Acropyga

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Acropyga
Temporal range: 19–0 Ma
Early Miocene – Recent
Acropyga bakwele
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Formicinae
Tribe: Plagiolepidini
Genus: Acropyga
Roger, 1862
Type species
Acropyga acutiventris
Diversity
41 species
1 fossil species
(Species Checklist)

Acropyga bakwele casent0104123 dorsal 1.jpg

Acropyga bakwele

Acropyga bakwele casent0104123 profile 1.jpg

Specimen Label

Synonyms
Evolutionary Relationships
Formicinae

Myrmelachistini
  (2 genera)




Lasiini
  (9 genera)




Melophorini
  (9 genera)




Formicini
  (8 genera)





Gesomyrmex, Oecophylla


Plagiolepidini

Anoplolepis
  (14 species)





Tapinolepis
  (18 species)




Aphomomyrmex
  (1 species)



Petalomyrmex
  (1 species)







Lepisiota
  (135 species)



Plagiolepis
  (80 species)





Acropyga
  (41 species)




Agraulomyrmex
  (2 species)



Undescribed genus










Gigantiops, Myrmoteras, Santschiella



Camponotini
  (8 genera)








Based on Ward et al. 2016.

Acropyga are found world wide in warm temperate and tropical areas. Workers are small, found mainly in soil or under objects. They rarely forage on the surface and are presumed to subsist entirely on their obligatorily-tended mealybugs, which they tend for honeydew.

Identification

LaPolla (2004) - Workers can be separated from other formicine ants by a combination of possessing 11 or fewer antennal segments; tubular, elongate torulae; small eyes (generally only a few facets) that are laterally placed at lower 1/4 of head; low palp formula (less than 6:4); large, round propodeal spiracles; and heads and gasters covered in a dense layer of short appressed hairs with scattered erect hairs throughout. Queens are very similar in general appearance to workers, though they always possess large, flat mesonota. Males are more difficult to diagnose, though they always have 12 or fewer antennal segments, palp formulae less than 6:4, and large, prominent genitalia.

Keys including this Genus

Keys to Species in this Genus

Distribution

LaPolla (2004) - Acropyga are limited to warm temperate and tropical areas around the world. In the New World, Acropyga occur from southern Arizona into northern parts of Argentina, and from the Lesser Antilles and Hispaniola (though curiously they are absent from elsewhere in the Greater Antilles). Two species are currently known from Africa, one in southern Africa, the other in West and East Africa. A single species is restricted to the Palaearctic having been found only in Greece. In the Indo-Australian/Oriental regions, species are known from warmer parts of temperate Japan and China, south through Australia. Acropyga have been found as far east as the Solomon Islands, west to India and Sri Lanka. Acropyga are present in all regions except the Malagasy.

World distribution based on political regions. View/Edit Data
Acropyga Distribution.png Worlddistribution legend.jpg

Species richness

Species richness by country based on regional taxon lists (countries with darker colours are more species-rich). View Data

Acropyga Species Richness.png

Biology

A nest under a large log in rainforest, Danum Valley, Sabah, Malaysia

LaPolla published a worldwide revision of the Acropyga in 2004 and the following synopsis is based on this excellent treatment of the genus. In overall appearance, Acropyga are small, robust, yellowish ants possessing a thin, easily collapsible cuticle. The species generally appear rather similar to each other morphologically. There are currently ~ 40 known species. The species diversity of the genus could increase significantly as litter sampling techniques are being more widely adopted and employed by ant collectors. In the past Acropyga have been poorly collected, and underrepresented in major ant collections, likely due to their being overlooked. An important implication of this poor collecting coverage is that our understanding of the range and habitat affinities of most species should, at best, be considered preliminary in nature.

An Acropyga goeldii worker carries a mealybug. Viçosa, Minas Gerais, Brazil (image by Alex Wild).

In some species workers and queens display an unusual range of phenotypic variation. Antennal segment number, for example, can vary within and between species and even a single specimen may possess differing antennal segment numbers from one antenna to the other. Workers in numerous speices possess one more antennal segment than conspecific males.

