Brachymna tenuis Stål, 1861 (Hemiptera: Pentatomidae), a new invasive bamboo pest in Korea with notes on insects associated with bamboos

Abstract Background We report first observations of the invasive bamboo pest, Brachymna tenuis Stål, 1861 in Korea as the first species of Brachymna Stål, 1861 (Pentatomidae) reported from the country. New information Comments on its pest status and distribution are provided. General information on this bamboo-feeding insect in Korea is analysed and provided for the first time.


Introduction
Bamboo grows in the tropics and subtropics and has received increasing attention because of its fast-growing nature, social usage and industrial demand, for example, foods, crafts, building material and energy resource . In Korea, there are 18 species of bamboos distributed mostly in the southern part of the country (Kong 1985). Amongst them, eleven dominant bamboo species either occur naturally or are planted and they occupy more than 22 thousand hectares ). The number of insects that feed on bamboos is estimated to be more than 1200 insects in the world (Shu and Wang 2015). The numbers may vary depending on the country and province, ranging from 97 to 244 insect species feeding on bamboos in China (Huang and Liu 2006, Zhao et al. 2006, Zhang and Zuo 2015. In Korea, the review of the entire bamboo-feeding insects has never been done before. Bamboo pest, Brachymna tenuis Stål, 1861 and its synonym, Balsa extenuata Walker, 1867 were described from Hong Kong and the Chinese mainland, respectively and subsequent records were made from twelve Provinces in China (Hoffmann 1932, Hsiao and Zheng 1977, Rider et al. 2002, Aukema and Rieger 2006, Huang and Liu 2006, Zhao et al. 2006, Zhang et al. 2008, Zhang and Zuo 2015, Japan (Aukema and Rieger 2006, Ishikawa et al. 2012, Tanaka 2013, Tanaka 2014, Igasaki 2016, Igasaki 2017, Igasaki 2018, Kanetada 2017 and Taiwan (Taiwan Encyclopedia of Life 2018). Recently, the first three authors observed somewhat large, exotic, invasive, bamboo-feeding stink bugs from southern Korea, which had never been recorded. The aim of the present paper is to report new records of invasive bamboo pest Brachymna tenuis from Korea, to discuss the distribution of the species and to provide, for the first time, a list of bamboo-feeding insects in Korea, based on a literature review.

Materials and methods
Surveys were conducted in natural and cultivated bamboos, located in the southern Provinces of South Korea (Gyeongsangnam-do and Jeollanam-do) in 2020. Adults and nymphs were observed by visual inspection. The specimens were morphologically identified using the reference books by Lin and Zhang (1993) and Ishikawa et al. (2012). Photographs of habitus were taken using a DSLR camera (Nikon D500, D7100, Nikon 60 mm Micro). The plant names follow The Plant List (2016). The examined specimens were deposited in the College of Agriculture and Life Science, Seoul National University (SNU), Seoul and the private collections of the authors.

Diagnosis
According to Lin and Zhang (1993), Brachymna tenuis resembles B. castanea. It differs from the latter by the yellowish-brown body colour (Fig. 1a, b) (ferruginous in B. castanea) and the pygophore bearing dentate postero-lateral processes that are obtusely curved from the postero-ventral margin (

Distribution
China, Japan, Taiwan and South Korea (new record).

Analysis
Provisionally, 61 species are associated with bamboos in South Korea with the majority of the insects belonging to sap-sucking Hemiptera (52.46%). They are mainly polyphagous and include mostly aphids and scale insects. Lepidoptera are the second largest group, making up 31.15% of the total; these include many defoliators, leaf-rollers and one bamboo-shoot cutworm (Bambusiphila vulgaris). Coleoptera are the third order, with 14.75% of the species, which include deleterious bamboo borers, such as Chlorophorus annularis (Cerambycidae) and Dinoderus spp. (Bostrichidae). The bamboo-feeding sawfly Tenthredo nigropicta (Tenthredinidae) is included in the list as the only member of Hymenoptera (Table 1). Demobotys pervulgalis (Hampson, 1913) Bamboo (Shu and Wang 2015) Leaf-roller (Shu and Wang 2015) Sinibotys butleri (South, 1901) Phyllostachys spp.  Possibly leafroller (not confirmed) Sinibotys evenoralis (Walker, 1859) Bambusa spp., Phyllostachys spp., Pleioblastus spp. (Kim and Lee 1986, Haoje et al. 2002, Robinson et al. 2010 Leaf-roller (Kim and Lee 1986) Erebidae The invasive stink bug was identified as Brachymna tenuis Stål, 1861 (Hemiptera: Heteroptera: Pentatomidae) that is recorded in South Korea for the first time (Figs 1, 2). It is one of the most important pest species feeding on bamboo branch and culm. A heavy infestation may cause defoliation, wilting of young shoots and branches and even death of the culm (Shu and Wang 2015). The species is polyphagous and is reported from various bamboo species in South Korea, for example, Phyllostachys elegans McClure and Semiarundinaria densiflora (Rendle) T.H.Wen (Poaceae). Sometimes, it feeds also on Miscanthus sinensis Andersson (Poaceae). Numerous adults and nymphs were observed on planted bamboos in the urban areas of Korean southern provinces. The species was also observed in Busan-si, Gwangyang-si and Yeosu-si without detailed collection data (Fig. 3).

Discussion
In East Asia, Brachymna tenuis is widespread in many tropical and subtropical Chinese Provinces (Anhui, Fujian, Guangdong, Guizhou, Henan, Hong Kong, Hubei, Hunan, Jiangsu, Jiangxi, Sichuan, Yunnan and Zhejiang) (Hoffmann 1932, Hsiao and Zheng 1977, Rider et al. 2002, Aukema and Rieger 2006, Huang and Liu 2006, Zhao et al. 2006, Zhang et al. 2008, Zhang and Zuo 2015 and it has been reported from subtropical Japanese Prefectures (Ryukyu, Oita and Yamaguchi) (Aukema and Rieger 2006, Tanaka 2013, Tanaka 2014, Igasaki 2016, Igasaki 2017, Igasaki 2018, Kanetada 2017 and Taiwan (Taiwan Encyclopedia of Life 2018). In Japan, after the first observation of the species in 1997 (Ishikawa et al. 2012), recent range expansion to the north and abnormal outbreaks have been observed (Tanaka 2013, Tanaka 2014, Igasaki 2017, Igasaki 2018. In South Korea, it was first found in 2020 on planted bamboos in the southern provinces (present paper). Since 2010, the first three authors carried out extensive field monitoring research a b c Figure 2.
a: Third instar nymph. b: Fourth instar nymph. c: Fifth instar nymph. mainly on terrestrial Hemiptera, but they had not seen any Brachymna species before. As the adults of the species have been found along with numerous nymphs in restricted areas, we concluded that the species was very recently introduced and established into the country. Little is known about the viability and host plant usage of the species in South Korea. More attention is required in order to limit the further spread of the pest species.