Pogonomyrmex mohavensis Johnson

Johnson, R. A. & Overson, R. P., 2009, A new North American species of Pogonomyrmex (Hymenoptera: Formicidae) from the Mohave desert of Eastern California and Western Nevada., Journal of Hymenoptera Research 18, pp. 305-314 : 308-310

Pogonomyrmex mohavensis Johnson , n sp.

(Figs 1A-E)

Worker description.-Head subquadrate (CI = 97.0-104.5), broadest just posterior to eye; posterior margin fiat in full-face view. Longitudinal cephalic rugae prominent, in full-face view median rugae diverging only slightly towards the posterior corners of the head. In side view, rugae posterior to eyes not converging or forming circumocular whorls, but rather extending to vertex. Vertex rugose, with rugae often becoming weak or absent on posterior corners. Cephalic interrugal spaces slightly punctate, moderately to strongly shining. Anterior margin of clypeus fiat to slightly concave. Mandible with six teeth, a seventh occasionally present as a denticle or very small tooth between the basal and subbasai teeth (76% had six teeth on both mandibles, 17% had an additional denticle on one mandible, 7% had an additional denticle on both mandibles, n = 98). Mandibular dorsum coarsely striated. MOD ranging from 0.21-0.24 X HL. Eyes in profile situated slightly posterior to middle of head, OMD = 1.2-1.6 MOD. Antennal scapes relatively long (SI = 72-82), reaching to or surpassing vertex by less than the length of the basal funicular segment. Basal flange of scape flattened and very well-developed, at least partially translucent near margin. Psammophore well developed.

Mesosomal profile flattened to slightly convex. All mesosomal surfaces with prominent parallel/subparallel rugae. Dorsum of promesonotum with transverse rugae that curve obliquely to posterior on the pronotal sides, or rugae traverse obliquely from anterior to posterior. Mesopleura with transverse rugae angling posteriodorsally. Propodeum lacking spines or teeth, in side view evenly convex; rugae on propodeal dorsum transverse, posterior face of propodeum smooth and shining. Propodeal spiracles narrowly ovate. Interrugal spaces on mesosoma smooth and shining to slightly punctate and moderately shining. Legs moderately to strongly shining.

Petiolar peduncle long, ventral surface usually smooth, lacking tooth or lobe, occasionally with small angular process. In side view, petiolar node broadly but asymmetrically rounded with anterior surface notably shorter than posterior surface. Apex of node rounded, sometimes weakly angulate. In dorsal view, petiolar node longer than broad, widest anteriorly. Sides and dorsum of petiolar node moderately punctate, subshining, sculpture on dorsal surface variable: either lacking rugae, or with few transverse rugae, or up to several longitudinal rugae. Dorsum of postpetiole convex in profile; in dorsal view, widest at or near posterior margin and tapering to anterior margin, maximal width about equal to length, moderately punctate, subshining. Gaster smooth and shining.

Erect whitish pilosity moderately abundant on head, variable in length, longest hairs not exceeding MOD. Moderately abundant suberect to semidecumbent pilosity on scape, abundant semidecumbent hairs on funicular segments. Legs with moderately abundant suberect white setae. Mesosoma, petiole, and postpetiole with moderately dense erect to flexuous white setae, often similar in length, longest reaching to or slightly exceeding MOD; gastric tergites with more abundant, slightly shorter pilosity. Entire body concolorous ferruginous orange, or with gaster sometimes slightly lighter or darker than rest of body, but never black..

Worker measurements.- Holotype (paratypes, n = 12, notation: minimum-maximum). All measurements are in millimeters. HL 1.56 (1.35-1.63); HW 1.61 (1.31- 1.67); MOD 0.37 (0.30-0.37); OMD 0.46 (0.36-0.50); SL 1.14 (0.94-1.21); PNW 0.98 (0.85-1.04); HFL 1.65 (1.21-1.71); ML 1.90 (1.60-1.99); PW 0.40 (0.31-0.41); PPW 0.52 (0.45-0.56). Indices: SI 70.81 (70.06-81.75); CI 103.21 (97.04-104.55); OI 22.98 (20.95- 24.82); HFI 102.48 (92.37-110.53).

