Strumigenys gundlachi group

Strumigenys gundlachi group Bolton (2000)

Species

Neotropical

eggersi and gundlachi also occur in the Neartic region.

Worker Diagnosis

Mandibles in full-face view and at full closure narrow, elongate and sublinear to linear, usually emerging far apart on the anterior clypeal margin; only their extreme apices fully engage. Proximal to apices either with a wide gap between the mandibles, through which the labral lobes are visible, or the inner margins broadly sinuate. In profile linear to curvilinear, broad basally and with a short vertical section at the extreme apex. In ventral view outer margin without an inflected prebasal angle. MI 30 - 85.

Dentition. Mandible with 3 to more than 10 preapical teeth or denticles, in some species very small and inconspicuous; preapical dentition may be restricted to the margin immediately proximal of the apex or may extend through most of the length of the margin. Apex of mandible with a short, near-vertical series of small teeth and denticles, the apicodorsal and apicoventral the largest and forming a fork, between which are 2- 4 minute intercalary denticles.

Basal lamella of mandible long stout and oblique, rectangular or tapering apically, its apex truncated or shallowly rounded; basal lamella not visible when mandibles fully closed. Base of mandible immediately proximal of the lamella with condyle massively expanded medially (dorsal view), in the same plane as the basal lamella, the two separated only by a cleft that is deep and very narrow.

Labrum terminates in a pair of triangular to conical lobes that may be quite short to very long; lobes partially or wholly visible in full-face view when mandibles closed.

Clypeus with anterior margin transverse or medially shallowly convex over the prominent labrum that projects forward between the mandibles. True lateral margins of clypeus very short or confluent with the preocular carinae almost immediately behind the anterolateral clypeal angles.

Clypeal dorsum with small simple to spatulate hairs. Lateral margins of clypeus with anteriorly curved spatulate to spoon-shaped hairs. Anterior margin with anteriorly projecting or medially curved hairs that are spatulate or spoon-shaped, the pair straddling the midpoint usually the largest.

Preocular carina clearly visible in full-face view.

Ventrolateral margin of head bluntly marginate in front of the eye, more or less straight or slightly indented at the postbuccal impression, the latter narrow, sharply incised to very shallow.

Cuticle within antennal scrobe finely reticulate-punctate.

Scape short to long, SI 46 - 100, almost cylindrical to strongly dorsoventrally flattened and broad, the leading edge rounded to thin and sharp. Subbasal angle shallowly rounded to bluntly lobate.

Leading edge of scape with a row of spatulate to spoon-shaped hairs; usually one to several of these hairs curve toward the base of the scape, only rarely with all hairs directed anteriorly or curving toward the apex of the scape.

Pronotum almost flat to transversely convex dorsally, sometimes bluntly marginate dorsolaterally but without a sharp median longitudinal carina.

Propodeum with a pair of triangular teeth or short spines; declivity with a carina or lamella running down each side below the teeth.

Legs with femoral gland bullae minute to absent.

Spongiform appendages of petiole very reduced; without a ventral spongiform strip or curtain; lateral lobes small to absent. Postpetiole usually with small lateral and ventral lobes but these reduced or vestigial in some species. Base of first gastral sternite with spongiform tissue a narrow strip to absent.

Pilosity. Pronotal humeral hair present, varying from short-spatulate or short-clavate through to long, fine and flagellate. Dorsal surface of mandible adjacent to masticatory margin with medially directed spatulate hairs that project across the margin into the space between the mandibles; may be restricted to basal zone. Dorsolateral margin of head with a laterally projecting hair either just behind level of eye or in apicoscrobal position (absent in 2 species). Cephalic dorsum with 0 – 2 pairs of short erect hairs, but only rarely with 0. Dorsal alitrunk usually without erect hairs except for a single mesonotal pair (numerous in 1 species). First gastral tergite with numerous short standing hairs that may be simple, remiform, clavate or flattened apically. Dorsal (outer) surfaces of middle and hind tibiae with short subdecumbent to appressed small spatulate hairs only.

Sculpture. Dorsum of head behind clypeus, entire alitrunk and waist segments predominantly to entirely finely reticulate-punctate. Usually a clear patch on mesopleuron and some species with disc of postpetiole smooth.

Notes

This group contains those species of Pyramica that most closely resemble Strumigenys in the general form of the mandible, as observed at full closure or when slightly ajar. Separation of these species from Strumigenys, when the critical labral characters are concealed or when dissection to show the labrum and mandible base is inconvenient, is relatively easy: New World Strumigenys species have 0 - 2 preapical teeth or denticles in total, whereas members of the gundlachi-group always have 3 or more preapical teeth or denticles. Care should be taken in ascertaining the number of preapicals as in several species the denticles may be very small and inconspicuous.

The structure of the mandibles and their dentition, coupled with the lack of spongiform tissue ventrally on the petiole, is immediately diagnostic of the gundlachi-group. The morphology of the mandible base (form of basal lamella, cleft, massive expansion of inner condyle) is apomorphic for the group.

Members of this group fall into two discrete complexes of related species. Earlier these complexes were treated quite differently as gundlachi, connectens and their relatives were regarded as a subgenus or two species-groups within Strumigenys, whilst crassicornis and its relatives constituted the genus Neostruma, now abandoned (Bolton, 1999). Within the group the two complexes are diagnosed as follows.

crassicornis complex

Inner margin of mandible approximately at the midlength or somewhat distal of the midlength (toward the apical third) with a submedian tooth or a denticle that is obviously enlarged. A number of smaller, sometimes inconspicuous, denticles occur between this and the apex, and other smaller denticles occur proximal to it. 3 - 5 intercalary denticles are present between apicodorsal and apicoventral fork teeth. Labral lobes very long and slender, in profile with mandibles closed the lobes freely project forward and downward. Trigger hairs at apices of labral lobes short, in profile the hairs are subequal in length to, or are shorter than, the labral lobes.

