Pseudomyrmecinae

The ant subfamily Pseudomyrmecinae is a pantropical group of arboreal, twig-dwelling ants. A few species occur in warm temperate regions, but most are confined to tropical forests, woodlands, and savannas. Pseudomyrmecine ants typically nest in preformed cavities in dead plant tissue, such as hollow dead twigs or grass culms that have been excavated by other insects. But a substantial number of species (about 20% of the estimated 300 species) are obligate inhabitants of specialized ant-plants. These ants occupy live plant cavities, such as the swollen thorns of certain acacia species or the swollen leaf petioles of leguminous trees of the genus Tachigali, in which they keep their brood and (often) scale insects. (Ward Lab Blog)

Identification
Ward Lab Blog - Adult pseudomyrmecine ants present a distinctive appearance (see figures above and below): workers and queens have large conspicuous eyes; the first antennal segment, or scape, is relatively short, less than three-quarters of head length; there is a well developed postpetiole (i.e., a second node-like structure at the “waist”); and a well developed sting. The pronotum and mesonotum of the worker are unfused, and freely articulate with one another.

Other technical characters useful for recognizing the worker and queen castes of these ants include: posteromedial margin of clypeus straight, not extending posteriorly between the frontal carinae; 12 antennal segments (reduced to 11 in two species); median lobes of antennal sclerites visible in a full-face view of the head (i.e., not over-reached by the frontal lobes); opening of metapleural gland located at extreme posteroventral margin of metapleuron; metacoxal cavities closed; and stridulitrum present on the pretergite of abdominal tergite IV. Males can be characterized by their 12-segmented antennae (at least one species is exceptional in having 13 segments), closed metacoxal cavities, well developed postpetiole, and extreme reduction of the volsella. The pseudomyrmecine larva has a trophothylax or “food pocket”, a unique structure located on the ventral surface of the thorax, in which the workers place small food particles.

Males: Boudinot (2015) - Pseudomyrmecine males are uniquely identified by the absence of the jugal lobes in combination with the following character combination: cuticle soft, flexible, weakly-sculptured; frontal carinae inconspicuous or absent; meso- and metatibia each with two ventroapical spurs; more than three forewing cells closed; abdominal segment III petiolated; abdominal sternum IX unpronged.

Nomenclature
PSEUDOMYRMECINAE [subfamily of Formicidae]
 * Pseudomyrmecinae Smith, M.R. 1952a: 98 [as subfamily of Formicidae]. Type-genus: Pseudomyrmex.
 * Senior synonym of Leptaleinae: Smith, M.R. 1958c: 112; of Pseudomyrmidae: Ward, 1990: 459. [Pseudomyrmecinae retains priority over Pseudomyrmidae and Leptaleinae under Article 40.2 of the International Code of Zoological Nomenclature (4th Edition), 1999: 46.]

Description
Ward (1990):

Diagnosis, worker and queen

1. Mandibles rather short, with 0-3 and 3-10 teeth on the basal and masticatory margins, respectively.

2. Clypeus without a conspicuous posteromedial extension between the frontal carinae.

3. Antennae with 12 segments; reduced to 11 segments in one species.

4. Palp formula 6,4, with reductions to 5 ,4; 6,3; 5,3; 4,3; and 3,3.

5. Compound eyes relatively large (REL usually >0.25).

6. Median lobes of antennal sclerites visible in a full-face view of head (i.e. not overreached by frontal lobes) and partly covering the basal condyles of the antennae.

7. Scapes relatively short, less than three-quarters of head length (SL/HL 0.20-0.70).

8. Pronotum and mesonotum not fused with one another, freely articulating.

9. Propodeal spiracle located on upper third of propodeum and far forward.

10. Opening of meta pleural gland directed laterally or ventrolaterally, and situated at the extreme posteroventral margin of the metapleuron.

11. Hind tibia with two apical spurs, the anterior one sometimes very reduced, but the posterior spur always well-developed and pectinate.

12. Hind coxal cavities closed.

13. Terga and sterna of abdominal segments II (petiole), III (postpetiole), and IV (first 'gastric' segment) not laterally fused; tergum overlapping sternum on segment IV.

14. Presternite of abdominal segment III overlapped laterally by the ventral margins of the pretergite, and not protruding mesioventrally below this.

15. Postpetiole distinctly developed.

16. Abdominal segment IV with differentiated presclerites, but these much narrower and shorter than the tergum and sternum proper: presternite notably shorter than the pretergite and the latter protruding ventrally at their lateral juncture.

17. Stridulitrum present on pretergite of abdominal segment IV.

18. Sting present and well developed.

19. Pupa naked.

20. Larva with trophothylax (food pocket).

Diagnosis, male

1. Mandibles short, with 0-1 and 2-18 teeth or denticles on the basal and masticatory margins respectively (proximal basal tooth lacking).

