Acropyga epedana

SPECIES NAME: Acropyga epedana

TAXONOMIC SUMMARY: DIAGNOSIS: (worker) Mandible slender, cutting margin oblique and quadridentate;eye minute, consisting of one or two facets; antennae 10-segmented, scape surpassing occipital margin, terminal segment longer than preceding four segments; pubescence and hairs abundant on all body surfaces.

BIOLOGY: This subterranean (hypogaeic) ant is the only species in its genus that occurs in the nearctic region. A. epedana is dependant on a mealybug species (Rhizoecus colombiensis) for their survival. The ants feed on the sugar-rich feces of the mealybugs, which in turn feed on root-sap. It is presumed A. epedana also feed mealybugs to their larvae. Workers in a laboratory colony (LaPolla et al. 2002) refused a variety a food items that ranged from dead insects to sugary substances (e.g. honey, sugar water).The ant’s relationship and dependence on R. colombiensis means they are obligate coccidiphiles. Newly produced queens leave their natal nest for their mating-flight carrying a mealybug in their mandibles. If the queen is able to mate and begin a new nest, this single mealybug will serve as the foundress of the ant colony’s mealybug “herd.” The coccid carrying behavior practiced by the queen is known as “trophophoresy.” A published account (Smith et al. 2007) of the mating flight of this species provides a relatively rare glimpse into this aspect of this genus’ biology. The mating aggregation was observed in a shallow ditch alongside a primitive asphalt road, bordered by short grass, just 200 m west of the Southwestern Research Station (1645 m N31°53.028’ W109°12.378’), near Portal, Arizona. Beyond the ditch was a steep incline without vegetation and the ditch and road received direct sunlight for most of the day. The surrounding habitat was dominated by an open oak-pine-juniper forest. The mating flight occurred 2 days after the first heavy summer monsoon rains (26 July 2005), although there was very little precipitation on the day of the flight. The aggregation was first seen at ~16:30h. Most of the males were hovering or swarming above small clumps of grass and rocks. Females entered the aggregation, after which multiple males simultaneously attempted to mate with them. Males outnumbered females by ~10:1. After mating most females immediately shed their wings and searched for suitable nest sites; only a few females flew from the aggregation. All females carried a mealybug in their mandibles. On 6 August 2005 at the same site, a single alate female carrying a mealybug was found actively mating, but no swarm could be found and only a single male was present.

DISTRIBUTION: Neartic. Arizona. Though A. epedana is presently known from 5 sites in southeastern Arizona, it probably ranges south into Mexico through the Sierra Madre Occidental mountain range. A. epedana appears to only occur at higher elevations (where annual rainfall is greater) between 1676 m - 1052 m, in open oak/juniper woodland habitat.

DESCRIPTION: Worker: (Holotype) Measurements: HL 0.50; HW 0.50; SL O.37; PW 0.03; WL 0.53; TL 1.75 mm. Head, in frontal view, as wide as long, Cl l00; widest at about eye level, sides nearly straight; occiput slightly concave in middle; in lateral view, thickest above eye level, occiput compressed, eyes at lower one-fourth of side. Mandibles slender, cutting margin strongly oblique, with three large triangular teeth and a minute tooth at basal angle. Apical margin of clypeus evenly slightly convex; clypeus in profile with apical third abruptly sloping to margin. Scape reach ing a little beyond occipital margin, SI 74; median flagellar segments distinctly broader than long, apical segment large, longer than preceding four segments combined. Thorax short and robust, PW 0.67 x WL. Pronotal face declivitous; meso- metanotum flattened, evenly curved from pronotum to propodeum. Propodeum entirely oblique, without distinct basal face, surface flat. Legs stout; tarsal segments flattened. Petiolar scale, in profile, compressed, fully erect, crest thin; in frontal view,crest very slightly concave. Integument smooth and shiny on head and thorax; head with abundant setigerous punctures; coarser and more conspicuous on lower half; gaster shiny, integument roughened and with obscure coarse piligerous punctures. Head with abundant appressed and subappressed short, coarse pubescence on sides and beneath; front and occiput with much pubescence fully erect; with scattered long erect hairs, numerous on clypeus. Thorax and propodeum with sparse subappressed to fully erect coarse pubescence and scattered long, erect coarse hairs. Gaster with abundant pubescence, subappressed to erect on ter gites, more closely appressed laterally, appressed on venter; with numerous long, fully erect hairs. Scape pubescence abundant, reclinate to suberect, coarse. Legs similar, coarse hairs abundant on tibiae; tarsal segments with coarse seta-like hairs and a coarse seta on apical corners of segments. Color uniformly brownish yellow, mandibles transparent, cutting margin piceous.

