Strumigenys brevisetosa Smith, 1935

Booher, Douglas B., 2019, Taxonomic clarification of two Nearctic Strumigenys (Hymenoptera: Formicidae), Zootaxa 4664 (3), pp. 401-411 : 405-408

Strumigenys brevisetosa Smith, 1935

( Figure 2 , 3 )

Strumigenys (Cephaloxys) clypeata var. brevisetosa Smith, 1935: 215 . Holotype worker: Lucedale, George Co., MS, USA, 17-January-1932, sifting for beetles (Dietrich) [USNM, USNMENT00533161, examined]. Raised to species: Wesson & Wesson, 1939: 108. Description of queen: Brown, 1953: 60. Junior synonym of pilinasis: Brown, 1964: 197 . In Strumigenys (Trichoscapa) : Smith, 1947: 587; Creighton, 1950: 304; in Smithistruma: Smith, 1951: 827 ; Brown, 1953: 59. Revived Status.

Strumigenys (Cephaloxys) medialis Wesson & Wesson, 1939: 94 , pl. 3, fig. 1. Syntype workers: Ohio, Pike County, Beaver [MCZC, four workers examined; USNM, one worker examined]. Junior synonym of pilinasis: Smith, 1951: 828 ; Brown, 1953: 60. New Synonym

Diagnosis. Strumigenys brevisetosa can be easily distinguished from most Nearctic species by the presence of a distinct peripheral groove that runs the entire free margin of the clypeus, placing it in the clypeata group. Of species in the clypeata group it is most similar to S. laevinasis M.R. Smith and S. clypeata Roger. Members of Strumigenys brevisetosa are distinguished from S. laevinasis by their linear-spatulate pilosity on dorsum and free margins of the clypeus (in S. laevinasis these hairs are fine and never expanded along their lengths). Strumigenys brevisetosa is distinguished from S. clypeata by the elevated positioning and elongated hairs on the clypeal dorsum (in S. clypeata , dorsal clypeal hairs are scale-like spatulate hairs that are tightly appressed), as well as the longer more linear hairs on the free margins of their clypeus (in S. clypeata , this fringe of hairs are spatulate, not linear spatulate).

Holotype measurements: HL = 0.656; HW = 0.435; ML = 0.133; PW = 0.289; SL = 0.359; FL = 0.477; HT = 0.32; EL = 0.055; TL = 2.477; WL = 0.641; CI = 66.3; MI = 20.3; SI = 82.5; Clypeal width =0.230; Clypeal length =0.219.

Non-type measurements (n = 29 workers). HL = 0.554 -0.696 (0.628); HW = 0.365 -0.428 (0.402); ML = 0.09-0.134(0.104); PW = 0.234 -0.335 (0.283) ; SL = 0.272-0.35(0.317); FL = 0.36-0.471(0.418); HT = 0.279 - 0.338 (0.311); EL = 0.035 -0.076 (0.054); TL = 2.319 -2.815 (2.608); WL = 0.527 -0.678 (0.61); CI = 60.8-68(64); MI = 13.8-20.2(16.8); SI = 73.1-86.1(80.6).

Description. Strumigenys brevisetosa belongs to the clypeata species group, sharing the diagnostic peripheral clypeal groove common to that group. For the description of the clypeata species group see Bolton (2000). The following description accounts for variation among all examined specimens of S. brevisetosa within the definition of the clypeata group.

Mandibles with acute triangular basal lamella followed by a minute to absent diastemmic gap (0.002 -0.015) that is almost always shorter than the first principle tooth. Basal tooth is followed by five principle teeth. Counting from base of mandible, first three teeth increase in size followed by a shorter fourth tooth and fifth tooth that is similar in sized as tooth two. Clypeus varies from longer than broad to broader than long (clypeal width/length n=31, 0.879 - 1.174).

