Aquarius najas De Geer, 1773

Berchi, Gavril Marius, Cianferoni, Fabio, Csabai, Zoltán, Damgaard, Jakob, Olosutean, Horea, Ilie, Daniela Minodora, Boda, Pál & Kment, Petr, 2018, Water striders (Heteroptera: Gerromorpha: Gerridae) of Romania with an update on the distribution of Gerris gibbifer and G. maculatus in southeastern Europe, Zootaxa 4433 (3), pp. 491-519 : 494-495

Aquarius najas De Geer, 1773

Material examined. ROMANIA: Caraș-Severin County: Baziaș , 44°49ʹ59ʺN 21°22ʹ13ʺE, 70 m a.s.l., 13.ix.2014, 1 ♂ (ap); Băile Herculane [stream], 44°58ʹ26ʺN 22°29ʹ27ʺE, 280 m a.s.l., 29.viii.2011, 3 ♂♂ (ap) 9 ♀♀ (ap); Belobreșca [stream], 44°48ʹ08ʺN 21°30ʹ02ʺE, 142 m a.s.l., 12.vii.2014, 1 ♀ (ap); Berzasca [stream], 44°39ʹ36ʺN 21°58ʹ33ʺE, 101 m a.s.l., 26.viii.2010, 7 ♂♂ (ap) 10 ♀♀ (ap) 2 ♀♀ (ma); Borlovenii Noi [stream], 44°56ʹ44ʺN 22°07ʹ56ʺE, 345 m a.s.l., 05.viii.2013, 4 ♀♀ (ap); Bozovici [stream], 44°58ʹ09ʺN 21°59ʹ37ʺE, 371 m a.s.l., 01.viii.2013, 2 ♂♂ (ap) 3 ♀♀ (ap); Carașova [stream], 45°12ʹ04ʺN 21°52ʹ10ʺE, 176 m a.s.l., 05.viii.2013, 1 ♂ (ap) 1 ♀ (ap); Dognecea [stream], 45°17ʹ48ʺN 21°46ʹ00ʺE, 319 m a.s.l., 04.viii.2013, 1 ♂ (ap); Ilidia [stream], 44°58ʹ32ʺN 21°43ʹ38ʺE, 254 m a.s.l., 02.viii.2013, 2 ♂♂ (ap) 1 ♀ (ap); Lăpușnicu Mare [stream], 44°54ʹ43ʺN 21°56ʹ04ʺE, 272 m a.s.l., 08.viii.2013, 1 ♂ (ap) 3 ♀♀ (ap); Padina Matei [stream], 44°45ʹ17ʺN 21°43ʹ40ʺE, 397 m a.s.l., 12.vii.2014, 2 ♂♂ (ap) 2 ♀♀ (ap); Radimna [stream], 44°49ʹ21ʺN 21°33ʹ35ʺE, 122 m a.s.l., 19.viii.2012, 2 ♂♂ (ap); Sichevița [stream], 44°42ʹ56ʺN 21°47ʹ54ʺE, 281 m a.s.l., 12.vii.2014, 1 ♀ (ap); Socolari [stream], 44°56ʹ50ʺN 21°44ʹ08ʺE, 306 m a.s.l., 02.viii.2013, 3 ♂♂ (ap) 1 ♀ (ap); Zlatița [stream], 44°51ʹ50ʺN 21°29ʹ03ʺE, 91 m a.s.l., 27.viii.2010, 1 ♂ (ap) 4 ♀♀ (ap) . Mehedinți County: Baia Nouă [stream], 44°33ʹ01ʺN 22°04ʹ47ʺE, 140 m a.s.l., 18.viii.2012, 14 ♂♂ (ap) 1 ♂ (ma) 15 ♀♀ (ap) 1 ♀ (ma); Eșelnița [stream], 44°43ʹ36ʺN 22°21ʹ39ʺE, 168 m a.s.l., 09.v.2014, 2 ♂♂ (ap) 2 ♀♀ (ap); Șușița [stream], 44°43ʹ33ʺN 22°35ʹ51ʺE, 214 m a.s.l., 26.vii.2012, 2 ♂♂ (ap) 1 ♀ (ap) 2 ♀♀ (ma).

Published records.? Cristea et al. (1968),? Benedek (1970), Kis (1975),? Davideanu et al. (2004).

Remarks. In Romania, it was identified at 18 sites at an elevational range of 70–397 m a.s.l. ( Fig. 1 ). It was found only in streams from May to September. The apterous/macropterous ratio was: 0.94: 0.06 (total 102/6).

The old records of A. najas by Cristea et al. (1968), Benedek (1970), and Davideanu et al. (2004) still require revision since we have found this species only in the southwestern area of the country. However, the species might have disappeared from various parts of Romania due to pollution, regulation and damming of the natural streams, and recolonization of such habitats is difficult due to their poor dispersal abilities ( Damgaard 2005a). The species is found in high densities in undisturbed parts of small and medium-sized streams, which can provide enough food for a large population. In northern Europe, it can also be encountered in large, oligotrophic lakes ( Damgaard 2005a).

Aquarius najas is known as univoltine; some populations may have a partial second generation ( Vepsäläinen & Nieser 1977, Damgaard 2005a). In northern and central Europe, this taxon is nearly monomorphically apterous through the year, with the macropterous morph being extremely rare (e.g., Vepsäläinen 1974b, Damgaard & Andersen 1996, Ahlroth et al. 1999, Damgaard 2005b), but in southern Europe it is often dimorphic with a high frequency of macropterous specimens ( Poisson 1957, Tamanini 1979, Cianferoni & Mazza 2012, Cianferoni et al. 2013).

Distribution. West Palaearctic: Europe and part of the Maghreb Region ( Morocco, Tunisia and Algeria) including several of the larger islands in the Mediterranean (cf. Andersen 1990, 1995; Damgaard 2005a; Fent et al. 2011; Damgaard et al. 2014). In the western Mediterranean, A. najas may be confused with A. cinereus (Puton, 1869) with which it can hybridize ( Zimmermann & Scholl 1993), and in the eastern Mediterranean it may be confused with A. ventralis (Fieber, 1860) . A high intraspecific genetic divergence within the Mediterranean lineages of A. najas occurs ( Damgaard 2005a). For the Romanian distribution, see Fig. 3 .

Figures

FIGURE 1. Boxplots representing the elevational distribution of Gerridae in Romania. Circles represent outliers and asterisks represent extreme values.

FIGURES 2–7. Distribution in Romania: (2) Limnoporus rufoscutellatus (Latreille, 1807); (3) Aquarius najas (De Geer, 1773); (4) Aquarius paludum paludum (Fabricius, 1794); (5) Gerris argentatus Schummel, 1832; (6) Gerris costae fieberi Stichel, 1938; (7) Gerris lacustris (Linnaeus, 1758). Blank dots represent published records, question marks represent dubious published records of A. najas and solid dots represent records from this study.