The small eyes, reduced antennae segmentation, lightly pigmented cuticle, and hairs covering the cuticle of Acropyga species are suggestive of a completely subterranean existence. Species also display photophobic behavior (Weber, 1944; LaPolla et al., 2002). Acropyga can survive in a wide range of habitats, from deserts to rainforests, though they do not seem able to survive in regions where temperatures below freezing persist for several months at a time. Some species, such as Acropyga pallida and Acropyga silvestrii for example, are found within a very wide range of habitats. Undoubtedly, the Acropyga lifestyle of existing below the surface buffers them against extremes of the outside environment. Acropyga nests are found in leaf litter, under stones, in rotten wood (lying on or near the soil surface) and in the soil. Species in which nesting habits are known possess large, consisting of at least several thousand individuals, the structure of which is diffuse, with apparently no central nesting location (LaPolla et al., 2002). Tunnels and indistinct chambers stretch out over large areas through the nesting medium. Polygyny has been suggested for several species. The origins of polygyny remains uncertain, but two routes are suggested based on field observations. Biinzli (1935) found both the occurrence of pleometrosis (founding of a colony by multiple queens) and the acquisition of young queens by established colonies in Acropyga exsanguis.

Profile view of an Acropyga glaesaria paratype, carrying mealybug in mandibles.

All Acropyga are thought to be hypogaeic (living entirely underground), surviving primarily, it is believed, by "tending" mealybugs (Hemiptera: Pseudococcidae) on underground roots for their exudate (sometimes referred to as "honeydew") (Weber, 1944; Williams, 1998). This mutually beneficial relationship is called trophobiosis (Holldobler and Wilson, 1990).

Mating pair of Acropyga sauteri. Note queen carrying a mealybug in her mandibles. This mealybug is a "seed individual" used by the queen to establish a new generation of mealybugs within her newly founded ant colony.

Evidence suggests that all Acropyga species are obligate coccidophiles, in other words the ants are dependent on the mealybugs for survival. The strength of this association is shown by a number of observations. Queens of eleven species have been observed emerging from their nests prior to their mating flight with a mealybug held in their mandibles (Biinzli, 1935; Wheeler, 1935b; Brown, 1945; Eberhard, 1978; Prins, 1982; Buschinger et al., 1987; Williams, 1998; Johnson et al., 2001). The mealybug that each queen carries presumably serves as a "seed individual" from which a new generation of mealybugs will be started in the newly founded ant colony (Weber, 1944; Williams, 1998). This behavior is called trophophoresy (LaPolla et al. 2002) with queens exhibiting this behavior said to be trophophoretic. The mealybugs utilized by Acropyga belong to the subfamily Rhizoecinae, and it is likely that the mealybugs are not able to survive independently of the ants (Williams, 1998). LaPolla et al. (2002) observed that Acropyga epedana keeps mealybugs with their brood. When a nest in captivity was starved, workers refused a variety of food items presented to them, suggesting that the ants are completely dependent on the mealybugs as a food source.

Fossil evidence suggests that the trophobiotic behavior ofAcropyga ants is an ancient one. Johnson et ai. (2001) first reported this relationship from specimens found in Dominican amber. Queens were holding mealybugs in their mandibles or had mealybugs nearby in the amber matrix. LaPolla (2005) described this species as Acropyga glaesaria. The amber was dated to the Miocene and is at least 15-20 million years old.

Castes

Immature Stages

LaPolla (2004) - Immature stages of Acropyga species are poorly known and a thorough analysis cannot be completed at this time. There may be an interesting trend however in that in the New World pupae have been found to be naked, while in the Old World pupae have cocoons. Given that pupae are known for only 3 species however, it is too early to draw any general conclusions.

Morphology

Worker Morphology

 • Antennal segment count 7-11 • Antennal club absent-gradual • Palp formula 5,3; 4,3; 2,3; 1,3 • Total dental count 3-7 • Spur formula 0, 0 • Eyes present • Scrobes absent • Sting absent

