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The genus Leptogenys is a mostly pantropically distributed group of ponerine ants. The taxonomy of the genus needs attention as the only recent revisionary work is that of Bolton (1975) for the African region, recognizing 70 species. The New World fauna was summarily covered by a key in Wheeler (1923) but his treatment has been rendered woefully inadequate due to the subsequent accumulation of descriptions and specimens. Lattke (2007) reviews the Colombian Leptogenys. An upcoming revision of the New World fauna by Lattke lists 82 species, more than half of which are new, and a good number known only from unique specimens or single collection events, enough to suspect that New World diversity eventually will easily surpass the hundred mark. Despite this diversity, they are not amongst the most common ants found in collections. Fortunately the last years have seen more specimens in collections, as ant collecting gathers impetus in the tropics and techniques such as pitfall traps and leaf litter sifting have become more common. Some of the difficulties in collecting Leptogenys lay with the nocturnal activity apparent in many species (Bolton 1975; Lattke & Longino 2009), a rhythm that would be in sync with activity of their favorite prey, isopods (Dejean & Everts 1997). Additionally, upon the uncovering of a nest the usual response of the ants is to flee and hide beneath any suitable cover, some species are extremely fast and nest members will be rapidly lost in the surrounding leaf litter before the collector has time to react.
Leptogenys Roger 1861
Leptogenys Roger, 1861:41. Type species: Leptogenys falcigera Roger, 1861; by subsequent designation of Bingham, 1903:52.
Lobopelta Mayr, 1862:733. Type species: Ponera diminuta F. Smith, 1857:69; by subsequent designation of Bingham, 1903:54. [Synonymy by Bolton, 1975:240].
Prionogenys Emery, 1895:348. Type species: Prionogenys podenzanai, by monotypy. [Synonymy by Taylor, 1988:33].
Machaerogenys Emery, 1911:100. Subgenus of Leptogenys. Type species: Leptogenys truncatirostris Forel, 1897:195; by original designation. [Synonymy by Bolton, 1975:240].
Odontopelta Emery, 1911:101. Subgenus of Leptogenys. Type species: Leptogenys turneri, by monotypy. [Synonymy by Brown, 1973:183].
Dorylozelus Forel, 1915:24. Type species: Dorylozelus mjobergi Forel, 1915:25; by by monotypy (= Leptogenys tricosa Taylor, 1969:132, substitute name for D. mjobergi due to secondary homonymy in Leptogenys). [Synonymy by Taylor, 1969:132].
Microbolbos Donisthorpe, 1948:170. Type species: Microbolbos testaceus Donisthorpe, 1948:170; by original designation. [Synonymy by Wilson, 1955:136].
New World worker description. Head shape ranges from elongate to wider than long in dorsal view; vertexal carina present, usually visible from cephalic dorsal view; compound eye usually situated anterad of mid-cephalic length, occasionally at mid-length, and either laterally or dorsolaterally on head; eye length varies from more than one third lateral cephalic margin with head in frontal view to strongly reduced with few ommatidia. Mandible variously shaped, from triangular to subtriangular, with semiparallel internal and external margins, sometimes strongly falcate and incapable of closing against clypeus; generally edentate or nearly so, rarely masticatory margin crenulate or with series of blunt denticles; mandible generally with laterobasal sulcus; masticatory margin usually shorter than internal margin. Median portion of clypeus projects anterad as distinct, usually triangular lobe, with longitudinal crest extending from apex to between antennal fossae, clypeus extends briefly posterad between frontal carina as narrow wedge; frontalclypeal suture straight and transverse, tentorial pit closer to compound eye than to antennal sclerite. Frontal lobe partially covers antennal insertion, frontal carinae very brief; antennae 12-segmented, usually weakly incrassate, apical club lacking; scape usually surpasses posterior cephalic margin, rarely shorter, funnicular segments usually subcylindrical.
