Strumigenys subnuda

This species is known from a single queen collected in a Berlese litter sample of grass clippings piled at the base of Quercus falcata. The site was in an open area near Jeff Davis Lake, Mississippi, with scattered trees and was surrounded by a mixed hardwood-pine forest. Subsequent extensive collecting in this area failed to find additional specimens.

Identification
In North America, S. subnuda is most similar to Strumigenys margaritae, from which it differs by the following: in S. subnuda, hairs on the body are slightly coarse to slightly clavate, whereas in S. margaritae, all hairs on the head, mesosoma, waist, and gaster are distinctly clavate and somewhat translucent, more erect, and more abundant; the mesopleuron and dorsum of petiole and postpetiole are smooth and shining in S. subnuda, whereas they are reticulate-punctate in S. margaritae; the propodeal spine length is much shorter in S. subnuda; and the gaster is only weakly shagreened, appearing shiny in S. subnuda, whereas it is densely striolate-punctate to shagreened with dense striolae in S. margaritae. The only other species of Strumigenys lacking or with reduced spongiform appendages known to occur in the United States is S. inopina. Strumigenys inopina is easily distinguished from S. subnuda by its more triangular shaped face, entire side of the mesosoma being shiny, having numerous, dense, long hairs, and total absence of spongiform appendages beneath the postpetiole.

The single specimen of S. subnuda differs from other species of Strumigenys known to occur in the southeastern United States by its lack of spongiform appendages beneath the petiole, smooth mesopleuron, and somewhat sparse setation. Attempts to identify the specimen with keys to species for all regions of the world in the worldwide revision of Dacetini by Bolton (2000) were unsuccessful. The closest match was at couplet 6 of the Nearctic Pyramica key, where it keyed to S. margaritae, but did not match all of the key characters or the description. The only other species similar to S. subnuda is S. inopina, which was not included in Bolton’s key to workers because workers for this species have not been discovered. Although the keys were written for workers, they also work well for queens, which share similar characters. Additionally, the new species was compared to and differed from a dealate queen of S. margaritae, which was collected in Alabama and the 2 specimens of S. inopina from Mississippi, both of which are deposited in the Mississippi Entomological Museum.

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



Biology
The single specimen of S. subnuda was collected on 11 Aug 2005 in a Berlese litter sample of grass clippings piled at the base of Quercus falcata Michx. (Fagaceae) in an open area near Jeff Davis Lake (Jefferson Davis County) with scattered trees present. A mixed hardwood-pine forest surrounded the entire area. Other ants collected in the same Berlese sample included Brachymyrmex patagonicus Mayr, Hypoponera opaciceps (Mayr), Strumigenys membranifera (Emery), Cyphomyrmex rimosus (Spinola), Solenopsis invicta Buren, and Pheidole moerens Wheeler, all of which are considered to be exotic species. An exotic tenebrionid beetle known to be associated with introduced fire ants, Poecilocrypticus formicophilus Gebien (MacGown 2005), also was found in large numbers in the sample. All of these species, including the tenebrionid beetle, were found in relative abundance on 2 subsequent trips to the site.

Nomenclature

 *  subnuda. Pyramica subnuda MacGown & Hill, 2010: 572, fig. 1 (q.) U.S.A. Combination in Strumigenys: unpublished.

Type Material
Holotype: Dealate female, Miss., Jeff. Davis Co., Jeff Davis Lake, 31°33’47”N 89°50’39”W, 11 August 2005, J. G. Hill, J.A.MacGown, in grass clippings at base of Quercus falcata in open woods near lake. Deposited in the Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts.

Taxonomic Notes
Due to the extremely cryptic nature of dacetine ants, many species are infrequently collected and have been described from only 1 or very few specimens. Despite this, we hesitated to describe this species based on only 1 specimen, hoping to find additional specimens, especially workers. Unfortunately, the type locality was devastated by Hurricane Katrina on 28 Aug 2005, only 2 weeks after the specimen was collected. Two subsequent collecting trips were made to the site on 25 Mar 2006 and 8 Sep 2006. Although hand collecting was conducted and twenty five 3.8-liter bags of litter and grass clippings were collected on the 2 dates, including three 3.8-liter bags of litter from the base of the same tree where the original collection was made, no additional specimens of the new species were discovered. Similarly, we have not collected any other specimens of this species during other collecting trips in southern portions of Mississippi.

