Aphaenogaster mariae Forel, 1886

Kirchner, Michelle, Bertone, Matthew, Blaimer, Bonnie B. & Youngsteadt, Elsa, 2023, Colony Structure and Redescription of Males in the Rarely Collected Arboreal Ant, Aphaenogaster mariae Forel (Hymenoptera: Formicidae), Proceedings of the Entomological Society of Washington 125 (1), pp. 77-88 : 82-86

Treatment of Male Aphaenogaster mariae Forel

Diagnosis ( Figs. 14–17 ).—Among North American Aphaenogaster , male A. mariae are most similar in appearance to the sister species, A. tennesseensis . In both species, the males have a head that is wider posteriorly than anteriorly, a short postpetiole, and swollen metapleural processes, but A. mariae can be separated by the lack of distinct spines on the propodeum, the presence of erect dorsal setae, an anteriorly shining scutum, and metapleural processes that barely extend past the propodeum ( Carroll 1975).

Measurements and indices.—Values are in mm and presented as mean ± SD (range). HL: 0.783 ± 0.02 (0.750–0.810); HW: 0.615 ± 0.02 (0.581–0.652); EL: 0.337 ± 0.01 (0.310–0.363); SL: 0.215 ± 0.02 (0.175–0.275); MscL: 0.782 ± 0.03 (0.744–0.829); MscW: 0.722 ± 0.02 (0.691– 0.782); ML: 1.581 ± 0.07 (1.416–1.673); PL: 0.424 ± 0.03 (0.349–0.475); PW: 0.231 ± 0.01 (0.211–0.249); PPL: 0.359 ± 0.03 (0.271–0.393); PPW: 0.306 ± 0.01 (0.271– 0.335); CI: 78.6 ± 2.25 (73.8–83.5); SI: 35.0 ± 3.39 (29.7–42.2); MI: 219.0 ± 12.0 (190.7–235.1).

Redescription.— Coloration ( Figs. 14–17 ): Head, mesosoma, and petiole dark brown. Postpetiole and gaster dark to medium brown. Pronotum, legs, antennae, and mandibles medium to light brown. Head ( Fig 16 ): Head subrectangular and distinctly wider posteriorly than anteriorly, lateral surfaces below eyes straight or slightly converging, occipital margin straight, sometimes with slight emargination. Anterior margin of clypeus usually slightly convex, but sometimes straight or with a slight concavity. Eyes large and oval. Mandibles shiny and faintly punctate. Clypeus shiny with delicate longitudinal striations medially that become coarser laterally. Sparse rugose sculpturing on frontal triangle and between mandible insertion and anterior edge of eye. Frontal carinae short and convergent, ending about 2/3 up the eye. Frons densely punctate posteriorly becoming rugose anteriorly. Gena and temples densely punctate to foveolate. Vertex with transverse rugae posteriorly becoming more punctate anteriorly. Long erect setae line midline of head and ventral edge of gena. Three pairs of long erect setae on clypeus near mandible insertion. Erect to decumbent setae on mandible of varying lengths. Antennal scapes short with short, decumbent setae. Mesosoma ( Figs. 14, 15 ): Mesosoma relatively slender. Mesoscutellum rounded, presenting an even convexity dorsally and gradually sloping laterally. Mesoscutellar disc projecting above maximum height of mesoscutellum. Propodeum subtrapezoidal, its dorsal surface usually flat and gently sloping, but occasionally slightly rounded. Propodeal spines absent, often replaced by a pair of thickened lobes. Lower metapleuron swollen posteriorly, ending in a flange that barely extends past the declivitous face of the propodeum. Pronotum finely reticulate. Anterior-most portion of mesoscutum smooth and shining. Finely lineate sculpture arising along longitudinal midline of mesoscutum, running along length of mesoscutum becoming rugose laterally. Mesoscutellar disc with longitudinal rugae. Medial dorsum of propodeum smooth and shining or delicately reticulate Lobes and declivitous face of propodeum rugose. Anepisternum finely lineolate anteriorly becoming carinulate posteriorly. Subalar area strongly costate. Katepisternum, metapleuron, and lateral propodeum lineolate to costate. Mesoscutum with sparse, long, erect setae and shorter, decumbent setae. Several erect setae on mesoscutellar disc. Propodeal lobes with fine, appressed pubescence. Metasoma ( Figs. 14, 15, 17 ): In lateral view, petiole triangular with a rounded node and postpetiole oval and broadly convex. Dorsally, both petiole and postpetiole with shallow longitudinal suture centrally. Postpetiole barely longer than wide. Dorsum of petiole and postpetiole finely punctate or rugulose. Gaster feebly striolate with faint striae radiating from postpetiolar attachment. Few decumbent setae on postpetiole and sometimes petiole. Gaster with sparse setae of varying lengths.