Propleural lateral and ventral faces separated by curvature, not carinate; pronotum never with carinate sides; mesopleuron with anepisternum and katepisternum usually indistinct; propodeal spiracle separated from declivitous margin in lateral view by at least 3 diameters; mesopleural carina usually distinct, sometimes weakly developed, especially ventrad; pronotal suture mobile; mesonotum always distinct; metanotal groove distinctly impressed, from shallow and fine to deep and wide; mesometapleural suture distinct; metapleural propodeal suture varies from indistinct to well-impressed. Propodeum with or without lateral teeth or lobes, declivitous face usually with broad transverse sculcus next to insertion of postpetiole.
Posterior face of anteroventral petiolar process medianly concave; postpetiolar process well-developed, usually as transverse crest or lobe; gaster usually smooth and shining, sometimes abdominal segments III-IV punctate; pretergite of abdominal segment IV with stridulitrum; constriction between abdominal segments III and IV from weakly-developed to well-developed; pygidium with or without longitudial crest; hypopygidium usually with a row of small setae. Claws pectinate, aroleum absent; meso- and metatibial apex each with 2 apical spurs. General body color ranges from black to ferruginous; mandibles, clypeus, antennae, legs, and gastral apex usually lighter colored than head, mesosoma, and gaster; blue or purple opalescence present in some species; sculpture varies from smooth and shining to striate, or punctate.
These ants may be locally abundant in some areas, which are usually of humid forest and with an abundance of isopod prey. In such an area direct collecting may uncover up to 5 or more nests in a single day, usually of the same species. Personal observations in at least 3 Venezuelan collecting localities with notably abundant Leptogenys colonies coincided with abundant isopod populations as evidenced by the scattering of numerous of these crustaceans upon treading the leaf litter late afternoon and early evening. Dejean (1997) confirms the pattern of abundant Leptogenys colonies in areas with an elevated presence of isopods in Mexico and Cameroon. Collections throughout time in single localities, such as La Selva in Costa Rica or Rancho Grande in Venezuela, indicate that as many as 5-6 species may be present in a given locality. Nests of New World Leptogenys may vary from 20 to 30 workers, rarely surpassing 50 (pers. obs). Small nest sizes (less than 30) are also reported for over 15 species of this genus in the oriental tropics (Ito 2000). The obvious exceptions are the army ant species of the Oriental tropics which have colonies numbering in the thousands.
The genus occurs from sea level to above 2000 meters, though most are lowland dwellers. The nests may be found in rotten wood on the ground, usually within cavities in logs or large branches, and also beneath bark. The wood soil, and rock soil interface is also used for nesting, as well as rock crevices, and a few such as L. ingens or L. famelica may nest directly in the soil. Some species may be adapted to disturbed areas, such as the case of the Pantropical tramp L. maxillosa, which has been found nesting in cracks and fissures of buildings in urban areas in Brazil (Freitas 1995). Nest entrances of the larger ground nesting species may recognized by the scattered exoskeletons of isopod prey dumped out of the nest. At least one species, L. elegans from West Africa, will nest in dead wood above the ground and forage on tree-trunks (Bolton 1975). Dejean & Olmsted (1995) report 4 species of Leptogenys nesting in epiphytic bromeliads and orchids in inundated forests in northern Yucatan. This record is of interest due to the arboreal nest sites, a situation unknown for any other New World species of the genus, and rarely encountered in other faunas (Bolton, 1975). At least three of the aformentioned Leptogenys species have also been found on nesting on the ground so there is no evidence yet for obligate arboreal Leptogenys, at least for the New World fauna. Even though these ants are more common in mesic habitats, they are no strangers to arid, desert conditions, with a number of species endemic to xeric areas such as Baja California (L. peninsularis), the Sonora desert (JEL- son), or the Galapagos Islands (2 undescribed species). The dry, interior part of Australia is also habitat for a number of Leptogenys species (Shattuck 1999), and several species of Leptogenys are known from semiarid parts of Africa (Bolton, 1975).
