Formica pressilabris Nylander, 1846

Seifert, Bernhard, 2000, A taxonomic revision of the ant subgenus Coptoformica Mueller, 1923 (Hymenoptera, Formicidae), Zoosystema 22 (3), pp. 517-568 : 541-543

Formica pressilabris Nylander, 1846

Formica pressilabris Nylander, 1846

TYPE LOCALITY. — Helsingfors , Finland. TYPE MATERIAL. — Lectotype by present designation 1 worker; paralectotypes 3, 5 workers ( FMNH) [investigated].

Formica exsecta var. rufomaculata Ruzsky, 1895 TYPE LOCALITY. — Simbirsk (Ulyanovsk), Wolga River. New synonym.

TYPE MATERIAL. — Syntypes 4 workers (MHN and NHM Wien) [investigated].

GEOGRAPHIC ORIGIN OF THE MATERIAL STUDIED. — The numerically evaluated 465 specimens (382 workers, 64 queens, 19 males came from Sweden 44, Finland 92, Denmark 21, Netherlands 3, Germany 2, Poland 75, Slovakia 18, France 12, Switzerland 161, Slovenia 4, Russia 14, Caucasus 11, S Tibet 5). Total number of specimens seen> 600.

DESCRIPTION

Worker ( Figs 2-4 ; 14)

Rather small (CL 1280 ± 73, 1046-1430; CW 1221 ± 70, 1000-1371). Head shape of average Coptoformica type (CL/CW 1.049 ± 0.020, 0.987-1.157). Scape short (SL/CL 0.974 ± 0.022, 0.914-1.031). Clypeal setae restricted to anterior margin ( Fig. 3 ), a second level seta in only 3% of specimens present (ClySet 1.03 ± 0.17,1-2). Clypeus lateral of the tentorial pit level only very exceptionally with single pubescence hairs surpassing the anterior margin by more than 10 µm (ClyPub 0.02 ± 0.16,0-1.5). Lateral semierect setae in the ocellar triangle always absent (OceSet 0%). Eye hairs fully absent or few minute hairs present (EyeHL 4.6 ± 1.9, 0-9). Pubescence hairs in the occellar triangle sparse ( Figs 4 ; 14; sqrtPDF 6.28 ± 0.57, 4.56-7.88). Craniad profile of forecoxae without setae (nCOXA 0.0 ± 0.0). Lateral metapleuron and ventrolateral propodeum without standing setae (nMET 0.0 ± 0.0). Outer edge of the hind tibial flexor side with few semierect first order setae, second order setae absent ( Fig. 2 , nHTFL 2.77 ± 1.20, 0-6.5). Erect setae on gaster often beginning on posterior margin of third tergite (TERG 3.16 ± 0.48, 2-4). Pubescence on first gaster tergite relatively sparse (sqrtPDG 6.68 ± 0.39, 5.79-7.86).

Queen

Size small (CL 1280 ± 39, 1189-1354; CW 1293 ± 33, 1197-1369; ML 2032 ± 67, 1843- 2192). Head proportions without pecularities (CL/CW 0.990 ± 0.020, 0.950-1.031), scape very short (SL/CL 0.849 ± 0.019, 0.822-0.892). Clypeal setae restricted to anterior margin (ClySet 1.02 ± 0.12, 1-2). Clypeus lateral of the tentorial pit level without pubescence hairs surpassing the anterior margin by more than 10 µm. Erect setae in the ocellar triangle absent. Eye hairs fully absent or very minute (EyeHL 4.5 ± 1.8, 0-8). Pubescence in the occellar triangle very sparse (sqrtPDF 6.09 ± 0.75, 4.49-7.85). Occipital corners of head with fully appressed pubescence (OccHD 0.0 ± 0.0). Dorsal head surface shining (GLANZ 2.56 ± 0.42, 1.5-3.0). Craniad profile of forecoxae without setae (nCOXA 0.0 ± 0.0). Dorsal mesosoma without standing setae (MnHL 0.0 ± 0.0), only with appressed, dilute pubescence. Outer edge of the hind tibial flexor side with very few suberect to subdecumbent first order setae, second order setae absent (nHTFL 1.31 ± 0.698, 0-3.5). Erect setae on gaster tergites beginning at the posterior margins of third to fifth tergite (TERG 3.77 ± 0.53, 3-5). Pubescence on first gaster tergite sparse (sqrtPDG 7.37 ± 0.66, 5.48-8.60). Whole body smooth and shining.

TAXONOMIC COMMENTS AND

DIFFERENTIAL DIAGNOSIS

The four syntype workers of Formica exsecta var. rufomaculata Ruzsky, 1895 , stored in MHN and NHM Wien, labelled “ F. pressilabris Nyl. var. rufomaculata Ruzsky, Ssimbirsk (Ruszky) ” have the following sample means: CL 1338, SL/CL 0.944, CL/CW 1.056, EyeHL 5.3, TERG 3.0, nCOXA 0.0, nHTFL 1.8, nMET 0.0, sqrtPDF 6.10, sqrtPDG 6.43, ClySet 1.0, ClyPub 0.0, OceSet 0, i.e. rufomaculata is in splendid agreement with the character combination of pressilabris and wellseparated from foreli in any diagnostic character. The syntypes have a completely reddish dorsum of head and a reddish base of first gaster tergite inducing Ruzsky to create a new taxon and misleading Dlussky (1964) to give it a species rank. Such a reduction of dark pigment is occasionally observed within several species of Coptoformica (e.g., exsecta , foreli , and pressilabris ) and without taxonomic significance.

