Strumigenys koningsbergeri group

Strumigenys koningsbergeri group Bolton (2000)

Species

Malagasy

Strumigenys dicomas

Malesian-Oriental-East Palaeartic

Worker Diagnosis

Malagasy

Apical fork of mandible with 2 spiniform teeth; without intercalary dentition. In full-face view inner margin of distal one-fifth to one-quarter of mandible, immediately proximal of apicodorsal tooth, strongly concave with respect to its previous line. Mandible with a rounded tumulus or a minute denticle at proximal end of concave section of inner margin, but without strong preapical dentition. MI 42-50.

Anterior clypeal margin conspicuously and quite deeply broadly, evenly concave.

Scape elongate, subcylindrical, widest just proximal of the midlength. SI 61-75.

Eye small and convex, maximum diameter of eye slightly less than maximum width of the scape.

Ventrolateral margin of head in front of eye with a deep and strongly incised preocular notch; notch so strongly incised that anterior portion of eye is detached from side of head. With head in ventral view the preocular notch forms the apex of a transverse impression or trench in the ventral surface of the head capsule that extends toward the midline. This ventral preocular groove is posterior to, and separated from, the marked postbuccal groove.

Scrobe always well developed behind level of eye, with sharply defined dorsal margin and conspicuously deeply concave.

Spongiform appendages of petiole weakly developed, petiole with a narrow ventral curtain.

Postpetiole with small but distinct lateral and ventral spongiform lobes.

Pilosity. All standing hairs short and stiff, simple to remiform; flagellate hairs always absent. Pronotal humeral hair absent. Dorsal (outer) surfaces of middle and hind basitarsi without long erect hairs. Ground-pilosity on dorsum of head spatulate to narrowly spoon-shaped, dilute and inconspicuous.

Sculpture. Dorsal surfaces of head, alitrunk and petiole reticulate-punctate; middorsum of head and pronotal dorsum frequently with longitudinal or oblique rugulae. Side of alitrunk with smooth patches on pleurae. Gaster un sculptured except for basigastral costulae.

Glands. Bullae of glands of scape, femur, tibia, calcar, and tarsomeres not visible. Mesopleural gland visible and set in a narrow circular notch.

Malesian-Oriental-East Palaeartic

Apical fork of mandible of 2 spiniform teeth; with 2-3 intercalary denticles on dorsal surface of apicoventral tooth, near its base. (Usually 3 but basal most often vestigial or absent; two species apparently with only a single intercalary denticle.) A single preapical denticle or tooth present. In koningsbergeri-complex inner margin of mandible in full-face view, in vicinity of preapical tooth , becomes concave with respect to its previous line, the preapical denticle or tooth located at proximal commencement of concavity; most species of ebbae-complex similar but some showing morphoclinal reversion to a straight margin. A translucent lamella present on inner margin of mandible in some species. MI 37-50.

Anterior clypeal margin evenly concave to broadly V-shaped or deeply indented. Scape subcylindrical to obviously dorsoventrally flattened; short to moderately long, SI 53-82.

Apical antennomere tapering slightly from midlength to base but not strongly constricted basally; apical segment broadly articulated with the preapical.

Ventrolateral margin of head in front of eye with a complete morphocline from straight to deeply concave immediately in front of eye (always deeply concave in koningsbergeri-complex).

Scrobe always well developed behind level of eye, with sharply defined dorsal margin and conspicuously concave.

Propodeal declivity usually with a moderate lamella that has its posterior (free) margin straight to convex, at least in part; less commonly with a narrow and inconspicuous lamella the posterior margin of which is concave and parallels the shape of the margin of the declivity.

Spongiform appendages of waist segments all present, small to moderate in size. Ventral spongiform curtain of petiole is absent in one species (Strumigenys wilsoni). Lateral lobe of petiole small, usually little more than an extension of the posterior collar, never extending the entire length of the side of the node.

Pilosity. All standing hairs short and stiff, simple to spatulate, usually stubbly and truncated apically; flagellate or long soft simple hairs entirely absent. Pronotal humeral hair stiff (absent in Strumigenys offina, wilsoni). Dorsal (outer) surfaces of middle and hind basitarsi without long erect hairs. Ground-pilosity on dorsum of head simple to spatulate, short and inconspicuous.

Sculpture. Dorsal surfaces of head, alitrunk and petiole finely densely reticulate-punctate. Pleurae and side of propodeum rarely entirely reticulate-punctate, usually with smooth areas at least on katepisternum. Gaster unsculptured except for basigastral costulae.

Notes

Malagasy

A single Malagasy species, Strumigenys dicomas, is referred to the koningsbergeri-group. The group is large and mainly Malesian-Oriental, with 32 species in those regions. The diagnosis above is adapted to stress the characters of the Malagasy species. The strangely scooped-out shape of the inner mandibular margin just proximal of the apicodorsal tooth, coupled with the dentition, is immediately diagnostic of the koningsbergeri-group in Madagascar.

