First record of Violet Dropwing Trithemis annulata (Palisot de Beauvois, 1807) (Odonata: Libellulidae) in Slovenia

. One adult male dragonfly Violet Dropwing Trithemis annulata was recorded at Lake Vogršček in the Vipava Valley (W Slovenia) during the Biological Students Research Camp – Otlica 2021. This first record for the country is presented and the species’ distribution in Europe outlined. Behavioural observations and data on the accompanying Odonata fauna are included. This widespread Afrotropical species has rapidly expanded its range in south and south-western Europe in the recent two decades, with global warming apparently being the main driver of this expansion. Hence, 73 Odonata species belonging to 29 genera and nine families are now reported for Slovenia. Trithemis is the seventh genus to be added to the family Libellulidae for the country. The discovery of T. annulata in the Vipava Valley in Slovenia is significant for the fact of being the northernmost observation on the Balkan Peninsula to date.


Introduction
Several dragonfly species (Insecta: Odonata) are strong fliers, able to cover long distances as occasional vagrants or regular true migrants, especially when supported by favourable winds (Corso et al. 2012, Dijkstra et al. 2020).Global warming is influencing also the distribution range of numerous Odonata species, causing northward expansions, while a tendency towards an increasing range of movements in their migratory patterns has been noticed as well (Boudot et al. 2009, Ott 2010a, b, Termaat et al. 2019).Some dragonfly species are spreading north from Africa or southern Europe, and are rapidly colonising new areas in central Europe, too.Violet Dropwing Trithemis annulata (Palisot de Beauvois, 1807) is also among such examples (Bonet Betoret 2000, Ott 2010a, Gheza et al. 2019, Dijkstra et al. 2020).
Trithemis annulata is common throughout most of Africa, except in areas with closed tropical forests, and widespread in most of the Arabian Peninsula, extending to eastern Iran and southern Turkey and rapidly colonizing south and south-western Europe (Kalkman et al. 2015).This ubiquitous and pioneer species inhabits a wide variety of sun-exposed, stagnant and slowflowing waters, including freshwater lagoons, sluggish streams and rivers, as well as artificial water bodies like ditches, reservoirs, gravel pits, quarry lakes and barrage lakes (Kalkman et al. 2015, Wildermuth & Martens 2019, Dijkstra et al. 2020).For Europe, quarry lakes and large reservoirs are reported as the main reproductive habitats of T. annulata (Brochard & van der Ploeg 2013, Ottonello & Oneto 2013, Cabana et al. 2014, Fabbri et al. 2016, Gheza et al. 2019).The species is bivoltine in the Mediterranean area (Boudot et al. 2017).It can develop in waters with low oxygen concentrations (Balzan 2008) and neutral or slightly alkaline pH (Bonet Betoret 2000).The larvae show fast development of about 7-8 weeks (Boudot et al. 2017), being able to colonize also temporary water bodies (Wildermuth & Martens 2019).Imagoes can be easily identified by abdomen colour and patterning, thorax patterning and wing coloration.Its size is the same as that of the medium-sized Sympetrum species (32-38 mm) (Dijkstra et al. 2020).The flight season of T. annulata in Europe is reported to range from February to November (Kalkman et al. 2015, Chiari et al. 2020).It is a good flier and is able to cover even long distances; although it is not considered a true migratory species (Wildermuth & Martens 2019), its movements are essentially erratic or nomadic (Gheza et al. 2019).
In Europe, 163 species of Odonata have been recorded together with species that occasionally migrate from other continents, especially Africa (Dijkstra et al. 2020).Observation of the first individual of T. annulata in Slovenia was an expected surprise in 2021.Until recently, 72 Odonata species belonging to 28 genera and nine families were reported from Slovenia (Kotarac 2015), although some species have not been recorded in the last decades (Vinko et al. 2020).
With this contribution, the first observation of T. annulata in Slovenia at Lake Vogršček in the Vipava Valley is presented together with information about the species' distribution in Europe.Slovene name for T. annulata has already been provided -ciklamni telovnikar (Geister 1999); ciklama -cyclamen (from its colour), telovnik -vest.English name is Violet Dropwing (Dijkstra et al. 2020).Odonate fauna of the Vipava Valley has been fairly well studied, with 53 species reported for the region (Vinko 2016).Considering dragonflies, some abandoned claypits and Lake Vogršček are biodiversity hotspots in the region.As regards dragonflies, the Vipava Valley is the second richest region in Slovenia (Vinko 2016).

Materials and methods
The north-eastern inlet of Lake Vogršček (45°54'40.1"N, 13°45'06.0"E, 100 m alt., Fig. 1) in the Vipava Valley (W Slovenia) was investigated on 22. and 24.7.2021 during the field work carried out by the odonatological group at the Biological Students Research Camp (Raziskovalni tabor študentov biologije, RTŠB) -Otlica 2021, organized by the Biological Students' Society (Društvo študentov biologije).Due to the observation of T. annulata on 24.7.2021,targeted short trips to the same site were conducted by the first author also on 25. and 31.7.2021.Apart from observations of adult dragonflies (imagoes), search for larval skins was also performed at the spot.No voucher specimens of adults were taken and no larvae were sampled.The weather was sunny and hot.

