Crematogaster isolata

An uncommon species that nests in dead branches of oaks (Quercus arizonica), at altitudes over 1500m. (Mackay and Mackay 2002)

Identification
Buren (1968) - This species is not closely related to any species occurring in the United States except Crematogaster marioni, which can be easly separated by its pilosity. Since their ranges appear completely allopatric, probably no confusion will arise. The distinctive epinotum of isolata (see description) will clearly distinguish this new species from all other species in the United States. C. isolata appears to be the only arboreal species of this subgenus other than marioni which nests in oaks (and perhaps also manzanita) at altitudes over 5000 ft. in the southwestern mountains. Crematogaster hespera, a quite different species, is largely confined to cottonwoods at lower altitudes.

Key to western US Crematogaster

Distribution based on Regional Taxon Lists
Nearctic Region: United States. Neotropical Region: Mexico.

Habitat
Mountainous areas.

Nomenclature

 *  isolata. Crematogaster (Crematogaster) isolata Buren, 1968b: 106 (w.) U.S.A.

Worker
Head, excluding mandibles, slightly broader than long, with convex sides and posterior border excised in the middle. Scapes surpassing posterior corners by about one diameter, less in larger workers. Humeri of pronotum absent or weak. Pro-mesonotum in profile evenly but not strongly convex above. Mesonotal declivity absent or short and rounded. Meso-epinotal impression a strong and deep groove above, deeper than in any preceding species. Mesonotal carina weak or absent. Base of epinotum long, noticeably longer than in most species. Spines short, one half of interbasal distance in length or even less, straight, divergent, not slender or sharp. Base of epinotum from above somewhat convex or tuberculate at sides. Petiole slightly broader than long, angularly trapezoidal. Hemilobes of postpetiole elongate, more produced behind, with slightly convex sides from above. Median impression fairly strong, especially behind, not groove-like but a fairly wide, evenly concave impression.

Genae striato-punctate to about middle of eyes. Head subshining on front, vertex, occiput, and corners, sometimes corners smooth and shining. Sides of venter striato-punctate. Vertex and middle of occiput punctate. Front faintly punctate. Front of pronotum punctate, and there may be a shining median streak. Pronotal dorsum punctate. Pronotal sides with larger but weaker punctures, subopaque. Mesonotum punctate, subopaque. Mesopleura densely punctate. Metapleura punctate above and below. Base of epinotum punctate with a few longitudinal rugae or striae. Declivity smooth and shining. Petiole and postpetiole punctate, subopaque. Gaster with reticulate shagreen, subshining.

Pubescence moderately or quite short on all parts, appressed; subappressed on scapes. Erect hairs rather bristle-like, very sparse, one or none each shoulder on thorax, and two to four at most each segment of gaster, thus much sparser than in marioni.

Head and thorax usually dark brown. Gaster black.

Type Material
The holotype and a number of paratypes were collected a few miles north of McDonald Observatory, Davis Mts., Texas, from a dead oak limb, Oct. 14, 1959, W. F. Buren. I have also marked as paratypes numerous specimens from the following localities: Madera Canyon, Santa Rita Mts., Ariz., June 21, 1951, crawling on manzanita, Wm. S. Creighton; Garden Canyon, Huachuca Mts., 5800', in dead oak stubs, Creighton (two records;) San Luis Pass, Animas Mts., N. Mex., 5400', Sept. 28, 1951, in Quercus emoryi, Creighton, (two records;) Sweetwater, Santa Rita Mts., Ariz., July 2, 1951, in dead oak stub, Creighton; Canelo Pass, Santa Cruz Co., Aug. 28, 1951, in dead oak limb, Creighton; Chiricahua Nat. Mon., Ariz., Sept. 20, 1951, in Quercus emoryi, Creighton. I have also seen and marked as paratypes a small series of 10 workers from Limpia Canyon, Davis Mts., Texas, altitude 5500 ft., and a single specimen each from the Guadalupe Mts. and Huachuca Mts., Ariz., L. F. Byars.

The holotype and a few paratypes from each series will be deposited in the National Museum. Other paratypes will go to the Museum of Comparative Zoology, the California Academy of Sciences, to the private collection of Dr. Creighton, and to my own private collection.