Pseudomyrmex species groups

Based on Ward 1985, 1989.

This list is incomplete

ferrugineus group

Worker, diagnosis. Medium sized species (HW 0.74-1.26, HL 0.86-1.42); head varying from moderately elongate to rather broad (CI 0.75-0.97), with relatively short eyes (REL 0.39-0.50, REL2 0.45-0.62). Masticatory margin of mandible with 6, rarely 7, teeth, MD8/MD9 0.70; mesial tooth on basal margin notably closer to apicobasal angle than to proximal tooth, MD4/MD5 0.74. Palp formula 5,3, reduced to 4,3 in two species. Anterior margin of median clypeal lobe somewhat blunt-edged, in dorsal view convex, straight or concave, laterally rounded or with sharp angles. Frontal carinae separated by about basal scape width in most species but more closely contiguous in two (FCI 0.03-0.10, FCI2 0.24-0.75, ASI 0.52-0.73), fusing anterolaterally with antennal sclerites. Funicular segments II and III about as broad as long (FU 1.46-2.45). Profemur slender (PI 0.35-0.41). Pronotum laterally rounded. Metanotal groove well marked (MPI 0.04-0.09). Basal and declivitous faces of propodeum moderately well differentiated and subequal in length (PDI 0.94-1.30), in profile the juncture between the two subangulate or gently rounded. Petiole relatively long (PL/HL 0.44-0.63), always much longer than high or wide (PU 0.47-0.71, PWI 0.46-0.75), small anteroventral tooth present; in two species anterior peduncle of petiole weakly differentiated and posterolateral corners of petiolar node not expanded (these are presumably the plesiomorphic conditions in the group), in other species petiole with distinct anterior peduncle and with expanded, (sub)angulate posterolateral corners. Postpetiole broader than long (PPWI 1.03-1.85), with small anteroventral tooth. Body sculpture varying from densely punctulate or punctulatecoriarious to coriarious-imbricate, the integument sublucid to opaque; dorsum of head never with extensive smooth, shiny interspaces (punctulae usually separated by their diameters or less); propodeum of some species overlain by a coarser but weak rugulo-punctate sculpture. Standing pilosity common, present on the scapes, head, entire meso soma dorsum (10 or more standing hairs visible in profile), petiole, postpetiole and gaster, absent from the extensor faces of tibiae. Appressed pubescence dense on most of body, including head and abdominal tergite IV. Color varying from light yellow- or orange-brown to black.

Queen diagnosis. Similar to worker except for caste-specific differences. Larger in size (HW 0.76-1.36, HL 1.05-1.81), head more elongate (CI 0.60-0.80). Ocular indices differing slightly: REL 0.38-0.48, REL2 0.51-0.70. Median clypeal lobe narrower and more protruding, anterior margin convex or straight, laterally rounded or subangulate. Petiole and postpetiole generally more slender (PL/HL 0.57-0.72, PLI 0.43-0.63, PWI 0.47-0.67, PPWI 1.06-1.50). Forewing with 2 cubital cells.

Male, diagnosis. Head varying from longer than broad to slightly broader than long (CI 0.82-1.04 in a sample of 70 males belonging to all species); compound eye large, prominent (REL2 0.49-0.62). Mandibles with 8+ teeth or denticles on masticatory margin. Palp formula as in females, but somewhat more variable (males with 5p4,3 commoner than in workers or queens). Surface of median clypeal lobe convex, its anterior margin subtriangular in shape (dorsal view) with sides converging medially to a rounded point. Petiole and postpetiole more slender than in workers (PLI 0040-0.55, PWI 0.35-0.51) and simpler in shape. Posterolateral corners of sternites IV -VIII not notably protruding ventrally. Subgenital plate (sternite IX) with a conspicuous posteromedial concavity. Posterior margin of pygidium (tergite VIII) convex, directed posteroventrally. Paramere with several characteristic features: a finger-like, posterodorsally directed mediodorsal lobe; angulate or expanded posterodorsal extremity; and mesial dorsoventral ridge which joins the mediodorsal lobe posteriorly. Aedeagus with expanded posterodorsal corner, a medial protrusion on the posterior margin,numerous small teeth (15+) on the posterior margin, and on the outer face a raised ridge curving posterodorsally from a basal origin.

