Strumigenys formosa (Terayama, Lin & Wu, 1995) Terayama, Lin & Wu, 1995

Tang, Kit Lam, Pierce, Mac P. & Guenard, Benoit, 2019, Review of the genus Strumigenys (Hymenoptera, Formicidae, Myrmicinae) in Hong Kong with the description of three new species and the addition of five native and four introduced species records, ZooKeys 831, pp. 1-48 : 12-15

Strumigenys formosa (Terayama, Lin & Wu, 1995) - new record Fig. 4 A–C

Epitritus formosus Terayama et al., 1995: 85, figs 1-4 (q.) TAIWAN. Indomalaya.

Pyramica formosus (Terayama et al., 1995). Combination in Pyramica : Bolton 1999: 1672.

Strumigenys formosa (Terayama et al., 1995). Combination in Strumigenys : Baroni Urbani and De Andrade 2007: 120.

Material examined.

HONG KONG, Sha Tin District, Tai Po Kau Nature Reserve, 22.426138N 114.181783E, 162 m, 6.VII.2017, R.H. Lee, RHL03476, pitfall trap, IBBL.

Measurements.

Worker (n = 1): TL 1.6, HL 0.35, HW 0.38, MandL 0.13, SL 0.18, EL 0.024, PW 0.24, ML 0.41, PL 0.18, PH 0.10, DPW 0.12, PPL 0.11, GL 0.41, CI 109, MI 37, SI 47, OI 6, LPI 57, DPI 68.

This species has been described from two queens collected in 1988 in Nantou County, Taiwan. To the best of our knowledge, no additional records have been reported in the following 30 years. A single worker was collected in Hong Kong which fits the morphological characteristics and size of S. formosa . In the absence of nest series, assigning this worker to this species might be uncertain, however, the extreme rarity of this species in Hong Kong and Taiwan limits the likelihood of collecting nest series. As a result, in the presence of several convergent characters, we assign the worker collected to S. formosa . Complete description and diagnosis are provided below.

Worker description.

(Fig. 4) Head. In full-face view, head slightly longer than wide with its widest portion near its mid-length. Occipital margin deeply, evenly concave; occipital corners well developed and flattened on their apical portion, then forming a rounded angle with lateral margins. Posterolateral margins divergent on more than half of their length, then more abruptly converging towards the centre of head. Anteromedian clypeal margin slightly convex. Scapes with a well-developed subbasal lobe on their anterior portion. Mandibles elongate and curvilinear. Inner margin of mandibles without spoon-shaped hairs and with teeth clearly visible. In the mid-part of each mandible, a single denticle present, followed by a well-developed tooth and further three denticles all similar to the first. In profile view, apical portion of mandibles distinctly enlarged and with apicoventral tooth distinct (but not in full-face view) and longer than other teeth. In anterior view of the mandibles, enlarged extremity of mandibles composed of a single apicodorsal tooth followed by a series of very fine, compact, baleen-like mandibular setae. Eyes present but reduced and indistinct, on lateroventral position.

Mesosoma. In profile view, dorsum of mesosoma continuous and slightly concave on its mesonotum portion. Pronotomesopleural suture visible and extending on about one-third on the height of the pronotum. Fine lamellae of spongiform tissues present on propodeal declivity, with its upper posterior portion slightly acute as in female holotype. Metapleural gland bulla well developed. In dorsal view, thorax trapezoidal with pronotum much wider than mesonotum and propodeum. Anterior margin of pronotum convex and forming rounded angles with lateral margins.

Waist segments. Petiolar peduncle long, its lateral margins slightly concave in shape when seen in dorsal view. In profile view, petiolar node low and rounded. In profile view, postpetiole lower than petiole. In dorsal view, postpetiole distinctly larger than petiole, bean shaped, and fully surrounded by spongiform tissues.

Pilosity. On posterior half of head, pilosity limited to a few short J-shaped hairs present on lateral margin of head and oriented apically when head observed in full-face view. More short J-shaped hairs visible in profile view, slightly denser on particular on the posterior margin of head. In full head view, as for the female reproductive caste, frontal lobes covered by about 15 appressed large orbicular hairs arranged longitudinally. Clypeus with sparse presence of small to medium-sized spoon-shaped hairs. Anterior clypeal margin with four spoon-shaped hairs pointing forward and directed towards the mid-point of the clypeus, with central hairs significantly larger than those present on lateral margins. Spoon-shaped hairs completely lacking on mandibles but with finer pubescence present. On scapes, spoon-shaped hairs present on lateral margins and arranged in a crescendo fashion from smaller hairs present from about two-third of the scape on its apical to larger hairs present on the subbasal lobes; all pointing anterodorsally towards the apex of subbasal antennal lobe. In profile view, a few short, acute and erected hairs visible on mesonotum and anterodorsal part of the propodeum. Legs with numerous suberected fine and long hairs present on femurs, with apical portion of femurs bearing a few spoon-shaped hairs. Petiolar node with a continuous collar of four large spoon-shaped hairs oriented backwards and extending from the lateral margin of the petiole at about its midpoint to its dorsal portion, with their size increasing posteriorly. Other thick hairs present on dorsal portion of the petiole and oriented backwards. Sparse erected spoon-shaped hairs present on gaster significantly longer with their basal portion elongated and thin. Fine elongated simple hairs present on sternites and arranged transversely.

Sculpture. Head finely aerolated in all visible portions, including scapes, but not on mandibles. Aerolate sculptures particularly well defined around the eyes, when specimen observed in profile view. In profile view, pronotum mostly reticulated at the exception of its most ventral region which is smooth. Mesopleuron and metapleuron almost entirely smooth and shiny. Posterodorsal part of the propodeum reticulated. In dorsal view, thorax with coarse reticulated sculpture. Coxa, femur and tibia aerolated. In profile view, petiole mainly reticulated at the exception of the anterior part of the petiolar peduncle smooth. In dorsal view, petiole clearly reticulated. Visible part of postpetiolar node smooth and shiny. Gaster entirely smooth and shiny, with only short longitudinal striae present on anterior portion of the dorsal part of the tergite of the fourth metasomal segment.

Colouration. Bright yellow for most of the body at the exception of the gaster which is slightly darker.

Comments.

The specimen clearly shares all characters of the S. murphyi -group ( Bolton 2000) for which five species occur within the Oriental realm. The absence of flattened hairs on the inner margin of the mandibles distinguishes it from S. dyschima , S. hemisobek , and S. murphyi . All hairs on the scape are curved toward the basis of the scape, in contrast to S. nannosobek , which has hairs that are pointing towards the apex. On the Hong Kong specimen, the posterior margin of the head is deeply concave, con trary to other species of the S. murphyi -group except for S. formosa (based on the queen description), which also lacks flattened hairs on the inner margin of the mandibles and has a similar disposition and orientation of spoon-shaped hairs on the scape.

Geographic range.

Hong Kong, Taiwan. This record of S. formosa represents the second record for this species and the first outside of Taiwan. Therefore, this species should not be considered as endemic to Taiwan.

Ecology.

The only worker known from Hong Kong (Fig. 2) was collected in a secondary forest at an elevation of 162 m.