BIOLOGY AND DISTRIBUTION

Geographic range

Formica pressilabris represents a boreo-alpinecontinental species. The boreal range goes north to 65°N in Fennoscandia and reaches with an atlantic extension Denmark and the Netherlands. The continental range (which is fully connected with the boreal range in S Finland and the E Baltic) goes west to central Poland and W Slovakia. The are no recent records from Germany and the species is most probably extinct. A sample with two workers and a male collected by M. Zwecker in the vicinity of Würzburg / N Bavaria in 1929 indicates that isolated relict populations may have survived outside the main ranges. The most eastern samples of pressilabris investigated come from Lake Baikal (105°E, 52°N) and S Tibet (exact locality not known; approximately 92°E, 28°N, elevation> 4000 m; German Tibet Expedition 1938/39; samples 13a-c and 14a-d). The alpine population is distributed in the Swiss, French, and Italian Alps at 1802 ± 200 m (1460-2250, n = 41; with 28 sites at 1750-2250 m) .

Habitat selection

In all parts of its geographic range, within the boreo-continental or the alpine range, nests of pressilabris are found in semidry to fresh oligotrophic grassland. These are either pastures, alpine meadows, clearings within woodland, or continental steppes.

Status as threatened species

The population in the W Alps is obviously stable, though mechanical stress by intensive cattle pasturing and alpine sports can clearly reduce populations. The Dutch, Danish, Polish, and Slovakian populations are probably much more threatened but exact data are not available. Germany: Red List 0 (extinct), Switzerland: Red List 3 (threatened).

Colony foundation

There is very sparse direct evidence which Serviformica s pecies is used for socially parasitic colony foundation; in the alpine range, Formica lemani is most certainly the major host. One nest sample from the Klausenpass / Switzerland (in coll. H. Kutter) still contained several lemani workers. Monodomous nests seem to be more frequent in continental Russia and polygynous/ polycalic colonies are more abundant in Central Europe. Polycalic colonies may have very instable nest positions in habitats with recource limitation.

Nest construction

Mound construction is not fundamentally different from the normal Coptoformica type. Mound material may also include seeds, soil particles and tiny pebles. The mounds are smaller than in exsecta and their diameter is normally <40 cm. An exceptionally large polygynous nest observed in the Bieszczady Mountains (Czechowski 1975) had a diameter of 100 cm and must have contained several hundred queens. A nest excavated by Dlussky near Voronesh showed galeries mainly to a depth of 50 cm, but a vertical duct led to chambers in a depth of 110 cm which were probably used during hibernation or excessive summer drought. On Swiss mountain pastures with intensive cattle grazing and condensed soil, the epigaeic nest parts can be small and the subterranean parts are mainly excavated in the very solid root turf that gives some protection against mechanical damage. In the Bieszczady Mountains, nests were frequently found in deserted or poorly inhabited earth mounds of Lasius flavus .

Demography of nests and colonies

Polycalic colonies may comprise> 100 nests/ 2000 m 2 and two colonies mapped by Czechowski (1975) contained 74 nests/ 1250 m 2 and 60 nests/ 580 m 2. An exact census of nest populations has not been performed but the situation seems similar to bruni or foreli . According to Pamilo & Rosengren (1984), monodomous populations are monogynous, have a sex ratio of <= 1: 1, and have mainly macraners. Polydomous populations are polygynous with related gynes, have a sex ratio> 1, and have mainly micraners. Diploid males were found in polydomous pressilabris colonies.

Swarming

With respect to the whole geographic range, alates are found in the nests July 31 ± 15.1 d (June 25- September 5, n = 16). In the Alps, the majority of alates occurs in the period July 17-August 5. In polycalic colonies of the Swiss Alps about 90% of females fly, the others are inseminated at the nest mounds (Schneider pers. comm.).

Schneider also discovered a mating place near Montana /Swiss Alps at 2100 m which was situated inside the territory of a polycalic colony. About 15 queens were waiting in tall grasses on the upper edge of a small grassy slope bordering a small grassy plateau. The males patrolled at the top level of grasses in the lee position of queens, apparently for a better perception of queen sex pheromones.

Intra- and interspecific behaviour

Polycalic colonies frequently exchange populations and show no aggressivity to members of distant polygynous nests of the same colony.

Food sources

The main energy supply is provided by trophobiosis with any suitable species of Aphidae while predatory activity is usually less important. Aphid colonies are guarded and adult beetles of Coccinella septempunctata are attacked by the ants. Large aphid colonies at lower sprouts of plants can be sheltered by thin walls of plant material.

Figures

FIG. 2. — Hind tibiae in workers of Formica exsecta, suecica, fennica, bruni, forsslundi, and pressilabris. The view is not fully directed on the large tibial diameter; there is a slight tilt for better visualisation of setae on outer margin of flexor profile. Scale bar: 400 µm.

FIG. 3. — Setae and pubescence on clypeus of Formica foreli, bruni, pressilabris, and fennica; the arrows in fore point to the tentorial pits. Scale bar: 400 µm.

FIG. 4. — Pubescence in the ocellar region of Formica foreli, bruni, pressilabris, and fennica. Scale bar: 300 µm.