Pogonomyrmex cunicularius

Robert A. Johnson, 2015, A taxonomic revision of South American species of the seed-harvester ant genus Pogonomyrmex (Hymenoptera: Formicidae). Part I, Zootaxa 4029 (1), pp. 1-142 : 44-50

Pogonomyrmex cunicularius

( Figures 18–20)

Pogonomyrmex cunicularius Mayr, 1887: 613 (worker, male). Syntypes examined: 3 workers [MSNG], 2 workers [NMW], URUGUAY, no location; 1 male [NMW], URUGUAY, Montevideo: Montevideo; 2 workers [NMW], ARGENTINA, Buenos Aires (Prof. Berg leg.). See also Gallardo, 1932: 120, fig. 13; Johnson, 2010: 169, fig. 2. NMW worker from URUGUAY here designated LECTOTYPE [CASENT0173372].

Pogonomyrmex cunicularis var. brevispinus Santschi, 1931: 275 (worker, ergatoid queen). Syntypes examined: 1 worker, 1 ergatoid queen [MACN], ARGENTINA, Entre Ríos: Estación Sosa (Mac Donagh leg.). Kusnezov, 1951: 251 (synonomy under cunicularius ; here confirmed). See also Gallardo, 1932: 123. MACN worker here designated LECTOTYPE [CASENT0249048].

Worker. Diagnosis. Within the P. cunicularius -group, the combination of: (1) in profile, petiolar node broadly rounded, (2) inferior propodeal spines rounded, (3) superior propodeal spines moderately long, shorter than distance between their bases, and (4) first gastral tergum smooth and strongly shining uniquely characterize this species ( Figure 18).

Measurements —lectotype (n = 16). HL 2.38 (1.85–2.47); HW 2.07 (1.52–2.10); MOD 0.38 (0.31–0.42); OMD 0.62 (0.45–0.69); SL 1.55 (1.44–1.92); PNW 1.44 (1.04–1.47); HFL 2.57 (2.09–2.68); ML 2.83 (2.05–2.87); PW 0.50 (0.40–0.54); PPW 0.72 (0.55–0.76). Indices: SI 74.88 (79.40–100.00); CI 86.97 (81.01–88.21); OI 18.36 (17.79–21.16); HFI 124.15 (119.23–139.38).

Redescription. Head elongate (CI = 81.01–88.21), widest immediately posterior to mandibles, narrowing posterior to eyes; posterior margin flat to weakly convex in full-face view. Cephalic dorsum with weak to moderately strong, wavy or irregular longitudinal rugae to weakly rugoreticulate, rugae often weaker to indistinct near posterior margin; in full-face view, medial rugae diverging weakly toward posterior corners of head. Cephalic interrugae weakly to moderately granulate, weakly shining. Vertex weakly rugose to weakly to moderately granulate, dull to weakly shining. Anterior margin of clypeus flat to weakly convex; dorsal surface with at least several subparallel longitudinal or oblique rugae. Mandibles with six teeth; mandibular dorsum coarsely rugose. Eyes small, MOD ranging from 0.15–0.18x HL. In profile, eyes situated anterior to middle of head, OMD = 1.36– 1.77x MOD. Antennal scapes long (SI = 74.88–100.00), surpassing vertex by less than length of first funicular segment; entire scape with longitudinal striae. Basal flange of scape well-developed with carinate margin. Psammophore poorly-developed, consisting of short to medium-length hairs scattered across ventral surface of head.

