Nylanderia, Emery, 1906

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 : 506-511

Illustrated identification key for the Nylanderia species from Southeast China and Taiwan

Species recorded for Hong Kong are indicated in the key with a single asterisk (e.g. N. amia *), while species recorded for Macao are marked with a double asterisk (e.g. N. picta **). Since N. yerburyi has a wide variation in length of the propodeum dorsum, it runs through two different couplets in the key.

1. Masticatory margin of the mandible with 7–8 teeth. Compound eye positioned posterior to the midline of the head ( Fig. 3.A )................................................................................ Nylanderia opisopthalmia

- Masticatory margin of the mandible with 5-6 teeth. Compound eyes positioned anterior to the midline of the head ( Fig. 3.B ).................................................................................................... 2

2. Masticatory margin of the mandible with 5 teeth. Metanotal groove not deeply impressed ( Fig. 4.A ).... Nylanderia integera

- Masticatory margin of the mandible with 6 teeth. Metanotal groove deeply impressed ( Fig. 4.B )....................... 3

3. Absence of erect setae on scape. Hind femur and tibia without erect setae........................... Nylanderia otome

- Presence of erect setae on scape. Hind femur and tibia with erect setae........................................... 4

4. Length of mesopleural notch ( Fig. 1.C ) almost a third the length of the mesonotum ( Fig. 5.A ); posteroventral pronotal margin widely separated from anterior mesopleural margin.......................................................... 5

- Length of mesopleural notch less than a third the length of the mesonotum ( Fig. 5.B and C ); posteroventral pronotal margin almost touching anterior mesopleural margin............................................................... 6

5. Malar area with several longitudinal rugulae. Interocular area and medial area of the frons completely smooth. Mesopleuron with fine longitudinal striae ( Fig. 6.A )...................................................... Nylanderia emmae *

- Malar area completely reticulate. Interocular area and medial area of the frons completely reticulate. Mesopleuron completely reticulate ( Fig. 6.B )............................................................... Nylanderia flaviabdominis *

6. In lateral view, dorsum of the propodeum almost as long as declivity; dorsum length 0.75–1.0x declivity length ( Fig. 7.A )...................................................................................................... 7

- In lateral view, dorsum of the propodeum shorter than declivity; dorsum length 0.25–0.5x declivity length ( Fig. 7.B )..... 10

7. Head and dorsum of mesosoma completely reticulate......................................... Nylanderia birmana *

- Head and dorsum of mesosoma either completely smooth, faintly and sparsely reticulate, or punctate................... 8

8. Body frequently bicolor; mesosoma and petiole normally lighter than head and gaster. Erect macrosetae reddish or light yellow ( Fig. 8.A )......................................................................... Nylanderia yerburyi *, **

- Body frequently concolor; mesosoma and petiole normally the same color as head and gaster. Erect macrosetae black or dark brown ( Fig. 8.B )...................................................................................... 9

9. Body color light brown to dark brown. Cuticle without a blue iridescence...................... Nylanderia bourbonica

- Body color dark brown to black. Cuticle with a blue iridescence................................ Nylanderia amia *, **

10. Mesonotum with abundant pubescence; pubescence not restricted to the dorsum of mesonotum, covering its lateral area as well............................................................................................... 11

- Mesonotum with sparse or without abundant pubescence; if present, pubescence restricted to the dorsum of mesonotum, not occurring at its lateral area............................................................................ 14

11. Eyes approximately 2.0x as long as malar distance (MaI 48.2–64.1)............................................ 12

- Eyes approximately 1.75x as long as malar distance (MaI 65.3–73.8)........................................... 13

12. Interocular distance approximately four times the eye width in dorsal view of the head (IoI 60.9) ( Fig. 9.A ). Distance between outer margin of the eye and the lateral margin of the head, in dorsal view, more than half the width of the scape.............................................................................................. Nylanderia formosae

- Interocular distance approximately three times the eye width in dorsal view (IoI 62.9–63.4) ( Fig. 9.B ). Distance between outer margin of the eye and the lateral margin of the head, in dorsal view, less than half the width of the scape................................................................................................... Nylanderia taylori *, **

13. Head as long as wide (CI 84.9–90.2). Interocular distance more than four times the eye width (IoI 56.2–58.6) ( Fig. 10.A ). In dorsal view, posterior margin of head medially convex...................................... Nylanderia yerburyi *, **

- Head longer than wide (CI 81.3–85.5). Interocular distance four times the eye width or less (IoI 59.5–62.1) ( Fig. 10.B ). In dorsal view, posterior margin of head almost straight........................................... Nylanderia indica *

