Strumigenys scotti group

Strumigenys scotti group Bolton (2000)

Species

Afrotropical

Malagasy

Malesian-Oriental-East Palaeartic

Worker Diagnosis

Afrotropical

Apical fork of mandible without intercalary teeth or denticles. Mandibles each with two preapical teeth, the proximal longer than the distal. MI 42-54.

Scape slender and subcylindrical to slightly dorsoventrally flattened; short to long, SI 59-95.

Ventrolateral margin of head with preocular notch absent to feebly developed; when present it is merely a weak indentation in the ventrolateral margin immediately in front of the eye; anterior portion of eye not detached from side of head. Ventral surface of head without an impression or trench that extends transversely from the preocular notch toward the midline. Postbuccal impression distinct in profile.

Eye with maximum diameter at least equal to, and usually exceeding, the maximum width of the scape.

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

Pilosity. Pronotal humeral hair usually present, rarely absent. Apicoscrobal hair absent; upper scrobe margin fringed by a continuous row of small hairs. Cephalic ground pilosity not scale-like on anterior half. Cephalic dorsum usually with 6 standing hairs, arranged as a transverse row of 4 near occipital margin and a pair close to highest point of vertex (only rarely reduced from this). Mesonotum with a single pair of standing hairs. First gastral tergite with simple to remiform hairs; flagellate hairs always absent.

Sculpture. Head and alitrunk dorsally reticulate-punctate but pleurae and side of propodeum smooth (except in Strumigenys cenagra); pronotal dorsum frequently with longitudinal or oblique rugulae or costulae. Gaster unsculptured except for basigastral costulae.

Malagasy

Apical fork of mandible with 2 spiniform teeth; without intercalary dentition but rarely with 12 denticles located at the ventral base of the apicoventral tooth. Mandible with 2 stout or spiniform preapical teeth, situated in the apical third of the length; proximal preapical tooth slightly longer than the distal. Mandibles in full-face view and at full closure with outer margins shallowly and evenly convex to almost straight and parallel; in some species inner margin of mandible with a distinct lamella in (see species-complexes, below).

Scape elongate and cylindrical.

Ventrolateral margin of head without trace of a preocular notch, the margin continuous in front of the eye. Ventral surface of head without a preocular transverse groove but postbuccal groove is distinct.

Spongiform appendages of petiole usually developed into at least a narrow ventral curtain, rarely completely absent. Postpetiole usually with lateral and ventral lobes.

Pilosity. Pronotal humeral hair usually present, rarely absent. Upper scrobe margin with curved or appressed slender to clavate hairs (no hairs in Strumigenys diux). Cephalic dorsum usually with 6 standing hairs, arranged as a transverse row of 4 near occipital margin and a pair close to highest point of vertex. Mesonotum with at least one pair of standing hairs. Dorsal surface of postpetiole, and gaster with short filiform to narrowly clavate hairs.

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

Glands. Scape gland absent (Strumigenys balux, Strumigenys bola, Strumigenys chroa, Strumigenys glycon, Strumigenys ipsea, Strumigenys langrandi, Strumigenys lura, Strumigenys odacon, Strumigenys tegar), or visible as an elongate patch near apex or rarely entire length of ventral scape (Strumigenys cabira, Strumigenys covina, Strumigenys deverra, Strumigenys diota, diux, Strumigenys doxa, Strumigenys epulo, Strumigenys europs, Strumigenys finator, Strumigenys inatos, Strumigenys lexex, Strumigenys livens, Strumigenys lucomo, Strumigenys origo, Strumigenys ravola, Strumigenys rubigus, Strumigenys scotti). Femoral gland bulla usually absent but present in cabira, covina, deverra, diota, epulo, inatos. Tibial gland bulla usually absent but present on at least the hind tibia in cabira, covina, deverra, epulo, langrandi, odacon. Gland at base of calcar conspicuous (absent in diota). Tarsal gland bullae visible on at least first three tarsi of foreleg, 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 in a concave impression in ipsea.

Malesian-Oriental-East Palaeartic

Apical fork of mandible of 2 teeth, without intercalary teeth or denticles. Mandible with two preapical teeth, the proximal longer and stouter than the distal. MI 46-50 (in regional fauna).

Scape slender and subcylindrical, SI 75-85 (in regional fauna).

Apical antennomere not constricted basally, the segment not spindle-shaped.

Ventrolateral margin of head with preocular notch absent. Ventral surface of head without an impression or trench that extends transversely from just in front of the eye toward the midline.

Ventral surface of petiole with a conspicuous spongiform strip or curtain; spongiform lobes of waist segments present but first gastral sternite without basal spongiform tissue.

Petiole node in dorsal view broader than long.

