Leptogenys unistimulosa

Observations in Venezuela indicate this species inhabits humid to deciduous forests, though the latter with a marked rainy season. Nests are situated within or beneath rotting trunks on the ground, and under stones as well. They flee rapidly upon discovery of the nest, the workers taking refuge beneath the leaf litter. Observations of nest middens, actively feeding larvae, and workers with prey in mandibles indicate this is an isopod predator. One prey item was determined as Lygia sp. (C. Schmidt det.). L. unistimulosa can be locally common, and such sites seem to coincide with localities having an elevated presence of isopods. Complementary to this are observations by Mill (1982) of L. unistimulosa preying upon Termes fatalis Linnaeus workers captured by the ants in the termite nest galleries. Dozens of specimens from different nest series, besides individually collected ants, have revealed none that could be determined as a queen using the usual morphological characters. It is very probable that egg laying workers are the mode of reproduction for this species. (Lattke 2011)

Identification
Key to Leptogenys of the New World

Lattke (2011) - A member of the unistimulosa species group. Eye large and bulging, occupying one-third of cephalic lateral margin; hypostomal tooth triangular and almost as long as basal mandibular width; scape surpasses posterior cephalic margin by one-half its length; mandible arched, slender and elongate, of uniform width; head, mesosoma, and petiole black, gaster ferruginous brown; petiolar node with an acutely pointed posterior spine.

Distribution based on Regional Taxon Lists
Neotropical Region: Brazil, Colombia, French Guiana, Guyana, Suriname, Trinidad and Tobago, Venezuela.

Castes
Queen unknown. Male not studied.

Nomenclature

 *  unistimulosa. Leptogenys unistimulosa Roger, 1863a: 175 (w.) BRAZIL. Senior synonym of bahiana, trinidadensis: Lattke, 2011: 221.
 * bahiana. Leptogenys unistimulosa var. bahiana Santschi, 1929a: 416 (w.) BRAZIL. Junior synonym of unistimulosa: Lattke, 2011: 221.
 * trinidadensis. Leptogenys unistimulosa var. trinidenysadensis Forel, 1901f: 328 (w.) TRINIDAD. [Justified emendation of spelling to trinidadensis: Forel, 1905b: 156.]. Junior synonym of unistimulosa: Lattke, 2011: 221.

Lattke (2011) - Unfortunately it was not possible to find the L. unistimulosa Roger types, though the description (Roger 1863a: 175) mentions the acutely pointed petiolar node, a trait of the species determined here as L. unistimulosa, but also of Leptogenys bohlsi as well. Even though the color pattern he describes seems to correspond more to coloration found in samples of L. bohlsi from São Paulo, some L. unistimulosa specimens can be similar. Stronger support for considering the present species as equivalent to Roger’s L. unistimulosa is the specimen length of 9.5 mm he describes, a size more like L. unistimulosa than L. bohlsi, which averages less than 8 mm. L. bohlsi is very similar in appearance to L. unistimulosa, including the color pattern, but on average L. bohlsi is smaller in size than L. unistimulosa and the apex of its petiolar spine is usually blunt, and less commonly acutely pointed though it is of similar length in proportion to the body. The scape in L. bohlsi surpasses the posterior cephalic margin by one-third to one-fourth of its length and the lateral cephalic margins are more parallel to each other, not as divergent as in L. unistimulosa. The compound eye in L. bohlsi is somewhat smaller, occupying about a fourth of the lateral cephalic length, and not as bulging. Given this conclusion as to the identity of L. unistimulosa, the forms L. bahiana and L. trinidadensis fall without difficulty into the present concept of L. unistimulosa.

This is one of the more widespread species of the genus, found throughout northern South America, and with the exception of some isolated specimens, it is not subject to marked morphological differentiation of populations, at least when compared with the situation in Leptogenys pubiceps. The head may vary in the degree of divergence of the lateral margins, giving some workers the appearance of having a very broad cephalic dorsum anterad, or others with a more slender cephalic dorsum. The ratio Posterior HW/Anterior HW can vary from 0.38 to 0.45. The hypostomal teeth are always quite visible in cephalic full-face view and fairly long, sometimes almost touching the mandible. The slope of the dorsal margin of the node may vary from 30–45° when seen laterally. The petiolar apical spine is always acutely pointed and overhangs the posterior margin of the node, varying a bit in length, and in dorsal view varying in width. The mesonotum can form a distinct convexity or can form a continuously curved margin in lateral view, along with the pronotum. None of the aforementioned differences appear to segregate into regional patterns, though a few specimens and series suggest at least some degree of differentiation in some populations. The Acre specimens appear to have a more slender mesosoma than usual, and more arched and slender mandibles. The Sergipe specimens are very dark coloured, including the gaster.

