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Crematogaster obscurata is a small (~2.3 mm) reddish brown arboreal species with a darker face and gaster, a trapezoidal petiole, and abundant flattened, semierect hairs dispersed across its head, mesosoma and gaster. The species is part of a complex of xerophilic species that occurs throughout the Neotropics (Longino, 2003), and has established a single introduced population in Florida (Deyrup, 2007; Deyrup et al., 2000). Crematogaster obscurata is treated in Longino’s (2003)revision, and Deyrup (2007)reviewed its identification, ecology and candidacy for eradication in Florida. The species is considered innocuous in both its native and introduced range.
Native Range. Mexico, Guatemala, Belize, Costa Rica, and Venezuela (Longino 2003).
Introduced Range. USA: Florida (Summerland Key, Monroe County).
In its native habitat in Costa Rica, Crematogaster obscurata occurs in dry forest habitats and beach margins, where it has been collected from trees (Longino, 2003). In Florida the species was first collected in 1995 and first reported as C. agnita Wheeler (Deyrup et al., 2000), which was subsequently synonymized with C. obscurata (Longino, 2003). Nests were found in dead portions of living trees, including hollow twigs and branches, and insect galleries in larger dead branches (Deyrup, 2007). One nest was in the stub of a dead branch of Piscidia piscipula (L.) Sargent, the others in Rhizophora mangle L. The discovery of two nests in separate red mangrove tress, each isolated in the intertidal zone, suggested to Deyrup that foragers might be confined to single trees. Having observed multiple dealate queens within collected nests, he also proposed that the species produces polygynous colonies capable of spreading by fission.
Deyrup presents arguments for and against the eradication of the single known C. obscurata population. On one hand, the species is apparently innocuous, hasn’t spread in the 11 years since first detected in Florida, and the need to unequivocally verify its status as introduced. On the other hand, the Florida C. obscurata population might eventually become more pernicious through ecological release, would be relatively easy to eradicate, and was likely introduced from Central America, possibly in association with the ornamental plant trade. Two US port of entry interception records of the species on Oncidium orchids from Guatemala (Longino, 2003)give credence to this last scenario.
In Costa Rica (Jack Longino)
Crematogaster obscurata occurs in dry forest habitats and beach margins. Mark Deyrup recently discovered a nest in the Florida keys, where it is most likely a recent introduction. I have collected the species twice in Costa Rica, both collections from Santa Rosa National Park in the seasonally dry habitats of Guanacaste Province. One collection was made while collecting at night in second growth dry forest near the park administrative headquarters. An aggregation of workers was in a tree knot. The second collection was from Playa Naranjo, at the upper beach edge. Small necrotic spots in live stems of a small Gliricidia sepium tree (Fabaceae) contained aggregations of workers only, with no brood or sexuals. The collection was made in the late afternoon, and the workers were not foraging. Even when the cavities were disturbed, the workers remained quiescent, appressed to the walls. The types of Wheeler's agnita were collected in hollow twigs, and workers have been twice intercepted in U.S. quarantine stations, in both cases in Oncidium orchids from Guatemala.
Diagnosis among workers of introduced and commonly intercepted ants in the United States. Head shape ovoid. Antenna 11-segmented. Antennal club 2-segmented. Antennal scapes not conspicuously short; easily extended beyond eye level. Antennal scrobe lacking. Eyes medium to large (greater than 5 facets) but distinctly less than half head length. Mandibles triangular. Pronotal spines absent. Propodeum armed with spines or teeth. Waist 2-segmented. Petiole flattened; lacking a distinct node; lacking peduncle; lacking large subpetiolar process. Petiole shape subtriangular with the dorsal profile sloping anteriorly. Postpetiole attached to upper surface of gaster. Head and mesosoma with abundant short flattened, semierect hairs.
This species may be distinguished from other Florida Crematogaster by its flattened, semierect hairs and by its granulate microsculpture on the sides of the head, mesopleura and propodeum. It can be separated from Crematogaster scutellaris, another commonly intercepted species, by the following characters: (1) a 2-segmented club (versus 3-segmented); (2) a more triangular petiole (versus trapezoidal); (3) abundant, flattened semierect hairs on its dorsal surfaces; (4) head not often a reddish color that contrasts with rest of body.
