Probolomyrmex longinodus

Kikuchi & Tsuji (2005) reported finding 5 colonies of Probolomyrmex longinodus. The nests were in snail shells, filled with soil, under the leaf litter in primary forest (Yonaguni Island, the Ryukyus ). They found a mean of 22 workers per colony and from 3 to 13 dealate queens. Only one of the queens was inseminated and had active ovaries. The remainder of the dealate queens were all virgin and ovarian condition indicated they had never produced any eggs. It is likely that they had failed to disperse, and may have engaged in non-reproductive activities.

Identification
Eguchi et al. (2006) - P. longinodus is most similar to Probolomyrmex longiscapus. Xu & Zeng (2000) gave the following diagnostic characteristics by which the latter is separated from the former in the worker: head longer, occipital margin almost straight; scape much longer; propodeal teeth larger; and in dorsal view posterior 1/3 of petiolar node narrowed backward. But when the additional nontype material was included in our examination, the two species were not separated by CI, condition of occipital margin, size of propodeal teeth, and shape of petiolar node. Although SI in the worker seems to be a valuable character separating the two species, the Taiwanese form has larger SI (122–127, 3 workers measured). In the present study we found only a small difference between the workers of the two species (as given in the key), while the male provides better characters which support the separation of the two species (see under P. longiscapus).

Anterior slope of petiole is gentler, posterior portion of subpetiolar process is slightly higher, and mesosoma in dorsal view is a little slenderer in the workers from Thailand than in those from the S. Ryukyus. However, there is almost no difference in SI between them.

Distribution
Sabah, Malaysia, S. Ryukyus, Taiwan, N. Thailand.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Borneo, Brunei Darussalam, Indonesia, Malaysia. Oriental Region: Taiwan, Thailand. Palaearctic Region: Japan.

Morphology
Kikuchi & Tsuji (2005) - Queens have spermatheca and ovaries. Workers have no spermatheca and their ovaries have neither mature oocytes nor yellow bodies, and the mean length of their ovarioles was significantly shorter than that of the inseminated queens. Both queens and workers have one ovariole in each ovary.

Nomenclature

 *  longinodus. Probolomyrmex longinodus Terayama & Ogata, 1988: 592, figs. 6-8 (w.) JAPAN. Eguchi, Yoshimura & Yamane, 2006: 14 (q.m.).

Worker
HL 0.66 mm; HW 0.44 mm; SL 0.51 mm; CI66.7; SI117.1; WL 0.90 mm; PW 0.34 mm; PNW 0.19 mm; PNI55.6; petiolar H 0.25 mm; PNL 0.36 mm; LPI 145; TL ca. 2.6 mm.

Smaller species. Head longer than broad with shallowly concave posterior margin and slightly convex sides in full face view. Mandibles small, covered by fronto-clypeal projection. Mouth parts not dissected, but at least one acute apical tooth of masticatory margin and short setae on mandible are recognizable. Antennae 12-segmented; scapes reaching posterior 1/4 of head length; 2nd and 3rd antennal segments each longer than broad, about 1.2 x as long as broad; 4th to 11 th segments each broader than long; apical segment large, almost as long as three preceding segments together. Eyes absent.

General form of trunk and petiole as in Fig. Trunk slender, with arched node, without any sutures dorsally; dorsal outline of trunk straight. Propodeum marginate posteriorly, with a pair of small dentiform projections posterodorsally; posterior declivity concave. Legs long; middle and hind tibiae each with a distinct pectinate spur, but lacking smaller simple spur; claws small and simple. Petiole narrow, distinctly longer than high, gently curved anteriorly and abruptly descent posteriorly; posterior face slightly concave and marginate; posterodorsal margin transversely straight in dorsal view; posterolateral margin slightly concave in lateral view; subpetiolar process low, with small anterior projection and concave ventral edge, but not forming posteroventral corner. Anterior portion of first gastric sternum strongly marginate; second gastric tergum excluding acrotergite, as long as first one.

Body surface finely shagreened, with overlying punctures, lacking distinct standing hairs; color reddish brown.

Eguchi et al. (2006) - HL, 0.65–0.75 mm; HW, 0.43–0.49 mm; SL, 0.50–0.62 mm; CI, 64–70; SI, 111–127; WL, 0.95–1.16 mm; PW, 0.33–0.40 mm; DPtW 0.18–0.23 mm; DPtI, 50–58; PtH, 0.23–0.30 mm; PtNL, 0.33–0.41 mm; LPtI, 137–148 (N=10).