Worker
Lattke (2011) - Metrics (n = 10): HL 1.31 – 1.72; HW 1.18 – 1.82; ML 1.01 – 1.58; EL 0.34 – 0.51; SL 1.55 – 2.29; PW 0.84 – 1.18; WL 2.36 – 3.27; PH 0.98 – 1.48; PL 0.71 – 0.98; DPW 0.57 – 0.71 mm. CI 0.90 – 1.08; MI 0.79 – 0.87; OI 0.26 – 0.34; SI 1.26 – 1.37; LPI 1.38 – 1.69; DPI 0.68 – 0.77.

Head wider anterad than posterad in full-face view, lateral margin broadly convex, almost straight, lateral cephalic margin interrupted by compound eye; posterior margin broadly convex, almost straight, usually forming continuous curve with lateral margins. Median clypeal lobe shaped as broadly triangular to rounded lobe, shorter than scape width, forms angle at base with rest of clypeus, 5–2 setae on apex; lateral clypeal lobe narrow and broadly convex, gradually expanding towards median lobe. Clypeus obliquely to transversely strigose, posteriorly bordered by transverse sulcus running from antennal sclerite to just below eye. Cephalic dorsum strigose to rugose; anterior third usually strigose; posterior two-thirds usually rugulose. Scape punctulate, surpassing posterior cephalic border by almost one-half its length; second and fourth antennal segments subequal in length, each two-thirds as long as length of third antennal segment. Mandibles elongate and slender, arched and crossing only at apex, dorsal surface smooth and shining with sparse punctulae; sometimes with small pre-apical denticle; masticatory margin concave, not longer than maximum scape width. PF: 4,4. Cephalic ventrum with low longitudinal strigulae along posterior half, the rest mostly smooth with low arching strigulae. Hypostomal tooth triangular, almost as long as basal mandibular width.

Mesosoma with broadly convex dorsal pronotal margin in lateral view, mesonotum forms distinct convexity, separate from broadly convex propodeal margin. Propodeal declivity curved, with 3–6 transverse carinae, no teeth. Lateral pronotum longitudinally strigulose, pronotal dorsum strigulose-punctuate; strigae arching around pronotum; mesonotum transversely strigose; propodeal spiracle elongate, facing posteriorly. Metapleural-propodeal suture mostly effaced except around spiracle, mesometapleural suture well marked, scrobiculate. Ridge separates mesopleuron from mesosternum; mesosternal sculpture mostly effaced. Meso-, metapleuron and lateral propodeal face with oblique strigulae. Propleuron mostly transversely striate anterad and rugulose to strigose posterad; mesosternal lobe broadly triangular, metasternal lobe with rounded external margin, basal margin straight; lobe leans medially.

Petiole with convex anterior margin, and straight ascending dorsal margin in lateral view, both margins joined by convexity; apex of node with acutely sharp point that overhangs mostly convex posterior margin in lateral view; node with anterior margin almost as wide as posterior margin in dorsal view, node length greater than width, excluding posterior spine. Node longitudinally strigose laterally; posterior face with transverse strigae laterally, sculpture effaced to varying degrees on discal area. Postpetiole with vertical anterior margin that becomes convex dorsad in lateral view, constriction not strongly marked; gaster mostly smooth and shining with sparse piligerous punctae. Pygidium without longitudinal crest. Head, mesosoma, and node black; antennae, mandibles, and legs brown to dark brown; gaster ferruginous brown to brown. Body with abundant standing and decumbent hairs.

Type Material
Lattke (2011)- Type: Brazil [not examined].

Leptogenys unistimulosa var. trinidadensis. Syntype workers: Trinidad (M. Ulrich) [examined].

Leptogenys unistimulosa var. bahiana. Holotype worker: Brazil, Bahia (Reichensperger) [examined].

Additional References

 * Lattke, J.E. 2011. Revision of the New World species of the genus Leptogenys Roger (Insecta: Hymenoptera: Formicidae: Ponerinae). Arthropod Systematics & Phylogeny 69:127-264.