Nomenclature

The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

  • ACROPYGA [Formicinae: Lasiini]
    • Acropyga Roger, 1862a: 242. Type-species: Acropyga acutiventris, by monotypy.
    • Acropyga senior synonym of Atopodon, Malacomyrma, Rhizomyrma: LaPolla, 2004: 16. [The former subgenera were listed as junior synonyms in Hölldobler & Wilson, 1990: 18, without reason; reverted to subgeneric status in Bolton, 1994: 51 pending revision; formally synonymised by LaPolla, above.]
  • ATOPODON [junior synonym of Acropyga]
    • Atopodon Forel, 1912m: 771 [as subgenus of Acropyga]. Type-species: Acropyga (Atopodon) inezae, by subsequent designation of Wheeler, W.M. 1913a: 79.
    • [Atopodon also described as new by Forel, 1913k: 100.]
    • Atopodon subgenus of Rhizomyrma: Forel, 1917: 249.
    • Atopodon raised to genus: Wheeler, W.M. 1922a: 695.
    • Atopodon subgenus of Acropyga: Emery, 1925b: 30.
    • Atopodon junior synonym of Acropyga: LaPolla, 2004: 16.
  • MALACOMYRMA [junior synonym of Acropyga]
    • Malacomyrma Emery, 1922d: 109 [as subgenus of Acropyga]. Type-species: Acropyga silvestrii, by monotypy.
    • Malacomyrma junior synonym of Acropyga: LaPolla, 2004: 16.
  • RHIZOMYRMA [junior synonym of Acropyga]
    • Rhizomyrma Forel, 1893g: 347 [as subgenus of Acropyga]. Type-species: Acropyga (Rhizomyrma) goeldii, by subsequent designation of Wheeler, W.M. 1911f: 172.
    • Rhizomyrma raised to genus: Emery, 1906c: 182; Kusnezov, 1956: 33.
    • Rhizomyrma subgenus of Acropyga: Emery, 1925b: 29.
    • Rhizomyrma junior synonym of Acropyga: LaPolla, 2004: 16.

Description

LaPolla (2004):

Characters marked with an (*) are considered synapomorphies for the genus.

Worker

1) Small, robust, yellow to brownish-yellow (to occasionally slightly reddish-yellow) formicine ants (Total length up to 5 mm as found in Acropyga rubescens, typically however most species smaller, around 2 mm in total length).

2) Monomorphic.

3) Cuticle seemingly always thin, shrinkage and collapsing of cuticle commonly observed in specimens.

4) *Antennae incrassate (apical segment always the largest and thickest) with 7- 11 segments.

5) Surface of scapes and flagellae covered in thick layer of appressed hairs.

6) *Torulae tubular and elongated, touching posterior clypeal margin, typically closely set together (only in Acropyga kinomurai are torulae very widely separated from each other); small triangular area between torulae.

7) *Median portion of anterior clypeal margin always with a single hair; length of hair highly variable, sometimes surpassing apex of closed mandibles.

8) Mandibles variable, narrow to broad, with 3-9 teeth possible, though if with more than 6 teeth, some of those teeth are usually quite small (intercalary).

9) *Palpal formula always less than 6:4, typically 2 : 3 or 3 :3 , though up to 5 :4 is known in Acropyga arnoldi and Acropyga paleartica.

10) *Eyes small, typically consisting of fewer than 10 facets, though more than 20 facets observed in Acropyga acutiventris and Acropyga rubescens; eyes laterally placed, at the lower 1/4 of the head.

11) Head typically covered in a thick layer of short, appressed hairs.

12) Maximum width of pronotum wider than that of remainder of mesosoma (in dorsal view).

l3) Mesosoma and legs robust; legs always with at least a layer of appressed hairs, occasionally with scattered erect hairs as well.

14) Metanotal area variable with regards to number of sulci present, though the region is never very deeply impressed.

15) *Propodeal spiracle large and round, placed near declivity border.

16) Metapleural gland present.

17) Petiole always thick and erect, occasionally slightly inclined forward.

18) Gaster robust, rounded and larger toward petiole end from where it becomes narrower (to a point) posteriorly; in lateral view tear-drop shaped; gaster sloping toward acidopore dorsally from anterior to posterior; venter more flattened than dorsum.

19) Proventriculus asepalous (see Eisner, 1957; Prins, 1980; this study [Acropyga ayanganna, new species; Acropyga keira, new species examined]).

20) Declivity distinct and steep.

21) Mesosomal-petiole muscle insertion point round.

22) Ventral mesosomal-petiole articulation point surpasses metacoxal insertions.

Queen

23) Yellow to dark brown (almost black) in color.

24) Three ocelli present, large and distinct at apex of head.

25) Pronotum small and collar-like.

26) Mesonotum dorsum flat and wide.

27) Propodeum short, and low; declivity typically indistinct from dorsal face of propodeum.