Strumigenys subnuda is provisionally placed in the schultzi group, of which it has several affinities. The schultzi group is comprised of 17 species, not including the species described here, with only 1 species, S. margaritae, known to occur north of Mexico (Bolton 2000). Members of this group have ventral spongiform appendages reduced or absent, lack flagellate hairs, have dense reticulate-punctation on head, mesosoma, and waist, possess large eyes, and tend to be associated with plants instead of being found in soil/litter or rotting wood. Mandibular dentition in this group is somewhat variable, with the general pattern consisting of a basal lamella (with or without a diastema), followed by 5 larger teeth, followed by 2 smaller teeth, then 4 denticles, and ending with an apical tooth (Bolton 2000). Strumigenys margaritae is unique in the group in that teeth 1, 3, and 5 are acute and longer than teeth 2 and 4, which are blunt, and this sequence is continued with tooth 7 being acute and longer than tooth 6, which is blunt. All other species in the group have slightly different dental patterns. However, the species S. subnuda has a similar dental array to S. margaritae, and otherwise appears to be most similar to this species.

Members of the schultzi group are largely tropical, with only S. margaritae known to occur in the United States in Alabama, Florida, Georgia, Louisiana, Mississippi, and Texas, where it is considered to be exotic (Bolton 2000; Dash 2005). It is not known for certain whether S. subnuda is native or an undescribed exotic species. Because the rest of the group is tropical, and because many of the species collected at the type locality were also exotic species, it raises the likelihood that S. subnuda could be an exotic species.

Description
Description of dealate female (Fig. 1) WL: 0.70; HL: 0.61; HW: 0.44; SL: 0.35; EL: 0.15; ML: 0.15; FFL: 0.39; MFL: 0.40; HFL: 0.42; PSL: 0.09; PNW: 0.18; PNL: 0.10; PPNW: 0.28; PPNL: 0.17.

Color yellowish-brown, appendages slightly paler. Head widest near occiput, pyriform (in frontal view). Mandible in frontal view triangular; lacking diastema; basal lamella in the shape of a large equilateral triangle with rounded apex, followed by 5 teeth: teeth 1, 3, and 5 longer and more acute than teeth 2 and 4, followed by 2 slightly smaller teeth with tooth 7 longer and more acute than tooth 6, followed by 4 small denticles, and terminating in a slightly enlarged apical tooth. Clypeus wide, pentagonal, with light sculpturing, not shining; anterior edge straight; hairs on clypeal dorsum and margins slightly clavate, of approximately the same length, and all curving anteriorly toward the midline of clypeus. Remainder of head reticulate-punctate with scattered, appressed, simple to coarse hairs all curving in toward midline of head (in frontal view); elongate flagelliform cephalic hairs absent; antennal scrobes absent. Scape subequal to antennal segments 5+6, hairs on scape rather sparse, proclinate, tapering, except those found on leading edge of scape, which are more coarse to slightly clavate with 4 hairs curving toward base of scape and other hairs curving toward apex; funicular segments with relatively dense, short, tapering proclinate hairs. Eye large, with 12 facets in greatest diameter, approximately 0.29 X length of head, placed in approximately middle of side of head. Three ocelli present, arranged in an equilateral triangle near the occiput in center of head (in frontal view).

Dealate, wing stumps present; pronotal angle rounded; pronotum, mesonotum, metanotum, propodeum (including declivity) with reticulatepunctate sculpture; mesopleuron mostly shiny, lacking sculpture except at extreme upper region of anepisternum and lower posterior region of katepisternum; scattered short, coarse, curved, reclinate hairs present on pronotum, mesonotum, and metanotum, lacking on mesopleuron, metapleuron, and propodeum; one pair of suberect, clavate hairs on posterior region of mesonotum and metanotum, elongate hairs absent on mesosoma; propodeal spine short, about as long as width of base, directed straight backward toward gaster, not subtended by a lamina. Coxae lightly reticulate-punctate, appearing somewhat shiny with sparse, coarse, proclinate hairs. Femora and tibiae smooth, shining, anterior surfaces with relatively sparse proclinate, tapering hairs. Tarsi with relatively dense, proclinate tapering hairs; dorsal surfaces of middle and hind basitarsi lacking projecting flagellate hairs.

Spongiform appendages absent from petiole and gaster, postpetiole with reduced spongiform tissue ventrally; petiole and postpetiole with lamina at posterior edges; dorsum and sides of petiole and postpetiole smooth and shining, petiolar stalk reticulate-punctate, with sparse reclinate tapering hairs; in dorsal view, petiole rectangular with rounded edges; postpetiole oval, approximately twice as wide as long and slightly more than 1.5 times as wide as petiole. First tergite of gaster lacking grooves, lightly shagreened, remainder of gaster shiny; gastral tergites with sparse, curved, simple to coarse appressed hairs placed approximately 1 hair’s length apart or more; longer, simple to bifurcate erect hairs present at edges of sclerites.