Native or Invasive? The Red-Haired Pine Bark Beetle Hylurgus ligniperda (Fabricius) (Curculionidae: Scolytinae) in East Asia

: The red-haired pine bark beetle, Hylurgus ligniperda (Fabricius), is one of the most rapidly spreading invasive forest insects. Originally from Eurasia, it has subsequently been introduced to Oceania, North, and South America. Yet, the status of H. ligniperda in East Asia is ambiguous. Here, investigation and analysis were conducted on the beetle in China, South Korea, and Japan. New occurrences in China and South Korea were recorded by ﬁeld surveys and the expansion of H. ligniperda spreading in East Asia was analyzed. The results show that H. ligniperda is likely an invasive species in East Asia, initially invading Japan, then South Korea. Now it has invaded and successfully colonized Shandong province, China. Furthermore, the species has spread rapidly and it is now widely distributed in South Korea and Japan.


Introduction
The red-haired pine bark beetle, Hylurgus ligniperda (Fabricius), is a well-known forest insect that colonizes the phloem of pine species [1,2]. It can attack stumps, freshly cut logs, and stored timber [1]. In some areas, H. ligniperda has become a predominantly root-dwelling species that usually bores into the host through the soil. Overwintering adults have been observed feeding on the root collars of 1-2-year-old seedlings [3,4].
Usually H. ligniperda does not kill trees and is considered a secondary pest. Part of the damage is mechanical and direct through brood galleries and feeding tunnels formed under the bark. Decay or sap stain fungi can also be introduced indirectly, which can reduce the quality and value of logs [5,6]. Blue stain fungi, Leptographium spp. (Ascomycota: Ophiostomatales), were found transmitted from beetles' galleries into the wood [3,7,8]. In New Zealand, the main damage by H. ligniperda in plantation forests is from wood-staining and decay fungal associations that enter with the adults into the brood galleries, and as a quarantine pest that may necessitate treatment of export logs and timber, which greatly increases the cost of exports [5].
Previously, when researchers recorded the original distribution, it included Europe, Russia, the Mediterranean area, and the nearby Atlantic Ocean islands. It was also reported as introduced to South Africa, Japan, South Korea, Sri Lanka, Australia, New Zealand, USA (NY and CA), Brazil, Uruguay, and Chile [1,[9][10][11][12]. It should be noted that the distribution of H. ligniperda in East Asia is ambiguous in literature. Wood and Bright [9] recorded the distribution of H. ligniperda as "Asia ('Manchuria' in China/ Japan)". Hoebeke [13] wrote "It is native to Eurasia and north Africa" and "introduced to Japan". Kim [8] only stated "It is native to Europe" without referencing Asia. CABI [12] listed that "native to Asia (China/Turkey)" and "Japan is invasive", which is reference to a misquotation of " Wood and Bright (1992)". So, whether H. ligniperda is native to Asia is still unclear.
In this paper, we aim to clarify the history of recorded collections and known records of H. ligniperda in East Asia (Japan, South Korea, and China) using new survey results. Our aim is to determine the status of the insect in East Asia based on the limited collection data. We tested whether the museum specimens and the new records conform to the scenario of native but rarely reported insect (old samples, widely distributed), or whether they conform to the scenario of recent introduction and rapid spread.
We present new records in China and South Korea. The updated distribution in East Asia will contribute to status as an introduced or native species that directly relates to its control and management.

Materials and Methods
The new occurrences in China and South Korea were recorded by field surveys from 2013 to 2020. In China, traps were set initially to monitor pine pests in several provinces ( Table 1). The lures include pine resin, α-pinene, monochamol, ipsenol, or ipsdienol. After H. ligniperda was first found in Shandong, two wood borer pest surveys that focused on damage of pine wood nematode Bursaphelenchus xylophilus were processed in Yantai and Weihai. Coincidently, more H. ligniperda were found. All those records were included. In Korea, nine sites were surveyed with a lure using a funnel trap. The lures were either alcohol + α-pinene or ipsenol + monochamol. The known localities of Hylurgus ligniperda in Japan were gathered from literature, herbarium records, and observations. The new collected beetles were firstly identified by comparing the external morphological features with published articles [11] and reference collection specimens from the Bark Beetle Academy (http://ambrosiasymbiosis.org/academy, accessed on 5 May 2021). Specimens from China and Korea are deposited at the University of Florida (USA), Shandong Agriculture University (China), and Research Institute of Forest Insect Diversity (Korea). The annotated maps were created in ArcMap 10.4.1.

