Colobopsis etiolata

The type specimens were collected in woody galls of Holcaspis cinerosus on live-oaks (Quercus virginiana).

Identification
The species is readily distinguished from Colobopsis impressa by its pale color, the sharp borders of the truncated surface of the head and the shape of the thorax in the soldier and worker. In the latter character it resembles the European Colobopsis truncata.

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

Biology
Wheeler (1904) - C. etiolata is nocturnal in its habits. Their colonies seem to be polydomous. The fertilized queen starts her colony in a single gall, and when her progeny become too numerous for these circumscribed quarters some of them emigrate with a portion of the brood to other galls on the same tree. The irregular central chamber made by a Holcaspis larva (spherical, woody galls produced by the cynipid Holcaspis cinerosis on the twigs of the live-oaks) is enlarged by the ants and extended as a number of short galleries into the hard ligneous substance of the gall. The heads of the soldiers are just large enough to fit into the round hole through which the Holcaspis fly escaped. In one gall four of these round holes were found and each was occluded by a soldier. In this case three of the holes must have been made by the ants. The etiolata soldiers behave in the same manner as those of impressa and truncata towards workers entering or leaving the gall. When the activity of the workers is suspended during the day-time or during spells of cold weather, the soldiers remain at their post, carefully occluding the entrance for hours at a time. A census of 15 galls, collected from different trees in different localities, gave about 24.4 as the average number of ants in a gall, with an average of 4.9 soldiers and 19.5 workers.

On one occasion I found a young queen that had just started her colony and was raising a small packet of larvae. By replacing the slice of the gall cut away in exposing the central chamber and waiting for some time till the insect had regained her composure, she was seen to take up a position like the soldier, with her head occluding the entrance. This was perhaps to be expected from the configuration of her head, but it is an interesting fact, nevertheless, because it indicates that the isolated Colobopsis queen does not, like the isolated queens of many other ants, close the nest opening with earth or wood-filings till it is reopened by the first-born workers.

The pupae of C. etiolata are always nude, as in the other species of the subgenus. The workers and soldiers are sharply separated from each other morphologically; at least I have never been able to find any mediae, although I have examined the personnel of many nests for this particular purpose. The males and virgin females make their appearance earlier in the year than the fertile sexes of C. impressa. I have taken them as early as the first week in May.

Nomenclature

 *  etiolata. Camponotus (Colobopsis) abditus var. etiolatus Wheeler, W.M. 1904b: 150, fig. 5 (s.w.q.m.) U.S.A. Wheeler, G.C. & Wheeler, J. 1970: 650 (l.). Raised to species: Wheeler, W.M. 1927f: 31; Wheeler, W.M. 1934g: 216. Combination in Colobopsis: Ward, et al., 2016: 350.

Worker
Major. Length, 5-6 mm.

Head subcylindrical, from above suboblong, about one and one half times as long as broad, a little broader in front than behind; sides and occipital border straight; anterior truncated surface circular, concave, marked off on all sides from the remainder of the head by a sharp ridge. The clypeal portion of this surface is a little broader above than below, its borders somewhat concave on either side below the middle; it extends beyond the ridge onto the upper surface of the head for a much shorter distance than in Colobopsis impressa. Frontal carinae far apart, distinctly converging in front. Eyes large, their anterior orbits two fifths the distance from the occiput to the truncated surface. Antennal scapes curved, slender at the base, incrassated towards the tip, which extends to a distance somewhat greater than its transverse diameter beyond the posterior angle of the head. First funicular but little longer than the succeeding joints. Mandibles much larger and more projecting than in impressa, with convex ventral borders, four apical teeth, and a straight, toothless basal border. Thorax in profile evenly and gently arcuate above, with very faint promesonotal and mesoepinotal incisures. Pronotum rounded, hardly broader than long; mesonotum as long as broad, somewhat narrower behind than in front. Epinotum much compressed laterally, with a pronounced angle between its basal and declivous surfaces, the latter only slightly concave and of about the same length as the former. Petiole low and thick, convex in front and above, flattened behind, its upper posterior margin entire and not transversely indented as in impressa. Gaster elongate, sub oblong, depressed. Legs rather short, femora flattened, anterior pair considerably dilated.