Study area
The Vipava Valley is one of the warmest parts of Slovenia.Climate is sub-Mediterranean.Annual average temperature is 12°C, 21°C in July; the number of hot days with above 25°C is far above the Slovenian average (Pavšič 2013).Compared to the rest of the country, except for the coastal areas of Slovenian Istria, the insolation is significantly higher and the vegetation period is longer (Pavšič 2013).Lake Vogršček, situated near the village of Šempas, is the largest water body in the Vipava Valley.This approximately 4 km long and 82 ha large reservoir was made between 1985 and 1989 upon eponymous stream, primarily for irrigation (Pavšič 2013).The lake is managed by the Ministry of the Environment and Spatial Planning, Slovenian Water Agency (Direkcija Republike Slovenije za vode).It is divided into three separate parts, with the two northern smaller inlets being more interesting for nature conservation.Here the depth of the lake reaches 6 m; on the surface, the water temperature reaches 28°C in summer (Mrzelj et al. 2020).Fishing as well as some water sports take place throughout the lake.The two northern smaller inlets, bounded by a highway embankment, are characterized by flat and overgrown shores, while in the rest of the lake the shores are barer and steeper.Thus, the diversity of microhabitats at northern inlets is greater, mainly owing to the better developed plant stands.Due to fishery, the vegetation at the north-eastern inlet is cut on several places (Fig. 1b), which in addition to the presence of fish also affects the lake's dragonfly distribution and diversity.Due to the dam maintenance on the western edge of the southern inlet and its surroundings, the largest inlet was almost dry during our visit.This somehow controversial maintenance, which is supposed to be finished by spring 2022, had no significant visual effects on the north-eastern inlet at the time of our fieldwork, although more than 12 tons of fish were transferred from southern to northern inlets in November 2021.
The lake has no conservation status; its shore borders Natura 2000 site Dolina Vipave (SI3000226) (Ur. l. RS 2004a, b).Prior to our field trips in 2021, a total of 37 dragonfly species had been recorded from both northern inlets (34 from north-eastern inlet alone) (Vinko 2016), with Ceriagrion tenellum (de Villers, 1789) being the most interesting as an endangered and nationally protected Odonata species (Vinko 2016).

Results
During four field trips in July 2021, 18 Odonata species were recorded at north-eastern inlet of Lake Vogršček (Tab.1).One singular vagrant male of T. The male individual at Lake Vogršček was observed while engaged in territorial behaviour with Crocothemis erythraea (Brullé, 1832) and Orthetrum albistylum (Sélys, 1848), utilising small black alder bush Alnus glutinosa (L.) and surrounding plants on the bank (Fig. 1b) as perching sites.Besides the aforementioned territorial behaviour, the individual was performing rapid flights low over the water before caught by the first author.Obelisk position with drooped wings on a twig about 1 m above the water level was also observed.

