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A new species, Formica ribbeckei Radchenko & Perkovsky, sp. nov. , is described based on four workers from late Eocene Rovno amber (Ukraine). It most resembles F. flori Mayr, 1868 but differs from the latter mainly by the 5-segmented maxillary palps with the preapical segment subequal in length to the apical one, and by the shorter first funicular segment. Fossil F. luteola Presl, 1822, F. trigona Presl, 1822, F. macrognatha Presl, 1822 and F. quadrata Holl, 1829 are considered incertae sedis in Formicidae. Thus, ten valid Formica Linnaeus, 1758 species (including F. ribbeckei ) are known now from late Eocene European ambers. The diversity of Formica in the early and middle Eocene deposits of Eurasia and North America is considered. It is assumed that the genus Formica most likely arose in the early Eocene.

A new fossil myrmicine ant genus and species Lelejus venustus gen. et sp. nov. , are described from late Eocene Rovno amber (Priabonian, 33.9–37.8 Ma). This genus differs from all extant and extinct Myrmicinae genera known from the late Eocene European ambers in the combination of morphological features, in particular: 13-segmented antennae with a very short scape and filiform funiculus; 3-segmented maxillary and 2-segmented labial palps; well-developed mandibles with dentate masticatory margin; scutum with broad notauli; forewings with closed cells 1+2r, 3r and mcu, the cell 3r of approximately the same length as cell 1+2r; free vein M branches off from RS approximately at the midlength between the junction of cross-vein 2r-rs with RS and vein m-cu; the cross-vein cu-a is located far from the base of wing, so the branch 1M+Cu is much longer than 2M+Cu. The taxonomic position of the described genus is discussed.

Strongylognathus Mayr, 1853 is a Palaearctic genus, comprising 25 ant species and one subspecies, all permanent social parasites, infesting colonies of various species of Tetramorium Mayr, 1855. They have patchy distribution throughout their areas and most of them are very rare and listed as vulnerable. The taxonomy of the Strongylognathus huberi group needs thorough revision and the results presented below can be considered as preliminary. Four species of the socially parasitic ant genus Strongylognathus ( S. karawajewi Pisarski, 1966, S. huberi dalmaticus Baroni Urbani, 1969, S. afer Emery, 1884 and S. italicus Finzi, 1924) are recorded for the first time from Bulgaria and, together with the previously-known S. testaceus and S. bulgaricus stat. rev., their total number reaches six. The taxonomic position and geographic distribution of all species are discussed and a Key for their identification, based on worker caste, is compiled.

The previously unknown queen of Stiphromyrmex robustus (Mayr, 1868) is described. The taxonomic position of the fossil genera Stiphromyrmex Wheeler, 1915, Enneamerus Mayr, 1868, and Thanacomyrmex Chény, Wang & Perrichot, 2019 is discussed, and their placement in the Myrmecina genus-group of the tribe Crematogastrini Forel, 1893 is confirmed. A key for the identification of fossil genera and species of this genus-group is provided.

Most described Mesozoic ants belong to stem groups that existed only during the Cretaceous period. Previously, the earliest known crown ants were dated to the Turonian (Late Cretaceous, ca. 94-90 million years ago (Ma)) deposits found in the USA, Kazakhstan, and Botswana. However, the recent discovery of an alate male ant in Kachin amber from the earliest Cenomanian (ca. 99 Ma), representing a new genus and species, Antiquiformica alata, revises the narrative on ant diversification. Antiquiformica can be distinctly differentiated from all known male stem ants by its geniculate antennae with elongated scape, extending far beyond the occipital margin of the head and half the length of the funiculus, as well as its partly reduced forewing venation. Furthermore, the combination of a one-segmented waist with a well-developed node, elongated scape extending beyond the occipital margin, and reduced forewing venation, particularly the completely reduced m-cu and rs-m crossveins and absence of rm and mcu closed cells, firmly places the fossil within the extant subfamily Formicinae. Fourier transform infrared spectroscopy (FTIR) confirmed that the amber containing Antiquiformica alata originated from the Kachin mines in Myanmar. This discovery significantly revises our understanding of the early evolution of Formicinae. The presence of Antiquiformica in Cenomanian amber indicates that the subfamily Formicinae emerged at least by the start of the Late Cretaceous, with crown ants likely originating earlier durin the earliest Cretaceous or possibly the Late Jurassic, although paleontological evidence is lacking to support the latter hypothesis.