Queen: Measurements (n= 6).- TL: 3.03- 3.17HW: .592- .612 HL: .571- .602SL: .443- .485 EL: .126-.147 EW: .105- .113 THL: .854- .956 GL: 1.51-1.71 CI: 100.3-111.0 SI: 74.580.7 EI: 21.3- 24.0 Head: yellow to brownish-yellow, darker along segmental margins; slightly broader than long and covered with a fine pubescence; apex slightly darker with three prominent ocelli; eyes large, positioned towards the anterior margin at lower 1/4 of side; eyes break lateral margins when viewed in full frontal view; antennae 11 segmented and incrassate; scape reaches to slightly passes posterior margin; posterior margin entire, with scattered, short, erect hairs; clypeus wide, medially slightly convex with several (usually around 12 or fewer) long, erect hairs, the longest hair placed medially; mandible infuscated with three distinct teeth, occasionally a smaller tooth is also present at basal angle; a large gap exists between anterior clypeal margin and inner mandibular margin. Thorax: yellow to brownish-yellow, darker along segmental margins; pronotum short and collar-like; anterior of mesonotum rounded, dorsum flat, covered in short, suberect hairs; scutellum distinct, roughly oval, slightly lighter than mesonotum, with fewer suberect hairs covering dorsum; propodeum with fewer short, suberect hairs than other parts of the thorax; declivity at ca. 45° angle. Gaster: petiole erect and short, triangular in lateral view with a rounded apex that is occasionally concave; gaster yellow to brownish-yellow darker along segmental margins; covered in a fine pubescence, with a few scattered suberect hairs present.

Male: Measurements (n= 3).- TL: 2.00- 2.13 HW: .419- .425 HL: .410- .424 SL:.330- .374 EL: .132- .144 EW: .108- .114 THL: .726- .775 GL: 2.00- 2.13 C1:100.5-102.4 SI: 78.88 - 8.0 E1: 31.0- 34.0 Head: brownish-yellow and covered with fine pubescence; apex darker brownish-yellow, with three prominent ocelli; eyes large, in frontal view bulging out from outline of head; antennae 12 segmented; scapes surpass posterior margin, by about the length of the first two funicular segments; clypeus with several long hairs on anterior margin, though clypeus generally less pilose than the rest of the head; mandibles with two distinct teeth, an apical tooth and a basal tooth, a smaller tooth is occasionally present at basal angle; a large gap exists between anterior clypeal margin and inner mandibular margin. Thorax: yellow to brownish-yellow, darker along segmental margins; pronotum short and collarlike; anterior of mesonotum rounded, dorsum flat, covered in short, suberect hairs; scutellum distinct, roughly oval, slightly lighter than mesonotum, with fewer suberect hairs covering dorsum; propodeum with fewer short, suberect hairs than other parts of the thorax; declivity at ca. 45° angle. Gaster: petiole erect and short, triangular in lateral view with a rounded apex; gaster brownish-yellow with more brown dorsally; covered in a fine pubescence, with a few scattered suberect hairs present. Genitalia: parameres long, rectangular, curving towards each other apically; anteriorally parameres without hairs, the posterior ends with scattered erect hairs; vol sellar lobes distinct, with many erect hairs; cuspi cylindrical, with short, peg-like teeth at the apex; digiti elongate with apical end roughly anvil-shaped; dorsal tip of digiti with short, peg-like teeth where they meet the cuspi, forming an oval-shaped space between them in ventral view; ventral side of penis valves without teeth; apical tips flattened and laterally expanded.

ETYMOLOGY: Gr., epedanos, weak or feeble, so-called because of the thin, collapsible integument.

LITERATURE:

LaPolla, J. S., S. P. Cover, and U. G. Mueller. 2002. Natural history of the mealybug-tending ant, Acropyga epedana, with descriptions of the male and queen castes. Transactions of the American Entomological Society 128:367-376.

Smith, C. R., J. Oettler, A. Kay, and C. Deans. 2007. First recorded mating flight of the hypogeic ant, Acropyga epedana, with its obligate mutualist mealybug, Rhizoecus colombiensis. Journal of Insect Science 7.

Snelling, R. R. 1973. Two ant genera new to the United States (Hymenoptera: Formicidae). Contr. Sci. (Los Angel.) 236:1-8.