In profile, pronotum evenly rounded and continuous with mesonotum, metanotal groove weakly impressed to absent. Propodeal teeth are well developed and triangular-spiniform to triangular. Lamella on declivitous face of propodeum between spine and lobe of metapleural gland narrow and never approaching length of tooth (rarely extending more than half the tooth length). Spongiform tissue is typical of the clypeata group, well developed as a ventral flange along the petiole, as a ventral and posterior lobe of the petiolar node, as a ventral process of the postpetiole, and as a collar surrounding the disc of postpetiole.

Pilosity. Clypeal dorsum and free margins of clypeus with linear-spatulate hairs. Those on dorsum vary but are slightly to moderately elevated and never tightly appressed. Hairs on free margin of clypeus vary in shape from finely to broadly linear-spatulate but are never simple. Ground pilosity of head and mesosoma consists of numerous arched simple hairs tending to orient medially, hairs on gastral tergites subflagellate to flagellate. Differentiated standing flagellate hairs vary as follows, scrobal margin with 1-2 (one pair always present at apicoscrobal position and if a second pair is present it occurs at near the midlength of the scrobal margin); dorsum of head with 2 and sometimes 3 pairs of hairs near posterior margin of head (one pair straddling the midline, one pair at posterior-most position of occipital lobes, and sometimes a pair between); humeral hair present as well as another pair present on dorsum of pronotum, and 1-2 pairs present on mesonotum; fore-tibia usually with no hairs but some specimens having up to two hairs; mesa- and meta- femur, tibia, and basitarsi with one to two.

Sculpture. Clypeus varies from punctate to smooth. Head and dorsum of mesosoma are reticulopunctate. Side of pronotum usually to punctate with heavier rugulo-striate sculpture but some specimens with a large smooth patch; the side of mesonotum and propodeum smooth and shining. Abdomen with well-developed basigastral costulae that extend near a third of the length of the first gastral tergite; the remainder of the abdomen free of sculpture and shining.

Comments. There is a fairly long history of confusion in the species concept of Strumigenys brevisetosa . It has the most variable clypeal hair and clypeal shape of any North American Strumigenys . It is likely that S. brevisetosa is a single species that has hybridized or still hybridizes with both S. laevinasis and S. clypeata ( Brown 1964) . It is also possible S. brevisetosa contains more than one cryptic species: one or two that are more closely related to S. laevinasis and one that is more closely related to S. clypeata . Strumigenys medialis (junior synonym of brevisetosa ) originally referred to species more similar to S. laevinasis and Strumigenys brevisetosa referred to species more similar to S. clypeata ( Brown 1964) . Another potential closely related species, mentioned as Strumigenys near pilinasis (see below), represents morphological variants that are closest to S. laevinasis . However, after examining all of the type specimens, nearly all the collection material available to previous taxonomists, and additional new collections, it has become clear that there are no distinct morphological characters to distinguish S. brevisetosa from S. medialis and I retain it as combined for the same reasons as Brown (1964) combined these two species. Specimens that are most similar to S. laevinasis tend to have one scrobal hair (at apical position, but this varies within the same nest series), have a smooth non-sculptured patch on the side of the pronotum, conical and stout teeth, and a clypeus that is longer than wide. Specimens that are more similar to S. clypeata tend to have two scrobal hairs (one along midlength and one at apical position, though rarely a specimen will have only one at apicoscrobal position), the side of pronotum with punctate and striate sculpture and without a smooth patch, spiniform elongate teeth, and a clypeus that is wider than long. However, after looking at many more specimens than were available to my predecessors, it has become clear that none of these characters are stable and at this time I am reluctant to separate S. brevisetosa into more than one species.

Brown (1964: 199) mentioned a possible new species as Strumigenys sp. near brevisetosa , based on two worker collections (Karber’s Ridge, Perry County, IL [Sanderson & Standard]; and Urbana, Champaign County, IL [Tanquary]). I identify these as Strumigenys brevisetosa .

Due to the great variability of this species and the potential for future taxonomic revision, I provide a complete list of examined material.

Figures

FIGURE 2. Holotype worker of Strumigenys brevisetosa [USNM: USNMENT00533161] Photographed by Matthew Kweskin.

FIGURE 3. Map of Strumigenys brevisetosa specimens examined in this study. Filled circles are measured specimens.