Technomyrmex horni

A forest species that has been collected from litter samples.

Identification
It is certain that more than one real species is concealed within this compound description, which effectively covers all lightly coloured samples of the Technomyrmex bicolor group of the southern Oriental and Malesian regions, under the single name of horni. Material is so sparse, samples are so small and variation within even the small samples is so obvious that more detailed resolution has proved impossible at this time.

There is variation in SI, with some evidence that it increases as HW decreases within single series, and that CI increases as HW increases. Also, the shape of the head seems to become more cordate with increased size. The shape of the clypeal notch is variable. It is frequently quite long and broadly U-shaped but it is shallower and broader in some. Density and intensity of clypeal sculpture varies considerably, as does distance of the metathoracic spiracles from the metanotal groove. The propodeal dorsum may be flat to shallowly convex, with variation within single short series, and the length of the propodeal dorsum also varies. In syntypes of horni it is much longer than the depth of the declivity to the spiracle but variants with the two about equal, to some with the dorsum shorter than the declivity depth to the spiracle, are also encountered. The junction of propodeal dorsum and declivity varies from angular to rounded. Colour variation is as noted above.

Of course, it is possible that all this variation is contained within a single plastic species, but I strongly suspect that further resolution will be possible when more material and lengthier series are available. For the present the following notes on the two already-named forms in this complex are included here.

T. horni syntype workers: Measurements: TL 3.4 - 3.9, HL 0.88 - 0.98, HW 0.80 - 0.95, SL 0.95 - 1.02, PW 0.52 - 0.59, WL 1.18 - 1.30 (4 measured). Indices: CI 90 - 97, SI 107 - 119, OI 23 - 25, EPI 65 - 73, DTI 150 - 159. With the general characters noted above. Median clypeal notch deeper than semicircular. Clypeus immediately posterior to notch punctulate. Metathoracic spiracle far in front of metanotal groove (about 3 spiracle diameters). Length of propodeal dorsum in profile about twice the depth of the declivity to the spiracle, the dorsum flat to shallowly convex; junction of dorsum and declivity angular. Head, mesosoma and petiole brownish yellow, gaster somewhat darker brown. Middle and hind femora and tibiae the same colour as the mesosoma; middle and hind coxae lighter. Middle and hind tarsi yellow, much lighter than femora and tibiae.

T. schimmeri syntype workers: Measurements: TL 2.9 - 3.2, HL 0.70 - 0.74, HW 0.62 - 0.66, SL 0.74 - 0.76, PW 0.41 - 0.42, WL 0.96 - 1.03 (4 measured). Indices: CI 86 - 89, SI 115 - 120, OI 27 - 29, EPI 70 - 79, DTI 152 - 161. With the general characters noted above. Median clypeal notch broad and shallow. Metathoracic spiracle closer than 3 spiracle diameters from metanotal groove. Length of propodeal dorsum in profile about equal to or slightly greater than the depth of the declivity to the spiracle, the dorsum flat; junction of dorsum and declivity angular. Head, mesosoma and petiole yellow to dirty yellow, gaster usually slightly darker in shade. Either all leg segments dull yellow, the same colour as the mesosoma, or the middle and hind coxae alone slightly lighter.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Borneo, Indonesia, Krakatau Islands, Malaysia. Oriental Region: Cambodia, India, Sri Lanka, Taiwan, Thailand. Palaearctic Region: China.

Nomenclature

 *  horni. Technomyrmex horni Forel, 1912a: 71 (w.q.) TAIWAN. See also: Bolton, 2007a: 84.

Worker
Bolton (2007) - TL 2.9 - 4.3, HL 0.70 - 1.06, HW 0.61 - 0.95, SL 0.74 - 1.20, PW 0.41-0.61, WL 0.90 -1.46 (26 measured). Indices: CI 82 - 97, SI 107 - 134, OI 23 - 30, EPI 65 - 80 DTI 130 - 160.

Head behind clypeus, dorsum of mesosoma, declivity of propodeum and first gastral tergite all entirely lack setae. Gastral tergites 2 - 4 with long stout setae present: second gastral tergite with 2 - 3 pairs, third and fourth tergites each with 3 - 4 pairs. Anterior clypeal margin with a distinct median notch that is semicircular to V-shaped, the margins of the notch meet the lateral portions of the anterior margin through rounded curves, not sharp angles. Posterior margin of head concave, more deeply 50 in larger workers; sides of head convex and convergent anteriorly. With head in full-face view the outer margins of the eyes fail to touch the outline of the sides of the head. Scape index 107 - 134. Clypeal sculpture fine to reticulate-punctulate between posterior margin of notch and clypeal suture. Mesosoma with DTI 130 - 160. In profile the straight-line length of the propodeal dorsum variable but without a conspicuous notch or indentation at its midlength. In profile the head, mesosoma, petiole and gaster yellow to light brownish yellow; usually the head and gaster slightly infuscated with respect to the mesosoma but sometimes the colour uniform. Anterior coxa yellow to light yellowish brown, the same colour as the mesosoma or slightly lighter. Middle and hind coxae off-white to yellow, the same colour as the mesosoma or slightly lighter. All trochanters off-white to yellow. Middle and hind femora and tibiae yellow to very light brown. Tarsi yellow, the same colour as the femora and tibiae or lighter. Sometimes all leg segments are uniformly coloured, the same shade as the mesosoma.

Type Material
Bolton (2007) - Syntype workers and queen, Taiwan: Pilam (H. Sauter) [examined].