Acropyga decedens

LaPolla (2004) - It has been reported as being trophophoretic, and associated with at least 3 mealybug species: Geococcus coffeae, Neochavesia sp., Rhizoecus coffeae. Though it should be noted that in the literature Acropyga goeldii has often been misidentified as A. decedens so the mealybug records must be considered suspect.

Identification
LaPolla (2004) - Worker: 9-11 segmented antennae; mandible broad with 4-5 teeth, nearly at right with inner mandibular margin; apical tooth distinctly longer than other teeth; head broader than long. Queen: as in worker with modifications expected for caste. Male: 12 segmented antennae; parameres taper to a point; cuspi bend toward and meet digiti. Compare with Acropyga donisthorpei, Acropyga goeldii and Acropyga guianensis.

This species can be distinguished from Acropyga donisthorpei by having an inner mandibular margin that is not at a distinct right angle with the anterior c1ypeal margin. A. decedens can be distinguished from Acropyga guianensis because that species always possesses a head that is distinctly longer than broad. In the case of Acropyga goeldii diagnosis can be difficult if the specimen possesses a 4-toothed mandible. The mandible is always broader in A. decedens than it is in A. goeldii, however the difference can be hard to distinguish if you haven't looked at a lot of Acropyga specimens. It is therefore not surprising given the similarity of A. decedens and A. goeldii workers that the latter species was considered a junior synonym of the former by Costa Lima (1931). The best way of separating the two species is with associated male specimens, for males of the two species are relatively easy to distinguish from one another, and in fact indicate they are not closely related to one another despite the similarity in the worker caste.

Distribution based on Regional Taxon Lists
Neotropical Region: Brazil, Ecuador.

From LaPolla (2004): I have only seen specimens of this species from one locality in Brazil (type locality) and one in Ecuador, though it has been reported from a number of localities throughout South America.

Nomenclature

 *  decedens. Brachymyrmex decedens Mayr, 1887: 521 (w.q.m.) BRAZIL. Combination in Rhizomyrma: Emery, 1906c: 184; in Acropyga (Rhizomyrma): Emery, 1925b: 29. See also: LaPolla, 2004a: 40.

Worker
LaPolla (2004) - (n=4): TL: 2.02-2.59; HW: 0.507-0.584; HL: 0.505-0.602; SL: 0.36-0.459; ML: 0.603-0.71; GL: 0.818-1.28; CI: 96.68-106.53; SI: 69.70-78.87.

Head: yellow; typically broader than long; covered in a thick layer of appressed hairs, with shorter erect hairs toward posterior margin; posterior margin entire to slightly concave; 9-11 segmented, incrassate antennae; scape reaches to posterior margin; mandible with 4-5 teeth; 3rd tooth smaller than others when 5 teeth present; apical tooth often distinctly longer than other teeth; inner mandibular margin and anterior c1ypeal margin at slight less than right angles to each other. Mesosoma: yellow; covered in thick layer of appressed to erect hairs; pronotum in lateral view rises toward rounded mesonotum; mesonotum slightly higher than propodeum, dorsally with longer erect hairs and thick layer of appressed hairs; metanotal area distinct; propodeum with short erect hairs; declivity steep. Gaster: petiole thick and erect, slightly thinner toward apex, reaching height of propodeal spiracle; gaster yellow; covered in a thick layer of appressed hairs with many erect hairs throughout.

Queen
LaPolla (2004) - (n=2): TL: 3.07-3.11; HW: 0.698-0.736; HL: 0.597-0.615; SL: 0.508-0.515; ML:1.08-1.1; GL: 1.37-1.41; CI: 116.92-119.67; SI: 69.02-73.78. As in worker with modifications expected for caste and the following differences: brownish-yellow; eyes black; head much broader than long; apical tooth very long, almost 2x length of 2nd tooth.

Male
LaPolla (2004) - (n=1): TL: -; HW: 0.381; HL: 0.402; SL: 0.304; ML: 0.687; GL: -; CI: 94.78; SI: 79.79.

