Polyergus topoffi

Identification
Of all the Nearctic species, topoffi is the one that most resembles Palearctic rufescens in sculpture, pilosity, head shape and appendage length. Where it overlaps with mexicanus in distribution, it is distinguished by a less shiny appearance and somewhat more tannish tinge to the base red color, longer scapes and legs, occurrence at lower elevations, and parasitism of different hosts. The scapes are longer than all other breviceps group species except vinosus. Wheeler’s unavailable variety montezuma, collected near Pachuca, Hidalgo, Mexico by Mann, belongs in this species, as it fits neatly within middle the range of metrics for Arizona topoffi (except with somewhat more abundant pilosity), and also comes from a subxeric, semi-open habitat. The three worker specimens of montezuma are more pilose than most Arizona specimens, with 22–26 macrosetae on the pronotum, and the three specimens each possess a few erect macrosetae lower on the sides of the pronotum.

Identification Keys including this Taxon

 * Key to Polyergus species
 * Key to US Polyergus species

Distribution based on Regional Taxon Lists
Nearctic Region: United States. Neotropical Region: Mexico.



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Biology
Polyergus topoffi is relatively well-studied. Studies of a population in the vicinity of Portal, AZ, and at the Southwest Biological Research Station, just 5 miles to the west, make this among the best studied of North American species. Colony foundation, sexual behavior, scouting and raiding of this species are documented in numerous publications by Howard Topoff and his students, under the name Polyergus breviceps (Topoff 1982, 1985, Topoff et al. 1984, 1985a, 1985b, 1988a, 1988b, 1989, Topoff and Greenberg 1988, Topoff 1990, Topoff and Mendez 1990, Topoff and Zimmerli 1993, Zimmerli and Topoff 1994), and even in National Geographic Society videos made with these authors’ cooperation, and at this writing, still occasionally aired on television nature programs. In the Chiricahua Mts. of AZ, the habitat of topoffi ranges from riparian desert scrub at 1450 m, to the ecotone of oak-juniper and conifer forest around 1900 m (and higher, in Mexico). It raids after the heat of the day, typically between 17:00 hr and dusk, robbing pupae from the host nests with little resistance and no mortality of the host workers, these known otherwise for their aggressive physical and chemical nest defense. Subtropical, Madrean scrublands and oak woodlands of the Mexican highlands are another habitat of this ant, where it is associated with the host species Formica subcyanea.

Nomenclature

 *  topoffi. Polyergus topoffi Trager, 2013: 519, figs. 15-17, (w.) U.S.A.

Description
Holotype [ARIZONA, Cochise Co., as above] HL 1.62, HW 1.56, SL 1.22, ½ VeM 1, ½ PnM 9, WL 2.42, GL 2.40, HFL 1.80, CI 96, SI 78, HFI 115, FSI 148, LI 4.04, TL 6.44.

Paratypes (N=5) [ARIZONA, Cochise Co., as above] HL 1.56–1.64 (1.60), HW 1.52–1.60 (1.54), SL 1.20–1.24 (1.22), ½ VeM 0–1 (0.55),, ½ PnM 6–9 (7.20), WL 2.32–2.42 (2.39), GL 2.16–2.40 (2.24), HFL 1.72–1.80 (1.76), CI 95–98 (97), SI 75–82 (79), HFI 111–117 (1.14), FSI 139–148 (144), LI 3.88–4.04 (3.98), TL 6.12–6.44 (6.22).

montezuma material (N=3) [MCZ] HL 1.48–1.60 (1.53), HW 1.50–1.53 (1.50), SL 1.20 (all 3), ½ VeM 0 (all 3),, ½ PnM 12–15 (13.67), WL 2.36 (all 3), GL 2.16–2.24 (2.20), HFL 1.64–1.72 (1.68), CI 96–100 (98), SI 78–81 (80), HFI 111–112 (1.12), FSI 137–143 (140), LI 3.84–3.9 (3.89), TL 6.08–6.12 (6.09).

Measurements, exclusive of montezuma syntypes (N=31)) HL 1.48–1.68 (1.60), HW 1.40–1.64 (1.53), SL 1.16–1.28 (1.23), ½ VeM 0–1 (0.23), ½ PnM 4–9 (6.87), WL 2.16–2.52 (2.37), GL 1.84–2.56 (2.20), HFL 1.68–1.88 (1.77), CI 93–100 (96), SI 75–86 (80), HFI 108–121 (116), FSI 139–155 (145), LI 3.68–4.20 (3.97), TL 5.54–6.64 (6.16).

Worker description. Superficially rather similar to Polyergus mexicanus, but slightly more gracile, and nearly restricted to a Mexican distribution. Head nearly rectangular or quadrate, straight-sided anterior to eyes, with vertex corners rounded, HL usually a bit greater than HW; with vertex pilosity lacking or up to 2 setae; scapes not reaching vertex corners by about 1.5 maximum scape widths, notably clavate in the apical third; pronotum with 8–22 dorsal erect setae (but see Discussion of montezuma “types”,); mesonotum with profile flat or only slightly convex for most of its length, with a short posterior declivity; propodeum evenly rounded with dorsal and declivitous faces, especially in smaller workers, usually at >90° angle; petiole straight-sided above spiracles, sides parallel or only slightly converging dorsad, flowing seamlessly into the semicircular petiolar dorsum; first tergite densely pubescent, pubescence very fine; first tergite pilosity evenly distributed or slightly denser anteriad, some setae flexuous near front of tergite, but most weakly flexuous or straight, suberect.

Head matte to weakly shining; mesonotum matte to weakly shining, with scant pubescence; gaster matte to weakly shining beneath pubescence, shinier on sides.

Color mostly tannish-red with infuscation of posterior portions of tergites and slightly darker legs. Mesosomal pilosity usually notably darker than body color, gaster pilosity more reddish; pubescence short and yellowish gray. Only minor individual variation was detected among the Arizona specimens studied, and the Mexican montezuma differed only in somewhat more abundant pilosity, but fit perfectly in the middle of the measurement cloud of other specimens measured.