Mandibles and anterior two-fifths of head subopaque, the former irregularly rugose-punctate, the latter more coarsely and reticulately rugose, with densely punctate interrugal spaces. On the cheeks and front the sculpture gradually passes over into umbilicately punctate, shallow and scattered foveolae. Posterior half of the head and remainder of the body shining, minutely shagreened.

Hairs yellow; short, clavate, and erect on the anterior half of the head, except its truncated surface; longer and tapering on the front. On the gastric segments there are a few scattered hairs, more abundant on the terminal segments. The tips of the antennal scapes and femora are furnished with a few hairs, and there are some very inconspicuous hairs on the legs.

Pale yellow. Mandibular teeth black. Anterior half of the head ferruginous red, gradually shading into the yellow color of the posterior portion. In soldiers from some nests the whole head is ferruginous, but always somewhat darker on the sculptured anterior portion. Segments of gaster each with a transverse brown band of variable breadth, but usually broadest on the terminal segments.

Minor. Length, 3.5-4.5 mm.

Head longer than broad, not very convex in front, and with much more prominent mandibles than in the workers of impressa. Clypeus nearly square, a little broader in front than behind, with a distinct median keel. Eyes large and flattened. Antennae slender, scape surpassing the posterior angle of the head by about two-fifths of its length, but slightly enlarged towards its tip. Thorax shaped like that of the soldier, but more slender and more compressed in the meso- and metapleural regions. Petiole in profile acute above, with convex anterior and flat or even slightly concave posterior surfaces; upper border very sharp, in some specimens broadly but faintly excised in the middle when seen from behind. Legs like those of the soldier. Gaster proportionally smaller and more pointed.

Shining throughout and very finely shagreened; clypeus, front, and cheeks with faint, scattered punctures.

Hairs yellow; sparse and erect, on the clypeus, upper surface of the head and gaster; on the cheeks and legs appressed and so minute as to be almost imperceptible.

Pale yellow. Mandibular teeth black. Head and antennae reddish; two or three terminal segments of gaster and in some specimens also the posterior portions of the preceding segments, infuscated.

Queen
Length, 5.5-6 mm.

Head like that of the soldier but narrower, with parallel sides, ocelli and somewhat larger and more convex eyes. Thorax elongate, elliptical from above, about three times as long as broad; mesonotum nearly one and one half times as long as broad. somewhat flattened; epinotum rounded, with no angle between the basal surface and declivity, which is somewhat concave below. Petiole low and thick, rounded above, with flattened anterior and posterior surfaces. Legs and gaster like those of the soldier.

Sculpture, color, and pilosity as in the soldier. Wings whitish hyaline, with distinct yellow veins and stigma; wing-insertions dark brown.

Male
Length, 3.7-4.5 mm.

Head, including eyes, about as broad as long, with moderately prominent eyes and ocelli; cheeks subparallel, about as long as the convex posterior borders which pass gradually into the nearly straight occipital border. Mandibles narrow, toothless, pointed, when closed overlapping with the tips. Clypeus sharply keeled. Antenna) slender, scape half as long as the funiculus, which is filiform and of uniform thickness, except for the distinctly incrassated' first joint. Thorax rather robust, mesonotum distinctly longer than wide, forming with the scutellum a regular ellipse. Basal surface of epinotum broadly rounded, declivity much shorter, obscurely concave below. Petiole small, anterior and posterior surfaces both somewhat convex, meeting above in a sharp transverse edge. Gaster and legs slender.

Shining throughout, minutely and obscurely shagreened.

Hairs pale and scattered, with about the same distribution as in the worker.

Yellowish brown; head behind, thoracic dorsum and gaster darker. There is a small deep black spot on the wing-insertions. Mandibles, mouth-parts, antennae, legs, thoracic sutures, genitalia, and extreme basal portion of each of the gastric segments, pale yellow. Wings whitish hyaline; veins and stigma pale yellow, less distinct than in the female.

Type Material
Described from numerous specimens of all four phases taken at Austin, Texas, in the woody galls of Holcaspis cinerosus on the live-oaks (Quercus virginiana).