Strumigenys rostrata group

Strumigenys rostrata group Bolton (2000)

Species

Neartic

Malagasy

Malesian-Oriental-East Palaeartic

Worker Diagnosis

The group is diagnosed, with slight differences, for three different regions:

Neartic

Mandibles in full-face view and at full closure triangular, either serially dentate with masticatory margins that engage through all their visible length or with an edentate gap present between basal tooth and anterior clypeal margin . In ventral view outer margin of mandible without an inflected prebasal angle. MI 15-25.

Dentition. Principal tooth row with 5 sharp triangular teeth. Tooth 1 (basal) and 2 subequal in size or one longer than the other, tooth 3 distinctly longer (longest tooth on margin) and 4 reduced , smaller than 3 or 5. Tooth 5 usually only slightly shorter than 3 and hence usually the second longest tooth on the margin. Tooth 5 followed by two small teeth, 4 minute denticles and a small apical tooth , giving a total dental count of 12.

Basal lamella of mandible triangular, broad-based and longer than the longest tooth, not visible to partially visible in full-face view with the mandibles fully closed. Basal lamella not separated from basal tooth or with a small to obvious diastema present (see note, below).

Labrum terminates in a pair of narrow digitate to conical lobes.

Clypeus with anterior margin broad , shallowly convex , transverse or shallowly concave in full-face view. Lateral clypeal margins approximately straight to convex, and weakly to distinctly convergent anteriorly. In ventral view the lateral clypeal margins extend well beyond the outer margins of the fully closed mandibles.

Clypeus without peripheral groove.

Clypeal lateral margins with a continuous fringe of anteriorly curved broadly spatulate to spoon-shaped hairs. Anterior margin with smaller hairs that are directed anteriorly or curved toward the midline. Clypeal dorsum with small spatulate or spoon-shaped hairs, without any other form of pilosity.

Preocular carina broad and conspicuous in full-face view.

Ventrolateral margin of head between eye and mandible bluntly to quite sharply marginate.

Postbuccal impression small and shallow to vestigial .

Cuticle of side of head within scrobe reticulate or reticulate-punctate.

Scape short to moderate, SI 67-82, weakly to moderately dorsoventrally flattened, the dorsum and ventre converging anteriorly so that the leading edge is sharp or even a thin flange or lamella. Ventral surface of scape behind the leading edge usually weakly concave.

Leading edge of scape with conspicuously spatulate to spoon-shaped hairs, some of which are curved toward the base of the scape.

Propodeum with triangular teeth subtended by a lamella on each side that is sometimes broad and engages the teeth through most of their length.

Spongiform appendages well developed on petiole and postpetiole; ventral spongiform curtain of petiole well developed. Base of first gastral sternite in profile with a narrow band or thin pad of weak or diffuse spongiform tissue that frequently appears hair-like.

Pilosity. Pronotal humeral hair usually present, elongate and straight or flagellate. Dorsum of head behind clypeus with spatulate to spoon-shaped ground-pilosity. Dorsolateral margin of head with or without an apicoscrobal hair. First gastral tergite usually with simple pilosity present, more rarely with flagellate hairs.

Sculpture. Dorsum of head behind clypeus reticulate-punctate. Pleurae, side of propodeum and disc of postpetiole smooth.

Malagasy

Mandibles in full-face view and at full closure triangular to elongate-triangular, with serially dentate masticatory margins that engage through all or most of their visible length; a small gap usually visible between basal tooth and anterior clypeal margin. In ventral view outer margin of mandible without an inflected prebasal angle. MI 16-20.

Dentition. Basal dental row of 7 short triangular teeth,either all about the same size or with alternating very slightly taller and very slightly shorter teeth. Basal lamella not separated from basal tooth or with a very short diastema present. Distalmost 2 teeth of the basal row small, followed by 4 minute denticles and a slightly enlarged apical tooth , giving a total dental count of 12.

Basal lamella of mandible low, triangular to rounded-triangular, not visible or partially visible in full-face view with the mandibles fully closed.

Labrum terminates in a pair of narrow digitate to conical lobes.

Clypeus with anterior margin broad, transverse to shallowly concave in full-face view.

Lateral clypeal margins approximately straight to weakly convex, and feebly convergent anteriorly. In ventral view the lateral clypeal margins extend well beyond the outer margins of the fully closed mandibles through the basal third or more of their length.

Clypeal lateral margins fringed with a continuous row of anteriorly curved spatulate to spoon-shaped hairs; anterior margin with similar but smaller hairs that are curved toward the midline. Clypeal dorsum with numerous small spatulate to spoon-shaped hairs, without any other form of pilosity.

Preocular carina conspicuous in full-face view.

Ventrolateral margin of head between eye and mandible quite sharply angular. Postbuccal impression small to vestigial.

Cuticle of side of head within scrobe reticulate or reticulate-punctate.

Scape short, SI 63-70 (in Malagasy species), conspicuously dorsoventrally flattened, the dorsum and ventre converging anteriorly so that the leading edge is a flange or even a thin lamella. Ventral surface of scape behind the leading edge usually distinctly concave.

Leading edge of scape with spatulate to spoon-shaped hairs, some or all of which are curved toward the scape base.

Pronotal dorsum without a median longitudinal carina.

Propodeum with triangular teeth sub tended by a lamella on each side that is sometimes broad and engages the teeth through most of their length.

Spongiform appendages well developed on postpetiole; ventral spongiform curtain of petiole may be well developed but in some is vestigial or absent beneath the peduncle. Base of first gastral sternite in profile with a pad of spongiform tissue.

