Nylanderia amia ( Forel, 1913 )

Guénard, Benoit, 2023, A checklist of Nylanderia (Hymenoptera: Formicidae: Formicinae) from Hong Kong and Macao SARs, with an illustrated identification key for species in Southeast China and Taiwan, Zootaxa 5301 (5), pp. 501-539 : 512-514

Nylanderia amia ( Forel, 1913)

( Figure 12 ; Figure 25.A )

Prenolepis (Nylanderia) bourbonica var. amia Forel, 1913 g: 197. Taiwan.

In Prenolepis (Nylanderia) : Emery, 1914f: 422; in Paratrechina (Nylanderia) : Emery, 1925d: 219; in Nylanderia: LaPolla et al., 2010 a: 127 ; raised to species: Terayama, 1999 c: 61.

Diagnosis. Nylanderia amia can be distinguished from other species of Nylanderia from Southeast China by the combination of the dorsum of the propodeum almost as long as declivity, abundant pubescence on head, head and dorsum of mesosoma faintly and sparsely reticulate, cuticle with a blue iridescence, pronotum with 10 to 12 erect macrosetae (PMC 5–6), and mesonotum with 6–8 erect macrosetae (MMC 3–4).

Measurements (n = 3 workers). ClL 0.197 –0.220; ClW 0.481 –0.498; HL 0.750 –0.799; HW 0.679 –0.716; EL 0.215 –0.228; MaD 0.123 –0.137; IoD 0.395 –0.417; SL 0.917 –0.948; ML 1.024 –1.119; PrL 0.356 –0.370; PrW 0.480 –0.513; PrFL 0.709 –0.767; MeL 0.258 –0.265; MeW 0.276 –0.307; PrpL 0.201 –0.246; PrpH 0.360 –0.423; PrpW 0.378 –0.399; PL 0.229 –0.273; Ab3L 0.498 –0.587; TL 2.501 –2.778; PMC 5–6; MMC 3–4; MI 52.2–52.7; CI 89.6–91.0; DNI 57.5–59.8; IoI 58.2–59.7; OI 31.4–32.9; SI 132.5–137.0; REL 28.1–30.0; MaI 53.9–63.7.

Compare with: N. birmana , N. bourbonica , N. IBBL-01, N. sharpii .

Morphology. Trager (1984) and Terayama (1999) both mention that N. amia can be easily differentiated from N. bourbonica by color, size, head width, pubescence, and genital structure. Likewise, both authors do not provide any further discriminatory information on the mentioned features in their diagnosis or commentaries on variation found in specimens of N. bourbonica ( Trager 1984) or in the diagnosis of N. amia ( Terayama 1999) — e.g., variation of pubescence in specific regions, such as pronotum, mesopleuron, propodeum, and first gaster tergite. In the current study, specimens previously identified as N. amia , sampled in distinct localities in Hong Kong and Macao had some variation in pubescence in the mesopleuron, with some species ascribed to N. amia presenting only some scarce pubescence in the sclerite.

In most specimens observed, the head, mesosoma, petiole, and gaster are completely jet black to dark brown. Other specimens (including the syntype) have these body parts completely light brown. Most specimens have a blue iridescence in the cuticle, although it is not easily seen in some instances (i.e., in certain light or positional conditions). This same iridescence could not be observed in images of some type specimens.

The identity of N. bourbonica has sometimes been disputed ( Trager 1984; Terayama 1999; Williams et al. 2022), meaning that, despite being variable in worker morphology and having a broad distribution, establishing unambiguous boundaries for the species is difficult. The species is commonly understood as a ‘complex of cryptic species’, given its overall superficial resemblance among specimens that are considered to constitute distinct lineages, based on distinct molecular delimitation methods ( Williams et al. 2022). However, the apparent ‘crypticity’ observed in workers belonging to this species can be better explored with a shift on framework and types of evidence used (e.g., Korshunova et al. 2019); in conjunction with molecular approaches, morphological data obtained from males and queens can be relevant to address species boundaries in the genus—as seen in Kallal & LaPolla (2012) and LaPolla et al. (2019) and discussed by Williams et al. (2022).

In Hong Kong and Macao, N. amia has been confused, understandably, with N. bourbonica . After Terayama’s (1999) study on the Japanese species of the former Paratrechina , the boundaries between both species have been made clearer, although they are still considerably hard to differentiate. Other species occurring in Hong Kong have also been equivocally identified as N. bourbonica ( Williams et al. 2022; also, see Morphology in the N. IBBL-01 discussion), although several morphological differences have been found among them.

Ecology. Specimens were found in areas with different degrees of disturbance, but mostly near urban areas (e.g., Shing Mun, Chek Lap Kok, and Cotai Ecological Zone II). This might indicate a preference of the species for more disturbed habitats, although more records are necessary to confirm this.

Distribution. Given the similarities between N. amia and N. bourbonica , the lack of relevant evidence for unambiguously demarcating both species and considering the most recent proposal of a putative insular origin for N. bourbonica ( Williams et al. 2022) , we opted to consider all records for N. bourbonica in Hong Kong, Taiwan, and neighboring mainland regions as dubious. Although the presence of this species is highly probable in those places, given its known invasive potential, we opt to take a conservative stance until a more inclusive revisionary study for the region is conducted.

Examined material. Image of a syntype worker from Hengshun, Taiwan (Form 10360001) deposited in TARI, Taichung City , Taiwan. Hong Kong: (1 worker) Tsuen Wan , Shing Mun, 22.38499 114.14395 ±500 m, elevation 197 m, 16.v.2016, Y. Luo col., #ISP0037; (1 worker) Chek Lap Kok , 22.3139 113.9398, 15.iii.16, AW4; (1 worker) Islands , Tung Chung, 22.28363 113.94063 ± 10 m, elevation 32 m, 20.ix.2016, M. Pierce col., #IAS-0062; (1 worker) Signal Hill Gardens , 22.296036 114.174716, elevation 62 m, 17.viii.2021, M. Hamer col.; (1 worker) Gilwell Campsite , 22.36003 114.22204, elevation 416 m, 24.ix.2021, M. Hamer col. [ IBBL]; Macao: (2 workers) Coloane Island , Cotai Ecological Zone II, 22.1418N 113.5519E, ca 2 m, 26.vi.2019, MAC_S20_LLSP_ Sp. 4, F. Brassard col. [ IBBL] .

Figures

FIGURE 12. Nylanderia amia. A: Lateral view of the whole body; B: Dorsal view of the head; C: Dorsal view of the whole body.

FIGURE 25. Distribution maps for seven of the thirteen Nylanderia species recorded for Hong Kong. A: Nylanderia amia; B: Nylanderia birmana; C: Nylanderia emmae; D: Nylanderia flaviabdominis; E: Nylanderia flavipes; F: Nylanderia IBBL-01; G: Nylanderia IBBL-02.