Dolopomyrmex pilatus, Cover, S. P. & Deyrup, M., 2007

Cover, S. P. & Deyrup, M., 2007, A new ant genus from the southwestern United States., Advances in ant systematics (Hymenoptera: Formicidae): Homage to E. O. Wilson - 50 years of contributions. (Memoirs of the American Entomological Institute 80), pp. 89-99 : 92-94

Dolopomyrmex pilatus , new species

Figures 1 - 3

Holotype worker: TL 2.0, HL 0.54, HW 0.49, CI 91, SL 0.33, SI 67, PW 0.33, ML 0.70.

With characters of the generic diagnosis and as illustrated in Fig. 1. Head broadly rectangular, posterior corners rounded, posterior margin flat, entire dorsal surface covered with coarse setigerous foveolae, generally separated by 1 - 2 Ã their diameters. Spaces between foveolae smooth and shining. Eye remnant barely visible; unpigmented. Numerous short, decumbent to appressed setae present on dorsal surface of head, sparse appressed setae present on ventral cephalic surface. Antennal scapes in repose extending about 3 / 4 the distance towards the posterior corners of the head, with numerous erect or suberect hairs on outer surfaces. Body surfaces generally smooth and shining on mesosoma, petiole, postpetiole, and remainder of abdomen. Numerous, short, curved erect hairs present on promesonotum, longer erect hairs present on propodeal dorsum, petiolar node, and postpetiole, respectively. Remainder of abdomen (= gaster) with evenly spaced erect hairs as in Fig. 1. Color pale yellow.

Paratype workers: TL 1.6 - 2.4, HL 0.47 - 0.56, HW 0.42 - 0.51, CI 89 - 91, SL 0.27 - 0.34, SI 67 - 68, PW 0.26 - 0.33, ML 0.59 - 0.74.

Paratype queen: TL 9.5, HL 1.27, HW 1.49, CI 117, SL 0.79, SI 53, ML 3.2. With characters in generic diagnosis and as illustrated in Fig. 2. Head broader than long, posterior margin flat, dorsal surface foveolate, foveolae larger and much sparser on posterior half of head. Spaces between foveolae smooth and shining, except on anterior half, where weak striae are present surrounding the antennal sockets and near the mandibular insertions. Clypeus foveolate, except for smooth median strip, erect setae numerous. Antennal scape in repose against head with many erect setae on outer surfaces. Mesosoma largely smooth and shining, sparsely and finely foveolate on most surfaces, coarser foveolae present on mesopleuron. Petiole and postpetiole smooth and shining with scattered fine foveolae, each with a tuft of long, erect setae on ventral surface. Remainder of abdomen smooth and shining with sparse, very fine foveolae and moderately abundant, short erect hairs. Outer surfaces of middle and hind tibiae with abundant, coarse, setigerous foveolae. Color: body generally light to medium yellowish-brown, appendages a lighter brownish yellow. Posterior dorsal surface of head with large, dark brown spot centering on the ocelli.

Paratype male: TL 5.0, HL 0.68, HW 0.72, CI 106, SL 0.45, SI 62, ML 1.85. With characters in generic diagnosis and as illustrated in Fig. 3. Head with fine striate sculpture over most of dorsal surface, except for smooth median clypeal strip and two lateral smooth, shining patches between the ocelli and compound eyes. Mesosoma generally unsculptured and shining with widely spaced very fine setigerous foveolae, except for some coarser foveolae on the mesopleuron, and fine striate sculpture on the mesopleuron and the propodeal sides. Petiole and postpetiole with small tuft of long, erect setae on ventral surface. Remainder of abdomen with widely-spaced, very fine setigerous foveolae, erect hairs sparse and short. Color: head and mesoscutum blackish brown, Mesosoma, petiole, and postpetiole variably light to medium yellowish brown. Legs light yellowish brown, antennae pale yellow.

Etymology:pilum is Latin for the short, but powerful throwing spear of the Roman legionaries. So Dolopomyrmex pilatus is the spear-bearing ambush ant.