Discussion
Trithemis annulata favours warm conditions and shallow waters (Dijkstra et al. 2020).This widespread Afrotropical generalist species has in recent decades rapidly expanded its range in south and south-western Europe.Global warming seems to be the main driver of this expansion (Boudot et al. 2009, Ott 2010a).
NATURA SLOVENIAE 23(2): 25-37 First recordings of T. annulata in Europe date back to the mid-19 th century from southern Italy and Cyprus (Kalkman et al. 2015).However, it remained rare and local until the second half of the 20 th century, when it expanded across the Mediterranean basin (Boudot et al. 2009).It colonised the entire Iberian Peninsula from 1978 onwards, was found on Corsica for the first time in 1988 and in continental France in 1994 (Bonet Betoret 2000, Boudot et al. 2009, Kalkman et al. 2015, Lohr 2021).In the following decade, T. annulata continued its expansion towards the western Mediterranean basin at progression rate of around 20 to 30 km per year (Renoult 2013), colonizing several waterbodies in a single flight season.Its colonisation in France is well documented, spreading separately on Atlantic and Mediterranean front (Deliry 2010), with records from the Loire River catchment representing the species' northern limit in Europe to date (GBIF 2021).Until the late 20 th century, the distribution of T. annulata was limited in Italy to its southern regions -Sicily, Sardinia, Calabria, Basilicata, Apulia, Campania, Lazio (Conci & Nielsen 1956, Battaglini & Percuoco 1967, Carchini et al. 1985) -and Tuscany (Terzani 1991), while in the last two decades it colonised Abruzzo, Marche, Umbria, Emilia-Romagna and Liguria (Fabbri 2011, La Porta et al. 2013, Ottonello & Oneto 2013, Fabbri et al. 2016).Now it is widespread mostly in the areas with the Mediterranean bioclimate (Gheza et al. 2019, Odonata.it 2019).It was recently reported from Lombardy, these records being the northernmost for the country, with abundant populations during the summer of 2018 in Milan and Brescia cities and their surroundings (Gheza et al. 2019, Chiari et al. 2020).Since several records of T. annulata NATURA SLOVENIAE 23(2): 25-37 were made in this region also in the ensuing years (iNaturalist 2021, GBIF 2021), it seems possible that its eggs or larvae are able to survive the winter season in more northern latitudes, or that imagoes migrate to these Italian northern provinces each year separately.In Lombardy, which is at about the same latitude as the Vipava Valley, T. annulata imagoes were observed from mid-June to early November (Gheza et al. 2019, Chiari et al. 2020, iNaturalist 2021).
Closest to Slovenia, from the Veneto region, there are records of mature imagoes of T. annulata near Padua and Treviso (Odonata.it 2019, Chiari et al. 2020, iNaturalist 2021, Observation.org 2021).Records date from 2018 onwards with the nearest record from about 120 km away from Lake Vogršček.Single record in Hungary at the Danube's oxbow in the Tolna Region (Farkas 2017) is the species' north-eastern limit in Europe to date, indicating at least occasional migration of the species to the east as well.Prior to the species' observation in Slovenia, the record from Hungary was several hundred kilometres away from the closest known sites (Fig. 3).In south-eastern Europe, T. annulata is rare (Kalkman et al. 2015) or at least less documented.There are only few records from Montenegro, Albania and Bulgaria (Gligorović et al. 2010, De Knijf et al. 2013, Pešić et al. 2017, Shkëmbi et al. 2018, Shkëmbi 2019, iNaturalist 2021, Observation.org 2021).In Montenegro, the species successfully reproduces at Lake Skadar (De Knijf et al. 2013).Although it was officially recorded in Montenegro for the first time in 2008 (Gligorović et al. 2010), an older observation dating to August 1990 from a single locality south of Ulcinj is mentioned as in need of confirmation in Jović et al. (2008).In Greece, it is quite common on most of the islands and on the Ionian coast (Lopau 2010), with several thousand individuals reported on some sites (Brochard & van der Ploeg 2013).Records from Croatia, Bosnia and Herzegovina, Serbia and Northern Macedonia are to be expected.
The discovery of T. annulata in the Vipava Valley in Slovenia is significant as being the species' northernmost observation on the Balkan Peninsula (Fig. 3).As its expansion in Europe originates from the Iberian and Apennine peninsulas (Ott 2010a), and with the species current distribution in mind, we assume that the recorded individual wandered to Lake Vogršček from Italy rather than from the south of the Balkans.The finding of only one imago at Lake Vogršček suggests that our record concerns a wandering specimen not belonging to a local population.We can exclude that the species has been previously overlooked, given that the Vipava Valley has been fairly well investigated in the recent past (Vinko 2016).
Trithemis annulata is rather territorial and often extremely aggressive towards both conspecifics as well as considerably larger species (Balzan 2008, Corso et al. 2012, Gheza et al. 2019).This behaviour, as well as the persistent territory defence, may have helped this species to establish itself in fairly wide ranges.In order to investigate the ecological consequences of the species' expansion, further monitoring of Odonata populations is required.It is known that in some cases habitat colonisation by T. annulata resulted in local decline of the formerly abundant C. erythraea (Bonet Betoret 2000), which is also widely present at Lake Vogršček.To mitigate the impacts of global and local alterations and to develop sustainable management strategies, there is a need for biodiversity monitoring as well as for assessing and understanding the consequences of ecosystem changes (Ott 2010b, Hooper et al. 2012, Termaat et al. 2019).Bio-assessments of Odonata provide cost-effective and sensitive tool to monitor the consequences of human activities (Kalkman et al. 2010).
NATURA SLOVENIAE 23(2): 25-37 Within the last decade, two new Odonata species have been discovered in Slovenia, Selysiothemis nigra (Vander Linden, 1825) (Šalamun 2012) and T. annulata, both assumingly arriving to Slovenia from Italy (Vinko 2019).Global warming has clearly favoured the expansion of both species during the last years (Boudot et al. 2009, Lohr 2021) and due to their ecological characteristics, further records, including proof of breeding, are to be expected at least in the Primorska region, western Slovenia.As recent changes in distributions of both species among others show, Odonata are regarded as a good indicator group for climatic change as well (Ott 2010a, Termaat et al. 2019).Contrary to other insect taxa (e.g., butterflies, grasshoppers), they depend mostly on aquatic ecosystems and their expansion is not directly aided by humans depending only on their own dispersal and migration behaviours.With only rare exceptions, they do not depend on the presence of other species, thus representing a unique climate change indicator (Ott 2010b).
Together with T. annulata, 73 Odonata species belonging to 29 genera and nine families are now reported for Slovenia.Trithemis is the seventh genus to be added to the family Libellulidae in Slovenia.For the Vipava Valley, 54 Odonata species have been recorded.
Consequently, a total of 39 Odonata species have been recorded for both northern inlets of Lake Vogršček, which represents 53 % of this insect group fauna for Slovenia.Apart from T. annulata and C. tenellum, the Odonata assemblage observed at Lake Vogršček during our field trips is composed by species which are widespread in the Vipava Valley (Vinko 2016).