Pheidole balcanica

Identification
Seifert (2016) - The Eurasian species Pheidole pallidula,  Pheidole balcanica and Pheidole koshewnikovi are hardly separable by simple eye inspection. There is a number of RAV-corrected shape variables with highly significant differences but also a very large overlap (Tab. 2). ''Ph. pallidula'' differs from the two eastern species by shorter scape, shorter hind femur, higher petiole and broader mesosoma. ''Ph. balcanica differs from koshewnikovi'' by smaller eye length and smaller minimum distance between the margin of antennal sockets. The larger postocular and preocular distances of ''Ph. balcanica'' are a consequence of the smaller eye length. With all characters expressed as absolute measurements in millimeter, ''Ph. pallidula'' can be separated from the two eastern species by the discriminant:

DPBK = 13.921+19.038*PoOc-4.581*ExOcc -39.321*CL+4.478*CW+16.902*dAN-17.701*SL +21.869*MW+14.712*PEW-13.948*PPW-0.689*PnHaa +69.968*PEH+46.064*PrOc +24.301*EL+9.049*GuHL-10.011*ML-14.540*Fe3L.

Positive DPBK values indicate ''Ph. pallidula'', negative ones the two eastern species.The classification error is 1.4% in 280 individuals. The two eastern species ''Ph. balcanica'' and koshewnikovi can be separated by the discriminant:

DBK = 4.071+29.323*PoOc+4.580*ExOcc -23.743*CL+5.688*CW-9.598*dAN+12.788*SL-16.049*MW-24.383*PEW+11.550*PPW +13.556*PnHaa+2.336*PEH+52.893*PrOc-81.249*EL+12.055*GuHL+7.378*ML-9.450*Fe3L.

Positive DBK values indicate ''Ph. balcanica, negative ones Ph. koshewnikovi''. The classification error is 3.1% in 191 individuals. Attempts to find a simpler species identification by use of a smaller number of characters unfortunately did not result in acceptable classification errors. Users may run their own analyses using the primary measurement data of all 280 individuals provided as an Excell file in the electronic supplement (www.soilorganisms.org).

Distribution based on Regional Taxon Lists
Palaearctic Region: Bosnia and Herzegovina, Bulgaria, Croatia, Greece, Montenegro, Turkey.

Nomenclature

 *  balcanica. Pheidole balcanica Seifert, 2016b: 15, figs. 5-7 (s.w.) CROATIA.

Worker
Major caste – All data of shape variables given in the following description refer to specimens with a cephalic size CS of 1.25 mm.

Medium-sized, on the average larger than ''Ph. pallidula'': CS 1.106–1.457 mm. Head rather short: ratio of maximum median cephalic length against maximum cephalic width 0.90–0.97. Outlines of head in dorsal aspect without linear components: pre- and postocular head sides and occipital corners convex, the hind margin is strongly concavely excavated, depth of excavation 7–12 % of maximum median head length. The eye is the smallest within the ''Ph. pallidula'' species complex: ratio of maximum eye diameter against cephalic size 0.118–0.148. Frontal carinae diverging caudad. Anterior half of dorsal head surface longitudinally carinulate caudad to about one eye length posterior of caudal eye margin. The space between carinulae rather smooth and shining, without conspicuous microsculpture. Posterior half of dorsal head surface smooth and shining. Frontal triangle smooth and shining. Clypeus with exception of a median carinula and several paramedian or lateral ones smooth and shining. Masticatory border of mandibles toothless with the exception of a very strong apical, strong subapical and a weak subbasal dent. Anterior margin of hypostoma with two dents or blunt protrusions. Scape and hind femur short: ratio of scape length against cephalic size 0.55–0.61 and ratio of hind femur length against cephalic size 0.71–0.79. Whole surface of head, scapes, femora, tibiae, promesonotum, waist and gaster with numerous, thin suberect setae. Mesosoma in lateral view with short but sharp and steeply erected propodeal spines, a linear dorsum of propodeum and a well developed metanotal groove. The overall profile of promesonotum is strongly convex and surmounts dorsal propodeum considerably relative to the level of longitudinal mesosomal axis. Outline of promesonotum in dorsolateral (oblique) view without very prominent lobes or protrusions but very flat, obtusely-angled corners – one on dorsolateral pronotum and one or two on dorsolateral mesonotum – are usually visible. Pronotum at small magnifications smooth and shining. Petiole in lateral aspect distinctly longer than high, with a rather straight anterior profile and a small semicircular dorsal crest that appears in dorsal view much wider than long. Whole surface of head, scape, femora, tibiae, promesonotum, waist and gaster with numerous, thin suberect setae.

Type Material
Holotype, a major worker, labelled ‘Holotype Pheidole balcanica Seifert, des. B. Seifert 2015’, ‘CRO: 45.08710°N, 14.84735°E, Smokvica Krmpotska-400 m W, 8 m, Wegrand, unter Stein, Juniperus, Gras, niedriger Wald, Seifert 2014.07.29–85’. Paratypes: 2 mounted major workers, 3 mounted minor workers, 7 ethanol stored majors and 16 ethanol-stored minors from the holotype nest with the same locality label; all material in Senckenberg Museum. für Naturkunde Görlitz.

Etymology
The name is given because large parts of the distributional range are in the Balkans.