Results and Discussion
Eight new sites of the H. ligniperda in Asia were included, three from China and five from Korea (Table 1).
All three sites in China are located within Shandong province (Taian, Yantai, and Weihai city; Figure 1, Supplementary Material Table S1). The earliest record is from Culai Mt., Taian, Shandong in 2019. Bottle traps with lure (slash pine resin) were set in the pine plantation. The host plant of H. ligniperda in Culaishan Forest Farm, Taian is unclear as the beetles were only captured in lure traps. Whereas, there are four pine tree species present at the farm, Pinus tabuliformis Carrière, P. thunbergii Parl., P. densiflora Sieb. et Zucc., and P. armandii Franch. One more sample was found from an unknown fallen branch in nearby mountain in 2020 (Supplementary Material Table S1). In Yantai and Weihai, all samples were collected from stumps of P. thunbergia, which are all under the attack of pine wood nematode. More than 15 stumps were peeled and dissected, and all were infested by H. ligniperda. Reports of H. ligniperda attacking these native trees in Shandong constitute the first natural occurrences recorded in China. The known localities of Hylurgus ligniperda in Japan were gathered from literature, herbarium records, and observations.
The new collected beetles were firstly identified by comparing the external morphological features with published articles [11] and reference collection specimens from the Bark Beetle Academy (http://ambrosiasymbiosis.org/academy, accessed on 5 May 2021). Specimens from China and Korea are deposited at the University of Florida (USA), Shandong Agriculture University (China), and Research Institute of Forest Insect Diversity (Korea). The annotated maps were created in ArcMap 10.4.1.