Malesian-Oriental-East Palaeartic

Strumigenys koningsbergeri itself forms an intermediate between this group and the loriae group as its head has the same strangely deformed shape as the latter (see diagnosis of loriae-group). However, the head of koningsbergeri grades back to the shape seen in most other members of the group through morphological intermediates such as Strumigenys seynoka and Strumigenys perturba. It is obvious that a complete morphocline exists between the most generalised head shape seen in this group (e. g. ebbae), through seynoka and koningsbergeri to the loriae-group. Differentiation into two groups may thus be artificial but the presence of sharply defined scrobes in koningsbergeri, and all other group members included below, contrasts strongly with their absence in species of the loriae-group, and has led to the retention of two groups.

The characteristic concave shape of the apical section of the inner margin of the mandible is also shared with the related omopyx group. However, in that group the basimandibular gland bulla is hypertrophied and the apical antennomere is very markedly constricted basally.

Most species in the koningsbergeri-group have a quite distinctive habitus. They are stockily built, dully coloured, reticulate-punctate species with relatively flat heads, sharply defined scrobes and sparse short stubbly pilosity. In most species the head in full-face view has prominent, quite broadly convex, dorsolateral margins. In this view the eyes in most species are not visible, or only the middle arc of their outer margins can be seen. Exceptions to this occur in those species in which the dorsolateral margin is eroded above the eye.

In broad terms the group falls into the following two complexes.

koningsbergeri complex

On right mandible preapical tooth minute or merely a denticle, its length only a tiny fraction of the mandible width at the point where the preapical tooth arises. Length of preapical tooth or denticle only equal to, frequently less than, its basal width.

Axis of preapical tooth or denticle distinctly inclined toward apicodorsal tooth, not at a right-angle to the long axis of the mandible. Concavity of inner margin of mandible distal of preapical tooth/denticle conspicuous.

In addition to these dental characters the inner margin of the mandible never bears a prominent cuticular lamella and the preocular impression in the ventrolateral margin of the head is always obvious, deep and narrow. The preocular impression is always continued onto the ventral surface of the head where it usually forms a broad shallow basin or depression. In a few species it is transversely elongated and extends almost to the ventral midline. Petiole node in dorsal view is broader than long.

Cephalic standing pilosity is always short and stubbly, and remarkably stable within the complex. In profile the cephalic dorsum has a pair of hairs at or near to the highest point of the vertex; there is a transverse row of 6-10 (rarely 4) hairs along the line of the occipital margin; there is a widely separated pair of hairs between these, located closer to the dorsolateral margin than to the midline. In full-face view the upper scrobe margins are fringed with simple to narrowly spatulate short hairs that are strongly curved anteriorly; there is a freely projecting short stubbly apicoscrobal hair; dorsolateral margin posterior to apicoscrobal hair has 1-3 even shorter laterally projecting hairs.

Within the complex the species can be subdivided as follows.

Species in which the pronotal dorsum lacks erect hairs except for the humeral pair (the latter also absent in one species): amasara, blanda, ignota, koningsbergeri, offina, penurba, seynoka, strygax, venigosa, discussed under koningsbergeri.

Species in which the pronotal dorsum has a pair of erect short hairs as well as the humeral pair; the second pair is located close to the anterodorsal margin of the pronotum, anterior to the humeral pair: amnesia, ataxia, chorosa, hyletha, nergala, taraxis, discussed under chorosa.

ebbae complex

On right mandible preapical tooth triangular or conical (may be slightly recurved), its length one-quarter or more of the mandible width at the point where the preapical tooth arises. Length of preapical tooth greater than its basal width, usually very obviously so. Axis of preapical tooth usually at a right-angle to the long axis of the mandible, not distinctly inclined toward apicodorsal tooth. Concavity of inner margin of mandible distal of preapical tooth conspicuous in some, indistinct or not apparent in others.

Among the 17 species of this complex the inner margin of the mandible sometimes bears a convex cuticular lamella. Development of this feature is very variable between species, being absent in some, weakly developed in others, and strikingly obvious in a few. The preocular impression in the ventrolateral margin of the head is variably developed, ranging from completely absent to deep. Degree of development of the preocular impression is associated with degree of concavity of the inner margin of the mandible distal of the preapical tooth/denticle. There appears to be a morphocline covering the two features that spans the complex. At one end of the morphocline are species with no preocular impression and no mandibular concavity, and at the other are species with both very well defined. Because of these, and other, gradient features this complex is difficult to subdivide further in any unambiguous way.

References

Bolton, B. 2000. The ant tribe Dacetini. Memoirs of the American Entomological Institute. 65:1-1028.