Trachymyrmex carinatus, Mackay & Mackay, 1997

Rabeling, Ch., Cover, S. P., Johnson, R. A. & Mueller, U. G., 2007, A review of the North American species of the fungus-gardening ant genus Trachymyrmex (Hymenoptera: Formicidae)., Zootaxa 1664, pp. 1-53 : 8-10

T. carinatus Mackay & Mackay

Trachymyrmex carinatus Mackay & Mackay , 1997: 43. Holotype worker ( MCZC) [examined], paratype workers, paratype queens, and males, 15km W Bellavista, Municipio Riva Palacio , Chihuahua, Mexico ( AMNH, WPMC, LACM, MCZC, USNM) [examined], (additional paratypes in MZSP, Universidad Nacional Autónoma de México: Instituto de Ecología)

Diagnosis

Worker: HL 0.8-1.0, HW 0.8-1.04, CI 96-108, SL 0.84-1.04, SI 100-105, ML 1.2-1.44. A relatively small species (HL 0.8-1, HW 0.8-1.04) with normally proportioned legs and antennal scapes (SI 100-105). Head more or less square (CI 96-108), sides subparallel posterior to the eyes, slightly tapering anteriorly between the eyes and mandibular insertions. Posterior margin weakly to moderately concave. Preocular carinae long, strongly curving mesially, and traversing nearly the entire distance between the eye and the frontal carinae, sometimes nearly touching the frontal carinae or appearing to do so. In full-face view, frontal lobes more or less symmetrical. Anterolateral promesonotal teeth moderate in size, pointed in dorsal view, projecting horizontally, not vertically. Anterior median pronotal tubercles small or reduced to denticles, or if toothlike short and broadly pyramidal. Propodeal teeth usually acute, about as long as the distance between their bases. Dorsal surface of body moderately tuberculate, tuberculi generally moderate in size, bearing recurved setae. First gastric tergite coarsely and conspicuously tuberculate. Color brownish to yellow to medium reddish-brown.

Queen: HL 1.1-1.25, HW 1.15-1.4, CI 105-112, SL 1.1-1.15, SI 82-96, ML 1.9-2.1. As in worker diagnosis, except for typical caste-specific morphology of the mesosoma related to wing-bearing and head with minute ocelli. Dorsolateral pronotal teeth well-developed, tuberculate, sharply triangulate in dorsal view, often blunt-tipped in anterior view. Mesoscutum coarsely and irregularly rugulose, sometimes with faint longitudinal pattern, minutely tuberculate, and with abundant short, suberect, slightly recurved setae.

Male: HL 0.72-0.81, HW 0.75-0.84, CI 104, SL 0.81-0.9, SI 104-111, ML 1.6-1.8. Somewhat variable in size, but presenting the following characters: Dorsolateral pronotal tooth absent in dorsal view, ventrolateral pronotal tooth small, broadly to narrowly triangular. Mesoscutum irregularly rugulose, interrugal spaces coarsely granulose. Preocular carina a prominent vertical ridge, remaining strongly developed at least until it reaches the midpoint of the posterior border of the antennal scrobe. In full-face view, posterior corners of head more or less rounded, their outlines obscured by the presence of several conspicuous toothlike tuberculi on each corner.

Discussion

In southern Arizona, T. carinatus co-occurs with T. arizonensis in mid elevation habitats. Workers and queens of these two species are easily distinguished by the distinctive frontal lobes of T. arizonensis and the preocular carinae nearly touching the frontal carinae in T. carinatus (not closely approaching the frontal carinae in T. arizonensis ). T. carinatus also sometimes co-occurs with T. pomonae from which it may be separated by its larger size and symmetrical frontal lobes (lobes notably asymmetric in T. pomonae ). In addition, workers of T. carinatus are superficially very similar to those of the allopatric T. septentrionalis , from which they may be separated by the characters given in the key.

Etymology

The species name "carinatus" refers to the well-developed carinae on the vertex of the workers ' and queens ' heads.

Biology

Trachymyrmex carinatus was described by Mackay & Mackay (1997), based on specimens collected in Chihuahua, Mexico, and the Chiricahua Mountains of southeastern Arizona. T. carinatus occurs in central and southern Arizona, western New Mexico and the Mexican States of Sonora, Chihuahua and Coahuila, often in sympatry with T. arizonensis . A single collection from the Kofa Mountains in southwest Arizona marks its westernmost limit. So far, T. carinatus has been encountered most commonly in the mountains of southern and central Arizona in mid elevation habitats (800-1800m).

Colonies may be found in open exposed areas with sparse ground cover, such as washes or road-sides, but are especially abundant in oak-juniper-pinyon woodlands. The Kofa Mountains specimens were collected from a nest next to a water seep shaded by palm trees on the wall of a canyon at ~800 m elevation (R. Snelling, personal communication). Nests are sometimes found under stones, but are more often encountered in open ground, where they can be recognized by the circular shape of the nest crater, which contrasts with the more amorphous nest excavations of T. arizonensis . Excavations by C. Rabeling reveal that nests in the Chiricahua Mountains of southern Arizona have one to three fungus garden chambers, with the shallowest chamber only 5 cm beneath the soil surface. Colonies have fewer than 100 workers. Mating flights occur near dawn on mornings following summer rains (Mackay & Mackay 1997).

Additional material examined: U.S.A.: Arizona, Cochise County: 5.5km W Portal (C Rabeling) , Chiricahua Mtns. Southwestern Research Station (RA Johnson, UG Mueller, C Rabeling & SP Cover) , Huachuca Mtns. Carr Canyon (SP Cover) , Huachuca Mtns. Sunnyside Canyon (RR Snelling) , Peloncillo Mtns. Cottonwood Canyon (WS Creighton) ; Gila County: Jct. USFS Rd. 287 & 287A (RA Johnson) , Sierra Ancha Mtns. Pocket Creek (RA Johnson) , Sierra Ancha Mtns. 14.8 mi N Salt River on Rt. 288 (RA Johnson, SP Cover) ; Pinal Co: USFS Rd. 287 at 0.4 mi SE Pinto Creek (RA Johnson) , Santa Cruz Co: 1mi E Atascosa Lookout (RA Johnson) , 1mi S American Peak, Harshaw Creek Rd (RA Johnson) , Pajarito Mtns 0.1mi W Jct FSR 4181 on FSR39 (SP Cover) , Pajarito Mtns Yanks Canyon (RA Johnson) , 8.8 mi W JctI-19 Rt92 on FSR368 (SP Cover) ; Yuma Co: Kofa Game Refuge, 2mi SE Jct24 (P Mehlhop & RR Snelling) ; New Mexico, Sierra Co: Hillsboro (PS Ward) ; MEXICO: Coahuila: Puerto de Ventanillas (E & WP Mackay) .