New and little-known ant species (Hymenoptera, Formicidae) from Bulgaria

Abstract Background Many faunistic studies on the myrmecofauna of Bulgaria have been carried out and about 180 ant species (Hymenoptera, Formicidae) from 43 genera and six subfamilies have been discovered as a result. Although the Bulgarian ant fauna is considered to be relatively well studied, the finding of unrecorded species continues, especially amongst the rare social parasites and the species with a more southern distribution in the Balkans. New information The current study presents data on 11 ant species recorded for the first time in Bulgaria (Messorhellenius Agosti & Collingwood, 1987, M.mcarthuri Steiner et al., 2018, Crematogasterionia Forel, 1911, Monomoriummonomorium Bolton, 1987, Temnothoraxaeolius (Forel, 1911), T.cf.exilis(formdarii Forel, 1911), T.finzii (Menozzi, 1925), T.rogeri Emery, 1869, Tetramoriumcf.punicum, Plagiolepisxene Stärcke, 1936 and Lasiusreginae Faber, 1967), as well as new locality data on 15 rarely found species. Some of the species, such as Hypoponeraeduardi (Forel, 1894), Strumigenysargiola (Emery, 1869), Temnothoraxgraecus (Forel, 1911), Tetramoriumdiomedeum Emery, 1908, Camponotusionius Emery, 1920 and C.tergestinus Müller, 1921, have been known so far only from a single locality in Bulgaria. The dataset of all records presented in this work was published separately through Global Biodiversity Information Facility (GBIF, https://doi.org/10.15468/mngbzp).


Introduction
Ants (family Formicidae) in Bulgaria, with about 180 reported species, represent one of the richest fauna on the Balkan Peninsula. This high number is due to the country's heterogeneous topography, proximity to large water basins and the presence of sub-Mediterranean climatic influence in the southern regions. Only Greek myrmecofaunawith at least 315 known species -outnumbers the diversity reported from Bulgaria  .
The present study adds new species records of taxa that were previously not known in Bulgaria, corrects some historical identifications and reports new localities of little-known species in the country. However, the doubtful presence of some species and the unidentified ant materials collected from some genera makes the final list incomplete.

Materials and methods
The present study is based on ant materials collected during field trips to several sites, mainly in the southern regions of Bulgaria: the mountains -Strandzha, Sakar, the Eastern Rhodopes, Pirin, Belasitsa, Ograzhden and Maleshevska -as well as the Thracian Plane and Struma Valley in the period 1994-2021. However, the majority of new ant records were found in the Eastern Rhodopes. The main collection method was by hand, unless other methods, such as pitfall and tree traps, sifting, sweeping, light traps, Malaise traps, suction sampler, were noted. The specimens were deposited in the collection of the Faculty of Biology, Sofia University (BFUS), if not otherwise specified. Notes: First record for Bulgaria. This species is known from Greece, the western coast of Anatolia and the European part of Turkey Borowiec 2019a, Kiran and.  suggested that the previous records of M. capitatus (Latreille, 1798) from eastern parts of the Balkan Peninsula concern M. hellenius. In this regard, it is very likely that the data on M. capitatus from the northern Black Sea coast (Markó and Csősz 2002) refer to M. hellenius.    Notes: First record for Bulgaria. This is a recently described member of the Messor structor species group (Steiner et al. 2018), distributed in Greece and Turkey (Kiran and Karaman 2020, . Specimens from the vicinity of the Meden buk and Golyam Dervent villages have intermediate characteristics between M. mcarthuri and M. hellenius, which may indicate a possible hybridisation between these species (Fig. 4).
Notes: Despite the rare finding of Strumigenys argiola, it is widespread in Europe and North Africa. This species was reported very recently for the first time from one locality in Bulgaria (Northeast Bulgaria, SW from Balchik) (Lapeva-Gjonova and Ljubomirov 2020) . The presented record supplements the knowledge on its distribution in Bulgaria.
Temnothorax aeolius (Forel, 1911) ( Salata and Borowiec 2019b). This species is known from Turkey, its type locality, as well as from Israel and the Greek islands (Borowiec and Salata 2012). It was recently recorded in Greek Thrace (Bračko et al. 2016). Notes: After the description of T. bulgaricus from Bulgaria ( Forel 1892), it has been reported from a number of places in the southern Balkans and Turkey. It was found in several thermophilous sites (Sliven, Zemen Gorge, Petrich, Asenovgrad, Obzor) in Bulgaria (Atanassov and Dlussky 1992). Here we provide additional findings as South Pirin Mt., East Rhodopes Mt. and Sakar Mt. are hitherto unknown distribution regions. Notes: First record for Bulgaria. This is a common Balkan form of the species belonging to the Temnothorax exilis group. It was described from the vicinity of Izmir in Turkey as var. darii ( Forel 1911) and synonymised with T. exilis by Baroni Urbani (1971). It is likely that the Balkan population is not conspecific with true T. exilis, described from the vicinity of Naples in Italy. Until the situation is clarified, we will leave the name of the morphospecies as Temnothorax cf. exilis ( form darii Forel, 1911).
Notes: First record for Bulgaria. Extremely rarely reported species known from Italy and the Republic of North Macedonia (Bračko et al. 2014), as its presence in Anatolia is doubtful (Kiran and Karaman 2020). (   Notes: First record for Bulgaria. Temnothorax rogeri is an eastern Mediterranean species, known from Croatia, Greece, Montenegro and Turkish Thrace (Borowiec andSalata 2018, Kiran and. Recently, it was recorded in Slovakia, but most likely this record is based on an introduced specimen (Klesniaková et al. 2018). Morphologically, it is very close to T. recedens (Nylander, 1856), which is known from the southern regions and the Black Sea coast in Bulgaria (Atanassov andDlussky 1992, Lapeva-Gjonova et al. 2010 Notes: Tetramorium diomedeum has east Mediterranean distribution-from Italy to the Anatolian part of Turkey (Salata et al. 2020). Prior to this study, T. diomedeum was reported from Bulgaria just once from Ahtopol (Southern Black Sea coast) (Csősz and Schulz 2010).
Notes: At least three morphospecies close to Tetramorium punicum (Smith, 1861), described from Israel, have been distinguished in the southern Balkans and the Greek islands. Accurate identification of this species complex requires the study of sexual castes. As our material consists only of workers, the species-level determination is not possible.

