Lasius magnus Seifert 1992

Seifert, Bernhard, 2020, A taxonomic revision of the Palaearctic members of the subgenus Lasius s. str. (Hymenoptera, Formicidae), Soil Organisms 92 (1), pp. 15-86 : 73-74

4.4.44 Lasius magnus Seifert 1992

Lasius magnus Seifert 1992 [type investigation]

Type material: Holotype and 20 paratype workers labelled ”Gogona, 3100 m 10.-12.6“,“Nat.-Hist.Museum Basel – Bhutan Expedition 1972“; depositories: holotype plus 16 paratypes NHM Basel, 4 paratypes SMN Görlitz.

All material examined. A total of 19 samples with 60 workers were subject to NUMOBAT investigation. These originated from Bhutan (10 samples), India (7) and Nepal (2). For details see supplementary information SI1.

Geographic range. Known so far from 16 sites at the southern flank of the Himalayas at elevations between 1700 and 3100 m and along a line delimited by 27.9°N, 86.2°E and 27.4°N, 90.5°E. Two sites from the Meghalaya Mountains (25.45°N, 91.76°E, 1800m; 25.50°N, 91.90°E, 1900 m) are isolated from the main population.

Biology. The main habitats are woodland biomes, mainly evergreen broad-leafed and evergreen coniferous mountain forest with mesophilic to very moist conditions, that is just below or within the zone of cloud forests. The highest known site at 3100 m was in the lower zone of Rhododendron -conifer woodland.

Diagnosis ( Tab. 9 , Figs. 85 –86; key; image in www. antWeb.org with specimen identifier CASENT0912294):

Largest species of the subgenus Lasius s.str. (CS 1153 µm). Head length index very large (CL/CW 900 1.138, mean CL/CW without RAV 1.076). Scape length indices large (SL/CS 900 1.034, mean SL/CS without RAV 0.978). Postocular and torulo-clypeal distances rather large (PoOc/CL 900 0.253, dClAn 900 4.90); terminal segment of maxillary palp of medium length (MP6/CS 900 0.191). Number of mandibular dents very small (MaDe 900 7.11). Pubescence on clypeus extremely sparse (sqPDCL 900 7.24); frontal pubescence of medium length (PLF 900 27.8). Pubescence on all surfaces smooth or rather smooth. Gaster tergites with a diagnostic pubescence pattern deviating from the strictly longitudinal orientation seen in other Lasius species: the paramedian pubescence hairs on posterior dorsum of tergites are directed caudomediad or even mediad. This unique pattern may be affected in case of polluted surfaces. Setae rather short and of medium numbers (PnHL/CS 900 0.119, GuHL/CS 900 0.080, nOcc 900 10.0, nGen 900 1.7, nGu 900 3.4, nSc 900 14.7, nHT 900 16.7). Coloration: all body parts rather concolorous, varying from pale yellowish-reddish brown, over medium brown with yellowish tinge to dark brown.

Comments: The unique character combination of Lasius magnus should exclude a confusion with any species. Small workers can be clearly distinguished from equal-sized specimens of other species by a combination of elongated head, low number of mandibular dents, short pronotal setae, extremely dilute clypeal pubescence and the diagnostic pubescence pattern on gaster tergites. There are three samples in NHM Basel having no setae but only a fine pubescence on dorsal crest and sides of petiole scale whereas in the other samples the scale is fringed in frontal view by a number of setae. I assume intraspecific polymorphism but the issue should be checked for taxonomic significance. The exceptionally large size of workers and queens in L. magnus , the exceptionally large size in the temporary social parasite Lasius (Chthonolasius) crinitus (Smith 1858) and syntopic occurrence, strongly suggest the former to represent the host of the latter.

Figures

Figs. 85 and 86: Lasius magnus; paratype