Crematogaster obscurata is part of a complex of species that occurs throughout the Neotropics. It is essentially a darker version of C. steinheili Forel, a yellow species that occurs on many Caribbean islands. In South America, versions of this complex include victima F. Smith 1858 and victima cisplatinalis Mayr 1877. These South American forms differ only in small details of color, sculpture, and pilosity. One character the South American forms exhibit is that the pronotal dorsum is densely punctate beneath the clathrate sculpture, rather than shiny or weakly microareolate. The entire lineage favors xeric regions.
Deyrup, M. (2007) An acrobat ant, Crematogaster obscurata (Hymenoptera: Formicidae), poses an unusual conservation question in the Florida Keys. Florida Entomol., 90, 753-754.
Deyrup, M., Davis, L. & Cover, S. (2000) Exotic ants in Florida. Trans. Am. Entomol. Soc., 126, 293-326.
Emery, C. (1895) Beiträge zur Kenntniss der nordamerikanischen Ameisenfauna. (Schluss). Zool. Jahrb. Abt. Syst. Geogr. Biol. Tiere, 8, 257-360, Tav. 8.
Longino, J.T. (2003) The Crematogaster (Hymenoptera, Formicidae, Myrmicinae) of Costa Rica. Zootaxa, 151, 1-150.
Wheeler, W.M. (1934) Neotropical ants collected by Dr. Elisabeth Skwarra and others. Bull. Mus. Comp. Zool., 77, 157-240.Add your content here.
Figure 4, Plate 2, 6
Crematogaster (Orthocrema) agnita WheelerHNS 1934:175. Syntype worker, queen: Guatemala, Zacapa ("an uncommonly arid locality") , 12 Dec 1911, in hollow twigs (Wheeler) [LACM; probable syntype workers with same data at NHMB, identified as sculpturataHNS by Santschi]. NEW SYNONYMY
USA (Florida), Mexico, Guatemala, Belize, Costa Rica, Venezuela.
Description of worker
Color red brown, gaster and face darker than rest of body.
Mandibles shiny, longitudinally striate, striae faint to pronounced; face with conspicuous microaerolate sculpture over most of surface, with a smooth shiny strip medially, extent of medial strip variable; scapes with abundant long subdecumbent to suberect pubescence, lacking differentiated long, erect setae; antennal club 2-segmented; clypeus shiny with 2-4 longitudinal rugulae; face with dense stubble of 30-40 short, stiff, erect setae; ventral surface of head smooth and shiny with sparse suberect to subdecumbent pilosity.
In lateral view, dorsal profile of pronotum, mesonotum, and propodeum forms continuous curve, dorsal and posterior faces of propodeum in same plane, sloping to petiolar insertion; propodeal spines projecting posterodorsally; pronotal dorsum with clathrate sculpture forming a lattice of longitudinal and transverse carinae with smooth and shiny interspaces; mesonotal dorsum with low, longitudinal carinulae laterally, microareolate sculpture medially; propodeal suture impressed medially but not visible in side view because lateral mesonotal carinulae continue onto dorsal face of propodeum; mesonotal carinulae have slight tooth at propodeal suture; dorsal face of propodeum very short, only visible in dorsal view, differentiated from posterior face by transverse carina, dorsal and posterior faces with faint microaerolate sculpture; propodeal spines short, thin, and sharp; side of mesosoma mostly microareolate/punctate, with variable degree of weakening of sculpture on side of pronotum, becoming entirely smooth and shining in some cases; setae on mesosomal dorsum stiff, relatively short, of variable length, longest approximately 0.14mm long, dorsum of pronotum with anterior row of four setae, anterolateral and posterolateral dorsum of mesonotum (at propodeal suture) each with a seta; propodeal spine with one long seta at base, subequal in length to spine; additional shorter setae dispersed among primary setae; legs with appressed to subdecumbent pubescence and no erect setae.
