Pheidole obscurithorax Naves, 2003

Wilson, E. O., 2003, Pheidole in the New World. A dominant, hyperdiverse ant genus., Cambridge, MA: Harvard University Press : 331

Pheidole obscurithorax Naves , new status

Pheidole fallax obscurithorax Naves 1985: 61; first valid use of name for Pheidole obscurithorax st. arenicola var. obscurithorax Santschi 1923d: 58, unavailable name (quadrinomial).

Types Naturhist. Mus. Basel.

Etymology L obscurithorax , dark thorax.

Diagnosis A member of the fallax group close to the species listed in the heading, distinguished as follows. Major: large (Head Width 1.70-1.80 mm); medium to dark reddish brown; robust; with relatively short scapes (Scape Length/Head Width 0.50-0.59 mm); posterior half of head heavily rugoreticulate; anterior half of first gastral tergite heavily shagreened and opaque; petiolar node thick from the side and from above, as illustrated.

Minor: dorsa of petiolar and postpetiolar nodes foveolate and opaque; anterior fringe of median strip of first gastral tergite shagreened.

Measurements (mm) Lectotype major: HW 1.70, HL 1.84, SL 0.98, EL 0.24, PW 0.86. Paralectotype minor: HW 0.62, HL 0.80, SL 0.94, EL 0.18, PW 0.48.

Color Major: head light reddish brown; mesosoma, waist, and appendages medium reddish brown; gaster dark reddish brown. Minor: body medium reddish brown to plain dark brown; appendages light reddish to yellowish or light plain brown.

Range Kempf (1972b) reports obscurithorax from Cordoba, Formosa, and Santa Fe in northern Argentina. I have also seen series from the Parana River and Canindeyii Province in Paraguay. In 1950 I discovered a colony nesting in Mobile, Alabama, within a kilometer of the ship docking area, an ideal entry point for exotic species, such as obscurithorax , that occur in or near potential embarkation areas along or close to the banks of the Paraguay and La Plata Rivers of southwestern Brazil, Paraguay and Brazil. Shipping has occurred regularly over decades between these areas and the ports of the southern United States. P. obscurithorax has since been found in Baldwin County, Alabama, across the bay from Mobile, and in adjacent, westernmost Florida (Naves 1985). Walter Tschinkel (personal communication) reports its appearance around Tallahassee, Florida, in the late 1990s.

Biology The Mobile, Alabama, colony mentioned above occupied a large crater nest in open, sandy soil. Stefan Cover, Lloyd Davis Jr., and Mark Deyrup (Cover, personal communication), found the species in western Florida mostly in disturbed areas, but once in secondary forest in a creek valley. On several instances the nests were located close to those of the imported fire ant, Solenopsis invicta , suggesting superior resistance to this formidable invasive.

figure Upper: lectotype, major. Lower: paralectotype minor. ARGENTINA: Alta Gracia, Cordoba. Scale bars = 1 mm.