Introduction
The genus Strumigenys is composed of minute, cryptic ants that typically occur in soil and leaf litter and prey upon small arthropods (Hölldobler and Wilson 1990).  In North America, species can be characterized by having six-segmented antennae; triangular to subtriangular mandibles that are well separated and possess distinct dentition; specially modified hairs on some parts of the body that may be clavate, spoon-shaped, forked, or otherwise atypical; and the usual presence of spongiform tissue below the petiole and postpetiole. 

Strumigenys epinotalis is a minute (TL 1.9–1.95 mm) arboreal attine ant previously known only from Brazil, Costa Rica, Ecuador, and southern Mexico, but recently discovered to occur in southern Alabama, Florida and southern Louisiana (Chen et al. 2012, MEM records). Here we report the first occurrence of S. epinotalis from Mississippi.

Diagnosis
This species is easily differentiated from other species known from the US by the combination of having the third tooth (from basal lamella) on mandible longer than the other teeth, the mesosoma of the worker being completely reticulate-punctate, having a curved row of spoon-shaped hairs on the pronotal dorsum, a distinct propodeal lamella, a ventral spongiform crest beneath the petiole, and fan-shaped patches of spongiform tissue on the petiole and postpetiole. Currently, the only other species reported from the US with which S. epinotalis might be confused is S. margaritae, another introduced species in the schulzi group. Strumigenys margaritae is the only other species known to occur in the United States that has sculpture on the entire side of the mesosoma; however, S. margaritae lacks a curved row of spoon-shaped hairs on the pronotal dorsum, has much longer propodeal spines, lacks a propodeal lamella, lacks spongiform bodies beneath the petiole, and has reduced spongiform tissue present beneath the postpetiole.

Identification
Worker: Minute (HL 0.52–0.58 mm, HW 0.39–0.42 mm, ML 0.1-–0.11 mm, EL 0.06– 0.-8 mm, SL 0.25–0.27 mm, MeSL 0.55–0.58 mm) (n=3) (MEM specimens). Overall reddish brown in color. Head pyriform, widest posteriorly; entire head including clypeus with fine microreticulation; dorsum of clypeus with numerous clavate setae directed anteriorly or away from midline of clypeus; clypeal margin with a fringe of clavate setae all curving anteriorly toward midline of clypeus; remainder of head with slightly larger clavate to spoon-shaped setae that curve toward midline of head; elongate flagelliform cephalic setae absent; leading edge of scape with a row of elongate, curved setae, all directed toward the base of the scape or downward; eye large with 5-7 ommatidia in longest diameter; antenna 6-segmented, scape short, apical flagellomere greatly enlarged forming a 2-segmented club with preapical flagellomere; clypeus somewhat pentagonal shaped, narrowing anteriorly, and with anterior margin slightly convex; mandibles subtriangular, lacking diastema; nine acute teeth present following basal lamella; third tooth from basal lamella spiniform, elongate and distinctly longer than other teeth, with subsequent teeth alternating in length with the fifth being longer than the fourth and the seventh being longer than the sixth, and the remaining two teeth smaller and blunter. Mesosoma entire, smoothly arched in profile view, with fine reticulation, dorsum with large, scattered semi erect clavate setae, elongate, flagellate setae lacking; propodeum with a pair of small spines directed upward; propodeal declivity with a spongiform lamella. Waist 2-segmented, with dense microreticulation; petiole pedunculate, node rounded rectangular in dorsal view, several elongate clavate setae present posterodorsally, a narrow curtain of spongiform tissue present ventrally, and spongiform tissue present posteriorly; postpetiole rounded rectangular, about twice as wide as petiole (in dorsal view), with a few scattered erect, clavate setae present dorsally, and with thick spongiform tissue present posteriorly and ventrally. Gaster shiny, with a few scattered appressed pubescent setae; scattered erect, clavate setae present dorsally; sting present.

Alate Female: Minute, slightly larger than worker (HL 0.59 mm, HW 0.45 mm, EL 0.14 mm, ML 0.11 mm, SL 0.31 mm, MeSL 0.68 mm, FWL 1.80 mm) (n=1) (MEM). Overall reddish brown in color. Head pyriform, widest posteriorly; entire head including clypeus with fine microreticulation; dorsum of clypeus with numerous clavate setae directed anteriorly or away from midline of clypeus; clypeal margin with a fringe of clavate setae all curving anteriorly toward midline of clypeus; remainder of head with slightly larger clavate to spoon-shaped setae that curve toward midline of head; elongate flagelliform cephalic setae absent; leading edge of scape with a row of elongate, curved setae, all directed toward the base of the scape or downward; eye large with numerous ommatidia; three ocelli present; antenna 6-segmented, scape short, apical flagellomere greatly enlarged forming a 2-segmented club with preapical flagellomere; clypeus somewhat pentagonal shaped, narrowing anteriorly, and with anterior margin slightly convex; mandibles subtriangular, lacking diastema; nine acute teeth present following basal lamella; third tooth from basal lamella spiniform, elongate and distinctly longer than other teeth, with subsequent teeth alternating in length with the fifth being longer than the fourth and the seventh being longer than the sixth, and the remaining two teeth smaller and blunter. Mesosoma squarish in profile, with fine reticulation except katepisternum, which is mostly shiny; mesosomal dorsum with large, scattered semi erect clavate setae; elongate, flagellate setae lacking; mesoscutum and mesocutellum smoothly arched in profile view; mesoscutum not completely overhanging pronotum in dorsal view; mesoscutellum raised above propodeum; propodeum with a pair of small spines directed upward; propodeal declivity with a spongiform lamella. Wings, if present, lacking pigmented veins, short brown pterostigma present, with fringe of setae along wing edges apically and on ventral sides of wings to about midway toward base. Waist 2-segmented, with dense microreticulation; petiole pedunculate, node rounded rectangular in dorsal view, several elongate clavate setae present posterodorsally, a narrow curtain of spongiform tissue present ventrally, and spongiform tissue present posteriorly; postpetiole rounded rectangular, about twice as wide as petiole (in dorsal view), with a few scattered erect, clavate setae present dorsally, and with thick spongiform tissue present posteriorly and ventrally. Gaster shiny, with a few scattered appressed pubescent setae; scattered erect, clavate setae present dorsally; sting present.

Biology and Economic Importance
This species appears to be arboreal. One specimen was collected in scrub habitat near a bayhead by Mark Deyrup in Highlands County ,Florida. All other known US specimens were collected in cypress-tupelo swamps in Ascension, Gramercy, and Jefferson Parishes, Louisiana in floating pitfall traps or in arboreal pitfall traps.

This species is unlikely to pose any economic problems.

For more info about this species, see Chen et al. 2012.

Pest Status

Distribution
Florida and Louisiana

Literature Cited

Bolton, B. 2000.  The Ant Tribe Dacetini.  Memoirs of the American Entomological Institute.  Vol. 65, part 1-2. 

Hölldobler, B., and E.O. Wilson. 1990.  The Ants.  Belknap Press of Harvard University Press, Cambridge, MA.  732 pp.

Chen, X., J. A. MacGown, B. J. Adams, K. A. Parys, R. M. Strecker, and L. Hooper-Bui.2012. First Record of Pyramica epinotalis (Hymenoptera: Formicidae) for the United States. Psyche. vol. 2012, Article ID 850893, 7 pages, 2012. doi:10.1155/2012/850893 [pdf]

Links

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