Strumigenys pergandei group

Strumigenys pergandei group Bolton (2000)

Species

Nearctic

Worker Diagnosis

Mandibles in full-face view and at full closure narrow and elongate, sublinear, dentate only in the apical third of their length and only engaging in the apical third. Proximal of dentate zone the mandibles edentate and enclosing a large gap through which the labral lobes are freely visible. In ventral view outer margin of mandible without an inflected prebasal angle. MI 25-33.

Dentition. Independently specialised in the two species of the group, discussed below.

Basal lamella of mandible triangular, fully exposed in full-face view with the mandibles fully closed, located a short distance in front of the anterior clypeal margin. Basal lamella separated from basal tooth by an extremely long diastema.

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

Clypeus with anterior margin very broad, more or less transverse; between the inner mandibular margins with a narrow translucent cuticular flange in front of the true clypeal margin. Lateral clypeal margins, in dorsal or ventral view, extend well beyond the line of the outer margins of the fully closed mandibles. Clypeus without peripheral groove.

Clypeal lateral margins with a continuous fringe of anteriorly curved 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 marginate. Postbuccal impression small and shallow to inconspicuous.

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

Scape short to moderate, SI 65-84, moderately to distinctly dorsoventrally flattened, the dorsum and ventre converging anteriorly so that the leading edge is sharp or even a thin flange or lamella.

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 sub tended by a lamella on each side that is sometimes broad and engages the tooth through most of its 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.

Pilosity. Pronotum with or without a proj ecting humeral hair. Dorsum of head behind clypeus with spatulate to spoon-shaped ground-pilosity. Dorsolateral margin of head without an apicoscrobal hair. First gastral tergite with simple pilosity present that may be very sparse.

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

Notes

The two species of this group, angulata and pergandei, are certainly related but have quite different dental arrays. In angulata teeth 1-4 (counting from the base) are narrowly triangular and acute, with 2 and 4 longer than 1 and 3 (relative lengths 2 > 4 > 3 > 1); apices of first (basal) teeth do not meet at full closure. Tooth 4 is followed by 10-11 minute dentic1es and the row terminates in an apical tooth that is about the size of tooth 4; total dental count is 15-16.

In pergandei teeth 1, 3 and 5 (counting from the base) are narrowly triangular and acute (relative lengths 1 > 3 > 5) and first teeth deeply intersect at full closure. The intervening teeth 2 and 4 are plate-like, very broad and almost flat-topped , shorter than teeth 1 , 3 and 5; basal width of tooth 2 is twice that of tooth 1. Tooth 5 is followed by 4 dentic1es and an apical tooth that is acute and about the same size as 5; total dental count is 10.

Five Pyramica species in North America have elongate narrow mandibles that engage only near the apex: eggersi, gundlachi, hexamera, angulata, pergandei. The first two of these belong to the Neotropical gundlachi group and have only been recorded from Florida in the U. S. A. They are easily recognised as they lack spongiform tissue ventrally on the petiole and have the postpetiole disc reticulate-punctate. In angulata and pergandeia ventral spongiform curtain is well developed on the petiole and the postpetiole is smooth and shiny. P. hexamera is an introduced species in Florida and Louisiana that belongs to the Old World argiola group. It has some features in common with pergandei-group species but its mandibles have a markedly different morphology.

P. pergandei is a widespread and moderately common species and is the only member of this genus so far recorded from Canada. P. angulata on the other hand is rare and has a much more limited distribution.

References

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