Plagiolepis barbara Santschi, 1911

Bernhard, Seifert, 2020, Revision of the Plagiolepis schmitzii group with description of Pl. invadens sp. nov. - a new invasive supercolonial species (Hymenoptera: Formicidae), Deutsche Entomologische Zeitschrift 67 (2), pp. 183-196 : 183

Plagiolepis barbara Santschi, 1911

Plagiolepis pygmaea var. barbara Santschi, 1911 Two type workers were investigated from NHM Basel, labelled "Kairouan Tunisie Santschi. 1903", " Plagiolepis barbara type Sant", "v. Plagiolepis barbara type Sant", "ANTWEB CASENT0912428 top specimen".

Plagiolepis maura Santschi, 1920 [syn. Plagiolepis barbara ] The collection data published by Santschi are "Maroc: Mogador (Vaucher), avril 1905, types w, m,g. Tanger (Vaucher), Rabat (Thery)". One type worker was morphometrically investigated from NHM Basel, labelled "4.905 Mogador Vaucher", " Plagiolepis maura type Sants", "ANTWEB CASENT0912424". This specimen belongs to the true type series as Santschi published only the Mogador specimens as types. Furthermore, no specimens in the Santschi collection from Tanger and Rabat are labelled as Pl. maura or as types.

Material examined.

A total of three samples with seven workers were subject to morphometric investigation.

Morocco: Mogador , 1905.04 (Vaucher), type Pl. maura [31.508°N, 9.76°W, 4 m alt.] . Tunisia: Kairouan, 1903, type Pl. barbara [35.671°N, 10.099°E, 67 m alt.] ; Kairouan, 1920.03.07 [35.671°N, 10.099°E, 67 m alt.] .

Diagnosis and taxonomy

(Table 1 , key, AntWeb, 2020: pictures of specimens CASENT0912424 and CASENT0912428):

Pl. barbara differs from Pl. schmitzii by a much shorter scape and a shorter postocular distance, from Pl. atlantis by larger eye and from Pl. invadens sp. nov. by larger eye and much longer 3rd funiculus segment. The most similar species is Pl. atlantis and it may be asked if there is a risk of synonymy, considering the small sample size in Pl. barbara . This risk is low.

Running a PCA with absolute head size and the 16 RAV-corrected shape, pubescence and surface characters, there is a very strong separation of all individuals by the first principal component (ANOVA, F1,61 149.0, p << 0.001):

Pl. atlantis -0.295 ± 0.532 [-1.337, 0.758] n = 56

Pl. barbara 2.363 ± 0.638 [1.564, 3.311] n = 7

Distribution and biology.

Distributed in west Mediterranean Africa. Biology unknown.

Excursus: The tramp-species-supercolony syndrome in Plagiolepis

Plagiolepis invadens sp. nov. is, together with Pl. schmitzii and Pl. pygmaea , the third Plagiolepis species known from areas north of the Alps to show anthropogenous introduction, supercoloniality and permanent outdoor nesting throughout the year. The situation in Pl. schmitzii is commented in the species chapter above and is not entirely new, but the case of Pl. pygmaea with an apparently new dynamics towards supercoloniality in introduction areas needs commentary. According to samples sent to me during last the three decades and deposited in SMN Görlitz, Pl. pygmaea has been anthropogenously introduced to settlements and inner urban areas - most of these are situated far north of its natural range. The first year of observation and localities are 1993 in Mainz-Hechtsheim (49.97°N, 8.27°E), 2007 in Berlin-Köpenick (52.49°N, 13.57°E), 2011 in Hanhofen (49.31°N, 8.34°E), 2019 in Haßloch (49.37°N, 8.24°E), 2019 in Zurich (47.39°N, 8.49°E) and 2020 in Lützelsachsen (49.52°N, 8.66°E). In three cases, introduction with plant material was apparent and, in the last two localities (Zurich and Lützelsachsen), the formation of supercolonies was observed.

Are there general traits or pre-adaptations in Plagiolepis ants for a career as a tramp species, for eventual transformation to supercoloniality and for developing a competitive advantage - traits that might also explain the sudden emergence of Pl. invadens sp. nov. as if from nowhere? There are four Plagiolepis species with known mating scenarios and colony demography: the Palaearctic Pl. pygmaea , Pl. cf. taurica and Pl. schmitzii , studied by Thurin et al. (2011) and Pl. alluaudi Emery, 1894 from the tropics of the old world observed by Buschinger (2012) in greenhouses of the Darmstadt Botanical Garden. All four species share characters facilitating anthropogenous introduction and transition to supercoloniality: (a) very small size, (b) wide food spectrum, (c) strong tendency for intranidal mating and (d) high degree of polygyny. A single medium-sized flower pot allows long-term survival and reproduction of these tiny ants and, placed at the right spot, it may serve as a beach head for supercolony formation by nest splitting.

Another factor is probably also important for the success of Plagiolepis ants. At least for Pl. taurica , we have direct observations that an unidentified secretion emitted from the gaster tip is extremely toxic and repellent to other ant species ( Seifert 2018) and which may explain that it is tolerated within the territories of dominant ants. Pl. taurica may share a bait or trophobiont colony with so-called dominant ants or even displace these. These observations are repeated in other species: Pl. pygmaea was the only ant species allowed to co-exist and move freely within the territory of a Linepithema humile (Mayr, 1868) supercolonies in France and Spain ( Charrier et al. 2020) and Pl. alluaudi was observed in the Bermudas ( Smith 1957), New Caledonia ( Le Breton 2003) and the Great Barrier Reef islands ( Burwell et al. 2012) to show, in contrast to other ants, no population decrease in the presence of dominant supercolonial Pheidole megacephala (Fabricius, 1793).