Gerris (Gerris) thoracicus Schummel, 1832

Gerris gibbifera (Schummel): Giglio-Tos (1894: 10), “Schtora [= Chtaura, Chtoura] alle falde del Libano ” (partim). Misidentification (verified).

Gerris thoracicus Schummel: Nieser & Moubayed (1986: 249), “ Liban [several stations]”;

Gerris (Gerris) thoracicus Schummel: Andersen (1995 b: 103), “ Lebanon ”; Fent et al. (2011: 47), “ Lebanon ”, quotation of Andersen (1995b); Damgaard et al. (2014: S16) and Ghahari et al. (2023j: 11), “ Lebanon ”, quotation of the previous records.

Material examined. Published records: “ Stora”, [1893], [E. Festa leg.], [E. Giglio-Tos det.] as G. gibbifera (Schum.), F. Cianferoni revid., 1 ♂ macr., MRSN.

Survey material: Basin of El Bared: aval El Bared Reservoir, 21.VI.1997, 1 ♂ macr., MLUB; Mare El Bared, 17.VII.2003, 1 ♀, MLUB; idem, 1 ♀ macr., CFC. Basin of Orontes: Aayoun Orghouche, 13.VI.1996, 1 ♂, ♀ macr., MLUB; El Haour at Marjhine, 21.X.2004, 2 ♀♀ macr., 1 IV instar nymph, MLUB; El Jamiaa at Marjhine, 20.V.2001, 2 ♂, 1 ♀ macr., MLUB; idem, 13.VIII.2003, 1 ♀ brach., MLUB; El Jammâssia at Marjhine, 13.VIII.2002, 1 ♂ macr., 1 IV instar nymph (♀), MLUB.

Extra-survey material: 2 km S Hermel (Coll. Am. Un. Beirut), 2.VIII.1952, K. Christiansen leg., L. Hoberlandt det., 1 ♀ macr. (NMPC). Akkar Governatorate, Akkar District, Jabal Qammoua, 1800 m a.s.l., 22.V.2010, A. Carapezza leg., “ Lebanon 22.V.2010 | caza Akkar 1.800 m | Jabal Qammoua | leg. A. Carapezza ”, 2 ♂♂, 1 ♀ macr., ACPI. Mount Lebanon Governorate, Chouf District, Wadi El Sitt, 700 m a.s.l., 16.V.2010, A. Carapezza leg., “ Lebanon 16.V.2010 | caza Chouf | wadi el-Sitt 700 m | leg. A. Carapezza ”, 3 ♂♂ macr., 2 ♀♀ apt., ACPI.

Extralimital material examined. ITALY: Maremma Regional Park: Grosseto, near Alberese, sulphurous water pool, 4.V.1988, F. Terzani leg., F. Cianferoni det., 1 ♀ macr., CFT; 1 ♀ brach., CFC; Maremma Regional Park: Grosseto, Orbetello, Fonteblanda, Tombolello, Collettore Centrale (artificial channel), about 0.5 m a.s.l., 42.589307° N 11.152848° E (WGS84), 14.V.2014, F. Cianferoni, S. Rocchi & F. Terzani leg., F. Cianferoni det., 3 ♀♀ brach., CFC.

General distribution. Species widespread in the Western Palaearctic but reaching Central Asia and Kashmir to the southeast (see Damgaard et al. 2014).

Remarks. The female specimen collected in El Jamiaa in 2003 has shortened wings, with anterior wings just surpassing the 7 th tergite and posterior wings not surpassing the 5 th tergite. This morph, classified as “submacropterous” by Brinkhurst (1960), “brachypterous” by Poisson (1921) and Vepsäläinen (1971) or simply “meiopterous” by Andersen (1982) seems uncommon in this species (see e.g., Poisson 1924, Brinkhurst 1960, Vepsäläinen 1974, Tamanini 1979, Andersen 1993). In Italy, for example, short-winged specimens of G. thoracicus were recorded at only 2 out of 72 sites (4 short-winged specimens—see examined material above—on 169 examined specimens) (F. Cianferoni, unpublished data), and Tamanini (1979) reported them only from some sites in the Po Valley. Concerning the Italian specimens examined the fore wings vary from the end of 6 th and the beginning of 7 th tergite and hind wings from first half of 5 th tergite and just surpassing its end (similar to the Lebanese specimen and those described by Vepsäläinen 1974 and Andersen 1982).

The species, although it is almost always found as long-winged (macropterous) specimens (mainly monomorphic species), however is to considered a dimorphic species since apterous (wingless morph), micropterous and brachypterous/submacropterous (short-winged phenotypes)—less frequent—and macropterous (long-winged)— the most common—morphs exist (see Poisson 1921, Andersen 1993); thus probably all the morphs ranging from apterous to full macropterous could occur also in this species like, for example, in G. lacustris (Linnaeus, 1758) in which there is an interminable series of intermediate forms between the wingless and the full winged morph (Tamanini 1979). It has been established that the mechanisms of wing-length determination in Gerris spp. include both environmental and genetic switches, although different species show the prevalence of one or the other (see Andersen 1982). Both the Italian and Lebanese short-winged specimens were collected in spring (May), but detailed studies are necessary to understand what basically determine (prevalence of seasonal or genetic switch mechanism) the emergence of short-winged morphs in this species (see Andersen 1982, Cianferoni & Santini 2012).