Queen
Eguchi et al. (2006) - HL, 0.68–0.70 mm; HW, 0.47–0.48 mm; SL, 0.52–0.58 mm; EL, 0.13–0.15 mm; CI, 68–71; SI, 108–121; EI, 27–31; WL, 1.06–1.12 mm; PW, 0.39–0.44 mm; DPtW 0.20–0.23 mm; DPtI, 49–54; PtH, 0.27–0.29 mm; PtNL, 0.36–0.38 mm; LPtI, 128–141 (N=7). Body ferruginous brown. Head in full-face view elongate, with weakly convex sides and almost straight occipital border. Frontal carina in profile relatively low as in the worker (see Fig. 9C). Eye as long as or a little longer than the width of apical antennal segment. Antennal scape when laid backward reaching or extending beyond the level of anterior margin of lateral ocelli; relative lengths of antennal segments II–XII as in the worker (see Fig. 10C); segment III a little longer than IV; IV a little shorter than broad. Pronotum large; mesoscutum 1.2–1.3 times as long as broad, in profile very weakly convex; notauli absent; parapsidal lines very fine or sometimes invisible; scuto-scutellar suture fine, very weakly and roundly curved posteriad; scutellum in profile with relatively gentle posterior slope; axilla poorly separated from scutellum by an obscure impression but not by a suture; mesopleuron (except in its posteriormost part) well divided by a suture into anepisternum and katepisternum; raised median portion of metanotum with gentle lateral slopes; suture between metepisternum and propodeum absent; a deep depression present dividing metepisternum into anepisternum and katepisternum; orifice of metapleural gland small, opening posterolaterad; posterior margin of dorsum of propodeum in dorsal view widely and moderately concave; posterior face of propodeum margined laterally with a carina which forms a triangular propodeal spine; outline from propodeal spine to propodeal lobe in profile weakly concave. Petiole including subpetiolar process much longer than high, in profile with weakly concave posterior outline (above the articulation with gaster), in dorsal view gently widened toward its midlength, and then parallel-sided or slightly constricted in front of the posterior margin; posterodorsal margin of petiolar node in dorsal view with a very shallow median emargination/concavity; subpetiolar process inconspicuous, only with an acute anterior projection. Abdominal segment III (gastral segment I) in profile relatively short, gently narrowed anteriad in the anterior 3/4. Wing structure and venation as in the male. Hind wing with three hamuli.

Male
Eguchi et al. (2006) - HL, 0.47–0.55 mm; HW, 0.54–0.59 mm; CI, 107–117; HD, 0.48–0.53 mm; HDI, 91–104; EL, 0.26–0.30 mm; SL, 0.34–0.42 mm; SI, 63–71; MstlL, 0.19–0.22 mm; MstlW, 0.23–0.28 mm; MstlI, 121–140; WL, 1.08 mm; PtNL, 0.31–0.39 mm; PtH, 0.24–0.28 mm; LPtI, 129–158 (N=4, but N=3 for HD and HDI, N=1 for WL). Head in lateral view relatively thick (HDI>90); protrusion of frontoclypeal region relatively long so that antennal insertion is situated in the middle of its dorsal surface. Frontal carina high, distinctly exceeding posterior margin of antennal insertions in full-face view. Eye relatively broad, strongly widened ventrally. Antennal flagellum relatively long, filiform; antennal segment III distinctly longer than segment II; segment XI (the third from apex) distinctly longer than broad; ventrolateral surface of the apical segment not concave. Mandible triangular, with four small dents and a single strong apical tooth on its masticatory margin; its basal angle not strongly angular but distinct. Palpal formula: maxillary 4, labial 2; maxillary palp relatively long; the second palpomere distinctly longer than the third, and the apical distinctly longer than the third. Pronotum distinctly higher than mesoscutum in lateral view; metanotum strongly produced posteriorly, and a suture separating it from mesoscutellum strongly notched; anepisternum of metapleuron separated from metakatepisternum and propodeum by a deep furrow; a suture between metakatepisternum and propodeum weak, but recognizable; dorsal margin of propodeum forming a weak angle with the posterior slope. With the mesosoma in dorsal view, mesonotum lacking notauli; parapsidal lines distinct; axillae distinct; mesoscutellum slightly broader than long; declivitous face of the propodeum very slightly convex with weak, obtuse posterolateral lamellae. Petiole without a distinct peduncle; petiolar node long, with gentle anterior and posterior slopes; posterodorsal margin not angular but rounded; subpetiolar process narrowly developed with its apex sharp. Abdominal sternum IX long; its apical margin gently pointed medially. Genitalia retractile. With the phallus in lateral view, the basal ring relatively short and its dorsal margin steeply declined; basiparamere with the dorsal margin suddenly raised in its basal portion and posterodorsal margin angular; digitus volsellaris somewhat steeply curved ventrally on its apical portion; penis valve distinctly narrowed apically, and its apical portion relatively sharp and not curved ventrally. Paramere thin; its expanded inner faces directed ventrally, with the apical portion very slightly curved dorsally. Aedeagal apodeme relatively wide. On fore wing, costa and radius apical to stigma vestigial; Rsf2 and Rsf3 completely absent; radial sector never reaching costal margin; Mf1, Rs+M and media apical to Rs+M present; cu-a cross vein present. On hind wing, Rsf4+5 present; jugal lobe absent.

Type Material
Eguchi et al. (2006) - Holotype: worker, Yonehara, Ishigaki Is., Ryukyus, Japan, 15/iii/1984, Y. Fukumoto (Faculty of Agriculture, Kyushu Univ., Japan) [examined].