Strumigenys rogeri group

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Strumigenys rogeri group Bolton (2000)

Species

Afrotropical

Malagasy

Strumigenys rogeri also occurs in the Austral, Neotropical-Nearctic and Malesian-Oriental-East Palaeartic regions.

Worker Diagnosis

Afrotropical

Apical fork of mandible usually without intercalary teeth; more rarely one or both with an intercalary denticle (in one species left fork with two dentic1es) . Right mandible with two preapical teeth , the proximal spiniform and longer than the distal (latter may be very small and concealed by opposing apicodorsal tooth at full closure) ; left mandible similar or with distal preapical tooth lost. MI 40 - 65.

Scape subcylindrical to very weakly dorsoventrally flattened, short to long, SI 62 - 97.

Ventrolateral margin of head with a deep, strongly incised preocular notch; notch so strongly incised that in dorsal view 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. Side of head immediately above preocular notch usually with a vertical impression.

Ventral surface of petiole usually with a conspicuous spongiform strip or curtain; spongiform lobes of postpetiole present but first gastral sternite without a basal spongiform pad.

Pilosity. Pronotal humeral hair absent or present. Apicoscrobal hair absent; upper scrobe margin fringed by a continuous row of small curved hairs. Cephalic dorsum with 0 - 6 standing hairs, usually with a transverse row of 4 near occipital margin and a pair close to highest point of vertex; variously reduced in some complexes and individual species. Mesonotum with a single pair of standing hairs. First gastral tergite with simple to remiform hairs; flagellate hairs always absent.

Sculpture. Head and alitrunk reticulate-punctate; pronotal dorsum frequently with longitudinal or oblique rugulae or costulae; pleurae and side of propodeum usually smooth, rarely punctate. Gaster unsculptured except for basigastral costulae.

Malagasy

Apical fork of mandible with 2 spiniform teeth, without intercalary teeth or denticles. Mandible with 1 or 2 stout preapical teeth which are situated in the apical third of the length; when 2 present then proximal slightly longer than distal. Mandible in full-face view almost straight and at full closure parallel (diverging apically in Strumigenys vazimba), MI 43-66.

Scape elongate and more or less cylindrical. SI 62-112.

Promesonotum flat to slightly convex dorsally and bluntly marginate laterally.

Ventrolateral margin of the head notched or indented immediately in front of the eye. With head in profile the preocular notch seen to continue vertically as a groove in the side of the head that extends towards the dorsal outline. Preocular notch extends onto the ventral surface of the head as a transverse preocular groove that runs toward but does not reach the midline. An extremely deep and sharply defined post-buccal groove also present, extending across entire width of head immediately posterior of buccal cavity; post-buccal groove sharply separated from ventral preocular groove. Spongiform appendages of petiole usually well developed into a ventral curtain, but occasionally very narrow or nearly absent. Postpetiole with lateral and ventral lobes. Lamella of propodeal declivity absent or very narrow.

Pilosity. Pronotal humeral hair either absent, or stiffly filiform, or rarely flagellate. Cephalic dorsum with a transverse row of 4-6 hairs near occipital margin and 1 pair near vertex. Upper scrobe margin posteriorly with 2-4 (usually 3) stiff erect hairs that are longer than hairs on leading edge of scape. Mesonotum usually with 1 pair of erect hairs, occasionally with two pairs.

Sculpture. Head and alitrunk reticulate-punctate, occasionally with longitudinal or oblique rugulae or costulae; pleurae usually smooth, rarely punctate. Gaster unsculptured except for basigastral costulae.

Glands. Scape gland absent (Strumigenys admixta, Strumigenys ection, Strumigenys labaris, Strumigenys luca, Strumigenys milae, Strumigenys nambao, Strumigenys rogeri, Strumigenys sphera, vazimba) or visible as an elongate patch near apex of ventral or leading edge of scape (Strumigenys carisa, Strumigenys fronto, Strumigenys hilaris, Strumigenys lysis, Strumigenys norax). Femoral and tibial gland bullae entirely absent. Gland at base of calcar conspicuous. Tarsal gland bullae visible on at least first three tarsi, decreasing in size from basitarsus where it is elongate to the third tarsal segment where it is oval. Mesopleural gland usually set in a circular notch but less commonly in a concave impression (carisa, hilaris).

Notes

Afrotropical

Members of the rogeri-group are instantly diagnosed by the presence of a deep preocular notch in the ventrolateral margin of the head that detaches the anterior portion of the eye from the side of the head. In ventral view the preocular notch is seen as the apex of a transverse groove or impression that extends across the ventral surface toward, but not reaching, the ventral midline. This preocular transverse groove is posterior to, and separated from, the postbuccal transverse groove. The latter is immediately posterior to the buccal cavity and is universally present in Afrotropical species. In profile the preocular notch is often also the base of a vertical groove that ascends the side of the head immediately in front of the eye; in some species this vertical groove interrupts the dorsolateral margin of the head.