Notes:
The only published record comes from the hill of Kozhuh, situated not far from the new locality. As noted by , this species is widespread in the Balkans and Turkey. Notes: Camponotus oertzeni is known from Greece, Serbia, Iran and Turkey ) and its first published record from Bulgaria was given under the name C. pilicornis (Roger, 1859) in Lapeva-Gjonova and Santamaria (2011).
Notes: Camponotus tergestinus is a rare arboricolous ant species, nesting in oaks. It has scattered east Mediterranean distribution-from Italy to the Anatolian part of Turkey (Markó et al. 2009, Bračko 2017. In Bulgaria, it was known from only one locality on the southern Black Sea coast (an oak forest near the village of Sinemorets) (Lapeva-Gjonova and Kiran 2012).
Notes: This is a species from the Camponotus kiesenwetteri group, which occurs in Greece, Turkey, the Republic of North Macedonia and Bulgaria . In Bulgaria, the species was reported in two localities: Struma Valley and South Pirin Mt. (Lapeva-Gjonova 2011).

Notes:
In the last revision of Cataglyphis livida complex,  proposed Cataglyphis viaticoides as a senior synonym of Cataglyphis livida bulgarica Atanassov, 1982. It is known from few sites in East Rhodopes in Bulgaria (Atanassov and Dlussky 1992) and its general distribution covers the south-eastern Balkans and Asia Minor .

Notes:
Although this species has a wide range of distribution (from Europe and Anatolia to the Near East), it is limited to xerothermous grasslands at relatively low altitudes (Borowiec andSalata 2018, Seifert 2018). Only three localities are known so far for Formica clara in Bulgaria ( Lapeva-Gjonova et al. 2010) and the Eastern Rhodopes is a new distribution area.
Notes: First record for Bulgaria. This is a very rarely recorded temporary social parasite of Lasius alienus recorded from several European countries, as well as from Turkey and Mongolia (Aibek andYamane 2010, Borowiec 2014). Lasius reginae joins L. carniolicus Mayr, 1861 as the second member of the subgenus Austrolasius known from Bulgaria. It differs from the latter in a reduced chaetotaxy (Fig. 8).
Notes: First record for Bulgaria. Plagiolepis xene is a rare workerless inquiline in nests of Plagiolepis pygmaea. Its distribution range covers southern and central Europe to Anatolia.

Discussion
In the present study, 11 new species of ants are reported for the fauna of Bulgaria -Messor hellenius, M. mcarthuri, Crematogaster ionia, Monomorium monomorium, Temnothorax aeolius, T . cf. exilis form (darii) , T. finzii, T. rogeri, Tetramorium cf. punicum, Plagiolepis xene and Lasius reginae. These new discoveries are added to the already known about 180 species. The number of ant species in Bulgaria is far higher than in the other Balkan countries, except Greece -most likely due to high number of endemic species known from this country.
Quite a few ant species in Bulgaria remain poorly studied due to their relatively rare detection, limited distribution or difficulties in identification. In the present study, for the first time, exact localities of Crematogaster gordani, previously reported for Bulgaria by Borowiec (2014), are given. New localities are added for another 14 rarely registered species. Some of the species, such as Hypoponera eduardi, Strumigenys argiola, Temnothorax graecus, Tetramorium diomedeum, Camponotus tergestinus and C. ionius, have been known so far only from a single locality in Bulgaria and Stenamma striatulum from two localities.
Almost all species included in this study, with the exception of Lasius reginae, are characteristic elements of southern European or eastern Mediterranean faunal complexes. This is directly related to the established localities, mainly in the southern regions of the country and the Black Sea coast, where the impact of the Mediterranean climate is more noticeable.
The two rare members of the socially parasitic species, Lasius reginae and Plagiolepis xene, were found together with their typical hosts: Lasius alienus and Plagiolepis pygmaea, respectively. Although their hosts can be common, both parasitic species are extremely rare, with Lasius reginae listed as vulnerable (IUCN 2022).
It is expected that future taxonomic revisions of some problematic groups of species from the southern Balkans, for example, of the genera Aphaenogaster, Messor, Temnothorax and Tetramorium, will significantly clarify the boundaries between species and will increase the knowledge of the extremely diverse fauna in this region.