Data on the distribution of Osmoderma barnabita Motschulsky, 1845 (Coleoptera: Cetoniidae) in Bulgaria from 1904 to 2022

: The hermit beetle, Osmoderma eremita s.l. (Scopoli 1763), is a species complex of scarab saproxylic beetles listed in the IUCN Red List of Threatened Species and protected in Bulgaria by Bern Convention, the Habitats Directive, and the Bulgarian Biodiversity Act. The taxonomic status of the species complex in Bulgaria is not fully known. It is believed that Osmoderma barnabita Motschulsky, 1845 is the main species present in the country, but it is also possible that Osmoderma lassalei Baraud and Tauzin, 1991 exists in the southernmost parts, where is the northern limit of its distribution. Data collected over the years on the presence of O. barnabita are very scarce due to its hidden lifestyle and lack of interest from the scientists. The present study aims to summarise all available data on O. barnabita in Bulgaria (literature, National Natural History Museum


Introduction
The hermit beetle, Osmoderma eremita s.l. (Scopoli, 1763), is a species complex of scarab saproxylic beetles associated with hollow veteran trees in the broadleaf forests of Europe (Maurizi et al., 2017). The complex consists of Osmoderma eremita s.str. in western Europe; Italian endemics Osmoderma italicum Sparacio, 2000 andOsmoderma cristinae Sparacio, 1994; Osmoderma barnabita Motschulsky, 1845 in eastern Europe; and Osmoderma lassallei Baraud and Tauzin, 1991 from Greece and European Turkey (Audisio et al., 2009). They are listed in the IUCN Red List of Threatened Species (Cálix et al., 2018) as priority species of community interest: O. eremita and O. barnabita have a Near Threatened status and decreasing population trend; O. lassallei has an Endangered status and decreasing population trend; O. italicum has an Endangered status and unknown population trend; and O. cristinae has an Endangered status and stable population trend (Nieto et al., 2010).The species complex is protected by the Bern Convention and the Habitats Directive (Council Directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora) under Annexes II and IV as a high-priority species. It is also a protected species under the Bulgarian Biodiversity Act (09.08.2002, latest amendment, State Gazette No. 102/23.12.2022, and it is included in the Red Book of Bulgaria (Guéorguiev, 2015). The main limiting factor for O. eremita s.l. populations is the disappearance of old hollow trees due to anthropogenic activities. As stated by Ranius et al. (2005), the conservation of O. eremita relates to three areas that are challenging for nature conservation in Europe: preserving natural woodlands, habitats associated with old agricultural landscapes and small pockets of nature in urban areas.
In the Balkan Peninsula as a whole, the species of the Osmoderma complex are not well studied, either taxonomically or ecologically. According to genetics studies, there are two well-defined clusters, each consisted by two species: the first cluster is restricted to western Europe (O. eremita and O. cristinae) and the second one to eastern Europe (O. barnabita and O. lassallei). The morphological characteristics used to distinguish Osmoderma species are not always clear, and they vary considerably. The lack of welldefined boundaries can lead to a high degree of uncertainty when studying populations living in areas of contact between the ranges of different taxa because of the presence of mixed morphological traits that make it difficult to assign individuals to one of the two neighbouring taxa. Furthermore, apart from O. lassallei and O. barnabita, a few poorly investigated taxa exist in the area between the Balkan Peninsula and the Caucasus Mountains. Although the nominative species O. eremita is relatively well studied, there is little information on O. barnabita; moreover, the ecology and distribution of O. lassallei are completely unknown (Audisio et al., 2007;Audisio et al., 2009;Landvik et al., 2017). The first records of O. eremita s.l. in Bulgaria were made by three authors between 1904 and 1909 (Markovich, 1904;Nedelkov, 1906Nedelkov, , 1909Yoakimov, 1904). Since then, data on O. eremita/barnabita from Bulgaria have been mentioned only in a few papers published in the period 1960-2005 (Anguélov, 1960;Nüssler, 1986;Palm, 1966;Ranius et al., 2005). In total, there are about 13 known findings, mainly from the south-western and south-eastern parts of Bulgaria. Reasons why so few data have been collected over the years have to do with the hidden lifestyle of this species and the lack of interest from scientists.
It should be noted that for practical conservation reasons, the species from the complex in Bulgaria is kept as O. eremita; this determination was made in line with EC recommendations ( The present study aims to summarise all available data on Osmoderma barnabita in Bulgaria to date, in order to facilitate environmental conservation efforts to protect the species.

