both species transfer and settlement. For these reasons, as well as their small land area, islands often have low biodiversity (Mauchamp 1997). Islandlike areas are also vulnerable to external intrusions, which represent a major threat to indigenous species (Kil et al. 2006). Recent developments in traffic pathways have decreased the number of isolated island ecosystems, thus allowing researchers to investigate the interactions between evolutionary and ecological processes that are responsible for island biodiversity (Gillespie et al. 2008).
The Intergovernmental Panel on Climate Change (IPCC) reports that climate change is causing sea levels and sea temperatures to rise and, if this trend continues, most coastal regions around the world will be at risk (Hong 2010, IPCC 2014. By 2100, these increases in sea level are estimated to reach at least 1 m, creating elevated flooding-related risks for large parts of the low-land island ecosystem, which could lead to significant habitat loss for many organisms worldwide (Bellard et al. 2013). The average annual sea level in Korean coastlines has been rising since 1989 and the average annual rate of sea level rise (5.67 mm/yr) around Ulleungdo has been particularly rapid (Korea Hydrographic and Oceanographic Agency 2020).
The Dokdo Islands, which are located at 37°14'26.8'' N and 131°52'10.4'' E, belong to an administrative district that includes the Ulleungdo Islands as well. The address of the Korean administrative district is 1-96 Dokdo-ri, Ulleung-eup, Ulleung-gun, Gyeongsangbukdo, Korea. Tourists cannot stay in Dokdo for more than 30 min, although the Korean Coast Guard (KCG) and some residents can visit for longer time periods. These Islands were formed during the Pliocene Epoch by an underwater volcanic eruption that occurred between 2.5 and 4.6 million years ago (Raman et al. 2016) and subsequently promoted the formation of the Ulleungdo volcanoes via tectonic plate movement (Lee et al. 2002). Dokdo is built on sea floor that is about 2,000 m deep; it comprises two main volcanic islands and 89 small islands (Sohn 1995, Ryu et al. 2012. The nearest land area to Dokdo is Jukbyeon, Uljin-gun, Gyeongsangbuk-do, which is 217.149 km away from Dokdo and 87.525 km from Ulleungdo (Hwang and Park 2007).
Dokdo is entirely composed of volcanic rocks and its island ecosystem is relatively disconnected from the outside world; therefore, it is an important subject for island ecology and biogeography (Cultural Heritage Administration 2009). In 1982, Dokdo was designated as Natural Monument No. 336 by the Korea Cultural Heritage Administration (KCHA) to be managed by the Dokdo Natural Reserve. Dokdo is very small, with an area of 187,554 m and, because it has been protected and has inaccessible geographical features, there is extremely limited knowledge of its insect fauna. The Dokdo Islands are located at the bridge that connects Ulleungdo in Korea and the Oki Islands in Japan. Due to the fact that previous investigations of insect species on Dokdo played a vital role in characterising the biogeographic limits of these regions, the study of insect fauna on Dokdo is considered to be geographically important (Yasunaga and Duwal 2015).
Since the initial assessment of insects on Dokdo by Jolivet in 1974, many researchers have conducted follow-up studies and, by 2017, 10 orders, 74 families and 165 species of insects have been identified (Jolivet 1974, Yoon 1978, Lee and Kwon 1981, Kwon et al. 1996, An 2000, Korean Ministry of Environment 2001, Ulleung Research Institute of Gyeongju University 2004, Park and Suh 2005, Kim and Yeom 2006, An 2008, Park et al. 2010, Park et al. 2011, Park et al. 2013, Daegu Regional Environmental Office 2012, Daegu Regional Environmental Office 2016, Choi et al. 2015, Park et al. 2017. Here, we report 23 newly-identified and unrecorded species and three undetermined species on the Island and provide an updated database.

Sampling methods
Study extent: Between September 2017 and September 2018, we collected samples from Dokdo four times, once each at Anyongbok-gil, Ulleung-eup, Ulleung-gun and Gyeongsangbuk-do, Korea (131°52'03.2''E, 37°14'27.2'N), using sweeping, beating, brandishing, black light traps and pitfall traps. The survey was divided into East (Dongdo) and West (Seodo) using terrain isolation (Fig. 1). Sampling description: In Dongdo, we performed sample collection along the slope leading from the marina, through the KCG facility and then to the old marina. In Seodo, we performed sample collection along a very steep slope leading to the fishermen's dormitory. Seodo has less vegetation distribution compared to Dongdo.
Collected specimen samples were stored in 70% ethanol in conical tubes. They were then transferred to the Animal Systematics and Taxonomy Laboratory and Pest Control Laboratory at Kyungpook National University, Korea. The samples were identified using the national species list of Korea and other references (National Institute of Biological Resources 2019, Chérot and Malipatil 2016, Yasunaga 2017, Göllner-Scheiding 1976, Slater and Zheng 1984, Siwi and Doesburg 1984, Malenovský 2013, ZHANG et al. 2013, Viraktamath 1979, YOO et al. 2008, Yang et al. 2014, Kurahashi and Samerjai 2018, Suh and Kwon 2017a, Suh and Kwon 2017b, Bourquia et al. 2019, Vane-Wright and Hughes 2007, Ang and Meier 2010.

Database update:
We created a new checklist by adding 23 newly-confirmed insect species with reference to the previous reports and compiled it into a database. The data have been registered in the Global Biodiversity Information Facility (GBIF).

Geographic coverage
Description: The survey was divided into Dongdo and Seodo.
Coordinates: 37-14 Latitude; 131-52 and 131-51 longitude.  (Fig. 2). In addition to the 23 previously unrecorded species on Dokdo, three undetermined species were identified to the genus level: two Empoasca species in the Family Cicadellidae and one Sisyra species in the Family Sisyridae. Furthermore, five of the 23 previously unrecorded species and one of the three unidentified species belong to new families, adding a total of six newly-added families to the Dokdo Insect Database. Finally, we generated an updated database of insect fauna on Dokdo that contains 10 orders, 81 families, 188 species and 23 unidentified species (Table 1). Amongst the 23 previously unrecorded species on Dokdo, B. diminuta was first discovered in Korea and the remainder of this species has been recorded in the Korean Peninsula. In addition, C. circumscriptus, a blood-sucking insect known for being extremely annoying to the KCG and residents of Dokdo, has been identified for the first time in Dokdo, using a black light trap with dry ice.

Taxonomic coverage
The 23 undetermined species that have been identified up to the genus stage are classified as unrecorded or new species in Korea. Due to geographical characteristics, the study of these insects is considered to be very important for understanding the biodiversity of Dokdo Island.

Conflicts of interest
The authors declare that there are no conflicts of interest.