Pogonomyrmex semistriata (Emery. It, 1906) Johnson, 2021

Johnson, Robert A., 2021, A taxonomic revision of South American species of the seed-harvester ant genus Pogonomyrmex (Hymenoptera: Formicidae). Part II, Zootaxa 5033 (1), pp. 1-230 : 177-184

Pogonomyrmex semistriata NEW STATUS

( Figures 87–89 )

Distribution—90A

Pogonomyrmex bispinosus var. semistriata Emery, 1906: 158 (worker, queen). Syntypes examined: 1 worker, 1 queen [MCZC], 3 workers [MHNG], 1 worker, 2 queens [MSNG]. CHILE, Valparaíso: Talca Province, Viña del Mar. MHNG worker here designated LECTOTYPE [ CASENT0281100 ] .

Pogonomyrmex brevispinosus var. spinolae Emery : Santschi, 1925: 223, misidentified workers.

Pogonomyrmex vermiculatus Emery : Snelling & Hunt, 1975:75, incorrect synonymy.

Worker diagnosis. Workers of this species are uniquely characterized by the following combination of features: (1) occurring in Chile, (2) concolorous medium to dark brownish-orange, and (3) first gastral tergum with striae along part to most of base to extending over anterior one-half of tergum, rest of tergum moderately to strongly coriarious, dull ( Figure 87 ).

Measurements — lectotype (n = 12). HL 1.51 (1.42–1.69); HW 1.64 (1.47–1.83); MOD 0.34 (0.29–0.39); OMD 0.35 (0.35–0.44); SL 1.11 (1.04–1.31); PNW 1.07 (0.99–1.16); HFL 1.67 (1.41–1.80); ML 1.91 (1.54–2.00); PW 0.38 (0.35–0.42); PPW 0.53 (0.50–0.60). Indices: SI 67.68 (61.20–79.39); CI 108.61 (99.40–109.58); OI 20.73 (18.07–23.64); HFI 101.83 (85.45–107.43).

Redescription. Head subquadrate to wider than long (CI = 99.40–109.58); posterior margin flat to weakly convex; in full-face view, medial rugae diverging toward posterior corners of head. Longitudinal rugae on cephalic dorsum weak to moderately prominent, wavy to moderately irregular. Interrugae on cephalic dorsum strongly to very strongly granulate-punctate, dull, with a beaded appearance; posterior corners rugose, interrugae moderately granulate, weakly shining. Anterior margin of clypeus moderately concave, dorsum with numerous subparallel, longitudinal rugae. Numerous long, curved, bristle-like, cream to light yellowish macrochaetae project from anterior margin of clypeus and basolateral margin of mandibles. Mandibles with six teeth; mandibular dorsum coarsely rugose. MOD ranging from 0.19–0.24× HL. In profile, eyes situated slightly anterior to middle of head, OMD = 1.00–1.34× MOD. In full-face view, eyes protruding slightly beyond lateral margins of head. Antennal scapes (SI = 61.20–79.39) reaching posterior corners or failing to do so by less than length of basal funicular segment; scape weakly to moderately striate, interstriae weakly to moderately punctate, weakly shining; basal flange moderately well developed with carinate margin. Psammophore well developed.

Mesosomal profile moderately convex; all mesosomal surfaces with prominent rugae to rugoreticulate. In dorsal view, humeral shoulders of pronotum enlarged, dorsolateral margins rounded to weakly angulate. Promesonotal suture rarely present. Wavy to irregular longitudinal rugae to weakly rugoreticulate on mesonotum, rugae diverging anterad toward humeral shoulders of pronotum. Irregular transverse rugae to rugoreticulate on dorsum and sides of pronotum. Irregular rugae on mesopleura angle posterodorsally; irregular transverse rugae on dorsum of propodeum traverse ventrally or anteroventrally on sides. Superior propodeal spines long, acuminate, length usually> 0.7× the distance between their bases. Inferior propodeal spines wider than high, triangular, apex broadly rounded to acuminate, height less than length of superior spines. Propodeal spiracles narrowly ovate facing posterad. Interrugae on mesosoma weakly to moderately granulate, weakly shining. Legs weakly to moderately coriarious, weakly shining to smooth and shining.

Peduncle of petiole about as long as petiolar node, anteroventral margin with a weakly to well developed, broadly rounded process. In profile, posterior surface of petiolar node weakly convex; anterior surface notably shorter than posterior surface, apex angulate to weakly rounded. In dorsal view, petiolar node longer than wide, widest near spatulate to broadly rounded anterior margin, narrowing posterad. Irregular transverse rugae (rarely oblique to longitudinal) on sides and posterior surface of petiolar node; interrugae weakly to moderately granulate, weakly shining. Dorsum of postpetiole convex in profile; in dorsal view, widest near posterior margin, narrowing to anterior margin, width and length similar; irregular, transverse rugae on dorsum of postpetiole finer, denser than those on posterior surface of petiolar node; interrugae moderately to strongly granulate, dull to weakly shining. First gastral tergum variable with longitudinal striae across part to most of base, or with striae extending over anterior one-third to one-half of tergum, rest of segment strongly coriarious, dull, or moderately coriarious posterior margin.