Promesonotal profile moderately convex, propodeum flat; all mesosomal surfaces with subparallel, irregular rugae to weakly rugoreticulate. In dorsal view, humeral shoulders of pronotum rounded. Dorsum of promesonotum and sides of pronotum with transverse, oblique to longitudinal, irregular rugae to rugoreticulate; mesopleura with irregular rugae that angle posterodorsally. Superior propodeal spines moderately long, acuminate, shorter than distance between their bases; spines connected by well-defined keel; wavy to irregular transverse rugae on propodeal dorsum traverse ventrally or anteroventrally on sides. Inferior propodeal spines well-developed, triangular, wider than high, tips broadly rounded to bluntly angulate. Propodeal spiracles narrowly ovate facing posterad. Interrugae on mesosoma smooth to weakly granulate, weakly to strongly shining. Legs long (HFL = 2.09–2.68 mm), weakly to moderately coriarious to granulate, dull to weakly shining.

Peduncle of petiole about 0.8x length of petiolar node, anteroventral margin with bluntly angulate to angulate triangular process. In profile, posterior surface of petiolar node flattened; node asymmetrical with anterior surface shorter than posterior surface, apex broadly rounded. In dorsal view, petiolar node about 1.5x longer than wide, widest near anterior margin. Sides and posterior surface of petiolar node with weak to moderately coarse, irregular, transverse rugae, or granulate-punctate. Dorsum of postpetiole convex in profile; in dorsal view, widest near posterior margin, narrowing to anterior margin, maximum width about equal to length, strongly granulate-punctate, dull to weakly shining. First gastral tergum smooth, strongly shining.

Erect to semi-erect yellowish pilosity moderately abundant on head, variable in length, longest hairs approaching MOD. Moderately abundant suberect yellowish pilosity on scape; abundant decumbent hairs on funicular segments. Legs with moderately abundant subdecumbent to decumbent yellowish setae. Mesosoma, petiolar node, postpetiole, and gastral terga with moderately dense erect setae, mostly similar in length, longest hairs not exceeding MOD. Body concolorous tannish-orange to tannish-red ( Figure 18).

Ergatoid Queen. Diagnosis. This caste is diagnosed by: (1) ergatoid, with small ocelli on head, (2) in profile, petiolar node rounded, (3) inferior propodeal spines wider than high, apex broadly rounded, and (4) first gastral tergum smooth and polished, strongly shining ( Figure 19).

Measurements —(n = 12). HL 2.26–2.66; HW 1.96–2.38; MOD 0.35–0.45; OMD 0.54–0.66; SL 1.53–1.87; PNW 1.23–1.60; HFL 2.27–2.70; ML 2.46–3.20; PW 0.51–0.67; PPW 0.71–0.93. Indices: SI 74.63–87.24; CI 85.38–90.49; OI 17.07–20.74; HFI 111.34–125.37.

Male. Diagnosis. This caste is diagnosed by: (1) first gastral tergum lacking striae, (2) femur long (HFL> 1.95 mm), HFI> 150.0, (3) head weakly elongate (CI <100.0), (4) posterior surface of petiolar node rugose to rugoreticulate, (5) in profile, petiolar node rounded, (6) superior propodeal spines consist of teeth to short spines, and (7) notauli present ( Figure 20).

Measurements —(n = 12). HL 1.30–1.77; HW 1.17–1.54; MOD 0.51–0.64; OMD 0.21–0.32; SL 0.38–0.49; HFL 1.98–2.48; ML 2.51–3.25; PW 0.48–0.67; PPW 0.63–0.97. Indices: SI 24.84–35.66; CI 82.89–92.81; OI 39.61–47.86; HFI 154.69–182.05.