The pronotum is broad and flattened, bluntly marginate laterally and with angular humeri. Standing hairs are always present on waist segments and gaster.

Two clusters of closely related species can be diagnosed in this complex.

i. Species related to crassicornis (Strumigenys aethegenys, Strumigenys crassicornis, Strumigenys metopia). Ground-pilosity on the head is conspicuous, spatulate and not appressed. The scape is narrow basally and suddenly broadened and sublobate near the subbasal angle. The scape is easily broadest at this point and thereafter tapers to the apex. Paired specialised hairs on body not of form or of distribution described below.

ii. Species related to brevicornis (Strumigenys auctidens, Strumigenys brevicornis, Strumigenys crementa, Strumigenys myllorhapha, Strumigenys pasisops, Strumigenys stenotes, Strumigenys zeteki). Ground-pilosity on head is inconspicuous, minute and appressed. The scape is not suddenly broadened at the subbasal angle but rather tends to have the anterior margin fairly evenly convex. Paired specialised hairs on head and alitrunk, filiform or short and flattened, are distributed as follows: one short apicoscrobal pair that project laterally; one erect pair dorsally on head very close to the occipital margin; one pronotal humeral pair; one mesonotal erect pair (very easily abraded).

This complex of closely related species was first revised by Brown (1959b) under the genus-rank name of Neostruma.

gundlachi complex

Inner margin of mandible with 2 or more denticles that may be minute and indistinct, but without an enlarged denticle near the midlength; denticles may be confined to the immediate preapical area or may extend along a considerable length of the margin. Usually 2 (rarely 3) intercalary denticles between apicodorsal and apicoventral fork teeth. Labral lobes short, in profile with mandibles closed the apices of the lobes are usually visible. Trigger hairs at apices of labral lobes long or very long, in profile the hairs are distinctly longer than the labral lobes. Cephalic dorsum with variable pilosity. Usually with a pair of short erect hairs located close to the occipital margin and with another pair anterior to this; sometimes erect pilosity absent, but only very rarely with hairs as in the preceding species-complex.

A number of clusters of closely related species can be diagnosed among the components of this complex.

i. Species related to and discussed under gundlachi, (Strumigenys denticulata, Strumigenys eggersi, Strumigenys enopla, Strumigenys gundlachi, Strumigenys jamaicensis, Strumigenys onorei).

ii. Species related to and discussed under laevipleura, (Strumigenys gemella, Strumigenys laevipleura, Strumigenys vartana, Strumigenys xenognatha).

iii. Species related to and discussed under nubila, (Strumigenys lalassa, Strumigenys nubila).

iv. Species related to and discussed under subedentata (Strumigenys connectens, Strumigenys decipula, Strumigenys subedentata, Strumigenys trieces).

In terms of relative lengths of labral lobes and trigger hairs trieces is more or less intermediate between the two complexes. Its labral lobes are conspicuous in profile and the trigger hairs, though longer than the lobes, are not remarkably so. However, its dentition and cephalic pilosity are decidedly not of the crassicornis-complex pattern.

The species most closely related to gundlachi, that form the core of this complex, were first revised by Brown (1960a).

Rigato & Scupola (2008) described two new Ecuadorian species that they assigned to a new cluster within this complex. They noted:

Comparing P. osellai and P. heterodonta with the gundlachi cluster they have a preapical dentition formed by alternatively large teeth and small denticles. In P. gundlachi and its relatives preapical dentition is formed by a series of quite similar denticles looking not as variable as in P. osellai and P. heterodonta. Also, the postpetiolar disc is not strongly reticulate-punctate as in P. gundlachi and allies.

The P. osellai cluster could be defined as follows:

1: mandibles of moderate length, MI 61-64, their inner margin weakly convex in their proximal half and slightly concave in the distal one;

2: two intercalary denticles arising from the space between apical mandibular teeth;

3: preapical dentition formed by 3 to 7 teeth and denticles placed in the distal two third or half of the mandibular shaft. These are strongly heteromorphy with alternation of very small and large ones;

4: main pilosity formed by several pairs of elongate, somewhat remiform, hairs: apicoscrobal, 2 pairs on the head dorsum, humeral hairs, one pair on the anterior mesonotum. Leading edge of scape with simple to narrowly spatulate curved hairs; 5: postpetiolar disc smooth to weakly reticulate-punctate.

Notes

Lattke and Aguirre (2015) - With the discovery of Strumigenys lojanensis (now Strumigenys onorei) it is possible to discern a group of 5 northern andean species of the gundlachi complex with a preference for cold forests above 2000 m altitude, where the presence of most ants is negligible (Longino, 2014). The other species are Strumigenys enopla, known from altitudes between 1900 and 2200 m in SW Colombia, Strumigenys nubila, sampled from altitudes between 2000 and 2500 m in Colombia and Venezuela, Strumigenys vartana, a Colombian species known from altitudes between 1800 and 2530 m and Strumigenys heterodonta which was recently described from 2940 m altitude in Ecuador (Rigato & Scupola, 2008).

References