The Asian bamboo borer Chlorophorus annularis is a beetle species that has been introduced in many countries globally. Originating in Southeast Asia, it can now be found in the Americas, South Africa, the Middle East, Australasia and Europe. The literature record of the species in Europe consists of findings of single individuals usually associated with imported bamboo products. A general European effort in surveying C. annularis was never undertaken, since the overall scientific consensus was that the species cannot establish here. Yet, recent records in Genk, Torhout (Belgium) and in Hamburg (Germany) do not seem directly associated with a recently imported product and hence may indicate otherwise. Such a shortfall in recording commonly imported, potentially invasive species may be counteracted through citizen science initiatives, allowing for continuous, high density monitoring. In this paper we present thirteen new records of the species from five European countries, including two new country records, mostly going back to interested citizen scientists.

bamboo, Cerambycidae, Coleoptera, Hamburg, insect, invasion biology, neozoa, pest organism

Non-native species, accidentally or purposefully introduced organisms, represent one of the big challenges in a globalized world (Kenis et al. 2009; Simberloff et al. 2013; Bellard et al. 2016; Bradshaw et al. 2016), with constantly rising numbers of newly recorded species (Hulme 2009; Seebens et al. 2017). These species, while often barely recognized, may represent severe economic and ecological threats (e.g. as agricultural pests, ecological competitors or predators of native species). However, despite their potentially high importance, surveying non-native species is still only performed for a limited number of highly invasive species, as it is time consuming and expensive. Including the general public in such surveying activities through citizen science initiatives and projects, or taxonomic interest groups and websites, may be a viable alternative (Gallo and Waitt 2011; Chandler et al. 2017). This approach has been proven to be powerful, for example, in demonstrating the decline of monarch butterflies (Schultz et al. 2017), and changes in ladybird populations (Gardiner et al. 2012) and has also been used to detect and monitor non-native species (Delaney et al. 2008; Crall et al. 2010, 2011).

While large invasive species, such as mammals, birds and fish, are detected more easily, smaller arthropod species often remain unspotted for some time after their introduction (e.g. Wolter and Röhr 2010; Fischer et. al. 2016). Nevertheless, arthropods, and especially insects have high invasion potential and can often be detrimental pests (Kiritani and Yamamura 2003). Insects are frequently transported with raw materials, and agricultural products, or living plants and plant material. One of the groups specifically commonly introduced with plants and wood are the longhorn wood boring beetles of the family Cerambycidae (Eyre and Haack 2017).

The family comprises more than 40,000 described species worldwide, which are all phytophagous, xylophagous or saproxylophagous. Fortunately, only some species are true pests of economic importance. In the past, only species with a long life cycle and species capable of lasting several generations in the same host material could bear the long times of transportation and emerge in the countries of importation to generate a possible invasion. Hylotrupes bajulus (Linnaeus, 1758) (Cerambycinae, Callidiini) and Nathrius brevipennis (Mulsant, 1839) (Cerambycinae, Nathriini) were probably two of these invasive pioneers. A first synthesis of imported beetles in Europe was done by Duffy (1953). The growth of international trade, the reduction of the length of transport and the increase in diversity of potential vectors of longhorn beetles since the 20^th century allowed an increase in the number of individuals and species accidentally imported, as shown by the numerous interceptions, introductions and establishments reported by national and international organizations (e.g. EPPO (in European Union), APHIS (in United States of America), AQIS (in Australia) and Biodiversity (in New Zealand), over the past four decades. Despite international sanitary and control measures, many new potential invasive cerambycids reach foreign areas on a regular basis (e.g. Cocquempot 2007; Cocquempot and Lindelöw 2010). While interceptions have become common, sometimes introductions may occur unrecognized, but rarely species are able to establish. Within the longhorn beetles, the Asian longhorn beetle (Anoplophora glabripennis (Motschulsky, 1853)) (Lamiinae, Monochamini) is among the most feared. The species originates in Central Asia, but has been introduced in North America and Europe, where it attacks a diverse range of trees (Meng et al. 2015). Other introduced cerambycids include the Citrus longhorn beetle (Anoplophora chinensis (Forster, 1771)), or the Red-necked longhorn beetle (Aromia bungii Falderman, 1835) (Cerambycinae, Callichromatini). Newly imported cerambycid species are constantly reported (e.g. Friedman et al. 2008; Burmeister et al. 2012; Cocquempot et al. 2015a, b; Sarto i Monteys and Torras i Tutusaus 2018).