Additional material examined. ARGENTINA: Corrientes: Rt 14 at km 423, 90 m, Feb 27, 2003 (CASC; RAJC); Mercedes, Feb 1918 (MACN; USNM). Entre Ríos: Pueblo Liebig, 70’, Dec 17, 2005 & Feb 13, 2010 (CSC; MCZ; RAJC); Rt 14 at 4.5 km N San José/Colón exit, 80’, Dec 13, 2006 (RAJC); Rt 14 at 5.1 mi N Gualeguychú, 60’, Dec 17, 2005 (RAJC); Estancia Sosa, no date (MACN; MLPA); Hernandarias, Jun 7, 1951 (FML; MZUSP); El Palmar, Nov 24, 2005 (CSC); Parque Nacional El Palmar, Jan 5, 2006 (RGPC); La Picada, May 1951 (FML). URUGUAY: Artigas: Pintado Grande, Feb 22, 1969 (FML; LACM); Grutas de Chiflero, Feb 22, 1961 & no date (FML; LACM); R de Chiflero, Feb 22, 1961 (FML); Rt 30, no date (FML). Colonia: Colonia Suissa (= Nueva Helvecia), Mar 11, 1969 (LACM). Maldonado: La Sierra, no date (LACM; MCZ; MSNG). Montevideo: Montevideo, no date (MCZ; MLPA; USNM). Paysandú: Paysandú, Feb 25, 1961 (FML) ( Figure 21 A).

Etymology. The specific epithet, cunicularius , (from Latin cunicul -, which indicates a miner or burrower, plus the Latin suffix - arius, which denotes belonging to) apparently refers to the soil nests excavated by this species. Mayr did not discuss the naming of this species, but Kusnezov (1949) wrote that P. cunicularius was the only Argentinian species of Pogonomyrmex that constructed a nest crater.

Discussion. Pogonomyrmex cunicularius is not known to co-occur with any other P. cunicularius -group species but additional collections may show it co-occurs with both P. pencosensis and P. serpens . Pogonomyrmex cunicularius can be distinguished from these two species based on the following characters: (1) in profile, petiolar node broadly rounded, (2) inferior propodeal spines rounded, and (3) first gastral tergum smooth and strongly shining. In P. pencosensis and P. serpens : (1) in profile, the petiolar node is angulate, (2) inferior propodeal spines are acuminate, and (3) first gastral tergum is weakly to moderately coriarious, dull to weakly shining.

Santschi erected P. cunicularius var. brevispinus because, compared to the type specimen, the propodeal spines were shorter (no longer than maximum eye diameter), the petiolar node was narrower, and the postpetiole was slightly longer than wide along the posterior margin. Kusnezov (1951) synonomized P. cunicularius var. brevispinus under P. cunicularius without discussion, and I concur with his synonomy. The propodeal spines were slightly shorter in the syntype worker of P. cunicularius var. brevispinus that I examined, but their length was within the range of variation observed among workers. The width of the petiolar node and shape of the postpetiole also were within the range of variation observed among workers. Finally, the syntype ergatoid queen of P. cunicularius var. brevispinus and queens of P. cunicularius did not display noticeable differences.

Biology. The biology of P. cunicularius is poorly known but it is likely similar to that of P. pencosensis . This species is a solitary forager that can travel>25 m from the nest. Nests of P. cunicularius usually have a pebble tumulus up to 25 cm in diameter with a nest entrance that is up to 2–3 cm in diameter. Colonies of P. cunicularius probably contain 500 to>1000 workers, and they can produce>100 ergatoid queens and numerous males (pers. obs.).

Sexuals have been collected from nests from 13 December to 13 February, and one founding queen was excavated on 17 February, indicating the mating flights occur during the austral summer. The large number of ergatoid queens produced by colonies (>100) infers that queens use independent colony founding (see Peeters et al., 2012), which is an unusual behavior for ergatoid queens (see Johnson, 2010). One excavated queen was haplometrotic, and founding queens are probably semi-claustral (they forage) (see Johnson, 2010). Queens contained 9–12 ovarioles (n = 3), compared to four in workers (n = 6).

Pogonomyrmex cunicularius is a lowland species that occurs at elevations from 20–90 m. This species is only known to occur east and north of Río Paraná in the Espinal, Uruguayan Savanna, and Humid Pampas ecoregions as defined by Olson et al. (2001) ( Figure 21 A). The very wide Río Paraná may act as a barrier to dispersal by ergatoid queens. At present, P. cunicularius appears to be rare with very fragmented populations that likely result from intense and widespread agricultural use over most of its historic range ( Figure 21 A).