Specialized predation seems to dominate in this genus, with observations from all tropical continents corroborating oniscoid isopods as the prey of choice for most species (Dejean & Evraerts 1997). Other predatory specializations have been detected such as earwigs (Steghaus-Kovac & Maschwitz, 1993) for an Oriental species and termite predation for the African nitida group (Bolton 1975), and also for an unidentified Leptogenys in Brazil (Mill 1982). The Oriental army ant species are generalists, taking diverse prey. Individuals in the larger species carry isopod prey slung beneath their bodies, between the legs, and smaller species will carry large prey items amongst several individuals. In Costa Rica a group of workers of Leptogenys JTL-001 were observed and photographed carrying a large isopod, suggesting group raiding (E. Rodriguez, D. Kronauer, pers. comm). The diet may have influenced the Gestalt of the mouthparts with variations in mandibular shape, width of the anterior clypeal margin and shape of the median clypeal process (Dejean & Evraerts 1997).
The two most common modes of reproduction in the genus are either through ergatoid queens or egg-laying workers (Ito 1997, Ito & Ohkawara 2000). The queen in Leptogenys is generally an ergatoid, and only in two New World species are normal queens found: L. langi (Wheeler 1923), and JEL- nig. Wingless queens, but with well-developed flight sclerites and ocelli, are known for L. dasygyna in the New World (Wheeler 1923) and L. ergatogyna in Africa (Bolton 1975). Ergatoid queens generally lack any trace of ocelli, though when present it is a single, somewhat reduced ocellus. The gaster is usually larger in comparison to the workers, and the petiolar node, when seen dorsally, is generally wider than long, and the propodeal margin is more convex when observed laterally than in the worker. Additional characters that may characterize queens are larger overall body dimensions, broader head with more convex sides when seen frontally, and the compound eyes may be slightly larger. At least three species belonging to the pusilla group - L. pusilla, L. ritae, and L. josephi - have ergatoid queens with greatly swollen mandibles of a pale yellow color. This unusual character was first reported for L. josephi by MacKay & MacKay (2004), and was thought to be a diagnostic character for the species.
Reproduction by workers may be the norm in at least 2 species groups, (unistimulosa group and ingens group) and in L. famelica, all belonging to the arcuata supergroup. This is suspected due to the total lack of recognizable queens in a number of species despite the repeated collection of many nests. Gamergate reproduction could be more widespread in this genus as indicated by Bolton's (1975) observation that out of the 56 species known for the Ethiopian Region, females are known for only 6 or 7. Freitas (1995) reported males copulating with workers just outside the nests of L. maxillosa, but never observed nuptial flights or winged queens during nest relocation events. It is possible that at least some of the observed workers may have actually been reproductives.
Most species seem to have relatively modest, localized geographic ranges, smaller than those observed in other Ponerini. None have a range that extensively includes both North and South America, or most of either continent such as the case for some species in Pachycondyla, Hypoponera, or Odontomachus.
The New World fauna can be divided into two supergroups using the shape of a cross-section of the petiolar node at midlength. One supergroup has a V-shaped section and has been informally denominated as the crudelis supergroup, on account of the oldest existing name for the lineage, and the other group has a rounded, oval section and has been named the arcuata supergroup. The crudelis supergroup is found from Costa Rica to northern Argentina, including two island endemics in the Caribbean, and has at least 25 species distributed within 5 species groups and 4 species left as incertae sedis since they do not fit into any of the other groups nor do they seem closely related amongst themselves using morphology as an indicator. The arcuata supergroup is found from southern United States to northern Argentina and has at least 57 species distributed within 10 species groups and 5 species left as incertae sedis. The maxillosa group with the African tramp species L. maxillosa is left outside the two clades as its relations with the New World fauna are unknown until a phylogenetic analysis of the genus with worldwide coverage can be done.
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