Insect fauna including unrecorded species in Ulleungdo, South Korea

Abstract Background Ulleungdo harbours a unique ecosystem owing to its isolation from the mainland alongside its maritime climate. The island, formed via volcanic activity, is the largest island in the East Sea of Korea and retains a primeval forest. The ecosystems are being destroyed owing to increasing human activity on the island. Therefore, through the investigation of the insect fauna of Ulleungdo, we tried to provide information that can be the basis for understanding the island ecology of Ulleungdo. This survey was conducted four times between April and October in 2020 at Seonginbong. New information The findings of the survey regarding insect fauna at Seonginbong, Ulleungdo included 10 orders, 105 families, 216 genera and 212 species, of which 12 families, two subfamilies, 13 genera and 74 species were previously unrecorded. The data have been registered in the Global Biodiversity Information Facility (GBIF; www.GBIF.org).


Introduction
In general, island ecosystems are isolated and have limited resources, which consequently results in simpler food chains than those in inland ecosystems (Polis et al. 1997). Therefore, the interrelationship between predators and prey in island ecosystems can be compared more clearly than in inland where the relationship is complex (Simberloff 1974). In addition, the biota of island regions is expectedly distinct from inland biota as the former is affected by oceanic climates, unlike inland ecosystems, which are affected by continental climates. However, islands surrounded by oceans are vulnerable to the effects of climate change, such as rising sea levels due to global warming, changes in temperature and precipitation, increasing incidences of unpredictable tropical cyclones and El Nino (Ahn 2011). In case such climate change continues in Korea, boreal plants in temperate regions in the Northern Hemisphere are expected to become extinct, whereas the distribution of temperate plants is expected to expand rapidly (Kim et al. 2022). Furthermore, human activities, such as island development and the influx of foreign species have added to the threat of biodiversity reduction in island ecosystems (Veron et al. 2019). For this reason, island ecosystems require constant monitoring.
Ulleungdo and its subsidiary islands are the sole island areas located in the East Sea of Korea, thereby representing the only island ecosystem in the East Sea. Ulleungdo is located in the southwest of the East Sea (37°30'N, 130°52'E) and at a distance of 130 km from the Korean Peninsula. The island was formed via volcanic activity and is an ocean island that has never been connected to land. Seonginbong (984 m) is located at the centre of Ulleungdo. The primeval forest of Seonginbong is an ecologically stable climax forest and includes plants that are unique to Ulleungdo (Cho et al. 1993).
An investigation about the insect fauna of Ulleungdo was first conducted by Cho, who reported four families and 16 species of butterflies (Cho 1929). Subsequent studies have identified various taxa, including 95 families and 345 species (Kim 1971), 125 families and 574 species (Lee and Kwon 1981), 141 families and 691 species (Kwon et al. 1996), 154 families and 828 species (Lee and Jung 2001), 153 families and 841 species (Lee et al. 2006), 81 families and 242 species (Lim and Lee 2012) and 96 families and 433 species ). According to , a total of 18 orders, 179 families and 1,177 species of insects were recorded on Ulleungdo during the survey period from 1929 to 2013. In addition, a recent survey by the National Institute of Biological Resources (National Institute of Biological Resources 2021b) involving aquatic insects in Ulleungdo identified 32 species of aquatic insects, including Ephemeroptera, Trichoptera and Plecoptera. Given its distinct geography as an island region, Ulleungdo has poor accessibility. In addition, owing to severe weather disturbances, such as typhoons and high waves, periodic insect fauna surveys have been difficult to conduct. Although there have been several surveys in the past, the overall insect fauna survey has not been carried out since the study of  and the most recent survey ( National Institute of Biological Resources 2021b) was not a general survey of insect fauna, but the aquatic environment. Therefore, there is a need to update the insect fauna data and it is possible that there are still many unrecorded insect species on Ulleungdo. Herein, a comprehensive survey of the insect fauna inhabiting Seonginbong in Ulleungdo was conducted using different collection methods and a species list, including that of previously unrecorded species, was prepared.