Type Locality: USA, Arizona: Cochise Co. Chiricahua Mtns . 0.8 mi NW Jct. Forest Service Road 42 on FSR 42 B ( Paradise Road ). 31° 55.24' N, 109° 09.67' W. elevation 4700' (1432 m.). Broad, grazed wash dominated by mesquite and acacia to 3 m. tall. Fine-textured, densely compacted, sandy soil with some clay. Note: this is privately owned land adjacent to the Coronado National Forest .

Type Series: holotype worker (SP Cover 1441) and the following paratypes: 22 workers, 13 males, 15 queens [3 - VIII- 1988, SPC 1441], 9 workers, 12 queens [4 - VIII- 1988, SPC 1454], 6 workers [17 - VIII- 1989, SPC 2173], 13 workers [17 - VIII- 1989, SPC 2174], 4 workers [3 - VIII- 1990, SPC 2530]. Holotype and paratypes deposited in the Museum of Comparative Zoology (Cambridge, Mass., USA). Additional paratypes will be deposited in the Natural History Museum (London, U. K), the Natural History Museum of Los Angeles County (Los Angeles, California), the National Museum of Natural History (Washington, DC), the California Academy of Sciences (San Francisco, CA), the Museu de Zoologia (Sao Paolo, Brazil), the Australian National Insect Collection (Canberra, Australia), the University of California (Davis, California) and in the collection of William P. Mackay. Note: images of the holotype will be available on the online MCZ Type Database [http: // mcz- 28168. oeb. harvard. edu / default. htm] and images of paratypes on AntWeb [http: // www. antweb. org].

Additional specimens examined: USA, California: Los Angeles Co. Saddleback Butte . 23 - IX- 1989. coll. G. C. Snelling (2 males, 2 dealate females) [ LACM] . New Mexico: Dona Ana Co., 45 km NE Las Cruces. Jornada LTER. 3 - X- 1970. colls. G. Richardson and C. W. O'Brien (3 alate females, 1 dealate) [ LACM] ; Socorro Co. Servilleta National Wildlife Refuge . Date unknown (not seen by the authors, but cited in Mackay and Mackay (2002) .

DISCUSSION

It is possible the California collections may represent a second species of Dolopomyrmex . The two queens are somewhat larger than those from Arizona and New Mexico and exhibit some differences in morphology and pilosity. The two males taken with them, however, closely resemble males from the type series. These specimens are tentatively assigned to D. pilatus pending the collection of workers, upon which their status should be re-evaluated.

The type locality is a desert wash with highly compacted, sandy soil located at the border between relatively flat desert and the foothills of the Chiricahua Mountains. It is a very arid, sunbaked habitat for most of the year. Ant species found at the site include: Crematogaster opuntiae , Aphaenogaster albisetosa , Pogonomyrmex barbatus , P. imberbiculus , Pheidole desertorum , P. rugulosa , Dorymyrmex insanus , Forelius maccooki , and Camponotus fragilis , all desert or desert foothills ants common throughout much of the American Southwest. The following notes summarize the circumstances of each collection at the type locality. SPC 1441 was collected when a single worker was seen entering a minute, nearly invisible hole with a trace of excavated soil around it, in bare soil between mesquite clumps a day after rain. Chambers containing winged queens, males, some brood, and workers were found between 30 - 50 cm. deep. SPC 1454 was found in soil while excavating a nest of another species and included winged queens as well as workers. SPC 2173, 2174 and 2530 are all small series of workers taken 15 - 25 cm deep in soil when excavating nests of Pogonomyrmex imberbiculus after rain at the type locality. The Pogonomyrmex nests were all located in bare soil between mesquite clumps. SPC 1441 was maintained alive for about a week in a large plastic petri dish with a plaster bottom and moist cotton in it. The workers fed intermittently on fresh ant brood and termite nymphs, but ignored other dead insects and sweet substances. Mackay & Mackay (2002) report this ant (as Tranopelta sp.) from Creosotebush scrub and mesquite dominant zones, often near desert playas or arroyos, sometimes in open desert or in forest meadows. Occasionally they are found in salt flats or saltbush communities.