2. Antennae nearly always with 12 segments but with 13 segments In one species.

3. Palp formula: as in workers and queens.

4. Hind tibia with two apical spurs, the posterior spur pectinate.

5. Hind coxal cavities closed.

6-10. Structure of abdominal segments II, III and IV: as in workers and queens (13-17, above).

11. Volsella highly reduced: present as a small setose finger-like lobe (without differentiated digitus and cuspis) or fused to the inner wall of the paramere.

12. Pupa naked.

13. Larva with trophothylax (food pocket).

Worker
Typically monomorphic ants (marked polymorphism known in only two species of Tetraponera); varying considerably in size (HW 0.45-2.20 mm) and colour. Mandibles relatively short (MD3/HL 0.30-0.68); basal and masticatory margins usually distinct, with 0-3 and 3-10 teeth respectively. Venter of mandible typically with a ridge or escarpment preceding the masticatory and basal margins, although this can become quite reduced in some Tetraponera. Trulleum and mandalus present. Palp formula 6,4; reduced to 5,4; 6,3; 5,3; 4,3; and 3,3 in various species. Anterior margin of clypeus with a weak to strongly developed median protrusion (median clypeal lobe) sometimes armed with teeth or lateral angles; posteromedial margin of clypeus more or less straight, not extending strongly backwards between the frontal carinae. Antennal sclerites inclined dorsomesially. Median lobes of antennal sclerites extending dorsolaterally and partly covering the basal condyles of the antennae, typically fusing anteriorly with the frontal carinae; frontal carinae not expanded laterally as frontal lobes, and as a result the median lobes of the antennal sclerites are visible in a full-face view of the head. Antennae 12-segmented (reduced to 11 segments in Myrcidris), usually without a distinct funicular club. Scapes relatively short (SL/HL 0.20-0.70). Compound eyes typically large (REL 0.19-0.68, usually >0.25). Number of ocelli: 3; reduced to 2 or 0 in many Tetraponera. Head shape varying considerably, from broader than long to markedly elongate (CI 0.56-1.14).

Pronotum and mesonotum articulating flexibly, not fused. Metanotal groove usually impressed, becoming weak to obsolete in some species; in others a distinct metanotal (or mesoscutellar?) plate is also present. Propodeal spiracle conspicuous, circular to elongate, located far forward on the upper third of the propodeum. Spinescence lacking on mesosoma; basal face of propodeum typically rounding gently into the declivitous face, occasionally meeting at a sharp angle, very rarely forming pointed lateral corners. Metapleural gland well developed, the opening (meatus) large, directed laterally or ventrolaterally, and situated adjacent to the posteroventral margin of the metapleuron, immediately above the hind coxal insertion; anterior to the meatus is a longitudinal impression which continues to the anteroventral corner of the metapleuron and which is flanked dorsally by a carina of variable length. Hind coxal cavities closed. Metasternal process weakly to moderately developed, consisting of a low rise or a pair of blunt triangular points; the equivalent mesosternal process weakly to moderately incised medially, sometimes flanked by blunt triangular prominences. Propodeal lobes well developed; distance from posterior margin of hind coxal cavity to posteriormost extremity of the propodeal lobe exceeds the diameter of the cavity. Posterior metasternal margin with a medial, U-shaped excavation, which extends forward past the posterior margin of the hind coxal cavity. Petiole and postpetiole with well developed nodes, anterior peduncles variable in length. Distance between propodeal lobes exceeding the anterior width of the petiolar tergum. Posterior margin of petiolar sternum appearing semicircular in posterior view, with flanking lobes; in some species the semicircular margin has retreated internally (dorsomesially) and a new posterior extension of the sternum forms the posterior margin. Presternite of postpetiole (abdominal segment III) overlapped laterally by pretergite, not protruding ventrally; presternite often somewhat reduced in size and underlain by a forward-shifted anteroventral postpetiolar process (this occurs in association with the aforementioned reformation of the posterior margin of sternite II). Abdominal segment IV with differentiated presclerites, much shorter and narrower than the tergum and sternum proper; presclerite notably shorter than pretergite, the latter protruding ventrally at their lateral juncture. Terga and sterna of abdominal segments II (petiole), III (postpetiole) and IV (first 'gastric' segment) not laterally fused, tergum IV conspicuously overlapping the corresponding sternum. Pretergite of abdominal segment IV with stridulatory file. Posterior margin of tergum VII (pygidium) simple, unarmed. Gonostylus I-segmented. Sting present, well developed; sting shaft with 1-3 (usually 2) barbs; lancets barbed, with 5 teeth. Tarsal claws with 2 teeth (apical, subapical), the subapical tooth occasionally reduced or absent; mid and hind tibiae each with 2 apical spurs, the posterior spur always (hind tibia) or nearly always (mid tibia) well developed and pectinate, the anterior spur smaller and sometimes very reduced in size. Mid and hind basitarsi often with a longitudinal sulcus. on the anterolateral face (but entirely absent in Pseudomyrmex). Standing pilosity varying widely: from abundant to very sparse. Appressed pubescence occurring in low to moderate density on most of body (these hairs sometimes very small). Integument sculpture usually rather lightly impressed, never strongly rugose or costate.