Sampling methods
Description: Throughout 2020 (April, July, August and October) four expeditions were carried out to collect data at Seonginbong (37°29'52.81''N, 130°52'03.72''E) in Ulleungdo (Fig. 1). Fifteen collection points were designated along the altitude of Seonginbong and four collection methods were used: light trap, molasses traps, pit-fall traps and sweeping.
Sampling description: Light trap was conducted at collection point 1 (lowland), collection point 6 (midland) and collection point 15 (highland). After fixing a tripod (height: 1 m) inside a tent (height: 1.7 m), a 400 W high-voltage mercury lamp was connected with a tripod. Samples attracted by ultra-violet light from a mercury lamp were collected by a handcollecting method. Light trap was operated after 20:00 h when the sun had completely set and it was operated for about 1 hour at each point. Molasses traps were conducted at all 15 collection points. The distance between each collection point is about 50 m. Tissue soaked in attractant was put in a mesh net and hung on a tree. The attracted samples were collected by a hand-collecting method. Molasses, made by mixing sugar, glacial acetic acid and grape juice, was used as an attractant (Scheller 1984, Singh et al. 2013, Dar et al. 2020. Molasses traps were installed at 15 points by altitude and maintained for 24 hours. Insects attached to the traps were collected one day after traps installation. Pit-fall traps were also conducted in all 15 collection points. A plastic cup (diameter: 9.2 cm; height: 13.5 cm; volume: about 475 cm ) containing an attractant was buried at the same level as the ground. Molasses, pork and octopus were used as attractant and, in the case of molasses, the same molasses as the molasses trap were used. Each attractant was separately put into a plastic cup and three types of pit-fall traps were installed at regular intervals of 3 m. Three pit-fall traps were installed for each attractant at one point and a total of 45 traps were installed at 15 points. Pit-fall traps, like molasses traps, installed at 15 points by altitude, were maintained for 24 hours from the time of installation and then the insects in the traps were collected next day.
Sweeping was conducted continuously while going up from collection site 1 to 15 and samples were collected by sweeping an insect net (pole: 2.5 m; net diameter: 50 cm; net length: 110 cm). Sweeps were performed at least 50 times for each point. The samples collected in the insect net were transferred into the conical tube using an insect aspirator. Sweeping was carried out while climbing the Seounginbong during the daytime.
Collected samples were stored in conical tubes containing 70% ethanol. Large insects, such as some Lepidoptera species, were stored in glassine paper and frozen to prevent damage. Afterwards, the collected samples were moved to the Animal Systematics & Taxonomy Laboratory at Kyungpook National University. The species were identified by referring to various references (Hardy and Takahashi 1960, Shin 2001, Park et al. 2012, Cho 2015a, Cho 2015b, Cho 2015c, Jang et al. 2015, Baek 2016, Dong 2017, National Institute of Biological Resources 2021a). In order to confirm that the identified species are unrecorded species of Ulleungdo, they were checked through the references which including a list of insect species previously investigated on Ulleungdo (Kim 1971, Lee and Kwon 1981, Lee et al. 2006, Lim and Lee 2012).

Database update:
A list of 212 insect species collected from Ulleungdo in 2020 was prepared and the data were registered in the Global Biodiversity Information Facility (GBIF).

Geographic coverage
Description: This survey was conducted at Seonginbong, Ulleungdo.

Column label
Column description taxonID An identifier for the set of taxon information (data associated with the Taxon class).
scientificName Full scientific name. taxonRank The taxonomic rank of the most specific name in the scientificName. kingdom The full scientific name of the kingdom in which the taxon is classified. phylum The full scientific name of the phylum or division in which the taxon is classified. class The full scientific name of the class in which the taxon is classified. order The full scientific name of the order in which the taxon is classified. family The full scientific name of the family in which the taxon is classified. genus The full scientific name of the genus in which the taxon is classified. specificEpithet The name of the first or species epithet of the scientificName.

Results and Discussion
This survey identified 10 orders, 105 families, 216 genera and 212 species of insects (Table 1, Fig. 2). This list includes 12 families, two subfamilies, 13 genera and 74 species that have not been previously recorded on Ulleungdo.  The largest number of unrecorded species belonged to Coleoptera (28 species), followed by Lepidoptera (14 species), Diptera (13 species), Hemiptera (9 species) and Hymenoptera (8 species). Additionally, one previously unrecorded species each of Dermaptera and Orthoptera were found. In Diptera, 11 families, one subfamily and seven genera that have not been classified to the species level were identified. If all of these were to be identified at the species level, at least 32 unrecorded species would be recorded.
Furthermore, Diptera appears to be the taxon with the highest possibility of unrecorded species being discovered. In the Braconidae family of Hymenoptera, Pyralidae family of Lepidoptera and Trichoptera, identification to the species level was difficult owing to the lack of experts. If accurate identification could be achieved, further previously unrecorded species would be identified.
The unrecorded species identified in this survey include pests, such as Aspidobyctiscus lacunipennis and Euplexia lucipara, which infest crops, such as grapes and beans and Newly-recorded insect species from Seonginbong, Ulleungdo in 2020. Aa. Bostrichidae sp.; Biston robustum, Pachyligia dolosa and Patania chlorophanta, which infest forests, such as oak, camellia and persimmon , National Institute of Biological Resources 2022, Korea Forest Service 2022). The results of this survey highlight the necessity of obtaining the latest insect fauna data in Ulleungdo, updating the insect fauna through continuous monitoring, preventing the introduction of pests and implementing efforts to minimise damage to crops and forest resources.

Conflicts of interest
The authors have no conflicts of interest to declare.