Tetramorium tanakai Bolton, 1977

Yamane 1, Seiki, Hosoishi 2, Shingo & Ito 3, Fuminori, 2022, Japanese Tetramorium queens: identification key and species diagnoses (Hymenoptera, Formicidae, Myrmicinae), ZooKeys 1084, pp. 43-64 : 43

Tetramorium tanakai Bolton, 1977 stat. rev.

Figs 1o , 3b , 4h , 6b

Tetramorium tanakai Bolton, 1977: 119-120, Mt. Omoto, Ishigaki I.; Onoyama 1980: 198; Ogata 1991: 102; Bolton 1995: 415.

Tetramorium kraepelini : Japanese Ant Database Group 2003: 136; Terayama 2020: 120.

Queen diagnosis.

Measurements (n = 1): TBL 2.63, HL 0.66, HW 0.61, SL 0.40, EL 0.19, EW 0.16, PtW 0.30, CI 92.4, SI 65.6, ELI 28.8. Body brown to dark reddish-brown, with gaster very dark. Head reticulate, with frons between clypeus and ocellar region longitudinally rugose. Clypeus with three longitudinal carinae; its anterior margin entire. Posterior ocelli widely separated from each other; distance between them as long as 4.5 × ocellar diameter. Dorsum of pronotum and propodeum coarsely reticulate; mesonotum longitudinally rugose (rugae on mesoscutellum irregular); lateral face of pronotum, upper portion of mesopleuron, metapleuron and lateral face of propodeum largely striate/rugose; lower portion and part of upper portion of mesopleuron smooth to very weakly sculptured and shiny; propodeal declivity irregularly sculptured; no transverse carinae between propodeal spines. Petiolar node entirely reticulate; sternite and peduncle microsculptured and mat; postpetiole with smooth area on its dorsum; its lateral face and sternite irregularly sculptured. Gastral tergite entirely smooth and shiny. Antennal scape and mid- and hind-tibiae with many erect hairs.

Caste difference.

Worker measurements (n = 5): TBL 2.0-2.4 (2.3), HL 0.59-0.63 (0.61), HW 0.53-0.58 (0.56), SL 0.36-0.40 (0.38), EL 0.13-0.16 (0.14), EW 0.08-0.10 (0.09), PtW 0.17-0.23 (0.20), PptW 0.20-0.25 (0.23), CI 86.4-93.2 (91.2), SI 65.5-70.6 (68.6), ELI 22.0-25.4 (23.1). Worker very similar to the queen in structure and sculpture, but differing in the following aspects. Eye smaller, distance between anterior eye margin and mandibular base as long as or slightly longer than major diameter of eye; in the queen the distance much shorter than major diameter of eye. Eye distinctly tapered anteriad; in the queen, eye anteriorly broadly rounded. Mesosomal dorsum entirely coarsely reticulate; mesonotum longitudinally rugose in the queen. Mesopleuron entirely sculptured; sculpture on mesopleuron much weaker especially in lower portion that is extensively smooth and shiny in the queen.

Specimens examined.

S. Ryukyus: 1q (dealate), Mandabaru, Yonaguni-jima, emerged in v. 2020 in colony (FI19-108) collected on 14.iii.2019 by R. Hosokawa and kept in lab (Figs 3b , 4h , 6h ). 1q (dealate), Yonaha-dake, Yonaguni-jima, 12.iii.2020, F. Ito (FI20-45).

Distribution in Japan.

Yaeyama Islands of the Ryukyu Islands (Ishigaki-jima and Yonaguni-jima).

Remarks.

Tetramorium tanakai was originally described based on the worker and queen castes collected on Ishigaki-jima, Yaeyama Islands, Japan ( Bolton 1977; no queen description provided). The worker is very similar to the Southeast Asian T. kraepelini , but is distinguished from the latter by the bicoloured body (dark brown head and gaster contrasted with lighter mesosoma, waist and legs) and the petiolar dorsum longer than the height of the tergal portion of the petiole ( Bolton 1977). The workers sampled from Yonaguni-jima and examined in this study had a nearly entirely dark brown body with yellowish antennae and legs and are clearly different from extensively yellowish-brown workers of T. kraepelini and the Japanese T. cf. kraepelini . The dorsal length of the petiole is variable, generally as long as or slightly longer than the height of the tergal portion. The present study shows that the queen collected from Yonaguni-jima is also similar to that of T. cf. kraepelini in structure and sculpture, but clearly different from the latter in the widely separated posterior ocelli and coarsely reticulate dorsal propodeum as well as much darker body. We also examined queens and workers from two colonies collected in Shuisheliao, Taiwan. These specimens have a more typical bicolorous body and longer petiolar dorsum as in the original description of T. tanakai . The queens have widely separate posterior ocelli as in the queen from Yonaguni-jima. We consider the populations of Ishigaki-jima, Yonaguni-jima and Taiwan all belonging to the same species, T. tanakai . As species delimitation among the T. kraepelini -complex is very confusing, we need to have more colony series from various localities.

Figures

Figure 1. Some important characters used in the key to species a-e petiole in profile view a T. pacificum b T. lanuginosum c T. bicarinatum d T. smithi e T. tsushimae f-h anterior half of first gastral tergite f T. bicarinatum g T. simillimum h T. lanuginosum i-k antennal scape showing pilosity on its anterior margin l-n left hindtibia i, l T. cf. kraepelini j, m T. nipponense k, n T. simillimum o, p configuration of ocelli o T. tanakai p T. cf. kraepelini.

Figure 3. Japanese Tetramorium queens: habitus in profile a T. smithi (Hirarahigashi, Miyako-jima, Okinawa-ken) b T. tanakai (Mandabaru, Yonaguni-jima, Okinawa-ken) c T. tsushimae (Nokono-shima, Fukuoka-shi). (Same specimens were used for ' head in full-face view' and ' habitus in dorsal view').

Figure 4. Japanese Tetramorium queens: head in full-face view a T. bicarinatum b T. cf. kraepelini c T. lanuginosum d T. nipponense e T. pacificum f T. simillimum g T. smithi h T. tanakai i T. tsushimae.

Figure 6. Japanese Tetramorium queens: habitus in dorsal view a T. smithi b T. tanakai c T. tsushimae.