Material and methods
To generate a map of the known distribution of O. barnabita in Bulgaria, we compiled presence records from the following sources: published scientific literature and country reports; the collection of the National Museum of Natural History -Bulgarian Academy of Sciences (NMNHS -BAS); field data collected by the authors and other professional entomologists in 2012-2021 and by citizen science (voluntary provided data from amateurs, members of the Bulgarian Facebook group 'The Insects and the Entomologists') incorporated in the SmartBirds.org database (Popgeorgiev et al., 2015). For the forest age and Natura 2000 sites analyses, only records with exact coordinates (accuracy up to 20 m) were used; this resulted in 47 records.

Results and discussion
We reported the distribution of Osmoderma barnabita in Bulgaria (Fig. 1), and 66 out of 79 records were new and unpublished (Fig. 2, Supplementary material 02 [*.xlsx] �). Their altitude ranged from 0 to 1700 m, mainly in mountainous areas with well-preserved forests. The findings in the plains and in some towns (Smolyan, Sliven) were interesting as they showed a wider distribution than those only in the mountain forests. Eighty-three percent of the records with exact coordinates were from forests aged above 50 years, and 35% were from forests aged above 100 years.
Although, not exactly validated within the boundaries, for such sites as BG0001011, 'Osogovska planina', it can be argued that the species is certainly present there. We show recent findings that are quite close to the administrative boundary of the area, which is enough to credibly claim that it is also present in other places in the zone where potential habitats exist. Unfortunately, there are also sites where the species has not only never been established but where almost complete degradation of the existing forests and a lack of old trees were also observed, making the existence of O. barnabita impossible (e.g. BG0000271, 'Mandra-Poda' and BG0000198, 'Sredetska reka').
Two main priority directions for species conservation in Bulgaria could be identified: the preservation of old-growth forests and the strengthening of systematic surveys on them. Considerable efforts are being made to identify and preserve old-growth forests and forest islands and to protect them and exclude them from forestry activities, both at the state level and by non-governmental organisations (NGOs) and the scientific community. There have been some successes, such as the declaration of areas with oldgrowth forests to be inaccessible for economic activi-ties (Order RD-49-421/02.11.2016 of the Ministry of Agriculture and Food; http://www.iag.bg/docs/lang/1/ cat/14/index �), as well as the Forest Stewardship Council (FSC) certification of all state forest enterprises, resulting in at least 10% of the natural forest area in Natura 2000 sites being designated as oldgrowth forest protection areas. These areas with oldgrowth forests were considered in the forest management plans and in the orders for the designation of the Natura 2000 protected sites, thus ensuring their persistence. Attention also needs to be paid to the protection of old urban trees (Carpaneto et al., 2010;Kadej et al., 2016) in parks, gardens and other green areas, as it is obvious that vital populations of the species could also exist there (the records from Sliven, Smolyan, etc.).
Although there has been some increase in the amount of presence data in recent years, including from citizen science, there is still an urgent need for further research using a variety of methods (Chiari et al., 2012;Maurizi et al., 2017). Especially, such research can help to establish the distribution and population characteristics and status of the species. Large-scale awareness-raising campaigns and data collection by volunteers (tourists, forest workers, schoolchildren, and students) can also help improve species presence data. At the same time, it is important that specific scientific studies, such as taxonomic composition, population dynamics and dispersal, be sufficiently funded by various projects (government, conservation, etc.) to ensure long-term and sustainable data collection and expert analysis. The combination of both approaches, citizen science and expert research, would greatly support the future preparation of management plans for this species and the areas it inhabits.