Polyergus bicolor, Trager, James C., 2013

Trager, James C., 2013, Global revision of the dulotic ant genus Polyergus (Hymenoptera: Formicidae, Formicinae, Formicini), Zootaxa 3722 (4), pp. 501-548 : 514

Polyergus bicolor new status

Figures 9, 10, 11

Polyergus rufescens bicolor Wasmann 1901: 639 . Syntype workers, gyne, male: USA,WISCONSIN Crawford Co., Prairie du Chien [MCZ, workers, red syntype label 22970] (examined); [LACM, workers, male, host, red “ type series” label] (examined); [USNM, workers, 59719] (images examined).

Polyergus rufescens breviceps (part): Emery 1893: 666 (misidentification, mixed syntype series).

Polyergus rufescens subsp. breviceps var. fusciventris Wheeler 1917: 555 (part). Unavailable name; following material referred here: CANADA, MANITOBA, South Cypress RM. Treesbank. (Wheeler) [USNM #59925, USNM ENT 00529453] (image examined).

Syntype [LACM, red “ type series” label, top specimen] HL 1.30, HW 1.28, SL 1.04, ½ VeM 0, ½ PnM 0, WL 1.96, GL 1.88, HFL 1.48, CI 98, SI 81, HFI 116, FSI 142, LI 3.26, TL 5.14.

Measurements (N=44) HL 1.24–1.66 (1.40), HW 1.24–1.74 (1.41), SL 0.92–1.16 (105), ½ VeM 0, ½ PnM 0– 2 (0.58), WL 1.88–2.32 (2.08), GL 1.60–2.80 (2.07), HFL 1.40–1.68 (1.55), CI 97–105 (100), SI 64–81 (75), HFI 97–120 (110), FSI 137–158 (147), LI 3.12–3.98 (3.48), TL 4.83–6.58 (5.56).

Worker description. Head subquadrate to suborbicular, its length and breadth about equal, sides often quite rounded; vertex concave, the concavity about half the head width in breadth, completely lacking vertex pilosity; scapes short, not reaching vertex corners, notably clavate in the apical third; pronotum lacking pilosity, or rarely with 1–2 dorsal erect setae; mesonotum profile flat or very weakly convex for most of its length; propodeum profile a rounded weakly obtuse angle; petiole with rounded sides, petiolar dorsum rounded, not at all or only feebly emarginate; first tergite moderately pubescent, with pilosity much like that of breviceps , in 4–5 transverse arrays; first tergite pilosity flexuous, subdecumbent.

Head matte; mesonotum matte; gaster matte to weakly shining.

Color of head, mesonotum and often petiole dull red, gaster very dusky red (nearly black); forelegs often redder than middle and hind legs; pilosity reddish brown, pubescence fine and grayish.

Discussion. P. b i c o l o r is usually easily distinguished from other Nearctic species by its distribution, distinctive two-tone coloring and sparse pilosity. Northern (ND to BC, CAN) populations of P. mexicanus may exhibit similar coloration, but mexicanus is always more pilose. Bicoloration and reduced pilosity occur commonly in the small workers from young colonies of mexicanus , causing possible confusion. Nanitics of mexicanus are usually recognizable by their slender heads with a rounded vertex and longish appendages, and at least a pair of erect pronotal setae. Large workers of other breviceps- complex species also may appear somewhat bicolored, but only rarely is the bicoloration so neatly defined by a nearly completely dark gaster as in bicolor , and these others have more pilosity on the head and mesosoma.

Etymology. Wasmann coined this name from the Latin nominal adjective “ bicolor ” meaning two-colored.

Natural history. This species is apparently endemic to the upper Mississippi Valley, from the western Great Lakes region west to the Dakotas and southern Manitoba. In the past it was found in southern Wisconsin and as far south as Rockford, Illinois, but it has not been seen in this area in recent decades.

P. bicolor normally parasitizes F. subaenescens , and normally nests with it in rotten stumps or fallen limbs in forests. Wheeler (1910) described raids occurring in early afternoon in a mature mesic forest in northern Illinois that originated from nests in stumps. Two samples examined in this study had F. neorufibarbis hosts, also a denizen of moist woods, especially tamarack bogs in the eastern part of its range. Through the course of this study I was not able to obtain or study any specimens of bicolor (nor of its host F. subaenescens ) collected within about the last 50 years, from bicolor ’s historic range, and I am led to wonder if they have contracted northward due to climatic warming or other causes. Just before submitting this manuscript, in July 2013, I collected a sample in northern Wisconsin. As in the published records, this sample occupied a rotting log with F. subaenescens . The log was about 35 cm in diameter, with bark beginning to loosen and wood in transition from white to red rot. At first glance, the mixed colony bore a striking resemblance to a young colony of the locally common F. aserva .

Distribution of studied specimens. ILLINOIS Winnebago Co. Rockford VII-12-01 WS Creighton (LACM); IOWA Back Bone State Park June 19,1940 Wm. Buren (LACM); MICHIGAN Cheboygan Co. VII-21-47 #13 CH Kennedy (LACM); MICHIGAN Iron Co. Crystal Falls VII-2-37 & 7/21/37 & 7/21/38 (3 coll’s) AC Cole (LACM); MINNESOTA Cook Co. Saganaga Lake, Chik Wauk Lodge 5-VII-1943 EV Gregg (FMNH); MINNESOTA Cook Co. Saganaga Lake Aug. 28, 1946 RE Gregg (FMNH); MINNESOTA Crow wing Co. Jenkins 7-10-40 WF Buren (LACM); MINNESOTA Hubbard Co. Akeley Aug. 12, 1941 Wm. Buren (LACM); MINNESOTA St, Louis Co. Duluth, 21.vi.1942, tamarack spruce bog. R. E. Gregg (FMNH); NORTH DAKOTA Bottineau 17-IX-38 #253 Joe Davis (LACM); NORTH DAKOTA Cass Co. Fargo 9-VI-1927 C. Schoberger (LACM); NORTH DAKOTA Cavalier Co. Storlie Twp. 13/7/54 (LACM); NORTH DAKOTA Cavalier Co. Fremont Twp. 7/9/54 #130 & #144 Don Sather (LACM); NORTH DAKOTA Cass Co. 10 Harwood Twp. X-10-36 C. Schonberger (FMNH); NORTH DAKOTA Pembina Co. Pembina VII-14-1949 EL Krause (LACM); NORTH DAKOTA Ramsey Co. Twp.153R 65S. 18 VIII-1-1951 #878 PB Kannowski (LACM); SOUTH DAKOTA Pennington Co. (Black Hills) Hill City Sept. 6, 1933 Creighton (LACM); SOUTH DAKOTA Todd Co. Okreak 21-VII-1941 HT Dalmat (LACM); WISCONSIN Bayfield Co. Chequamegon N.F. 46.6168N 91.2122 W Large, rotten jack pine log. 19 July 2013 J.C. Trager; CANADA ONTARIO Renfrew Co. Arnprior 1914 Wasmann (CAS).

Figures

FIGURES 9 – 11. Lateral, full face, and dorsal views of Polyergus bicolor worker CASENT 0281068. Photographs by Erin Prado from www. AntWeb. org.