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The geographic range of the rare coleopteran Tragosoma depsarium (Linnaeus, 1767) is summarized, and the Eurasian distribution is mapped for the first time. Particular attention is paid to the eastern Palaearctic part of the species’ range, where dubious data prevail. Distributional data from the Russian Far East have been published, but not confirmed, are considered, and new records of this species in Eastern Siberia are reported.


Introduction
Tragosoma depsarium (Linnaeus, 1767) is the sole species of the genus Tragosoma Audinet-Serville, 1832 and the tribe Meroscelisini J. Thomson, 1861 in the Palaearctic (Drumont and Komiya 2010). Previously, this species was considered Holarctic; however, modern data show that it does not occur outside the Palaearctic (Laplante 2017).
Throughout its entire range, T. depsarium is rarely and sporadically found. This species is ecologically vulnerable. Rapid reduction of forests with optimal habitats is the main limiting factor for this species' distribution. Tragosoma depsarium prefers coniferous forests where the proportion of mature trees is more than 25%, lighting conditions are good and stand density is low, and there is considerable dry, windfallen pines or spruces having a large diameter and no bark. Soil under these trees should have an optimal moisture content, which is important for symbiotic fungi (Wikars 2003(Wikars , 2004. The current forest management regulations, including extinguishing forest fires, sanitary felling of old trees and clearing of windfallen trees, as well as replacing mature forests cut for industrial purposes with man-made, high-density stands, do not ensure good environmental conditions for this rare species. Even within protected areas, where stand density becomes too high without felling and fires, populations of this species can be threatened. The gaps between the isolated populations also impair the chances of this species' long-term survival. Tragosoma depsarium is protected in Europe (Nieto and Alexander 2010) and many regions of Russia (Jakovlev 2007;Tikhomirov 2007;Nikitsky 2008;Egorov 2010;Dedyukhin 2012;Sitnikov 2013;Potanin 2014;Yuferev 2014;Vlasov 2015;Gus'kova 2016;Gorbunov 2018;Shapovalov 2018;Dolgin and Kolesnikova 2019). However, more accurate data on this species' distribution are needed to ensure efficient protective measures. It is not always possible to be sure that T. depsarium still occurs in sites where it was found over 100 years ago, and its presence has not been confirmed later. The fact that vast forests are now growing in places where old forests used to grow does not guarantee that T. depsarium population can be where they once were. Because of the strict ecological requirements of T. depsarium and the possible changes in local conditions, this species could have disappeared in these parts of the range. Meanwhile, records have recently been made for the first time in some territories. The data on the distribution of T. depsarium in the Asian part of Russia are insufficient. In this study, we attempt to summarize the scattered data on the distribution of T. depsarium from all available sources. We also present new distributional data from the eastern part of the species' range.

Methods
We used an extensive list of available literary sources, web resources, and personal reports from observers and collectors to summarize the geographic range of Trago soma depsarium. The entomological collections of the Zoological Institute of the Russian Academy of Sciences (Saint Petersburg), Federal Scientific Center for Terrestrial Biodiversity of East Asia FEB RAS (Vladivostok) and the Institute of Systematics and Ecology of Animals SB RAS (Novosibirsk) were studied. Furthermore, we publish for the first time data on the easternmost record of T. depsarium, which we confirmed by the study of the actual material.
The image of the specimens from Zabaykalsky Krai was taken using a Canon EOS 5d Mark II camera with a Volna-9 50 mm f/2.8 macro lens. The maps were prepared using the CorelDRAW Graphics Suite X7 software.
The following symbols were used in the text and on the map: in the text -Tomsk Oblast (TOM): Pervomaysky District (3); on the map -TOM3. No figure denotes that no other records were made within this territory: ZAB -Zabaykalsky Krai. The material provided by the Institute of Systematics and Ecology of Animals is referred to as ISEA in the text; Zoological Institute of the Russian Academy of Sciences -ZIN. Data on the age of the records are graphically shown on the maps.   Identification. Tragosoma depsarium, the only of the genus Tragosoma and tribe Meroscelisini in the Palaearctic fauna, morphologically differs very much from other species of this subfamily found in Eurasia, which makes it is easily identifiable. The imago has elongated elytra and a small pronotum and is brownish-rusty in color. The head is small, with a groove between eyes. The antennae have the apices reaching the middle of the elytra in males, or not reaching this level in females. The pronotum bears dense, rusty hairs. The body is brownish-rusty and ventrally has long, golden hairs.

