Formicoxenus sibiricus ( Forel 1899 )

Seifert, Bernhard, 2023, Two new species of Formicoxenus Mayr 1855 and Leptothorax Mayr 1855 from Tibet (Hymenoptera: Formicidae), Soil Organisms 95 (2), pp. 129-142 : 135-137

Formicoxenus sibiricus ( Forel 1899)

Leptothorax sibiricus Forel 1899 [images of type specimen]

Forel (1899) described this taxon from East Siberia without giving a more precise type locality: ‘Sibérie orientale (recu de M. Nassonow).’ Investigated were the images of the lectotype worker, designated by A. Francoeur and labelled ‘ L. sibiricus For’, ‘ L. sibiricus For Nassonov’, ‘Siberie orient.’, ‘Typus’, ‘ LECTOTYPE Formicoxenus sibiricus (FOREL) A.F.-1984’ and ‘ANTWEB CASENT 0909066’. This lectotype fixation was published by Francoeur et al.(1985). Depository: Muséum d’histoire naturelle de Genève, Genève, Switzerland. We have a very good idea of the morphological characters of this species as the images of the type correspond very well to the characters of my own sample from East Kazakhstan on the basis of which the species is re-described below. Formicoxenus orientalis Dlussky 1963 [original description]

Dlussky (1963) described this taxon from East Siberia based on workers collected within a nest of Formica pressilabris . He gave the data: „Golotyp. 1 rabotschi iz gnezda Formica pressilabris . No 288, 9 IX 1957, Chitinskaya obl., Sretenskij raiyon, Dunayevskoje lesnichestvo, pad’ Kulinda.“ Type-depository: Zoological Museum of Moscow Lomonossov University, Moskva / Russia .

Dlussky’s description is very detailed and is in no character in disagreement with the re-description of Formicoxenus sibiricus presented below. This refers to any feature of body shape, sculpture and the characteristic shape of setae.

Leptothorax zhengi Zhou et Chen 2011 [original description]

Zhou et al. (2011) gave the following collecting data: ‘ Holotype locality: Inner Mongolia: Shantangzi Monitoring Station, Helanshan National Nature Reserve, 29 July 2010, leg. Chen Zhi-Lin.’ The type depository was not specified but is possibly the collection of Guangxi Normal University, Guilin, China. As mean measurements of three type workers in mm can be derived from the data of Zhou et al. (2011) CL = 0.790, CW 0.581 (adapted to the measuring mode used here), SL 0.460, MW 0.385, ML 0.845. This translates into CS 0.686, CL/CW 1.360, SL/CS 0.671, MW/CS 0.560, ML/CS 1.230 (compare with Tab. 1). Even if considering some measuring inaccuracy, these measurements as well as images given in the original description indicate a junior synonymy with F. sibiricus . This refers in particular to the much elongated head, the small eyes, the mesosoma and waist profile with a very broad subpetiolar process and an acute, well-developed spine of postpetiolar sternite, the characteristic sculpture on head, mesosoma and waist, and the short blunt setae on whole body. Hence there is in no character a disagreement with the re-description of Formicoxenus sibiricus presented below. No data on the circumstances of collecting were given.

Material examined. Direct investigation was performed in a sample of five workers, collected from a nest of Formica clara Forel 1886 , and labelled ‘KAZ: 47.17.39 N, 85.37.03 E, 1486 m, Saur Mts. Steppe, mit Serviformica , leg. Seifert 2001.07.24 – 179’. Depository: SMN Görlitz.

Geographic range. Southern Central to East Siberia. The three collecting sites with useful geographical data are in the Saur Mountains (47.2933°N 85.6177°E) , the Helanshan National Nature Reserve (38.7°N 105.9°E) and Kulinda waterfall near Dunayevo (52.501°N 116.720°E) .

Diagnosis: --Worker ( Figs 10–13 , key; pictures CASENT 0909066 in www.antweb.org). Numeric data given are arithmetic means based on measurement of 5 specimens (for standard deviation, minimum and maximum values see Tab. 1). Rather small size, CS 676 µm. Head much elongated, CL/CW 1.333. Genae in dorsal view parallel or even slightly diverging frontad. Anterior margin of clypeus in dorsal view semicircular. Occipital margin straight to weakly concave. Frons very broad ( FRS / CS 0.478). Scape comparably long, SL/ CS 0.737. Eye very small, EYE / CS 0.173, with notable microsetae. Dorsal profile of promesonotum largely linear, propodeum convex, metanotal depression moderately deep (MGr/ CS 2.69 %). Spines rather short and acute (SP/ CS 0.144), their bases moderately distant ( SPBA / CS 0.294). Petiole with strong anterolateral corners, in profile without peduncle and with a broad subpetiolar lobe. Postpetiole narrower than in other species (PpW/ CS 0.344), its sternite with a well-developed spine. All surfaces of head, mesosoma, waist and appendages matt due to a reticulate microsculpture. Dorsal vertex strongly longitudinally carinulate-rugulose. Gaster glabrous and with very dilute pubescence. Head, mesosoma, waist, scape, femora and tibiae with very short (PnHL/ CS 0.062) setae, which widen from base to apex, are apically fringed ( Fig. 13 ) and form in cross-section a tridentate star. Color of head, mesosoma, waist and gaster homogenously yellowish brown .

Taxonomic comments. As a combination of short, blunt and fringed setae with a well-developed sculpture on head, mesosoma, waist and appendages, Formicoxenus sibiricus is unmistakable.

Biology. Similar to the situation in Formicoxenus nitidulus , there is obviously no host specificity in this xenobiotic ant. Confirmed host species are Formica (Serviformica) clara Forel 1886 and Formica (Coptoformica) pisarskii Dlussky 1964 . The latter host had originally been determined by Dlussky (1963) as F. (Coptoformica) pressilabris Nylander 1846 but later he corrected the identification ( Dlussky 1964). The mistake becomes already apparent by zoogeography: the site near Dunayevo (52.07°N, 117.06°E) should exclude F. pressilabris the known range of which does not extend east of 61°E ( Seifert & Schultz 2021).

Figures

Figure 10–13. Formicoxenus sibiricus; (10) head in dorsal view; (11) lateral view; (12) dorsal view; (13) dorsolateral view on eye. Kazakhstan: Saur Mountains, 2001.07.24