Comments. Workers and queens of the P. ferrugineus group can be distinguished from all other Pseudomyrmex by their possession of the following combination of traits: mandibles with 6-7 teeth; palp formula 5,3 or 4,3 ; standing pilosity common on mesosoma dorsum but absent from external faces of tibiae; worker metanotal groove conspicuously impressed ; and head densely punctulate, sub lucid to opaque. The relatively short eyes (worker REL 0.50, queen REL 0.48) and slender petiole (worker PLI 0.71, queen PLI 0.63) are also characteristic. Among the eight other major species groups of Pseudomyrmex (diagnosed in Ward, 1989) only the P. viduus and P. oculatus groups have workers and queens approaching these conditions. Those of the P. viduus group have a shinier head, a shorter and more robust petiole (worker PLI > 0.70, worker PWI > 0.70), and standing pilosity on the tibiae (reduced in one species), while workers and queens of the P. oculatus group have a palp formula of 6,3 (reduced to 5,3 only in smallest species with worker and queen HW < 0.67), tectiform and sharp-edged median clypeal lobe with a broadly convex margin (dorsal view), elongate eyes (worker REL 0.48-0.61, worker REL2 0.62-0.86, queen REL 0.43-0.57, queen REL2 0.68-0. 89), and short petiole (worker PLI 0.67-1.06, queen PLI 0.57-0.94). Among taxonomically isolated species not belonging to one of the major species groups, Pseudomyrmex fervidus (F. Smith) bears perhaps the closest phenetic resemblance to the P. ferrugineus group, but its workers and queens can be distinguished by their shinier and less densely punctulate head, shorter petiole (worker PLI 0.71-0.76, worker PL/HL 0.41-0.44 (n=9); queen PLI 0.65, queen PL/HL 0.49), and standing pilosity on the outer faces of the tibiae. In addition the queens of Pseudomyrmex fervidus have a distinctive, pointed median clypeal lobe not seen in P. ferrugineus group queens.

Males of the Pseudomyrmex ferrugineus group can be characterized by their palp formula, medially subangulate clypeal lobe, emarginate subgenital plate, configuration of the paramere, and shape of the aedaegus. They are approached most closely in this combination of traits by males of Pseudomyrmex haytianus (Forel) and two undescribed Central American species (P. sp. PSW-02 and P. sp. PSW-54) although, curiously, the workers and queens of those species do not bear a close resemblance to those of the P. ferrugineus group.

All species in the P. ferrugineus group are obligate inhabitants of Central American swollen-thorn acacias, a biological trait not characterizing any other species group of Pseudomyrmex, although a few species in the otherwise quite different P. gracilis group and one species in the P. subtilissimus group have independently developed an obligate association with the acacias.

Distribution. Members of the P. ferrugineus group are found from eastern (San Luis Potosi, Tamaulipas) and western (Sinaloa) Mexico south through Central America to northern Colombia. Although no single species spans the entire range of the group, their collective distribution is virtually identical to that of the swollen-thorn acacias.

gracilis group

Large black, orange, or bicolored species (HW > 1.20), with broad head, large eyes (REL > 0.50), and relatively long scapes (SI ~ 0.50); frontal carinae subcontiguous; lateral margins of pronotum angled; petiole usually long, with a distinct anterior peduncle. Erect pilosity abundant on body and appendages, including propedeum, scapes and legs.

oculatus group

Diagnosis (worker). Small to medium-size species (HW 0.47-0.98), head longer than broad, often markedly so (CI 0.61-0.88), with medium to large eyes (REL 0.48-0.61); mandibles with external and basal margins parallel or diverging slightly (MD1/MD2 0.87-1.00); basal margin of mandibles with a single distal tooth, masticatory margin with five or (less commonly) six teeth; frontal carinae subcontiguous (FCI 0.017-0.047), fusing anterolaterally with the antennal sclerites, so that in lateral view the frontal carinae do not form a continuous curve with the clypeus (in contrast to the P. subtilissimus group); median lobe of clypeus tectiform, notably produced anteriorly, the anterior margin sharp-edged and weakly flared; in dorsal view anterior margin of median clypeal lobe convex and laterally rounded; petiolar node relatively short and high (PU 0.67-1.06), anterior peduncle not conspicuously developed. Head and mesosoma at least partly punctate, and usually with substantial areas of the integument opaque or subopaque. Erect pilosity conspicuous on most parts of body, including the antennae, legs, head, and dorsum of mesosoma. Body covered with light to moderate density of fine pubescence. Palpal formula: 6,3 (reduced to 5,3 in Pseudomyrmex eduardi, Pseudomyrmex pisinnus, and in some individuals of Pseudomyrmex caeciliae and Pseudomyrmex urbanus; these species are among the smallest in the group).