14. Dorsum of head with abundant pubescence................................................................ 15

- Dorsum of head without or with sparse pubescence......................................................... 17

15. Eyes relatively small (REL 20.3); seven ommatidia in the longest row........................... Nylanderia kraepelini

- Eyes relatively large (REL 27.7–29.7); 10 to 12 ommatidia in the longest row.................................... 16

16. Yellow to light brown macrosetae generally on the whole body, at least on the mesosoma............ Nylanderia flavipes *

- Dark macrosetae on the whole body..................................................... Nylanderia sharpii *, **

17. Eye relatively small (REL 17.1–18.4), with six ommatidia in the longest row...................... Nylanderia picta *, **

- Eye relatively large (REL 21.2–23.2), with nine to 12 ommatidia in the longest row................................ 18

18. In lateral view, dorsum of the propodeum evenly convex ( Fig. 11.A )........................................... 19

- In lateral view, dorsum of the propodeum angulate (with a well-defined inflection) ( Fig. 11.B )....................... 21

19. Head and mesosoma dark brown to black................................................... Nylanderia guanyin

- Head and mesosoma yellow to light brown................................................................ 20

20. Dark macrosetae on whole body. Eye length 4.5x times the lateral margin of the head (REL 22.7). Third to fifth gastral segments yellow to light brown. In dorsal view, posterior margin of head without a median incision.................................................................................................... Nylanderia IBBL-01*, **

- Yellow to brown macrosetae on whole body. Eye length 3x times the lateral margin of the head (REL 34). Third to fifth gastral segments dark brown. In dorsal view, posterior margin of head with a median incision........ Nylanderia yaeyamensis *, **

21. Head usually subrectangular, smooth, without sculpture. Ocelli usually absent. Cuticle without a blue iridescence............................................................................................. Nylanderia vividula

- Head always relatively oval, with faint reticulation. Ocelli always present. Cuticle with a blue iridescence............................................................................................... Nylanderia IBBL-02*, **

Figures

FIGURE 1. Schematic illustration of areas and structures frequently used in Nylanderia descriptions and identification. Abbreviations. as: antennal socket; cl: clypeus; ey: eye; fl: flagellum; fn: flagellomere count; md: mandible; oc: ocelli; pd: pedicel; sc: scape; white star: petiolar scrobe. Bottom-right corner contains basic positional standards used in this study.

FIGURE 3. Schematic illustration showing the position of the eyes in relation to the midline of the dorsal margin of the head. A: eye positioned posterior to the midline of the head (MCZENT00532865, Jason L. Williams, from www.antweb.org); B: eye positioned anterior to the midline of the head.

FIGURE 4. Schematic illustration showing the degree of impression of the metanotal groove, indicated by a black arrow. A: metanotal groove not deeply impressed; B: metanotal groove deeply impressed.

FIGURE 5. Schematic illustration showing the length of the mesopleural notch in relation to the length of the mesonotum, indicated by proportion bars and black arrows. A: length of mesopleural notch almost a third the length of the mesonotum; B: length of mesopleural notch a fifth the length of the mesonotum; C: length of mesopleural notch a sixth the length of the mesonotum.

FIGURE 6. Schematic illustration showing the type of sculpture present in the mesopleuron. A: mesopleuron with fine longitudinal striae; B: mesopleuron completely reticulate.

FIGURE 7. Schematic illustration showing the proportion of the dorsal margin length in relation to the posterior margin length. A: dorsal margin length 0.75–1.0x posterior margin length; B: dorsal margin length 0.25–0.5x posterior margin length.

FIGURE 8. Schematic illustration showing differences in erect macrosetae color. A: erect macrosetae color reddish or light yellow; B: erect macrosetae color black or dark brown.

FIGURE 9. Schematic illustration showing differences in proportion between the interocular distance and eye width. A: interocular distance approximately three times the eye width in dorsal view (CASENT0911006, Will Ericson, from www. antweb.org); B: interocular distance approximately three times the eye width in dorsal view.

FIGURE 10. Schematic illustration showing differences in proportion between the interocular distance and eye width. A: interocular distance more than four times the eye width (CASENT0911013, Will Ericson, from www.antweb.org); B: interocular distance four times the eye width, or less than four times (CASENT0911008, Will Ericson, from www.antweb.org).

FIGURE 11. Schematic illustration showing differences in shape of the dorsal margin of the propodeum. A: dorsal margin of propodeum convex; B: dorsal margin of the propodeum angulate.