Erect, short to medium-length, whitish pilosity moderately abundant on head, no hairs> 0.7–0.8× MOD. Moderately abundant suberect to semidecumbent pilosity on scape; abundant decumbent hairs on funicular segments. Legs with moderately abundant suberect to decumbent whitish setae. Rest of body with erect, moderately dense, medium-length, whitish setae, longest about 0.8–1.0× MOD. Body concolorous medium to dark brownish-orange or with petiolar node, postpetiole, gaster, and legs slightly darker than rest of body ( Figure 87 ).

Queen diagnosis. Queens of this species are diagnosed by the following combination of features: (1) caste-specific morphology of the mesosoma related to wing-bearing and presence of ocelli on head, (2) first gastral tergum lacking striae or striae extending to posterior margin or portion lacking striae coriarious, (3) small (HW = 1.41–1.58 mm), only slightly larger than conspecific workers, (4) transverse rugae on posterior surface of petiolar node and dorsum of postpetiole, (5) superior propodeal spines consist of short, acuminate, triangular denticles to long spines, and (6) body concolorous brownish-orange ( Figure 88 ).

Measurements —(n = 2 + 3 paralectotypes). HL 1.32–1.51; HW 1.41–1.58; MOD 0.31–0.36; OMD 0.32–0.42; SL 1.02–1.22; PNW 1.06–1.29; HFL 1.32–1.65; ML 1.83–2.22; PW 0.37–0.45; PPW 0.55–0.67. Indices: SI 64.56– 86.52; CI 102.17–112.88; OI 21.99–23.23; HFI 85.16–117.02.

Male diagnosis. Males of this species are diagnosed by the following combination of features: (1) first gastral tergum moderately to strongly coriarious over anterior two-thirds or more of segment, (2) bicolored: head and mesosoma black, gaster dark orange to orangish-black, and (3) numerous delicate, long, nearly flexuous hairs on first gastral tergum ( Figure 89 ).

Measurements (n = 4). HL 1.07–1.20; HW 1.10–1.29; MOD 0.39–0.43; OMD 0.15–0.20; SL 0.32–0.39; HFL 1.52–1.68; ML 1.97–2.28; PW 0.44–0.465; PPW 0.63–0.70. Indices: SI 29.09–30.77; CI 99.10–112.17; OI 32.56– 36.36; HFI 122.58–138.18.

Additional material examined. CHILE: Bíobío: Talcahuano, no date ( MCZC) . Coquimbo: 30 km N Illapel , 5000’, Nov 30, 1950 ( CASC) ; Fray Jorge Forest , Dec 11, 1950 ( CASC; LACM) ; Fray Jorge Forest , 5 km W Pachingo, 550 m, Apr 30, 1966 ( CASC) ; Parque Nacional Fray Jorge, 15 km SW Pachingo , 100–200 m, Oct 20, 1966 ( CASC) ; 35 mi S Ovalle , Nov 30, 1950 ( CASC; LACM) ; Rt D-540 at 1.0 km W Rt 5, Jan 16, 2019 ( RAJC) ; Valle de Encantado , 6700’, Feb 17, 2019 ( RAJC) . Maule: Curicó, 1300’, Oct 1, 1909 ( USNM) , Carrizalillo, 250 m, Jan 30–Feb 5, 1981 ( RAJC; USNM) . Metropolitan: Peñaflor, no date ( MSNG) ; Pirque, 2660’, Apr 9–27, 2017 ( RAJC) . Valparaíso: 10 km E Papudo , Nov 28, 1950 ( CASC) ; E entrance to tunnel 90 km S Illapel , Nov 28, 1950 ( CASC; LACM; RAJC) ; Punta Molles, Oct 26, 1971 ( LACM) , Algarrobo, Oct 24, 1923 ( MZSP) ; 8 km SE Quintay , 150 m, Feb 17, 1967 ( CASC; LACM) ; Viña del Mar , Feb 1931 ( MACN) ; Marga Marga (= Estero Marga Marga), Dec 15, 1929 ( IFML; MCZC; USNM) ( Figure 90A ) .

Etymology. Emery did not discuss derivation of the name semistriata (Latin, from semi - = half and striatus = furrowed, striated), but his description suggests that it was derived from the first gastral tergum of the worker having longitudinal striae, while that of the queen lacked these striae.

Discussion. Pogonomyrmex semistriata is endemic to Chile, and it is readily separated from Chilean congeners by: (1) body concolorous medium to dark brownish-orange, (2) first gastral tergum with striae along part to most of base to extending over anterior one-half of tergum, rest of tergum moderately to strongly coriarious, dull or first gastral tergum (including posterior margin) moderately to strongly coriarious, dull, (3) irregular transverse rugae to rugoreticulate on dorsum and sides of pronotum. Pogonomyrmex araucania , P. bispinosus , and P. spinolae are the only Chilean congeners in which the body is concolorous or nearly concolorous light to dark ferruginous orange to reddish-brown, but all three species lack striae on the first gastral tergum and the posterior margin is usually smooth and shining.