Aneuretinae is an enigmatic ant subfamily with poorly defined morphological boundaries. Aneuretus simoni Emery, 1893, found only in Sri Lanka, is a \"living fossil\", the only known extant species of Aneuretinae. In the distant past, however, Aneuretinae was more diverse and widespread, including eight extinct genera spread across North America, Europe, and the Russian Far East. Here, we report two fossil Aneuretinae species, Protaneuretus succineus Wheeler, 1915 and Paraneuretus tornquisti Wheeler, 1915, found in late Eocene (Priabonian, 37.8-33.9 Ma) Rovno amber (Ukraine), providing distinguishing morphological features and measurements. These species, the first recorded Aneuretinae in Rovno amber, were originally described from Baltic amber of similar Priabonian age. These new records raise the number of reported ants in Rovno amber to 77 species from 39 genera and 9 subfamilies, and indicate that in the late Eocene Aneuretinae were distributed both on the northern and southern coasts of the Paratethys. Fossil evidence suggests that Aneuretinae originated in the Northern Hemisphere and only entered India and Sri Lanka after the Indian subcontinent collided with Asia ~59 Ma. Why Aneuretinae survived to the present only in Sri Lanka remains a mystery.

The present catalogue of the ants (Hymenoptera, Formicidae) of Bulgaria is made on a base of critical reconsideration of literature (covering the period from 1892 till 2009 and part of 2010) as well as on examination of the authors' and several museum's collections. A lot of data were omitted in the previous Bulgarian monograph on ants, lots of new data were recently added and many important additions and alterations were made due to taxonomic revisions of Eurasian Formicidae during the last three decades. Two new species are reported for the country [Temnothorax graecus (Forel, 1911) and Temnothorax cf. korbi (Emery, 1924)].This catalogue contains a list of 163 ant species belonging to 40 genera of 6 subfamilies now known from Bulgaria. Synonyms and information on the previously reported names in relevant publications are given. Known localities of the species are grouped by geographic regions. Maps with concrete localities or regions for each species were prepared. The conservation status of 13 ant species is given as they are included in IUCN Red List of Threatened Species and Bulgarian Biodiversity Act. In comparison with adjacent Balkan regions the ant fauna of Bulgaria is quite rich and its core is composed of South European elements.

Competition is a major force organizing ant communities and results in co-occurring species evolving different strategies for foraging and use of space. Territorial species, as top dominants exclude each other, while shaping the local ant communities both qualitatively and quantitatively. In this study the authors examined how two territorial species, Formica polyctena and Lasius fuliginosus, can coexist in adjacent territories over long periods of time, and whether they affect co-occurring species of ants in different ways. Field observations in the absence and in the presence of baits were carried out around a L. fuliginosus nest complex surrounded by a polydomous F. polyctena colony in S Finland in 2007-2009. During the three years of the study almost no overlaps in the territories of the two territorial species were recorded, and there were mostly minor shifts in the boundaries of the territories. Differences between the two territorial species in their use of space and competitive effects ensured their coexistence at this particular site in Finland.

In the course of ongoing revision of the ant genus Myrmica Latreille, 1804, we located, in the collections of the Russian and Polish Academies of Sciences, pieces of Baltic Amber (Late Eocene, ca. 40 Ma; earlier this amber was considered to be Oligocene, e.g., see Wheeler, 1915; Larsson, 1978; Bolton, 1995; Dlussky, 1997), that each contained a fossilized specimen of Myrmica. We were also fortunate to be given access to a piece of Saxonian Amber (the same age as Baltic Amber) from the collection of Manfred Kutscher that contained three specimens of Myrmica. Four of the specimens belong to two new species. We describe these below, placing them in context with extant species, and we re-appraise all previously described fossil Myrmica, providing a key to the identification of the five extinct “true” Myrmica species.

Wood ant colonies that appear to consist of individuals representing different species are described in several previous papers. The present study is the first to elucidate the genetic basis of the spectacular morphological variability observed within such colonies. Two seemingly mixed colonies (FM-1 and FM-2) from southern Finland were investigated. On the basis of the morphology of their workers these colonies were comprised of individuals with phenotypes typical of Formica rufa L., F. polyctena Först., and F. aquilonia Yarr. The sequence of an mtDNA fragment (5' end of the cytochrome b gene) was used to examine the phylogenetic relationships among haplotypes of workers from homogeneous colonies of different wood ant species and the two supposedly mixed colonies, and to sort the individuals within the colonies into matrilines. Six microsatellite loci were used to analyse the genetic differentiation between colonies and among workers within colonies, and to detect putative hybrids. The results show that, independently of their phenotype, workers from the \"mixed\" colonies were genetically more similar to other individuals in their colony than to those in the homogeneous F. rufa, F. polyctena or F. aquilonia colonies. However, while colony FM-1 consisted of offspring of the same queen or more likely several maternally related queens, colony FM-2 consisted of the offspring of at least four unrelated queens. The data suggest hybridisation between F. polyctena × F. aquilonia and F. polyctena × F. rufa (and possibly subsequent mating between these hybrids) as the most probable mechanism leading to the existence of these two colonies, which implies that the hybrids are fertile. This study shows that colonies of wood ant hybrids can arise spontaneously and persist under natural conditions. The results also revealed that even some morphologically homogeneous colonies are genetically heterogeneous. In the case of closely related, morphologically similar species that interbreed, morphology can be a bad predictor of genetic differences between individuals. [PUBLICATION ABSTRACT]