Queen
Similar to the worker in most features, except for the presence of wings and differences in mesosomal morphology. Ergatoid queens known in one Tetraponera species. Apicobasal area of mandible occasionally much broadened; juncture of basal and anterodorsal faces of mandible occasionally marked by sharp margination or carina; in some species mandible incised or geniculate basally such that the dorsal abductor swelling and immediately distal section of the mandible form an angle of 1000 or less (in a frontal vie", of the head). Median clypeal lobe often more protuberant than that of worker, occasionally (e.g. Pseudomyrmex tachigaliae) strikingly so. Ocelli always present. Mid and hind basitarsal sulci somewhat more prominent than in the worker. Forewing with one closed radial cell, and (typically) two cubital cells (reductions to one cubital cell occur). Hindwing with 8-18 hamuli; anal lobe lacking.

Male
Basal margin of mandibles typically devoid of teeth (proximal basal tooth always lacking; occasionally a mesial basal tooth present); masticatory margin with 2-18 teeth or denticles, when more than 6 in number those preceding preapical tooth usually rather indistinct. Ventral mandibular ridges less developed than in workers. Palp formula as in worker; in a few species where workers have a reduced palp formula, males may possess an additional maxillary palp segment (e.g. 4,3 in workers; 5,3 in some males of the same species). Second and third maxillary palp segments occasionally much elongated. Median clypeal lobe broadly rounded to medially angulate, rarely emarginate; upper surface non-truncate. Posterior margin of clypeus straight, not extending backwards between the antennal insertions. Frontal carinae usually absent, at best very weakly developed. Median lobes of antennal sclerites not prominently developed, but in some Tetraponera the antennal sclerites are produced anterodorsally and partly overhang the frontal triangle. Antennae usually 12-segmented; 13-segmented in one species. Scapes not long, typically length of first two funicular segments and less than one-sixth the length of the entire funiculus. First funicular segment one-quarter or more the length of the second. Compound eyes and ocelli prominent. Notauli absent; in some Tetraponera mesonotum centrally constricted, with resulting broad transverse or arched-transverse furrows. Parapsidal lines present, usually well developed and extending about half the length of the mesonotum. Hind coxal cavities closed. Petiole and postpetiole distinct, as in worker, but tending to be more slender. Tergosternal structure of petiole, postpetiole and fourth abdominal (first gastric) segment as in worker. Stridulitrum present on fourth abdominal pretergite. Subgenital plate (stemite IX) variable in shape but never furcate. Cerci (pygostyles) present. Paramere narrowing apically, typically complex in shape with a series of lobes and impressions; in contrast, volsella highly reduced: a small, setose, finger-like lobe, sometimes fused to the inner wall of the paramere and very inconspicuous. Aedeagus variable in shape, with or without marginal teeth. Tarsal claws and tibial spurs as in worker. Mid and hind basitarsal sulci always lacking. Wing venation as in queen.

Subfamily Synapomorphies
Synapomorphies supporting the monophyly of the subfamily Pseudomyrmecinae include:

1. Worker, queen, male: larva with a trophothylax (food pocket) on the ventral surface of the thorax (for a more extensive description of pseudomyrmecine larvae see Wheeler & Wheeler, 1956, 1973, 1976).

2. Worker, queen: posteromedial margin of clypeus more or less straight, not extending posteriorly between the frontal carinae.

3. Male: volsella highly reduced.

4. Worker, queen: opening of metapleural gland located at extreme posteroventral margin of metapleuron, immediately above the hind coxal insertion.

5. Worker, queen: scapes short (SL/HL≤ 0.70).

The last two conditions are seen in some other ants: the opening of the metapleural gland tends to be in an extreme posteroventral position in Cerapachyinae; and short scapes appear in various ponerines, cerapachyines, and army ants (Dorylinae and Ecitoninae).

Other features of the Pseudomyrmecinae which are possibly derived within the 'poneroid complex' (sensu Taylor. 1978) but are probably not autapomorphies for the subfamily, include the following:

1. Worker and queen: mandibles short, with 10 or fewer teeth on the masticatory margin.

2. Male: scape length more than one-third the combined length of the first two funicular segments (SL/(LFI + LF2) 0.40-0.90).

3. Male: first funicular segment one quarter or more the length of the second funicular segment.

4. Worker, queen. male: hind coxal cavities closed.

5. Worker. queen, male: postpetiole distinctly developed.

6. Worker, queen, male: presclerites of abdominal segment IV much shorter in length than the total length of the segment (presternite 5-20% of the midline length of the entire sternum).

7. Worker, queen, male: presternite of abdominal segment IV notably shorter in length than the pretergite, the latter produced ventrally at their lateral juncture.

8. Worker, queen, male: pupa naked (cocoon lost).