Comments. The present concept of the P. oculatus group is a much expanded one from that given in Kempf (1961), who treated only three species. Within the P. oculatus group, I have included also the cluster of species allied to Pseudomyrmex elongatus (Mayr) (the "elongatus group" of Ward [1985]). As presently defined, the P. oculatus group is minimally diagnosed by the following combination of worker features: tectiform clypeal lobe, with weakly flared, sharp-edged, anterior margin; relatively short, high, apendunculate petiole); and conspicuous standing pilosity. Relationships with the P. subtilissimus group are discussed under the latter.

Within the P. oculatus group are several reasonably distinctive species, but a bewildering residue of forms remains centering around Pseudomyrmex caeciliae (Forel), Pseudomyrmex cubaensis (Forel) and Pseudomyrmex urbanus (F. Smith). Species relationships within what may be called the urbanus complex have not been resolved fully in this study, and will require more extensive material and further analysis (particularly larger samples of worker-associated males and queens).

pallens group

pallidus group

Small yellow, orange or brown species (HW 0.55 – 1.04), with elongate head (CI 0.75 – 0.91); scapes usually short; frontal carinae contiguous or subcontiguous; lateral margins of pronotum rounded; petiole usually slender, with an anterior peduncle (PLI 0.43 – 0.69; PWI 0.68 – 0.65). Erect pilosity scarce, lacking on the mesonotum and propeum.

sericeus group

The following features are characteristic of all species in the group. Mandibles with 8–10 teeth on the masticatory margin; median clypeal lobe tectiform, with convex anterior margin; distance between frontal carinae slight to moderate (see MFC and FCI values of each species); eyes elongate, eye length more than half head length (see REL values); standing pilosity sparse, absent from the external faces of tibiae (HTC = 0); usually fewer than ten standing hairs visible in outline on mesosoma dorsum, typically 1–2 pairs on the pronotum, and 0–1 pair on the propodeum at the juncture of the basal and declivitous faces (worker MSC 2–12); petiole usually with a single pair of stout setae directed posterodorsally; integument densely punctulate and subopaque, and this, in combination with a very dense but exceedingly fine pubescence, imparts a silky lustre to the body.

subtilissimus group

Diagnosis (worker). Small species (HW 0.48-0.73), with subopaque, densely punctulate, and elongate head (CI 0.56-0.73); mandibles as in the P. oculatus group; frontal carinae distinctive: subcontiguous (FCI 0.023-0.066), raised anterodorsally, and merging insensibly into the clypeus (rather than fusing with the antennal sclerite), so that in lateral view they form a continuous curve with the median clypeal lobe; the latter tectiform and protruding, with the anterior margin weakly flared and sharp-edged laterally, but not medially; in dorsal view, median clypeal lobe broadly rounded anteriorly; scapes very short (SI2 0.44-0.59); funicular segments II and III much broader than long (FLI 0.96-1.30); fore femur notably broadened (FI 0.44-0.60); petiole relatively low, long, and slender (PLI 0.54-0.75, PWI 0.48-0.68), without a differentiated peduncle and node, appearing dorsally flattened in lateral profile. Erect pilosity very sparse, lacking on the antennae, legs, and most of head and mesosoma; a characteristic pair of rather long setae present on the pronotal humeri, on the propodeum at the juncture of the basal and declivitous faces, and on the petiolar dorsum. Pubescence covering most of the body, exceptionally fine and inconspicuous in three of the four species. Palp formula: 6,3.