Petiole in side view trapezoidal; side densely microareolate/punctate; with acute anteroventral tooth; dorsal face subquadrate, about as wide as long, faintly microareolate or smooth and shining; posterodorsal face short, densely microareolate; posterolateral tubercles each with two stiff setae; postpetiole in dorsal view subrectangular, wider than long, with slight posterior emargination; postpetiole with small anteroventral tooth; dorsum and sides with microareolate sculpture; with 4-6 stiff erect setae; fourth abdominal tergite with very faint, areolate microsculpture, shiny, with about 50 stiff erect setae evenly dispersed over surface.
HL 0.593, 0.555, 0.622; HW 0.633, 0.608, 0.657; HC 0.584, 0.542, 0.611; SL 0.539, 0.511, 0.546; EL 0.161, 0.145, 0.162; A11L 0.242; A11W 0.119; A10L 0.116; A10W 0.109; A09L 0.061; A09W 0.065; A08L 0.041; A08W 0.067; WL 0.646, 0.580, 0.671; SPL 0.137, 0.116, 0.130; PTH 0.161, 0.150, 0.162; PTL 0.173, 0.163, 0.191; PTW 0.196, 0.166, 0.186; PPL 0.149, 0.124, 0.135; PPW 0.210, 0.173, 0.196; CI 107, 110, 106; OI 27, 26, 26; SI 91, 92, 88; PTHI 93, 92, 85; PTWI 113, 102, 97; PPI 141, 140, 145; SPI 21, 20, 19; ACI 1.75.
I have not observed the syntype queen of Wheeler's agnitaHNS, and I have seen no other queens of obscurataHNS. Given the similarity of obscurataHNS to steinheiliHNS, I assume it has queens like those of steinheiliHNS, which are normal queens (dorsal face of propodeum drops steeply from postscutellum and much of propodeum appears ventral to scutellum and postscutellum, Fig. 1) with general shape, sculpture, and pilosity characters of the worker.
Crematogaster obscurataHNS occurs in dry forest habitats and beach margins. Mark Deyrup recently discovered a nest in the Florida keys, where it is most likely a recent introduction. I have collected the species twice in Costa Rica, both collections from Santa Rosa National Park in the seasonally dry habitats of Guanacaste Province. One collection was made while collecting at night in second growth dry forest near the park administrative headquarters. An aggregation of workers was in a tree knot. The second collection was from Playa Naranjo, at the upper beach edge. Small necrotic spots in live stems of a small Gliricidia sepium tree (Fabaceae) contained aggregations of workers only, with no brood or sexuals. The collection was made in the late afternoon, and the workers were not foraging. Even when the cavities were disturbed, the workers remained quiescent, appressed to the walls. The types of Wheeler's agnitaHNS were collected in hollow twigs, and workers have been twice intercepted in U.S. quarantine stations, in both cases in Oncidium orchids from Guatemala.
The combination of punctate face, appressed tibial pilosity, and normal propodeal spines (as opposed to spines that are reduced to denticles or tubercles) uniquely identify this species in Costa Rica.
Crematogaster obscurataHNS is part of a complex of species that occurs throughout the Neotropics. It is essentially a darker version of C. steinheili ForelHNS, a yellow species that occurs on many Caribbean islands. In South America, versions of this complex include victima F. SmithHNS 1858 and victima cisplatinalis MayrHNS 1877. These South American forms differ only in small details of color, sculpture, and pilosity. One character the South American forms exhibit is that the pronotal dorsum is densely punctate beneath the clathrate sculpture, rather than shiny or weakly microareolate. The entire lineage favors xeric regions.
Found most commonly in these habitats: 1 times found in Playa Naranjo, 3 times found in beach, 1 times found in coastal hammock, 1 times found in dry forest, 1 times found in garden, 1 times found in littoral vegetation, 1 times found in tropical dry forest.
Found most commonly in these microhabitats: 1 times dry for. beach edge, 1 times Omphalea oleifera, 1 times under stone, 1 times nest in tree, 1 times in tree knot, 1 times in hollow twigs, 1 times in dead stub on small piscidia piscipula in understory, 1 times ex Oncidium splendidum, 1 times ex Oncidium cavendishianum, 1 times ex dead stem of Canavalia maritima.
Collected most commonly using these methods: 2 times Search.
Elevations: collected from 5 - 500 meters, 85 meters average