Octostruma wheeleri

Longino, John T, 2013, A revision of the ant genus Octostruma Forel 1912 (Hymenoptera, Formicidae), Zootaxa 3699, pp. 1-61 : 55-59

Octostruma wheeleri (Mann, 1922)

(Figs 1A, 3A, 5I, 14A, 41, 43)

Rhopalothrix (Octostruma) wheeleri Mann , 1922: 43. Holotype worker: Guatemala, Livingston (Barber & Schwarz) [USNM] (not examined). Combination in Octostruma : Brown, 1949: 92.

Geographic range. Mexico (Chiapas), Guatemala, Honduras, Costa Rica, Panama.

Description. Worker. HW 0.69-0.85, HL 0.63-0.75, WL 0.75-1.05, CI 108-114 (n=10). Labrum as in Fig. 1A, sides straight, strap-like lateral portions converging from base to apex, fused apically (not bilobed, at most with minute notch apically), joined medially by thin translucent cuticle; mandible triangular, in profile view with mandible closed, in same plane as clypeus, apex of mandible not down-turned; mandible with 8 teeth (Fig. 3A), basal rim of dorsal surface slightly offset from base of tooth 1, forming small denticle, teeth 1-5 acute, similar in shape, teeth 5-8 forming an apical fork, with 5 and 8 large, 6 and 7 small partially confluent denticles; dorsal surface of mandible roughened; ventral surface flat and parallel to clypeus apically, twisting basally to nearly perpendicular orientation basally, smooth and shining; interior surface concave, smooth and shining; scape flattened, with pronounced anterobasal lobe, dorsal surface roughened, dull; clypeus with broad, shallow emargination anteriorly; clypeus and face sculpture varying from almost completely smooth to very shallowly, irregularly rugulose, generally matte; frontal carinae faint, nearly obsolete; antennal socket deep, dorsal rim of socket continuous with pronounced dorsal margin of antennal scrobe; antennal scrobe deep, strongly delimited dorsally, posteriorly, and ventrally with sharply defined thin cuticular rim; compound eye small, circular, composed of about 7 ommatidia; distinct carina extends from ventral margin of antennal socket across floor of scrobe to compound eye; scrobe floor faintly foveolate, matte; vertex margin anterior to occipital carina smooth, sublucid (top of head, not visible in face view); occipital carina extends anteriorly on ventral surface of head to level of compound eye; undersurface of head rugulose.

Promesonotum convex in profile, promesonotal suture not impressed; metanotal groove not impressed; propodeum with distinct dorsal and posterior faces; dorsal face weakly convex; propodeal spines well-developed, in the form of acute flattened perpendicular plates, extending ventrally as thin carinae; single well-defined transverse carina extends between propodeal spines, separating dorsal and posterior faces of propodeum; propodeal spiracle medium-size, diameter less than width of base of propodeal spine, located below propodeal spine and abutting posterior margin; most surfaces of mesosoma matte, dorsal face of propodeum sublucid, posterior face shining; dorsum of promesonotum with sculpture similar to face, dorsal and posterior face of propodeum smooth, lateral pronotum smooth; meso-metapleuron and side of propodeum confluent, smooth.

Petiole in profile with peduncle differentiated from node, node with differentiated anterior face; node triangular, with long sloping dorsal face; anteroventral margin with peg-like tooth; postpetiole low, broad, crescent-shaped in dorsal view; dorsum of petiolar node and postpetiole shallowly rugulose, matte; first gastral tergite densely punctate, interspaces sublucid; first gastral sternite uniformly punctate.

Anterior labral lobe with radiating tuft of soft, thick, translucent, capitate setae of unequal length projecting from apex (like Fig. 2); each larger mandibular tooth with fully appressed seta running length of tooth; anterior margin of scape with about 8 stiff clavate setae; clypeus and face with fine, sparse fully appressed ground pilosity; face typically with 6 erect clavate setae arranged as in Fig. 5I; mesosomal dorsum lacking erect setae; mesotibia with about 5 clavate seta of variable length at apex; petiole, postpetiole, first gastral tergite lacking erect setae; ground pilosity of first gastral tergite short, sparse, fully appressed; first gastral sternite with abundant clavate setae clustered on posterior half, anterior half devoid of setae.

Color dark brown.

Queen (previously undescribed). HW 0.86, HL 0.75, WL 1.06, CI 115 (n=1). Head shape as in Fig. 14A; labrum, mandible, scape, antennal scrobe similar to worker; clypeus and face shallowly irregularly rugulose, tops of rugulae sublucid; face with one pair erect setae in front of eyes, one pair on posterolateral margin, one pair on posteromedian margin, one pair on medial frons (8 total); ocelli distinct; compound eye large, multifaceted, about 12 ommatidia in longest row.

Mesosoma with queen-typical alar sclerites; pronotum matte, faintly and sparsely punctate anteriorly and laterally, coarsely rugulose on humeri; mesoscutum, scutellum, dorsal face propodeum coarsely longitudinally rugose; anepisternum and katepisternum separated by strong sulcus; anepisternum, katepisternum, and side of propodeum matte, smooth; propodeal spines triangular, acute; pronotum with 2 erect setae, mesoscutum with about 12, axilla with 1, scutellum with 2, metanotum with 2, petiolar node with 2, postpetiolar disc with 2, first gastral tergite with about 25. Other characters similar to worker.

Biology. Octostruma wheeleri occurs in lowland rainforest, seasonal moist forest, and occasionally in cloud forest habitats. It occurs from sea level to 1100 m elevation, with greatest abundance below 600 m (up to 16% of 1 m 2 plot litter samples in quantitative sampling). It is only known from Winkler and Berlese samples of sifted leaf litter.

Comments. Brown and Kempf (1960) measured and redescribed the holotype. The measurements (HW 0.71, HL 0.64, CI 111) and description clearly match the concept of O. wheeleri adopted here. Quantitative sampling in Chiapas revealed a sharp parapatric distribution with the highland O. triangulabrum , with a narrow zone of sympatry around 1000 m elevation. At three lowland sites in Chiapas, O. wheeleri occurred in 12%, 11%, and 12% of 100 plot samples, and O. triangulabrum was absent. At Naha, at 980 m elevation and only 20 km away from one of the lowland sites (Laguna Metzabok at 570 m elevation), O. triangulabrum occurred in 13% of samples and a single O. wheeleri specimen was found.

Specimens from Chiapas to Honduras are uniform with respect to face setae. A worker from Las Marias in eastern Honduras is lacking the posteriomedian pair. The single worker from Hitoy Cerere, Costa Rica, has a single posteromedian pair, lacking the lateral and ocular setae.