Comments. This is a small, discrete group of species, uniquely characterized by the configuration of the frontal carinae and the clypeus. The elongate head, short scapes, flattened apedunculate petiole, and patterns of pilosity are also distinctive. Features shared with the P. oculatus group include the protruding, tectiform, median clypeal lobe; palp formula of 6, 3; and elongate head and eyes. In addition preliminary observations suggest similarities in the male genitalia which, together with the shared worker characters, support the notion of a close relationship between these two groups.

tenuis group

viduus group

Worker, diagnosis. Medium to large sized species (HW 0.74–1.51, HL 0.91–1.55, LHT 0.57–1.36). Head varying from rather elongate to notably broader than long (CI 0.70–1.16), with relatively short eyes (REL 0.32–0.48, REL2 0.35–0.57). External and basal margins of mandible subparallel, MD1/MD2 about 1.00 (except in P. kuenckeli, where MD1/MD2 approximately 0.84); mesial tooth on basal margin closer to apicobasal angle than to proximal tooth, MD4/MD5 about 0.65–0.80. Masticatory margin of mandible with 5–7 teeth, MD8/MD9 approximately 0.60–0.82. Palp formula 6,4, with reductions to 5,3 and 4,3. Anterior margin of median clypeal lobe usually broadly rounded, but becoming laterally angulate in some species. Frontal carinae generally well separated (FCI 0.027–0.170, AS12 0.55–0.87), fusing anterolaterally with antennal sclerites. First funicular segment 1.6–2.6 times longer than broad; funicular segments 2 and 3 varying from markedly broader than long to slightly longer than broad (LF2/WF2 0.43–1.39; FLI 0.97–2.49); funicular segments 4–10 consistently broader than long in all species except P. kuenckeli. Profemur relatively slender (FI 0.31–0.49). Pronotum laterally rounded (submarginate in P. kuenckeli). Metanotal groove usually well marked (exception: P. kuenckeli) (MPI 0.011–0.092). Basal and declivitous faces of propodeum moderately well differentiated and subequal in length (PDI 0.83–1.51), in profile the juncture between the two varying from rounded to subangulate. Petiole relatively short (PL/HL 0.35–0.49), high (PLI 0.70–1.28), and broad (PWI 0.71–1.40), anteroventral tooth usually present and well developed, sometimes conspicuously recurved. Minimum (anterior) petiolar width rather large, so that in dorsal view the articulation of the petiole with the propodeum is broad (MPW/PL 0.34–0.58, MPW/DPL 0.19–0.29). Postpetiole notably broader than long (PPWI 1.29–1.90). Body sculpture varying from smooth and shining with scattered punctulae to densely corarious-imbricate and opaque. Dorsum of head usually with smooth, shiny interspaces; punctulae separated by more than their diameters on at least some upper parts of the head (P. tachigaliae has exceptionally dense sculpture). Standing pilosity usually common to abundant, present on the scapes, head, entire mesosoma dorsum, petiole, postpetiole, gaster, and extensor faces of tibiae. Ten or more standing hairs visible in outline on the mesosoma dorsum, except P. tachigaliae where there may be as few as six (this species also exceptional in lacking standing pilosity on the external faces of the tibiae). Appressed pubescence moderately dense on most of body, ranging from sparse to dense on abdominal tergite IV. Colour varying from light yellow- or orange-brown to dark brown, and including various bicoloured combinations.

Queen, diagnosis. Similar to worker except for caste-specific differences. Larger in size (HW 0.71–2.01, HL 1.18–2.26, LHT 0.76–1.60), head more elongate (CI 0.56–1.08). Ocular indices differing slightly: REL 0.32–0.48, REL2 0.35–0.57. Mandibles tending to be more modified than those of workers, with basal incisions, dorsal ridges, and reductions in dentition seen in various species. Palp formula as in worker. Median clypeal lobe narrower and usually more protruding, anterior margin convex or straight, laterally rounded or subangulate. Petiole and postpetiole generally more slender (PL/HL 0.35–0.58, PLI 0.54–1.28, PWI 0.61–1.31, PPWI 1.21–1.95). Forewing with 1 or 2 cubital cells.