Natural History

This article reports the first documented collection of a colony of the arboreal ant species Aphaenogaster mariae . The nest was in a dead branch 17 m in the canopy of a mature Quercus alba and presumably inaccessible to most collectors. While this ant’s range spans much of the eastern United States, it is relatively rarely collected, likely due to its arboreal lifestyle. Wesson and Wesson (1940) are a notable exception, as they collected A. mariae “frequently” from oaks while cataloguing ants of south-central Ohio, but their publication does not report any specific collecting methods. MacGown and Brown (2006) collected a series of A. mariae workers and four dealate queens and found a nest in a standing dead tree in the Tombigbee National Forest in Mississippi, but still listed the species as “uncommon” among their intensive terrestrial collections. In another study, MacGown et al. (2012) suggested that A. mariae can be “easily collected with peanut butter bait” on large oak and hickory trees and, indeed, most of the records of the species on AntWeb were collected with peanut butter ( California Academy of Science 2022). Aphaenogaster mariae has also been collected by others at baits ( Ellison et al. 2012, DeMarco 2015), in pitfall traps ( Munsee 1967, MacGown and Brown 2006, Vogt et al. 2022), Lindgren funnel traps (AntWeb data), and in Berlese funnels ( MacGown and Brown 2006, MacGown et al. 2012), but typically only as single individuals. It seems the most reliable method for collecting this species is by baiting trunks of mature hardwood trees with peanut butter, if the collector is primarily interested in workers, or active hand-collecting on oak trees as high in the canopy as possible, particularly if the collector is interested in locating nests ( Wesson and Wesson 1940, Carter 1962, DuBois 1985, Frye and Frye 2012, MacGown et al. 2012).

It is possible that this ant is not actually rare, but only rarely collected with common ground-based collecting methods. If this were the case, canopyfocused collections might regularly detect this species. In the past three years, we have surveyed canopy ants at seven sites in central North Carolina by hand-collecting in 30 Quercus alba canopies and deploying baits (178 tuna and 178 jam) in 89 additional tree canopies. These efforts detected A. mariae at two sites and nests at only one. At the same site described here, we found two additional nests (not collected) in a dead branch at 15 m and 19 m high, each in a separate Q. alba . Both nests were similar in structure to the one described here. In addition, at this site and one other, we detected one worker per site at a canopy bait but observed no other individuals in those trees. This leads us to conclude that A. mariae is rarely collected not only because of its arboreal nesting strategy, but also because its populations occur in low, localized densities, at least in our study region.

An explanation for this species’ relative rarity may exist in its reproductive strategy. Wheeler (1910) suggested that queens of A. mariae and the sister species, A. tennesseensis , may be temporary social parasites of other Aphaenogaster early in the colony lifecycle, relying on established nests of their congeners to provide for their incipient colony. Due to high host-specificity, social parasites are nearly always less abundant or more localized in distribution than their host species ( Hölldobler and Wilson 1990, Thomas et al. 2005). While temporary social parasitism has yet to be proven for either species, dealate A. mariae queens have been collected from Berlese funnels that also contained nests of A. fulva ( MacGown and Brown 2006) . Both species exhibit relatively late nuptial flights ( Wheeler 1916, Carroll 1975), which could allow socially parasitic queens to take advantage of nascent colonies of earlier-flying congeners. Additionally, queens of both species share morphology suggestive of social parasitism, including small body size (similar to the workers) and large propodeal spines—traits unique within the genus ( Wheeler 1910, DeMarco 2015). If A. mariae is a temporary social parasite of A. fulva or other congeners, it would follow that populations of A. mariae would occur in relatively low and/or localized densities. This could also explain the occurrence of dealate A. mariae queens in soil and leaf litter samples, despite their arboreal nesting habits ( MacGown and Brown 2006). While she raises her first brood, a newly mated A. mariae queen may temporarily dwell in the soil nests of other Aphaenogaster species, ascending into the canopy once there is a wellestablished colony of her own workers.

Figures

Figs. 14–17. Aphaenogaster mariae male. 14, Dorsal. 15, Lateral. 16, Frontal. 17, Dorsal view of 1st gastral segment (A4); arrow indicates the barely impressed striae radiating from the post-petiolar attachment.