Crematogaster acuta (Fabricius

Longino, J. T., 2003, The Crematogaster (Hymenoptera, Formicidae, Myrmicinae) of Costa Rica., Zootaxa 151, pp. 1-150 : 32-35

Crematogaster acuta (Fabricius 1804)

Plate 3, 6

Formica acuta Fabricius 1804:411. Holotype worker: Guyana, Essequibo [ ZMUC] (examined). Wheeler, G. C. and Wheeler, J. 1952:258: description of larva. Roger, 1862:291: combination in Crematogaster . Santschi 1918:182: combination in C. (Euchrema) .

Crematogaster quadriceps Smith, F. 1858:140. Holotype worker: Brazil (not examined) . Synonymy by Roger, 1862:291.

Crematogaster (Eucrema) acuta var. centralis Santschi , 1932:412. Syntype worker, queen: Panama, Juan Diaz , 11 June 1930 (A. Bierig) [ NHMB] (examined). NEW SYNONYMY

Range

Mexico to southern Brazil, Bolivia.

Description of worker

Color dark red brown to black.

Head subquadrate, with compound eyes projecting beyond lateral margins in full face view; mandibles shiny, coarsely striate; clypeus shiny, smooth or with widely spaced weak rugulae; face punctatorugose over much of surface [Central American and northern South American material punctate with rugae very feeble; grading into forms in Amazonia, southeastern Brazil, Peru, and Bolivia with more pronounced, almost clathrate rugae and reduced punctation], with variably developed anteromedian strip on face smooth and shiny; vertex margin shallowly emarginate; scapes with abundant long, suberect setae that are almost as long as width of scape; scape etched, subopaque; antennal club not well defined, terminal 3-5 segments gradually lengthening and becoming increasingly densely pubescent; face with abundant long erect whitish setae; malar spaces and ventral surface of head with abundant short erect to suberect setae.

In lateral view, dorsal profile of promesonotum strongly convex, mesonotum differentiated from pronotum, projecting and forming elevated anterior boss; propodeal suture broad, well impressed; mesonotum meeting dorsal face of propodeum at angle, dorsal and posterior faces of propodeum distinct; propodeal spines stout, conical, evenly tapering to sharp points, much longer than dorsal face of propodeum, projecting posterodorsally and divergent; side of pronotum evenly punctate and medially impressed; katepisternum evenly punctate; anepisternum punctate to rugose; side of propodeum punctate, somewhat swollen, with distinct longitudinal sulcus beneath spiracle and shorter, oblique sulcus anterodorsal to opening of metapleural gland; promesonotal dorsum and dorsal face of propodeum with variable sculpture, punctatorugose with varying density of puncta and varying strength of clathrate rugae, paralleling variation in face sculpture; posterior face of propodeum grades from shallowly microareolate and opaque to completely smooth and shiny; propodeal spines smooth and shiny; promesonotum with abundant long whitish setae, abundant shorter setae on dorsal face of propodeum and propodeal spine, no setae on posterior face of propodeum; legs with abundant erect to suberect setae on all surfaces, longer and more erect on tibia than on femur.

Petiole robust, in side view trapezoidal, side strongly to faintly punctate; anteroventral tooth pronounced, forming right to acute angle; dorsal face rectangular, longer than wide, faintly microaerolate to smooth and shining; posterolateral tubercles vary from simple gibbosities to short, acute, posteriorly directed teeth; postpetiole with acute anteriorly directed ventral tooth, in dorsal view subquadrate, posterior margin emarginate, with weak to pronounced longitudinal median sulcus; anterolateral margin nearly perpendicular to stem of helcium, node of postpetiole separated from helcium by a distinct sulcus; fourth abdominal tergite with faintly microareolate sculpture; petiole, postpetiole, and fourth abdominal tergite with abundant erect to suberect whitish setae of variable length.