28) Similar in overall appearance to workers (though always larger) with modifications expected for caste; antennal segment count and mandibular dentition typically same as found in workers.

Male

29) Yellow to dark brown (almost black) in color.

30) * Antennae with 8- 12 segments.

31) Three ocelli present, large and distinct at apex of head.

32) Eyes large, breaking outline of head in full face view

33) Mandibles narrow to broad, with 1 to 6 teeth possible.

34) Mesosoma robust, mesonotum large, with flat dorsum.

35) Pronotum small and collar-like.

36) Propodeum short, and low; declivity typically indistinct from dorsal face of propodeum.

37) Genitalia large (proportional to body) and prominent.

Larvae and Pupae

38) Larval body hairs adundant and of three types: simple, denticulate, and branched (Wheeler and Wheeler, 1953).

39) Pupae both naked and with cocoons; naked pupae reported for Acropyga ayanganna, new species and Acropyga keira, new species; pupae with cocoons reported for Acropyga acutiventris.

References

  • Agosti, D. 1991. Revision of the oriental ant genus Cladomyrma, with an outline of the higher classification of the Formicinae (Hymenoptera: Formicidae). Syst. Entomol. 16: 293-310 PDF (page 296, Acropyga in Formicinae, Lasius genus group)
  • Ashmead, W. H. 1905c. A skeleton of a new arrangement of the families, subfamilies, tribes and genera of the ants, or the superfamily Formicoidea. Can. Entomol. 37: 381-384 (page 384, Acropyga in Formicinae, Plagiolepidini)
  • Blaimer, B. B.; LaPolla, J. S.; Branstetter, M. G.; Lloyd, M. W.; Brady, S. G. 2016. Phylogenomics, biogeography and diversification of obligate mealybug-tending ants in the genus Acropyga. Molecular Phylogenetics and Evolution 102:20-29.
  • Biinzli, G.H. 1935. Untersuchungen iiber coccidophile Ameisen aus den Kaffeefelden von Surinam. Mitteilungen der Schweizerischen Entomologischen Gesellschaft 16:455-593.
  • Bolton, B. 2003. Synopsis and Classification of Formicidae. Mem. Am. Entomol. Inst. 71: 370pp (page 95, Acropyga transfered into tribe Lasiini)
  • Brown, W.L., Jr. 1945. An unusual behavior pattern observed in a Szechuanese ant. Journal of the West China Border Research Society 15:185-186.
  • Buschinger, J., J. Heinze & K. Jessen. 1987. First European record of a queen ant carrying a mealybug during her mating flight. Naturwissenschaften 74:139-140.
  • Dalla Torre, K. W. von. 1893. Catalogus Hymenopterorum hucusque descriptorum systematicus et synonymicus. Vol. 7. Formicidae (Heterogyna). Leipzig: W. Engelmann, 289 pp. (page 174, Acropyga in Camponotinae)
  • Dlussky, G. M.; Fedoseeva, E. B. 1988. Origin and early stages of evolution in ants. Pp. 70-144 in: Ponomarenko, A. G. (ed.) Cretaceous biocenotic crisis and insect evolution. Moskva: Nauka, 232 pp. (page 77, Acropyga incertae sedis in Formicinae)
  • Eberhard, W.G. 1978. Mating swarms of a South American Acropygia [sic.] (Hymenoptera: Formicidae). Entomological News 89(1 & 2):14-16.
  • Eisner, T. 1957. A comparative morphological study of the proventriculus of ants (Hymenoptera: Formicidae). Bulletin ofthe Museum of Comparative Zoology 116:439-490.
  • Emery, C. 1895l. Die Gattung Dorylus Fab. und die systematische Eintheilung der Formiciden. Zool. Jahrb. Abt. Syst. Geogr. Biol. Tiere 8: 685-778 (page 771, Acropyga in Camponotinae, Plagiolepidini)
  • Emery, C. 1925d. Hymenoptera. Fam. Formicidae. Subfam. Formicinae. Genera Insectorum 183: 1-302 (page 27, Acropyga in Formicinae, Plagiolepidini)