Dolopomyrmex fits comfortably within the myrmicine tribe Solenopsidini , as newly expanded by Bolton (2003). Its affinities within the tribe are the subject of some disagreement. Since the discovery of Dolopomyrmex in 1988, several myrmecologists have suggested informally that it is most likely an undescribed species of the exclusively New World myrmicine genus Tranopelta . Indeed, Mackay & Mackay (2002) place the ant in that genus (without formally describing it) and summarize the reasons for doing so. The hypothesis makes some sense. Dolopomyrmex and Tranopelta share important character states. The workers of both lack a bicarinate clypeus and a median clypeal seta, and instead possess a pair of subparallel setae that straddle the clypeal midpoint. The antennae of both are 11 segmented with a prominent 3 segmented apical club. The queens and males also share some notable similarities. Both Dolopomyrmex and Tranopelta have fully subterranean life-histories, workers yellow in color and with highly reduced eyes, and sexual forms far larger than the corresponding workers. In addition, the geographic range of Tranopelta extends north into southern Mexico, so it is not impossible that a species might occur in the extreme southwestern United States.

In our opinion, however, a closer examination reveals differences that not only preclude the inclusion of D. pilatus in Tranopelta , but also in fact, reveal that the two genera are not closely related. For example, in the worker caste of Dolopomyrmex the clypeus is narrow, the median portion strongly elevated, and the antennal sockets closely approximated (clypeus broad, median portion weakly elevated, antennal sockets well-separated in Tranopelta ), the cutting edge of the mandible is strongly oblique (more or less transverse in Tranopelta ), the petiolar node is low, rounded, and nearly circular in dorsal view (strongly upright and wider than long in dorsal view in Tranopelta ), the petiolar spiracle is located on the anterior side of the node (on the welldeveloped peduncle in Tranopelta ), and a subpetiolar process is lacking (one, sometimes two present in Tranopelta ). In addition, compound eyes are vestigial or lacking in Dolopomyrmex (present, with at least several well-defined and pigmented ommatidia in Tranopelta ), and the workers are monomorphic (weakly polymorphic in Tranopelta ). Lastly, the males are strikingly different. Those of Dolopomyrmex possess a true antennal scape nearly as long as the funiculus, and the petiolar and postpetiolar spiracles are located at the tips of unique lateral connules. In Tranopelta males, the first antennal segment is very short, no longer than the following two funicular segments taken together, and the petiolar and postpetiolar spiracles are normal in configuration.

Instead, within the Solenopsidini Dolopomyrmex appears to be closer to two exclusively Old World solenopsidine genera, Anillomyrma and Bondroitia . A comparison of the workers is instructive and striking. All three genera share a closely similar structure of the clypeus, frontal lobes, and antennae, strongly oblique mandibular cutting margins with 4 teeth (3 teeth in one Anillomyrma species), and similar petiolar structures, most notably having the spiracle located anterolaterally on the side of the node, reduced palpal counts, and vestigial or absent compound eyes. The only truly discordant note is the absence of a median clypeal seta in Dolopomyrmex , present in Anillomyrma , Bondroitia , and most other Solenopsidine genera. The presence of a median clypeal seta was once thought to be a diagnostic character for the Solenopsidini (Bolton, 1987), but is presently seen to be more variable and less important than previously thought. Bolton's (2003) recent redefinition of the tribe reflects this change. We look forward to future discoveries that will help further clarify the phylogeny within this important and interesting group of genera. With respect to Dolopomyrmex in particular, we need better collections of the sexual forms of both Anillomyrma and Bondroitia . Two damaged males and a fragmentary queen of Bondroitia lujae at the MCZ collection show important similarities, as well as some notable differences, with the comparable castes of Dolopomyrmex . See also the figures of Bondroitia lujae in Bolton (1987).