Measurements

HL 0.873, 0.860, 0.980; HW 0.997, 0.951, 1.135; HC 0.906, 0.876, 1.052; SL 0.960, 0.900, 1.085; EL 0.191, 0.187, 0.222; A11L 0.347; A11W 0.133; A10L 0.171; A10W 0.125; A09L 0.119; A09W 0.105; A08L 0.094; A08W 0.079; WL 1.169, 1.104, 1.295; SPL 0.420, 0.384, 0.552; PTH 0.260, 0.244, 0.300; PTL 0.416, 0.359, 0.460; PTW 0.318, 0.283, 0.343; PPL 0.270, 0.246, 0.329; PPW 0.343, 0.323, 0.405; CI 114, 111, 116; OI 22, 22, 23; SI 110, 105, 111; PTHI 63, 68, 65; PTWI 76, 79, 75; PPI 127, 131, 123; SPI 36, 35, 43; ACI 0.03.

Queen (Costa Rica)

In lateral profile dorsal face of propodeum sloping obliquely from postscutellum, such that most of propodeum is posterior to scutellum (in contrast to normal queens, in which dorsal face of propodeum drops steeply from postscutellum and much of propodeum appears ventral to scutellum and postscutellum, Fig. 1); scape etched and subopaque as in worker, but entire remainder of head, mesosoma, legs, petiole, postpetiole, and fourth abdominal tergite smooth and shining; propodeal spines long, acute; petiole and postpetiole robust, generally similar to worker in shape but lacking anteroventral petiolar tooth and ventral postpetiolar tooth; antennae, head, mesosomal dorsum, legs, petiole, and postpetiole with abundant long erect to suberect whitish setae; side of pronotum with abundant setae anterodorsally, a dense fringe of short setae along ventral margin, and lacking setae posteroventrally; katepisternum, anepisternum, and side of propodeum lacking setae; fourth abdominal tergite with sparse erect to suberect whitish setae; size characters as in Figures 4 and 5.

Biology

My field observations in Costa Rica, Colombia, and Venezuela suggest that this species prefers open disturbed habitats. Many collections are from roadside vegetation, pasture edges, and young second growth forest. Perfecto collected the species in an area of hurricane-flattened forest on the Atlantic coast of Nicaragua. The species occurs in wet and seasonally dry climates. My highest elevational record is 1000m in Bolivia, but most records are from below 500m. Colonies are very large, but not high density, and the species is only occasionally encountered.

I have observed nests on four different occasions, and each time they have been large, polydomous colonies nesting in dead wood. One nest was in dead Piper stems, one in chambers in fence posts along a fencerow, one in dead Cecropia branches, and one in the exposed dead core of a living tree trunk. In this last example, the dead part was dry and brittle, and one section was riddled with holes and filled with workers. There were few large chambers, and the workers seemed distributed evenly, like filling the spaces of a sponge. In addition to workers there were abundant alate females scattered throughout the wood, and I found a single male. There was very little brood. I could only excavate a small portion of the dead trunk, and it looked as though the colony continued up the side of the tree and deep into the dead core.

Workers have been collected by sweeping during the day and at night, and they have been collected at tuna baits. In Peru, Davidson has observed them foraging on the ground and invading myrmecophytic Triplaris trees. When nests are disturbed workers emerge in great numbers, wave their gasters in the air, and exude copious quantities of a white frothy material from the tip of the gaster. However, they rarely bite.

Nothing is known of colony founding, but queens exhibit a morphology often associated with social parasitism (see Natural History Overview).

Comments

Crematogaster acuta and the similar species C. evallans share a unique combination of characters: largely punctate face, erect tibial pilosity, and abundant clear to whitish (not amber, as in arcuata ) long erect setae on the face and mesosomal dorsum. The two species may be distinguished by several characters (see Key), but perhaps the most discrete is the acute ventral postpetiolar tooth on acuta , contrasted with a bluntly rounded lobe on evallans .