Formica sentschuensis Ruzsky 1915

Schultz, Roland & Seifert, Bernhard, 2025, Formica sentschuensis Ruzsky 1915 and Formica tibetana n. sp. - two unique and little known Formica species from Tibet (Hymenoptera: Formicidae), Soil Organisms (Northwood, London, England) 97 (1), pp. 85-95 : 88-91

Formica sentschuensis Ruzsky 1915

Formica sentschuensis Ruzsky 1915

This taxon has been described from two locations in NE Tibet. Ruzsky (1915) explicitly gave “1) rechka Sen-chu / bassein r. Goluboi , 12000’, Kam , 2/ 3. VIII 1900 (gynes, workers). 2) gory Amnen-Kor , 14-15000’ abs. vys., VI 1900 (gyne, workers). [translation: (1) rivulet Sen-Chu, basin of Goluba river, 12000 feet, Kam, 2./ 3. August 1900 (gynes, workers). (2) Amnen-Kor Mountains, 14-15000 feet absolute height, June 1900 (gyne, workers)]. Dlussky (1965) designated a lectotype in a gyne from the first locality for which he published the collecting data in English “Northeast Tibet; river Sen-Chu, bass. of Yangtse, Kam, altitude 3600 m, III 1901 [sic!], coll P. K. Kozlov ”. A loan of the lectotype from Zoological Institute St. Petersburg was not possible but images of the specimen kindly provided by Dmitry Dubovikoff clearly showed only very few setae on dorsal plane of scape and extensor profile of hind femur. Hence the seta characters of the lectotype gyne are in line with those of the paralectotype worker received as a loan from MCZ Cambridge. This worker is labelled “ M.C.Z. Cotype 33835” and “rechka Sen-chu 12T’/ bacc. Goluboi r./ Koslov. nach. III 00” [translation: rivulet Sen-Chu, 12000 feet / basin of Goluba river / Koslov. beginning of March 1900 ”]. The rea- sons for the disagreements between the collecting dates at the lectotype locality – August 1900 by Ruzsky, March 1901 by Dlussky and March 1900 on the label of the MCZ Cotype – are perhaps due to writing and or reading er- rors by Ruzsky and Dlussky. Another possibility is that Kozlov was at the Sen-Chu river both in March (outward bound from Lanshou) and in August (during return). We consider the MCZ cotype worker as true paralectotype since both locality and collecting month are coincident with that of the lectotype. We base our identification of Formica sentschuensis on the paralectotype worker and the images of the lectotype gyne .

Formica (Neoformica Wh.) dalailamae Ruzsky 1915

This taxon has been described in two workers from Amnen-Kor Mountains, collected by the Kozlov expedition in June 1900 at a height of 14-15000 feet. Ruzsky (1915) placed them near to Formica (Neoformica) pallidefulva Latreille 1802 . However, Dlussky (1965) recognized Formica dalailamae Ruzsky 1915 as junior synonym of Formica sentschuensis that was described in the same paper one page before. We follow here Dlussky’s concept as he apparently investigated these two specimens. He reported that these were very badly mounted and by no means attributable to North American “ Neoformica ” species near to Formica pallidefulva Latreille 1802 , because they showed the diagnostic excavation in anteromedian clypeal margin. Furthermore, and important in our context, a senior synonymy of Formica dalailamae over Formica tibetana n.sp. is unlikely because Ruzsky stated in his rather detailed description of pilosity: “antennal scapes without standing hairs”.

Tabele 1. Morphological data of worker individuals; sequence of data – arithmetic mean ± standard deviation [minimum, maximum]. The column in between gives the F values and significance levels of a one-tailed ANOVA. F values of the three most separating characters are given in bold.

Material examined. Numeric phenotypical data were taken in 16 worker nest samples with 36 workers. They originated from the Chinese provinces Quinghai (1 sample) and Sichuan (15 samples). For details see supplementary information SI1 .

Geographic range. The westernmost known site is the holotype locality Sen-Chu in the province Quinghai (33°N, 97°E, 3900 m). It was not possible to determine more precise coordinates from the data given by Kozlov – the error could be more than 50 km. All remaining samples were collected in the province Sichuan at elevations from 3005 to 4420 m a.s.l. and between 100.0 and 103.5° E, 28.9 and 32.2°N ( Fig.1 map) .

Diagnosis: --Worker (Tab. 1, Figs. 2-4 ): All shape ratios given below are primary ratios taken in 36 specimens and all data are given as arithmetic mean ± standard deviation. Verbal statements such as “long”, “short”, “small” etc. are comparative in relation to the average situation in Palaearctic Serviformica . Rather small size, CS 1157 ± 134 µm. Head and scape short (CL/CW 1.087 ± 0.033, SL/CS 1.014 ± 0.022). Distance between posterior ocellae moderately large (OceD/CS 0.195 ± 0.012). Eye small (EYE/CS 0.268 ± 0.009). Distance between (a) metathoracal spiracles, (b) between metathoracal and propodeal spiracle and (c) between metathoracal spiracle and caudoventral metapleuron moderately large (MtSt/CS 0.143 ± 0.020, MtPpSt/CS 0.340 ± 0.012, MtMtP 0.612 ± 0.012). Setae on whole body long (GHL/CS 12.06 ± 1.16%). Head, mesosoma, petiole and gaster with numerous setae (nGen 5.2 ±2.2, nCH 24.8 ±4.0, nGu 13.2 ±2.7, nMn 13.9 ± 4.7, nPrMe 25.5 ± 6.1, nPe 7.6 ± 2.1). Extensor sides of femora and tibiae with a lower number of setae (nHFex 6.2 ± 3.5, nHT 5.7 ± 3.8). Dorsal plane of scape without or with only very few short, suberect or subdecumbent setae (nSc 0.7 ± 1.0). Distance of pubescence and of transverse microripples on gaster tergites large (sqPDG 7.24 ± 0.62, RipD 6.96 ± 0.58). Frontal triangle with strong transverse microripples. Clypeus with a sharp median keel stretching over 75% of its length in the largest and over 95% in the smallest workers. The excavation of anteromedian clypeus is conspicuous in frontodorsal view ( Fig. 4 ), but only suggested in full face view. Vertex usually dark brown. Genae, clypeus, mesosoma, legs and scapes usually light reddish brown. Gaster dark reddish brown. Specimens with darker overall pigmentation do occur.

-- Gyne: Compared to Formica tibetana n.sp., the images of the lectotype gyne show a strongly reduced pilosity on the dorsal plane of scape, and the extensor profiles of hind femur and hind tibia with nSc about 2, nHFex about 5 and nHT about 5.

Taxonomic comments. For separation from its sister species Formica tibetana n.sp. see there.

Biology: There are no reports on biology of this species. All findings are in the montane to subalpine zone at elevations of 3005 to 4420 m. Habitats in Sichuan were stony grassland with scattered conifer trees (5 findings), grassland with shrubs (2), stony grassland (2), light conifer stands (2), a rubble field with sparse vegetation (1) and a grassland (1).

Figures

Figure 1. Geographic distribution of Formica tibetana n.sp. (pink dots) and of Formica sentschuensis Ruzsky, 1915 (black dots, black rhomb type locality) in the Chinese provinces Quinghai, Ganzu and Sichuan. The size of dots is proportional to the number of samples found in a site.

Figure 2. Head of the paralectotype of Formica sentschuensis in full face view.

Figure 4. Clypeus of the paralectotype of Formica sentschuensis in frontodorsal view.