Head: brownish-yellow, brown toward apex around 3 prominent ocelli; head longer than broad; eyes large, filling nearly all of lower lateral sides of head; covered in a layer of appressed to short erect hairs; 12 segmented antennae; scapes surpass posterior margin by about half the length of pedicel; c1ypeus broad, slightly convex, with erect hairs; mandible with 3 distinct teeth, the 2nd tooth smaller than others; a diastema present between apical and 2nd teeth; gap present between inner mandibular margin and anterior c1ypeal margin. Mesosoma: pronotum collar-like, overarched by mesonotum; mesonotum flat, covered in appressed to short erect hairs; propodeum flat with short erect hairs; declivity steep. Gaster: petiole erect, slightly convex at apex; gaster brownish-yellow, lighter than head and mesosoma; covered in appressed hairs, with scattered suberect to erect hairs throughout. Genitalia: parameres taper to a point; parameres with many long erect hairs across surface; cuspi bent toward digiti, and meet digiti dorsally; both structures with short, peg-like teeth at apex; digiti thick, rounded apically.

Type Material
Brachymyrmex decedens Mayr, 1887: 521 (w.q.m.). 6 syntype workers, 3 syntype queens, 1 syntype male, BRAZIL: St. Catharina (G. Mayr) (NHMV) [examined]. The designated lectotype is a worker labeled JSL TYPE # 115 and is deposited at NHMV. Emery, 1906: 184, first combination in Rhizomyrma; Emery, 1925: 29, first combination in Acropyga.

References based on Global Ant Biodiversity Informatics

 * Borgmeier T. 1927. Um caso de trophobiose entre uma formiga e um parasita do caféeiro. Boletim do Museu Nacional de Rio de Janeiro 3: 285-289.
 * Dias N. S., R. Zanetti, M. S. Santos, J. Louzada, and J. H. C. Delabie. 2008. Interaction between forest fragments and adjacent coffee and pasture agroecosystems: responses of the ant communities (Hymenoptera, Formicidae). Iheringia, Sér. Zool., Porto Alegre, 98(1): 136-142.
 * Fichaux M., B. Bechade, J. Donald, A. Weyna, J. H. C. Delabie, J. Murienne, C. Baraloto, and J. Orivel. 2019. Habitats shape taxonomic and functional composition of Neotropical ant assemblages. Oecologia 189(2): 501-513.
 * Franco W., N. Ladino, J. H. C. Delabie, A. Dejean, J. Orivel, M. Fichaux, S. Groc, M. Leponce, and R. M. Feitosa. 2019. First checklist of the ants (Hymenoptera: Formicidae) of French Guiana. Zootaxa 4674(5): 509-543.
 * Groc S., J. H. C. Delabie, F. Fernandez, M. Leponce, J. Orivel, R. Silvestre, Heraldo L. Vasconcelos, and A. Dejean. 2013. Leaf-litter ant communities (Hymenoptera: Formicidae) in a pristine Guianese rainforest: stable functional structure versus high species turnover. Myrmecological News 19: 43-51.
 * Kempf, W.W. 1972. Catalago abreviado das formigas da regiao Neotropical (Hym. Formicidae) Studia Entomologica 15(1-4).
 * LaPolla J.S. 2004. Acropyga (Hymenoptera: Formicidae) of the world. Contributions of the American Entomological Institute 33(3): 1-130.
 * Rosa da Silva R. 1999. Formigas (Hymenoptera: Formicidae) do oeste de Santa Catarina: historico das coletas e lista atualizada das especies do Estado de Santa Catarina. Biotemas 12(2): 75-100.
 * Silva R.R., and C. R. F. Brandao. 2014. Ecosystem-Wide Morphological Structure of Leaf-Litter Ant Communities along a Tropical Latitudinal Gradient. PLoSONE 9(3): e93049. doi:10.1371/journal.pone.0093049