Queen.-Unknown.

Male.-Unknown.

Diagnosis.- P. mohavensis is likely to be confused only with P. californicus but may be distinguished by the following characters: (1) P. mohavensis is slightly smaller (HW = 1.31-1.67) than sympatric P. californicus (HW = 1.22-1.78), (2) P. mohavensis has six mandibular teeth (a seventh sometimes occurs as a denticle between the basal and subbasai teeth), and (3) in side view, the cephalic rugae extend more or less directly to the vertex and do not converge posterior to the eyes or form circumocular whorls. In P. californicus , the mandible has seven more or less normally sized teeth and the cephalic rugae converge posterior to the eye, sometimes forming circumocular whorls. In addition, in some populations of P. californicus (including the population at the type locality of P. mohavensis ) the gaster is dark brown to black. In P. mohavensis , the gaster is concolorous with the head and mesosoma, or sometimes a bit darker, but never dark brown to black.

In some specimens of both P. californicus and P. mohavensis , the cephalic rugae become weak or may even more or less disappear directly posterior to the eye, making evaluation of this sculptural character difficult, especially if magnification is low or the lighting is not good. In these cases, it appears that the number of mandibular teeth can secure separation. Even in examples of P. mohavensis with seven mandibular teeth, the extra tooth is much smaller than the flanking basal and subbasai teeth. This seventh tooth is fully developed in P. californicus and is subequal in size with the flanking teeth. Also note that substantial mandibular wear is common in older Pogonomyrmex workers, such that it is strongly recommended that at least several workers from each colony series be examined when attempting identification.

Type material.- Holotype (worker) plus 123 paratypes. USA: California: Inyo Co.: Alabama Hills, 1.3 km S Junction Horseshoe Meadows & Whitney Portal Roads , 1450 m (36° 34.8'N 118° 7.1 'W), 24 May 2008, leg. R.A. Johnson #4136 . Nests were in mixed Mohavean Desert woody scrub habitat; dominant plant species included Acamptopappus sphaerocephalus, Atriplex polycarpa , Atriplex canescens, Hymenoclea salsola, Grayia spinosa, Krascheninnikovia lanata, Eriogonoum fasciculatum, Coleogyne ramosissima, Ephedra sp., Gutierrezia sp., Lycium sp., and Cuscuta sp. The holotype is deposited in the MCZ. Paratypes (n = 123 workers) ali from the same locality and date as the holotype and leg. R.A. Johnson # 4136 are distributed as follows: 3w CIDA, 9w CASC, 9w LACM, 15w MCZ, 9w UCDC, 12w USNM, 6w WPMC, 15w RAJC. Additional paratype series ( RAJC) include RAJ # 4135 (12w), # 4145 (15w), and # 4146 (24w); ali series have additional workers in ethanol .

Additional material.- USA: California: Inyo Co.: Alabama Hills at 7.5 km W Lone Pine , 1540 m, 23 May 2008 (36° 35.6'N 118° 8.5'W) (R.A. Johnson RAJ # 4129 , 15w; # 4130, 6w; RAJC) , Alabama Hills at 6.4 km W Lone Pine , 4950', 14 May 2006 (R.R. Snelling # 06-007 , lw; RAJC) , Artists Drive , Death Valley National Monument , 800 feet, 29 Apr. 1952 ( CR-537 , 9w; LACM) . Kern Co.: 20 mi N Bakersfield , 5 Aug. 1959 (A.C. Cole CAL-345,16 w; LACM) . Nevada: Nye Co.: Hwy 374 at Rhyolite , 1090 m, 18 Apr. 2009 (R.A. Johnson, RAJ # 4218 , 3w; RAJC) , Rock Valley at 9 mi ENE Lathrop Wells , 14 Apr. 1970 (G. & J. Wheeler NEV-777 , 3w; LACM) . Figure 2 shows the known geographie distribution of P. mohavensis .

Etymology.-The specific epithet, mohavensis , is derived from this species occurring in the Mohave Desert.