The group contains 14 species in the Afrotropical region and is also well represented in Madagascar where an extensive radiation has taken place. In the Afrotropical fauna five complexes of closely related species can be recognised.

Rigato (2006) described Strumigenys bartolozzii as a member of this species group but did not place this species in any of the complexes defined below.

londianensis complex

Left mandible with 1 spiniform preapical tooth (the proximal); right mandible with 2 preapical teeth but the distal very small and usually concealed by the opposing apicodorsal tooth at full closure. Apical fork of left mandible with 1 intercalary denticle or small tooth; apical fork of right mandible without intercalaries. Cephalic dorsum without standing hairs or at most with 1 pair present close to occipital margin. Scape relatively long, SI 82 – 97.

cacaoensis complex

Left and right mandibles each with 2 small preapical teeth, these either about the same size or the proximal slightly shorter than the distal. Apical fork of left mandible with 2 intercalaries, the upper a sharp tooth and the lower a denticle; apical fork of right mandible with 1 minute intercalary denticle. Cephalic dorsum without standing hairs. Mesopleuron, metapleuron and side of Propodeum reticulate-punctate. Head relatively broad and scape short, CI 86 - 91, SI 62 –67. Arboreal.

rogeri complex

Left and right mandibles each with 2 preapical teeth, the proximal spiniform and longer than the distal (for exceptions see under bernardi); preapical teeth not crowded together near apical fork. Apical fork on each mandible without intercalary teeth or denticles. Cephalic dorsum with a transverse row of 4 erect short hairs close to occipital margin and with similar pair close to highest point of vertex. Scapes and mandibles relatively long, SI 79 – 92, MI 50 –65; head tending to be somewhat longer and narrower than in following two complexes, CI 65 – 75.

pretoriae complex

Left and right mandibles each with 2 apical teeth, the proximal spiniform and longer than the distal; preapical teeth crowded together near apical fork. Apical fork on each mandible without intercalary teeth or denticles. Cephalic dorsum either with a transverse row of 4 erect short hairs close to occipital margin or with this row and a pair close to highest point of vertiex. Eyes large, maximum diameter 0.18 – 0.24 X HW. Scapes and mandibles relatively short, SI 64 – 77, MI 44 – 49; head tending to be shorter and broader than in rogeri-complex, CI 71 – 81.

rufobrunea complex

Left and right mandibles each with 2 preapical teeth, the proximal spiniform and longer than the distal; preapical teeth not crowded together near apical fork. Apical fork on each mandible without intercalary teeth or denticles. Cephalic dorsum with a transverse row of 4 erect short hairs close to occipital margin and with similar pair close to highest point of vertex. Maximum diameter of eye about 0.15 X HW or less. Scapes and mandibles relatively short, SI 64 – 74, MI 44 – 50; head tending to be shorter and broader than in rogeri-complex, CI 73 – 83.

Malagasy

S. rogeri-group is immediately diagnosed by the following combination of characters: preocular and ventral preocular grooves present in head; scrobe and its dorsal margin extend posteriorly well beyond level of eye; mandible has 1 or 2 sharply defined acute preapical teeth or denticles. The group also contains 13 species in the Afrotropical region (see there).

Members of this group fall into 6 discrete complexes of related species in the Malagasy region, defined below. The first complex noted contains only rogeri, a cosmopolitan trampspecies discussed under the Afrotropical fauna, which is its region of origin. S. rogeri is easily isolated from other member of the group in Madagascar by its possession of a flagellate pronotal humeral hair. It also has a characteristically shaped preocular notch. In profile, the width of the notch just in front of eye is narrow, distinctly less than the maximum diameter of the eye.

rogeri complex

Left and right mandible each with 2 preapical teeth, the proximal spiniform and longer than the distal. Pronotal humeral hair flagellate. Head tending to be somewhat shorter and narrower than in lysis- and hilaris-complexes, HL 0.59-0.61, HW 0.44-0.47.

lysis complex

Left and right mandible each with 2 preapical teeth, the proximal spiniform and longer than the distal. Pronotal humeral hair erect and stiffly filiform. HL 0.63-0.74, HW 0.47-0.60.

hilaris complex

Left and right mandible each with 2 preapical teeth, the proximal spiniform and longer than the distal. Pronotal humeral hair absent. HL 0.63-0.75, HW 0.52-0.61.

carisa complex

Left and right mandible each with 1 preapical tooth or denticle. Pronotal humeral hair long and filiform, stiffly projecting. HL 0.80-1.00, HW 0.63-0.76.

sphera complex

Left and right mandible each with 1 preapical tooth or denticle. Pronotal humeral hair absent. Head shorter and narrower than in vazimba-complex, HL 0.64-1.06, HW 0.51-0.88.

vazimba complex

Left and right mandible each with 1 preapical tooth or denticle. Pronotal humeral hair absent. Head longer and broader than in all other complexes, HL 1.32-1.66, HW 1.28-1.65.

References