Yunodorylus eguchii

Katsuyuki Eguchi, Riou Mizuno, Fuminori Ito, Rijal Satria, Dang Van An, Bui Tuan Viet & Phung Thi Hong Luong, 2016, First discovery of subdichthadiigyne in Yunodorylus Xu, 2000 (Formicidae: Dorylinae), Revue suisse de Zoologie 123 (2), pp. 307-314 : 308-313

DESCRIPTION OF THE SUBDICHTHADIIGYNE OF YUNODORYLUS EGUCHII

Description ( Figs 1-12 ): Head in full-face view subrectangular, longer than broad, broadest slightly behind midlength of head, with lateral margins weakly convex and posterior margin broadly and strongly concave ( Fig. 1 ), relatively low dorsoventrally ( Fig. 4 ); preoccipital carina absent ( Fig. 8 ); frontal lobes present as narrow erect to suberect walls narrowly separated from each other by a longitudinal strip of median portion of clypeus ( Fig. 2 ); anteriormost portion of frontal lobe extending anteriad far beyond the anterior margin of clypeus (red arrow in Fig. 2 ); parafrontal ridges completely absent; antennal socket in full-face view fully exposed, very close to anterior margin of head; clypeus narrow from front to back, with a weakly convex anteromedian margin; lateroclypeal teeth low and blunt (blue arrow in Fig. 2 ); mandible triangular, with a large apical tooth followed by two small teeth on the masticatory margin; antenna 12-segmented; segment II longer than broad; segment III to XI broader than long; apical segment bullet-shaped with blunt apex, much longer than broad; compound eye absent; median ocellus vestigial, recognized as a small impression (red arrow in Fig. 4 ), but lateral ocelli absent; palp formula unknown (not dissected); mesosoma almost box-shaped, stout, in lateral view with dorsal margin slightly convex, in dorsal view slightly constricted in front of propodeum lateral margins, without flight sclerites; promesonotal suture weakly recognized, convex anteriad (red arrow in Fig. 8 ); metanotal groove relatively conspicuous dorsally and laterally, in dorsal view convex posteriad (blue arrow in Fig. 8 ); anterior margin of mesopleuron forming a small lobe projecting over basal part of forecoxa (black arrow in Fig. 9 ); metapleural gland orifice concealed beneath a ventrolaterally directed cuticular flange (red arrow in Fig. 9 ); propodeum without any spines, carinae, etc. posteriorly, in lateral view with posterodorsal corner bluntly angulate, in posterodorsal view with a faint median longitudinal depression; an endophragmal pit distinct on the lateral face of propodeum (blue arrow in Fig. 9 ); propodeal lobe very low; mesotibia and metatibia with a small simple spur in front of a large pectinate spurs; inner margin of pretarsal claws of all legs without teeth; metatibial gland absent; waist consisting of a single small segment (petiole); petiole without tergosternal fusion, in dorsal view much broader than long, broadest around the posterior 1/3 length of the petiolar length, with anterior margin weakly concave and lateral margins weakly convex; subpetiolar process developed as a rectangular lobe, with an obtuse anteroventral and acute posteroventral angle ( Fig. 7 ); abdominal segments III– VII without tergosternal fusion; abdominal segment III with anterodorsal face (above helcium) vertical, with anteroventral face (below helcium) weakly humped; the anteroventral face without any margin or carina; pygidium convex, but not flattened nor impressed dorsally ( Fig. 10 ), apically with relatively long, thick and truncate-tipped setae (red arrows in Fig. 12 ), but without any peg-like or spine-like setae on posterolateral margins; hypopygium flattened ventrally, with a U-shaped posterior margin, without any peg-like or spine-like setae on posterolateral margins ( Fig. 11 ); sting developed ( Fig. 12 ).

Body densely covered with short standing hairs, less sculptured but densely with hair pits, yellowish-brown (see Figs 1 , 5, 6 ); sclerotization of body relatively weak (head and some of legs deformed during dry-mounting).

HL 1.013 mm; HW 0.865 mm; SL 0.351 mm; ML 1.266 mm; MH 0.520 mm; PNW 0.609 mm; MFL 0.499 mm; PL 0.452 mm; PH 0.569 mm; PW 0.613; A3 W 0.750 mm; A3L 0.516 mm; CI 85; SI 35; MI 208; MFI 58; A 3I 122.