Male, diagnosis. Of medium size (HW 0.90–1.33, LHT 0.89–1.45; n=53), head usually as broad as, or broader than, long but occasionally more elongate (CI 0.85–1.19). Masticatory margin of mandible with 6–9 teeth, often small or obsolete. Palp formula as in female. Dorsal surface of clypeus slightly to strongly convex; median clypeal lobe small, with convex anterior margin. Eye moderately large (REL 0.44–0.56, REL2 0.43–0.61). Scape of typical length for the genus (SI 0.20–0.30, SI2 0.40–0.60); length of second funicular segment varying from about two-thirds of scape length to slightly longer than the scape (LF2/SL 0.64–1.18). Profemur, petiole and postpetiole more slender than in worker (PLI 0.51–1.04, PWI 0.45–1.01). Posterolateral corners of sternites IV–VIII not notably protruding ventrally. Hypopygium (sternite IX) with a posteromedial concavity, varying from slight to pronounced. Pygidium (tergum VIII) posteromedially constricted, its margin somewhat thickened, directed posteroventrally, and straight or (more often) emarginate; in one species (P. tachigaliae) posteromedial margin of pygidium furnished with a prominent spine. Paramere appearing somewhat truncated distally in lateral view. Posteromesial face of paramere with a saucer-shaped concavity, variously modified in different species. Posterior margin entire or furnished with a set of small teeth (two large teeth in P. kuenckeli); portions of the dorsal margin lamellate, either in the form of a thin posterodorsal lobe or an anterodorsal keel.

Comments. Workers and queens of the P. viduus group can be distinguished from all other Pseudomyrmex by their possession of the following combination of traits: eyes relatively short (worker REL 0.32–0.48, queen REL 0.33–0.50); standing pilosity common on mesosoma dorsum and external faces of tibiae (secondarily reduced in Pseudomyrmex tachigaliae); petiole broad posteriorly (worker PWI 0.71–1.40, queen PWI 0.61–1.31) and anteriorly (worker MPW/PL 0.34–0.58, queen MPW/PL 0.32–0.65, queen MPW/LHT 0.25–0.38); and head densely punctulate with conspicuous shiny interspaces. In most species the frontal carinae are well separated and the worker metanotal groove is conspicuously impressed. Among the eight other major species groups of Pseudomyrmex, the P. tenuis group, P. sericeus group, P. oculatus group and P. subtilissimus group can be distinguished by their more elongate eyes and general scarcity of tibial pilosity. The species in the P. gracilis group have longer eyes, a laterally submarginate worker pronotum, and more teeth (7–10) on the masticatory margin of the mandibles. In the P. pallens and P. pallidus groups worker eye length overlaps with that of the P. viduus group but standing pilosity is absent from the external faces of the tibiae and usually sparse on the mesosoma dorsum, and the petiole is more slender. Among the remaining species of Pseudomyrmex not assigned to a species group, those most likely to be confused with the P. viduus group are Pseudomyrmex duckei (Forel), Pseudomyrmex filiformis (Fabricius), Pseudomyrmex depressus (Forel), Pseudomyrmex fervidus (F. Smith) and Pseudomyrmex perboscii (Gue´rin). The workers of these species have more slender and/or anteriorly constricted petioles, and those of the first two species have longer eyes (REL >0.48). In addition, P. depressus and P. duckei have more closely contiguous frontal carinae (worker FCI »0.025), and P. filiformis and P. perbosci lack standing pilosity on the external faces of the tibiae.

Distribution. The Pseudomyrmex viduus group as a whole is distributed throughout most of the Neotropics, from Mexico (and possibly also Cuba; see discussion under Pseudomyrmex viduus) to Argentina, Bolivia and southern Brazil. Most species are confined to mainland South America, however, and species richness is highest in the Amazon basin and adjacent foothills.

References

Ward, P. S. 1985b. The Nearctic species of the genus Pseudomyrmex (Hymenoptera: Formicidae). Quaest. Entomol. 21: 209-246.

Ward, P. S. 1989a. Systematic studies on pseudomyrmecine ants: revision of the Pseudomyrmex oculatus and P. subtilissimus species groups, with taxonomic comments on other species. Quaest. Entomol. 25: 393-468.

Ward, P. S. 1999b. Systematics, biogeography and host plant associations of the Pseudomyrmex viduus group (Hymenoptera: Formicidae), Triplaris- and Tachigali-inhabiting ants. Zool. J. Linn. Soc. 126: 451-540 (page 487, Senior synonym of endophyta)