Results and Discussion
Eight new sites of the H. ligniperda in Asia were included, three from China and five from Korea (Table 1).
All three sites in China are located within Shandong province (Taian, Yantai, and Weihai city; Figure 1, Supplementary Material Table S1). The earliest record is from Culai Mt., Taian, Shandong in 2019. Bottle traps with lure (slash pine resin) were set in the pine plantation. The host plant of H. ligniperda in Culaishan Forest Farm, Taian is unclear as the beetles were only captured in lure traps. Whereas, there are four pine tree species present at the farm, Pinus tabuliformis Carrière, P. thunbergii Parl., P. densiflora Sieb. et Zucc., and P. armandii Franch. One more sample was found from an unknown fallen branch in nearby mountain in 2020 (Supplementary Material Table S1). In Yantai and Weihai, all samples were collected from stumps of P. thunbergia, which are all under the attack of pine wood nematode. More than 15 stumps were peeled and dissected, and all were infested by H. ligniperda. Reports of H. ligniperda attacking these native trees in Shandong constitute the first natural occurrences recorded in China.  Park et al. [11] first recorded Hylurgus ligniperda in Korea based on deposited specimens in several institutes. After checking the survey results for wood-boring beetles, more samples were found from lure traps in five locations at various sites between 2013 to 2020 (Table 1, Supplementary Material Table S1). In areas such as Boryeong-si in 2013, Inje-gun in 2017 and 2019, Yanggu-gun in 2017 and 2020, Sangju-si in 2018-2019, and Chuncheon-si in 2018 and 2020, a total of 252 H. ligniperda specimens were captured. In South Korea, the suspected first individual was captured in Jeollanam-do in 1999 [11]. Before 1999, several forest surveys had been conducted with a focus on bark beetles in local fauna, but no H. ligniperda were found [17,18]. The lack of collections during this period is problematic. Possible scenarios include the beetle not being present, the beetle being undetected at low populations, or the survey methods may not be ideal for capture, such as seasonality or flight time. After 1999, H. ligniperda quickly made a spread to nearby regions in Korea, suggesting an expanding nascent population was present at this time.
Because there are only limited reference sequences in NCBI and we only have sequences from Asian samples, we do not provide the genetic population analysis at this time. However, Chinese samples are 100% identical to Korean samples in COI with the closest matching sequence on NCBI being H. ligniperda from New Zealand (COI: HM002621; 99.75% similarity). Our results show that the populations in China and Korea are closely related to those in New Zealand, and all Asian populations may have the same origin.
Biotic invasions pose major threats to agriculture, forestry, natural environments, and public health. With the globalization of the world's economy and a drastic increase of human activities, the number of invasive species is also increasing [32]. Scolytines feature prominently among invasive species because they are easily transported through international trade inside wooden products and wood packaging materials in which they are concealed and protected [33,34]. Between 2003 to 2016, H. ligniperda was the second most frequently intercepted scolytine in ports of China, with 10,199 interceptions [35]. A worldwide survey of pine bark beetles on several continents also indicated that H. ligniperda was one of the most abundant and widespread invasive species [36]. Considering that there are several big ports managing timber import in Shandong, it is possible that H. ligniperda invaded China through international timber trade or contaminated wooden packages. However, it cannot be ruled out that it naturally spread to Shandong province through South Korea as the distance between both is only 310 km. The molecular tools in this survey show an identical match for COI between the China and South Korean samples. While important, it should be noted this result is based on a limited sample size (n = 5). More precise genetics methods, such as Single-nucleotide polymorphisms (SNPs) on specimens collected from the invaded areas and native ones, would help to clarify the invasive process and pathways.
Hylurgus ligniperda was first recorded in New Zealand in 1974. Three years later, it was found throughout New Zealand, including travelling between the two main islands [2]. To date, H. ligniperda has been one of the most highly abundant exotic wood borers and bark beetles in New Zealand [37]. Chase and Kelly [38] noted that the contributing factors to H. ligniperda's invasion success could be their effective long-distance dispersal, and it can mate with siblings before dispersal to increase the probability of colonization success. The rapid spread also occurred in other introduced areas, such as Japan, South Africa, and South America [12]. The survey data show that H. ligniperda spread rapidly in South Korea between 2010 and 2019. Unfortunately, the recent survey area of H. ligniperda in China is only limited to some parts of Shandong Province. The local government is eager to control and investigate it in more regions. Given the number of localities already occupied by the species in China, it can be considered established.
Wood and Bright [9] recorded H. ligniperda from "Manchuria" in China. Historically, "Manchuria" has often referred to Northeast China, including three provinces of Heilongjiang, Jilin, and Liaoning, as well as the current border area with Russia. "Manchuria" has also been called "Guandong" in Chinese. We speculate that this is the origin of the CABI's misquotation "Guangdong is present", because there is no record of the occurrence of H. ligniperda in "Guangdong" in the CABI reference list and other literature. Tsai and Li [39] [9] is likely erroneous due to difficulties in translation or a record of an adventive specimen intercepted at a port.
In recent years, several economically significant Scolytinae invaded China, such as Dendroctonus valens (LeConte, 1860), Xyleborus affinis (Eichhoff, 1868), Xyleborus ferrugineus (Fabricius, 1801), Hypothenemus hampei (Ferrari, 1867), Ips calligraphus (Germar, 1824), and Ips grandicollis (Eichhoff, 1868) [43][44][45][46][47]. Many of the recent invasions are attributed to the increased global trade in timber, as China has become the second largest timber importer in the world [48]. There are likely more invasive scolytines yet to be detected or intercepted in China. It is urgent to carry out a national surveillance program for invasive scolytines in China, which can provide the basis for subsequent prevention and control.

Conclusions
Investigation and analysis showed that the previous record of the occurrence of H. ligniperda in China was likely misplaced; new observations suggest it has recently invaded and successfully colonized parts of Shandong Province, China. In South Korea, it has spread rapidly in recent years, and its current distribution effectively covers the majority of South Korea. In Japan, its distribution has covered the entirety of Honshu Island due to decades of colonization. The reporting of the East Asian invasion by H. ligniperda has been confused by semantic issues. More measures should be taken to control the rapid spread of this pest in Asia.