Specimen used for the description: MHNG; VIETNAM, Tay Ninh Province, Lo Go Xa Mat National Park, N11˚35’17”, E105˚53’01-10”, ca. 5-15 m alt.; K. Eguchi leg.; 20/IX/2015; subdichthadiigyne (specimen no. IMG20160315-1; colony no. Eg 20ix15-01).

Specimens used for the species determination: ACEG; VIETNAM, Dong Nai Province, South Cat Tien National Park; K. Eguchi leg.; 21/X/2004; 2 paratype workers. ‒ ACEG, IEBR, MCZC, MHNG, VNMN; for collection data see above; 20 workers (Eg 20ix15-01). ‒ ACEG, IEBR, MCZC, MHNG, VNMN; VIETNAM, Tay Ninh Province, Lo Go Xa Mat National Park, N11˚32’18-19”, E105˚53’03-11”, ca. 0-20 m alt.; K. Eguchi leg.; 19/IX/2015; 20 workers (Eg 19ix15-01).

Remarks: The “full-dichthadiigyne” in the dorylomorph lineages is usually defined by a combination of the following characteristics: compound eyes vestigial or absent; head swollen and subglobular, often with falcate mandibles; mesosoma without flight sclerites; petiole hypertrophied, commonly bilaterally cornulate; gaster distended ( Bolton, 1990; Hölldobuler & Wilson, 1990; Gotwald, 1995). Thus, it is safe to conclude that the queen of Y. eguchii is subdichthadiiform, based on the following exceptions: head less swollen and not subglobular; mandibles triangular (as seen in the worker); petiole less hypertrophied and simple in shape. In other words, the worker-queen dimorphism is weaker in Yunodorylus than in the dorylomorph lineages with a full dichthadiigyne. The remarkable differences between the worker and queen in Yunodorylus are the body proportion, presence (worker) or absence (queen) of metatibial gland, and presence (worker) or absence (queen) of pygidial peg-like or spine-like setae. Interestingly, the absence of pygidial peg-like or spine-like setae is also known in the normal and subdichthadiiform queens of the genus Acanthostichus ( Brown, 1975; Mackay, 2004).

Bionomics: The colonies Eg 20ix15-01 and Eg 19ix15-01 were found in thick soil walls of termite mounds built on the ground of lowland evergreen forest fragments of Lo Go Xa Mat National Park ( Fig. 13 ). The Eg 20ix15-01 colony contained tiny larvae probably in earlier instar only, and the Eg 19ix15-01 colony contained many larger larvae probably in the final instar and a few pupae only. These field observations suggest the presence of synchronized brood development in Yunodorylus . Both colonies were brought back to our laboratory in Kagawa Univ., Japan, and their foraging and reproduction behaviors had been observed for several months (Fig. 14). During the observation the subdichthadiigyne of Eg 19ix15-01 died or was killed, and then the body was destroyed or eaten by workers. Thus it was unusable for our morphological examination. The results of our laboratory observation will be presented in a separate paper.

Figures

Fig 13. Termite mound in which the colony Eg 19 ix 15 - 01 was found (photographed by Rijal Satria). Fig 14. Subdichthadiigyne of the colony Eg 19 ix 15 - 01 in the egg-laying phase (reared and photographed by Riou Mizuno in Kagawa University).

Figs 1 - 4. Subdichthadiigyne (specimen no. IMG 20160315 - 1; colony no. Eg 20 ix 15 - 01). (1) Head in full-face view. (2) Clypeus in fullface view. (3) Left antenna. (4) Vertex in full-face view.

Figs 5 - 7. Subdichthadiigyne (specimen no. IMG 20160315 - 1; colony no. Eg 20 ix 15 - 01). (5) Body in lateral view. (6) Body in dorsal view. (7) Mesosoma and waist in lateral view.

Figs 8 - 9. Subdichthadiigyne (specimen no. IMG 20160315 - 1; colony no. Eg 20 ix 15 - 01). (8) Mesosoma and waist in dorsal view. (9) Propodeum in lateral view.

Figs 10 - 12. Subdichthadiigyne (specimen no. IMG 20160315 - 1; colony no. Eg 20 ix 15 - 01). (10) Pygidium in dorsal view. (11) Hypopygium in ventral view. (12) Apex of pygidium in dorsal view.