Emery (1906) described the worker and queen of P. bispinosus var. semistriata from coastal Chile, indicating that this variety differed from the type by: (1) presence of transverse rugae on the posterior surface of the petiolar node and dorsum of the postpetiole (transverse rugae lacking in P. bispinosus ; see Johnson, 2015), (2) presence of subtle striae near the base of first gastral tergum and opaque near the middle (entire tergum smooth and shining in P. bispinosus ), and (3) petiolar node and postpetiole of queen as in workers, whereas the entire first gastral tergum was smooth and shining. The only subsequent taxonomic work on P. bispinosus var. semistriata removed this taxon from synonymy under P. bispinosus and placed it as a junior synonym of P. vermiculatus ( Snelling & Hunt, 1975) . In their discussion, Snelling & Hunt (1975) indicated that P. bispinosus was a distinct species and that P. bispinosus var. semistriata and several Chilean forms usually assigned to P. bispinosus (i.e., intermedia, spinolae ) were more closely related to P. vermiculatus . Consequently, Snelling & Hunt (1975) synonymized all three forms under P. vermiculatus , saying “there are no appreciable differences between Patagonian P. vermiculatus and the several Chilean infraspecific forms usually assigned to P. bispinosus . There are so many populations of indeterminate status that recognition of any of these nominate forms is impossible, hence the synonymy”. Problematically, these authors did not examine syntypes of P. vermiculatus , and it appears that they examined only one series P. vermiculatus from Magallanes Province, Chile.

Workers and queens of P. semistriata display several morphological differences from P. vermiculatus that include: (1) both castes are concolorous medium to dark brownish-orange, whereas those of P. vermiculatus are bicolored (dark red head and black mesosoma and gaster), and (2) queens of P. semistriata are diminutive (similar in size to conspecific workers) compared to those of P. vermiculatus , which are significantly larger than their workers. Thus, I raise P. bispinosus var. semistriata from synonymy to rank as a valid species.

Santschi (1925) described the worker of P. bispinosus var. spinolae (misspelled as P. brevispinosus var. spinolae ), placing it as conspecific with sexuals (queens and males) that Emery (1906) had moved from P. bispinosus to P. bispinosus var. spinolae . Santschi (1925) took this action without having sexuals to match with his workers, and it appears that he described these workers as var. spinolae because they differed from workers of P. semistriata . The description by Santschi compared his newly described workers with P. semistriata , saying “almost all of the first gastral tergum striate, both nodes of the petiole with transverse rugae as in var. semistriata Emery. It differs from the latter ( var. semistriata ) because it has slightly longer spines and longer pilosity. It is darker red, turning darker towards the mandibles, the front of the cheeks, and top of the gaster. Size a little larger (6 to 6.2 mm.)”. Most workers of the series that Santschi identified as P. bispinosus var. spinolae had relatively long superior propodeal spines and pilosity, but pilosity on some workers was shorter with a length similar to that on syntypes of P. semistriata . The morphology of P. semistriata syntypes also varied as the MCZC and MSNG workers had short superior propodeal spines, while the NHMW worker had longer spines whose length was similar to that of Santschi’s worker series. The author collected nest series of P. spinolae that contained workers and sexuals, and workers lacked striae on their first gastral tergum that characterize P. semistriata . Lastly, Santschi’s worker series was collected in Valparaíso (no details were given as to whether this was the city or region), which is near the type locality of P. semistriata , but outside the known geographic range for P. spinolae (see below). Moreover, syntypes of P. semistriata and Santschi’s workers display considerable variation, but there are no consistent morphological differences between them.

Biology. Several studies have examined foraging, activity patterns, and recruitment chemistry for P. vermiculatus in Chile ( Medel & Fuentes, 1995; Torres-Contreras, Olivares-Donoso, & Niemeyer, 2007, 2009). Vouchers from these studies have not been examined, but it is doubtful that P. vermiculatus was the species investigated because these studies used workers from Las Chinchillas National Reserve and Fray Jorge National Park, both of which are in central Chile, several hundred kilometers north of the known range of P. vermiculatus . It is probable that all of these studies were conducted on P. semistriata . Two alate queens (paralectotypes) were collected on 26 March, and two other alate queens were collected on 21 April, suggesting that mating flights occur during the austral summer.

Pogonomyrmex semistriata is restricted to coastal and low elevation habitats (0–2100 m) in central Chile in the Valdivian temperate forests and Chilean matorral ecoregions, as defined by Olson et al. (2001) ( Figure 90A ).

Figures

FIGURE 87. Photographs of Pogonomyrmex semistriata worker: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922466). Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 88. Photographs of Pogonomyrmex semistriata alate queen: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0923352). Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 89. Photographs of Pogonomyrmex semistriata male: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0923351). Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 90. Geographic distribution of: (A) Pogonomyrmex semistriata, (B) P. spinolae, and (C) P. strioligaster. The large black circle in each panel denotes the type locality.