Pilosity. Pronotal humeral hair elongate, straight or flagellate. Cephalic dorsum with curved-clavate to spoon-shaped hairs, almost suborbicular in some. Dorsolateral margins of head without freely laterally projecting elongate simple or flagellate hairs.

Sculpture. Dorsum of head behind clypeus reticulate-punctate. Pleurae, side of propodeum and disc of postpetiole smooth.

Malesian-Oriental-East Palaeartic

Mandibles in full-face view and at full closure triangular to elongate-triangular, with serially dentate masticatory margins that engage through all or most of their visible length; sometimes apices of the basal most few teeth meet but do not fully engage, rarely a small gap visible between basal tooth and anterior clypeal margin. In ventral view outer margin of mandible without an inflected prebasal angle. MI 8-23.

Dentition. Basal dental row of 5-7 triangular teeth, when 7 the distalmost 2 are distinctly smaller than the proximal 5; in some species dentition from the base consists of alternating taller and shorter teeth. Basal lamella not separated from basal tooth or with a short diastema present. Basal row followed by 4 minute denticles and a slightly enlarged apical tooth, giving a total dental count of 12.

Basal lamella of mandible low, acutely triangular to rounded-triangular, not visible or partially visible in full-face view with the mandibles fully closed.

Labrum terminates in a pair of narrow digitate to conical lobes.

Clypeus with anterior margin broad, extremely shallowly convex (almost transverse) to concave in full-face view. Lateral clypeal margins approximately straight to weakly convex, and convergent anteriorly. In ventral view the lateral clypeal margins extend well beyond the outer margins of the fully closed mandibles through at least the basal third of their length.

Clypeal lateral margins fringed with a continuous row of anteriorly curved spatulate to spoon-shaped hairs; anterior margin with similar but smaller hairs that are straight or urved toward the midline. Clypeal dorsum with numerous small spatulate to spoon-shaped hairs, without any other form of pilosity.

Preocular carina conspicuous in full-face view.

Ventrolateral margin of head between eye and mandible bluntly to quite sharply angular. Postbuccal impression small to vestigial.

Cuticle of .side of head within scrobe reticulate or reticulate-punctate.

Scape dorsoventrally flattened, the dorsum and ventre converging anteriorly so that the leading edge is a flange or even a thin lamella. Ventral surface of scape behind the leading edge usually distinctly concave.

Leading edge of scape with spatulate to spoon-shaped hairs, some or all of which are curved toward the base of the scape.

Pronotal dorsum without a median longitudinal carina.

Propodeum with triangular teeth sub tended by a lamella on each side that is sometimes broad and engages the teeth through most of their length.

Spongiform appendages well developed on postpetiole; ventral spongiform strip of petiole present to vestigial beneath the peduncle. Base of first gastral sternite in profile with or without a pad of spongiform tissue.

Pilosity. Pronotal humeral hair present, stout and straight or flagellate. Cephalic dorsum with curved-clavate to spoon-shaped hairs, almost suborbicular in some. Dorsolateral margin of head with or without freely laterally projecting elongate simple or flagellate hairs.

Sculpture. Dorsum of head behind clypeus reticulate-punctate. Pleurae, side of propodeum and disc of postpetiole smooth.

Notes

Neartic

At a glance the North American members of this group are quickly recognised by their possession of 5 principal mandibular teeth, presence of basally curved stoutly spatulate to spoon-shaped hairs on the leading edge of the scape, and presence of an anteriorly curved fringing row of stout spatulate or spoon-shaped hairs on the lateral clypeal margin. The group remains as it was conceived by Brown (1953a), with the addition of a few later described species.

Development of a mandibular diastema is morphoclinal through the group. In arizonica, californica and rostrata a diastema is absent or minute; in bunki and carolinensis it is present but short, shorter than the length of the basal tooth; finally, in chiricahua and hyalina the diastema is very conspicuous, longer than the basal tooth.

Malagasy

The four species are known only from Madagascar.

Malesian-Oriental-East Palaeartic

The members of the rostrata-group are very widely distributed, with representatives in Madagascar, the Oriental and Malesian regions, Japan and North America. The group falls into several discete complexes of related forms. The fautrix-complex includes all the Malagasy species together with the Oriental and Malesian species Strumigenys atropos and Strumigenys nepalensis. These tend to be small species in which the clypeus is relatively narrower and has more narrowly rounded anterolateral angles. The preocular laminae are not strikingly broadened, but the occipital lobes are markedly expanded laterally in full-face view. The species of the rostrata-complex, including the Japanese species Strumigenys incerta and Strumigenys rostrataeformis, the Chinese Strumigenys emeswangi and several of the North American species tend to be larger forms that have the clypeus broad, with more broadly rounded anterolateral angles. The preocular laminae are wide, especially anteriorly, and the occipital lobes are quite narrow in full-face view. Other North American species tend to fall between these two but have developed a marked diastema between basal lamella and basal tooth on the mandible. It would be possible, and may in fact be correct, to call each of these a separate group, but because they share so many characters I think it best to treat them as members of a single group, at least for the time being. Differences in regional faunas of the group account for the slight differences seen in their respective diagnoses, each of which concentrates on the fauna of the region under consideration.

Because of shortage of material the dentition details of the Sino-Japanese species emeswangi, incerta and rostrataeformis have not been investigated.

References

Bolton, B. 2000. The ant tribe Dacetini. Memoirs of the American Entomological Institute. 65:1-1028.
Brown, W. L., Jr. 1953a. Revisionary studies in the ant tribe Dacetini. American Midland Naturalist. 50:1-137.