Pilosity. Pronotal humeral hair flagellate. Apicoscrobal hair absent; upper scrobe margin fringed by a continuous row of small hairs. Cephalic ground-pilosity spatulate. Cephalic dorsum with 6 standing short hairs, arranged as a transverse row of 4 near occipital margin and a pair close to highest point of vertex. Mesonotum with a single pair of standing hairs. First gastral tergite with simple to remiform hairs; flagellate hairs always absent. Hind tibia and basitarsus without long erect projecting hairs.

Notes

Afrotropical

The 14 species included here are very close and morphologically form a group roughly intermediate between the rogeri group and arnoldi group. They can be crudely and artificially divided into two complexes based on relative scape length. The species Strumigenys adrasora, Strumigenys dyshaula, Strumigenys ettillax, Strumigenys relahyla, Strumigenys rukha, Strumigenys totyla and Strumigenys xenohyla together have a collective SI range of 59-77. Of these only two species (adrasora, totyla) have individuals in the upper part of the range (SI ca. 73-77). Among the remainder (cenagra, Strumigenys hastyla, Strumigenys helytruga, Strumigenys murshila, Strumigenys percrypta, Strumigenys sibyna, Strumigenys zandala) the SI averages higher, range 75-95.

Two species of this group occur in Indonesia, Strumigenys integra and Strumigenys yanintra. I suspect that these may eventually prove to be introductions from the Afrotropical region. Both have the metapleuron and side of the propodeum entirely reticulate-punctate. This character only occurs in cenagra among the Afrotropical members of this group and, while cenagra is not conspecific with the Indonesian species, it may be their closest relative.

Malagasy

The absence of a preocular notch in the ventrolateral margin of the head and absence of a preocular transverse impression in the ventral surface of the head, combined with the presence of 2 stout preapical teeth on each mandible and elongate cylindrical to subcylindrical scapes, is immediately diagnostic of the scotti-group.

This group also contains 14 species in the Afrotropical region and two in the Malesian region. In the Malagasy region the group can be divided into 5 complexes, as follows.

chroa complex

Mandibles in full-face view almost straight and at full closure parallel. Inner margin of mandible with a translucent lamina that extends from proximal preapical tooth, or close to tooth, to level of anterior clypeal margin (absent in ipsea). Flagellate hairs usually absent (present at pronotal humeri in bola and deverra). Dorsolateral margin of head posteriorly without stiff erect hairs that are longer than hairs on leading edge of scape.

epulo complex

Mandibles in full-face view with outer margins shallowly convex. Inner margin of mandible without a translucent lamina extending from vicinity of proximal preapical tooth to level of anterior clypeal margin. Cephalic dorsum, pronotum, mesonotum, petiole and postpetiole with standing fine, flagellate hairs. Dorsolateral margin of head posteriorly without stiff erect hairs that are longer than hairs on leading edge of scape.

Strumigenys epulo

diux complex

Mandibles in full-face view with outer margins shallowly convex. Inner margin of mandible without a translucent lamina extending from vicinity of proximal preapical tooth to level of anterior clypeal margin. Flagellate hairs absent. Pronotal humeral hair stiff, filiform. Dorsolateral margin of head posteriorly with 1 or more stiff erect hairs that are longer than hairs on leading edge of scape.

Strumigenys diux
Strumigenys doxa

diota complex

Mandibles in full-face view with outer margins very shallowly convex. Inner margin of mandible without a translucent lamina extending from vicinity of proximal preapical tooth to level of anterior clypeal margin. Flagellate hairs absent. Pronotal humeral hair absent. Dorsolateral margin of head posteriorly without stiff erect hairs that are longer than hairs on leading edge of scape.

Strumigenys diota

scotti complex

Mandibles in full-face view with outer margins shallowly convex. Inner margin of mandible without a translucent lamina extending from vicinity of proximal preapical tooth to level of anterior clypeal margin. Pronotal humeral hair flagellate. Dorsolatereal margin of head posteriorly without stiff erect hairs that are longer than hairs on leading edge of scape.

Malesian-Oriental-East Palaeartic

The scotti-group is predominantly Afrotropical and Malagasy in distribution but two species, Strumigenys integra and Strumigenys yanintra, have been found in Indonesia. I suspect that they may be introductions from another region but conspecific forms have not yet been discovered elsewhere. The two Indonesian species share a character not otherwise observed in the group. They both have the metapleuron and side of the propodeum reticulate-punctate, with unsculptured cuticle only on the katepisternum. All the Afrotropical species have the pleurae and side of the propodeum entirely smooth.

Within the regions currently under discussion members of the scotti-group are immediately recognisable by their preapical dentition coupled with a lack of apicoscrobal hairs and lack of spongiform tissue at the base of the first gastral sternite.

References

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