Acropyga exsanguis

From LaPolla (2004) - Bünzli (1935) extensively documented the natural history of A. exsanguis (under the synonym A. paramaribensis). This species is highly polygynous. Bünzli found both pleometrosis (founding of a colony by multiple queens), and the acquisition of young queens by established colonies in A. exsanguis, suggesting multiple possible origins of polygyny. Bünzli found that A. exsanguis possesses large, diffuse nests in the soil (similar to those described by LaPolla et al. (2002) for Acropyga epedana). The species is known to make vertical nest movements in the soil depending on soil conditions. For instance, as the upper layers of soil dry, Bünzli found the ants moved deeper into the ground.

Identification
From Lapolla (2004):

Diagnosis - Worker: 8-9 segmented antennae; scape typically slightly fails posterior margin; head about a broad as long; head width < than 0.52 mm; mandible with 3 distinct teeth; mesonotum dorsum with a thick layer of hairs, with scattered erect hairs. Queen: as in worker with modifications expected for caste. Male: 9-10 segmented antennae; parameres long and rectangular with many long erect hairs covering lateral surface; parameres often with distinct dorsolateral expansions. Compare with Acropyga keira and Acropyga romeo.

Workers are distinguishable from other species in the decedens species-group by the 8-9 antennal segments and the small head width (<0.52 mm). Worker mandibular dentition seems to be stable at 3 distinct teeth. However Bünzli (1935) reported observing 4 teeth and 7 antennal segments in A. paramaribensis (a junior synonym). Fortunately a large sample of this species was available for study, and I never observed a 4th mandibular tooth or 7 antennal segments among any specimens. Therefore, I suspect that Bünzli was in error or that the latter conditions are extremely rare abberations. He may have confused A. exsanguis with Acropyga smithii, which does have 4 mandibular teeth and can possess as few as 7 antennal segments. This species could be confused with Acropyga romeo, but can be separated from it based on the presence of a 4th smaller basal tooth.

Males of this species are distinct, with dorsolateral expansions of varying degrees found in the parameres (from slight lateral expansions to expansions that completely cover the digiti and cuspi in dorsal view). Variation in the dorsolateral expansion of the parameres at first led me to believe that there were several species present, but after examining multiple male specimens it is clear that the variation is a continuum and the specimens were indeed conspecific. Examination of the penis valves revealed that they are the same structural type regardless of the extent of the dorsolateral expansion.

Key to New World Acropyga Workers / Queens / Males

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Belize, Colombia, Costa Rica, Guatemala, Guyana, Honduras, Mexico, Panama, Suriname.

From LaPolla (2004): This species has a wide distribution, ranging from central Mexico to northern Argentina.

Other Insects
From LaPolla (2004) - A number of mealybugs have been recorded living with this species: Neochavesia sp., Geococcus coffeae, Rhizoecus coffeae, Pseudorhizoecus proximus, Rhizoecus caladii, and Rhizoecus falcifer. Trophophoretic behavior by queens has been observed on at least three separate occasions: queens carrying Rhizoecus coffeae by Bünzli (1935) and Roba (1936) and Pseudorhizoecus sp. by Weber (1957).

Nomenclature

 *  exsanguis. Rhizomyrma exsanguis Wheeler, W.M. 1909b: 238 (w.) MEXICO. Combination in Acropyga (Rhizomyrma): Mann, 1922: 53. Senior synonym of bruchi, paramaribensis, robae, wheeleri: LaPolla, 2004a: 47.
 * wheeleri. Acropyga (Rhizomyrma) wheeleri Mann, 1922: 52 (w.q.) HONDURAS. Junior synonym of exsanguis: LaPolla, 2004a: 47.
 * bruchi. Acropyga (Rhizomyrma) bruchi Santschi, 1929d: 308 (w.) ARGENTINA. Junior synonym of exsanguis: LaPolla, 2004a: 47.
 * paramaribensis. Acropyga paramaribensis Borgmeier, 1933c: 263 (w.q.) SURINAM. Borgmeier, 1934: 109 (m.); Bünzli, 1935: 519 (l.). Combination in Acropyga (Rhizomyrma): Kempf, 1972a: 17. Junior synonym of exsanguis: LaPolla, 2004a: 47.
 * robae. Acropyga (Rhizomyrma) robae Donisthorpe, 1936b: 108, figs. 1-3 (w.q.m.) COLOMBIA. Junior synonym of exsanguis: LaPolla, 2004a: 47.