One of the species of longhorn beetles that is more frequently intercepted is the Bamboo borer Chlorophorus annularis (Fabricius, 1787) (Cerambycinae, Clytini). This beetle originally inhabits temperate to subtropical regions of Southeast Asia (native range: Cambodia, China, India, Indonesia, Japan, Korea Laos, Malaysia, Myanmar, Nepal, New Guinea, Philippines, Singapore, Sri Lanka, Taiwan, Thailand and Vietnam (Monné 2005; Cocquempot 2007; Friedman et al. 2008). It has been reported to attack species of fourteen different plant families: Aceraceae, Anacardiaceae, Betulaceae, Dipterocarpaceae, Hamamelidaceae, Juglandaceae, Lamiaceae, Malvaceae, Mimosaceae, Paeoniaceae, Poaceae, Rosaceae, Ulmaceae, Vitaceae (for genera and species see Monné 2005). Most notable is the damage the species is causing to bamboo, which is the main product it is contaminating outside of its natural range. So far, it has been intercepted in the Middle East (Israel: Friedmann et al. 2008), South Africa (Suma and Bella 2018), South America (Brazil: Monné 2005; Uruguay: Suma and Bella 2018), North America (Unites States: Mattson et al. 1994; Eyre and Haack 2007; Canada: NAPPO 2014), Australasia (Australia: Hanks et al. 1997; New Caledonia: Suma and Bella 2018; New Zealand: MPI 2013) and ten European countries (Cocquempot 2007; Suma and Bella 2018). The first European specimen was captured in the United Kingdom in 1924, followed by records in Finland and Czech Republic in 1936 and subsequently in Germany, Austria, Spain, Hungary, France, Denmark and Italy (for map and references see Fig. 2 and Table 1). So far, the species is only regarded as invasive in Spain with the potential to get established in other Mediterranean areas as well (Vives 1995; Cocquempot and Lindelöw 2010). Here we report Chlorophorus annularis as newly intercepted to the Netherlands and Belgium, as well as the first traceable record for Denmark. For Czech Republic, France, Germany and the United Kingdom, new records are presented, mostly based on records from citizen scientists.

We here present thirteen new records of Chlorophorus annularis from seven European countries including two new country records displaying the wide spread of this commonly overlooked non-native species. Most records were provided by citizen scientists, clearly displaying the impact of taxonomic interest forums and recording platforms such as iNaturalist, iRecord and waarneming.nl to provide data for rare and non-native species. Other social media platforms, such as Facebook, also provide an invaluable tool in biological recording of invasive species, as many records are sent into entomology and nature-themed groups, where both amateurs and scientists help in identifying them. The awareness raised by these citizen science tools may, in the future, even help to act as an early warning system for invasive species.

Despite custom controls at import sites, like harbors and airports by national plant protection services and despite international standards for the importation of products and wood packaging, more and more invasive species arrive in Europe and are intercepted (see all Pest alerts from European Plant Protection Organization (EPPO/OEPP)). However, even more accidental imports remain undetected or are discovered only years after the introduction, potentially facilitating the establishment of detrimental species. This may also be true in the case of C. annularis, which resembles local species across Europe and hence may often be mistaken and not recognized. Therefore, the number of specimens reaching Europe every year likely remains grossly underestimated. This may also explain, why the species so far has not been reported from the Scandinavian Peninsula, Balkan countries and European countries east of Germany (Czechia, Austria and Hungary). Similarly, Portugal, Switzerland and Ireland in western and Central Europe currently lack records. Yet, it remains likely that the species is also imported into these countries via the bamboo trade. While the species has been intercepted in many European countries, it is mostly represented by single or a few individuals, which are clearly associated with the substrate they were imported with, and hence are likely not established. However, current records from Genk, Torhout (Belgium) and Hamburg (Germany), where the species was found without direct association to an imported product, may indicate that C. annularis could establish in European countries other than Spain. However, due to a lack of data it is currently not predictable where. Furthermore, climate change may facilitate future establishment, where host plants are available. These conditions could be met in the major cities of southern Europe. Therefore, recent records in Sicily and in the Hérault and Var departments in southern France are concerning and should be further surveyed. One tool to do so may be directed citizen science efforts as recently done in several European countries, for example for the Asian hornet Vespa velutina or for non-native mosquitoes (Walther and Kampen 2017).

In order to use the power of citizen science for the monitoring of non-native species more effectively, two approaches may be specifically promising. On the one hand, specialized platforms introducing non-native species of interest to the general public and providing reporting tools may increase public awareness and also recording activities for these taxa. On the other hand, drawing records of specific non-native species of interest, which are flagged and regularly exported from other citizen science databases and platforms may help to provide a better overview of distributions of these taxa. Both approaches combined may be the most effective way to channel citizen science activities towards a better monitoring of non-native species.

We thank Rodica Serafim (Grigore Antipa National Museum of Natural History, Bucharest, Romania), Aslak Kappel Hansen (Zoological Museum, Copenhagen, Denmark), Michael Geiser (Natural History Museum, London, United Kingdom) and Zdenko Lucbauer (Malacky, Slovakia) for information on Chlorophorus annularis. We are grateful to Christophe Hanot (Palaiseau, France) for information on his previous recordings. Thanks to Dick Belgers (Wageningen, the Netherlands), Sheena Cotter (University of Lincoln, United Kingdom), Stephen Rolls (Sudbury, United Kingdom), Andy Slater (EcoRecord, Birmingham, United Kingdom), Václav Hanzlík (Neratovice, Czechia), Petr Jansa (Obříství, Czechia), Jérôme Sudre (Montpellier, France), Jean-Yves Poirier-Baldovini (Bastia, France), Tineke De Blauwe (Torhout, Belgium), Koen Verhoeyen (Deinze, Belgium), Alain Drumont (Royal Belgian Institute of natural Sciences, Brussels, Belgium) and Jørn Misser (Østbirk, Denmark) for providing information on their records and allowing us to use their images.