Discussion
The range of Tragosoma depsarium can be conditionally subdivided into two parts: the European one, which includes the European countries and Russia stretching as far as the Ural Mountains, and the Asian one, including only Siberia, where the easternmost limits of the species' range are insufficiently known. We summarize the distributional data of T. depsarium and the conservation status of the species in various territories, as well as present maps showing the locations and the age of the records.
Tragosoma depsarium, a boreomontane species, is predominantly found in the foothill and mountain subboreal and boreal forests of Eurasia and it sporadically distributed throughout its range.
In Europe, T. depsarium has been studied since its first description by Linné (1767). The Swedish population of T. depsarium is currently quite large and stable (Jeppsson et al. 2010). Tragosoma depsarium is also found relatively regularly found in the Alps, Pyrenees, Carpathians, and mountains of the Balkan Peninsula. Outside of these mountainous regions and Scandinavia, the largest number of new records was made in central and eastern European Russia. In of its European range, the most recent records were made over 20 years ago, and sometimes even more than 100 years ago. Today, T. depsarium definitely does not occur in Belgium, and its presence in Poland, Italy, Ukraine, and Estonia needs to be confirmed. The status of T. depsarium populations within Russia, in the Pskov, Bryansk, Kaluga, and Orenburg Oblasts and the Republic of Tatarstan is currently unknown; all published records from these territories were made a very long time ago. The presence of the species in the Caucasus (Bílý and Mehl 1989) is unconfirmed (Danilevsky 2014).
Much less is known about the distribution of T. depsarium in Siberia, as entomological studies here were started later and then on a smaller scale and in less detail than in Europe. The vastness of Siberia and the poor development of transport infrastructure is the cause. Most of the records are known from in the western part of the West Siberian Plain: Sverdlovsk, Tyumen, Tomsk and Kemerovo Oblasts and in Altai. We have found no published records of T. depsarium made in the lowlands of the central West Siberian Plain. It is unclear whether this is due to habitat discontinuity or insufficient investigations.
Many records of T. depsarium have been made near Lake Baikal, especially in the Irkutsk Oblast. The records of larvae south of Lake Baikal have for a long time been considered the easternmost ones (Danilevsky 2014). Many researchers reported that this species occurs east of Lake Baikal to the Pacific Ocean, along the Amur or the northern borders of China (Hamilton 1892;Saalas 1923;Plavilstshikov 1936;Samoylov 1936;Gressitt 1951;Bílý and Mehl 1989). Shabliovsky (1956) included the Khabarovsk Krai and Primorsky Krai in the range of T. depsarium and mentioned that the species develops on Picea jezoensis (Siebold & Zucc.) Carr., Picea obovata Ledeb., and Pinus koraiensis Siebold & Zucc. and provided detailed descriptions of the shape of larval galleries. However, none of these authors have reported records based on confirmed material from the Russian Far East. We failed to find specimens of T. depsarium in the entomological collection of the Federal Scientific Center of the East Asia Terrestrial Biodiversity FEB RAS. According to Danilevsky (2014), the occurrence of T. depsarium in the Russian Far East and in North China cannot be considered established. Today, the easternmost record of this species is that made in the Zabaykalsky Krai and presented in this study. Substantiation of the occurrence of T. depsarium in the Russian Far East requires additional research.
Hence, based on our study of reliable materials, T. depsarium has a western-central Palaearctic range, and with the greatest number of records in the west. This species' farther east in Siberia, near the Pacific Ocean, remains to be proved.