  • Forel, A. 1878c. Études myrmécologiques en 1878 (première partie) avec l'anatomie du gésier des fourmis. Bull. Soc. Vaudoise Sci. Nat. 15: 337-392 (page 379, Acropyga as genus; Acropyga in Camponotinae [Camponotidae])
  • Forel, A. 1886a. Einige Ameisen aus Itajahy (Brasilien). Mitt. Schweiz. Entomol. Ges. 7: 210-217 (page 212, Acropyga in Camponotinae, Plagiolepidini)
  • Forel, A. 1893b. Sur la classification de la famille des Formicides, avec remarques synonymiques. Ann. Soc. Entomol. Belg. 37: 161-167 (page 165, Acropyga in Camponotinae, Plagiolepidini)
  • Forel, A. 1895b. A fauna das formigas do Brazil. Bol. Mus. Para. Hist. Nat. Ethnogr. 1: 89-139 (page 107, Acropyga in Camponotinae, Plagiolepidini)
  • Forel, A. 1912j. Formicides néotropiques. Part VI. 5me sous-famille Camponotinae Forel. Mém. Soc. Entomol. Belg. 20: 59-92 (page 88, Acropyga in Camponotinae, Plagiolepidini)
  • Forel, A. 1917. Cadre synoptique actuel de la faune universelle des fourmis. Bull. Soc. Vaudoise Sci. Nat. 51: 229-253 (page 249, Acropyga in Camponotinae, Plagiolepidini)
  • Johnson, c., D. Agosti, J.H. Delabie, K. Dumpert, OJ. Williams, M. von Tschimhaus & U. Maschwitz. 2001. Acropyga and Azteca Ants with Scale Insects: 20 Million Years of Intimate Symbiosis. American Museum Noviates 3335:1-18.
  • Klein, R.W., Kovac, D., Schellerich, A., Maschwitz, U. 1992. Mealybug-carrying by swarming queens of the Southeast Asian Bamboo-inhabiting ant. Naturwissenschften. 79: 422-423.
  • LaPolla, J.S. 2004a. Acropyga of the world. Contributions of the American Entomological Institute. 33(3):1-130. PDF (page 16, Acropyga senior synonym of subgenera Atopodon, Malacomyrma, Rhizomyrma)
  • LaPolla, J. S., Cover, S.P. and Mueller, U.G. 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(3):367-376 PDF
  • Mayr, G. 1863a. Formicidarum index synonymicus. Verh. K-K. Zool.-Bot. Ges. Wien 13: 385-460 (page 394, Acropyga as junior synonym of Plagiolepis)
  • Prins, AJ. 1982. Review of Anoplolepis with reference to male genitalia, and notes on Acropyga. Annals of the South African Museum 89:215-247.
  • Roger, J. 1862a. Einige neue exotische Ameisen-Gattungen und Arten. Berl. Entomol. Z. 6: 233-254 (page 242, Acropyga as genus)
  • Smith, F. 1871a. A catalogue of the Aculeate Hymenoptera and Ichneumonidae of India and the Eastern Archipelago. With introductory remarks by A. R. Wallace. [part]. J. Linn. Soc. Lond. Zool. 11: 285-348 (page 319, Acropyga as genus)
  • Weber, N. A. 1944b. The neotropical coccid-tending ants of the genus Acropyga Roger. Ann. Entomol. Soc. Am. 37: 89-122 (page 91, Key to Neotropical species)
  • Wheeler, G.C. & J.C. Wheeler. 1953. The ant larvae of the subfamily Formicinae. Annals of the Entomological Society of America 46:126-171.
  • Wheeler, W. M. 1910b. Ants: their structure, development and behavior. New York: Columbia University Press, xxv + 663 pp. (page 143, Acropyga in Camponotinae, Plagiolepidini)
  • Wheeler, W. M. 1922i. Ants of the American Museum Congo expedition. A contribution to the myrmecology of Africa. VII. Keys to the genera and subgenera of ants. Bull. Am. Mus. Nat. Hist. 45: 631-710 (page 695, Acropyga in Formicinae, Plagiolepidini)
  • Wheeler, W.M. 1935b. Ants of the genus Acropyga Roger, with description of a new species. Journal of the New York Entomological Society 43:321-329.
  • Williams, D J . 1998. Mealybugs of the genera Eumyrmococcus Silvestri and Xenococcus Silvestri associated with the ant genus Acropyga Roger and a review of the subfamily (Hemiptera, Coccoidea, Pseudoccidae). Bulletin of the British Museum (Natural History)(Entomology) 67:1-64.