Worker
From LaPolla (2004) - Head: yellow; head about as broad as long; covered in a dense layer of appressed hairs, with scattered erect hairs toward posterior margin; posterior margin slightly concave medially; 8-9 segmented, incrassate antennae; apical segment about as long as preceding 4 segments; scape reaches or slightly fails posterior margin; clypeus with dense layer of erect hairs of varying lengths; mandible with 3 distinct teeth; gap exists between inner mandibular margin and anterior clypeal margin. Mesosoma: yellow; in lateral view, pronotum rises steeply toward mesonotum; pronotum with appressed hairs, erect hairs more posteriorly placed; mesonotum usually high and dorsally rounded, covered in dense layer of appressed hairs, with erect hairs scattered throughout; metanotal area distinct; propodeum below level of mesonotum, rounded with appressed and erect hairs; declivity steep. Gaster: petiole thick and erect; petiole reaches about midline of propodeal spiracle; gaster yellow; covered in a dense layer of appressed hairs, with scattered erect hairs throughout.

Measurements (n=22): TL: 1.72-2.38; HW: 0.462-0.511; HL: 0.451-0.522; SL: 0.318-0.380; ML: 0.427-0.592; GL: 0.710-l.32; CI: 94.64-104.7; SI: 67.37-76.14.

Queen
From LaPolla (2004) - As in worker, with modifications expected for caste and the following differences: scutellum with appressed and erect hairs; two longest hairs (almost as long as scutellum) anterolaterally placed opposite each other.

Measurements (n=5): TL: 2.17-3.48; HW: 0.52-0.547; HL: 0.508-0.547; SL: 0.367-0.443; SL: 0.367-0.443; ML: 0.828-0.963; GL: 1.14-l.97; CI: 100-107.28; SI: 67.34-82.96.

Male
From LaPolla (2004) - Head: brownish-yellow anteriorly becoming dark brown around 3 prominent ocelli; head about as broad as long; 9-10 segmented, incrassate antennae; apical segment about as long as preceding 3 segments; scape reaches or slightly surpasses posterior margin; clypeus with dense layer of appressed and erect hairs; mandible with 1-2 teeth; basal tooth, when present, small and indistinct, separated from apical tooth by wide diastema; gap exists between inner mandibular margin and anterior clypeal margin. Mesosoma: pronotum short and collar-like, overarched by mesonotum; anterior mesonotum broadly rounded; mesonotum dorsum flat, covered in a layer of largely short appressed hairs, with scattered longer appressed to erect hairs throughout; propodeum slightly rounded, with appressed hairs; declivity very short, but steep. Gaster: petiole thick and erect; gaster brownish-yellow, dorsum darker. Genitalia: in lateral view, parameres elongate and rectangular, covered in scattered sub erect to erect hairs; parameres with dorsolateral expansions apically, varying from completely covering to only slightly covering digiti and cuspi in dorsal view; cuspi cylindrical, curved apically toward digiti; apices of cuspi with short, peg-like teeth; digiti anvil-shaped apically, meeting cuspi on dorsal surface, where short, peg-like teeth are present.

Measurements (n=6): TL: l.87-2.41; HW: 0.346-0.412; HL: 0.388-0.410; SL: 0.267-0.311; ML: 0.67-0.785; GL: 0.79-1.28; CI: 89.18-105.93; SI: 67.65-75.49.

Type Material
Rhizomyrma exsanguis W.M. Wheeler, 1909: 238 (w.). 3 syntype workers, MEXICO: Jalapa (F. Silvestri) (MCZC) [examined]. The designated lectotype is a worker labeled JSL TYPE # 118 and is deposited at MCZC. Lectotype is 1 of 3 specimens on the same card. The lectotype is the specimen to the right of the middle specimen if the card is oriented away from an examiner. The worker is raised up slightly off the card and the head is not glued down to the surface. Mann 1922: 53, first combination in Acropyga.

Acropyga (Rhizomyrma) wheeleri Mann, 1922: 52 (w.q.). 8 syntype workers, HONDURAS: Lombardia (Hugrich) (MCZC) (USNM) [examined]. NEW SYNONYM.

Acropyga (Rhizomyrma) bruchi Santschi, 1929: 308 (w.). 3 syntype workers, ARGENTINA: Santa Fe, Rosario (NHMB) [examined]. NEW SYNONYM.

Acropyga (Rhizomyrma) paramaribensis Borgmeier, 1933: 263 (w.q.). Syntype workers, syntype queens, SURINAM: Paramaribo (depository unknown) [not examined]. NEW SYNONYM. Borgmeier 1934: 109, description of male; Bünzli 1935: 519, description of larva; Kempf 1972: 17, first combination in (Rhizomyrma).

Acropyga (Rhizomyrma) robae Donisthorpe; 1936: 108 (w.q.m.). Holotype worker, COLOMBIA: La Esperanza (R. Roba) (BMNH) [examined]; 7 paratype workers, 5 paratype queens, 1 paratype male, same locality as holotype (BMNH) (MCZC) [examined]. NEW SYNONYM.

Additional References

 * [[Media:Donisthorpe 1936b.pdf| Donisthorpe, H. 1936b. Acropyga (Rhizomyrma) robae sp. nov. (Hym. Formicidae), a new S. American ant, with remarks on the genus, etc. Entomologist 69: 108-111 PDF]]