Wasmannia auropunctata

An infamous tramp ant that has been introduced to many areas outside of its native range. It has a notoriously strong sting for an ant of its size. Longino & Fernández (2007) offered the following account of one myrmecologist's experience with this ants famous stinging abilities: These are extremely tiny ants, barely visible in the field. When the senior author first began studying ants in Costa Rica, he was at first puzzled about Wasmannia. By literature accounts Wasmannia was reputed to have a terrible sting, but he had been collecting them for months in Corcovado National Park without ever experiencing the famous sting. One day he was collecting from a populous nest and some workers made it up to the soft skin of his inner forearm and began to sting. The sting was definitely noticeable, about as severe as a fire ant (i. e., Solenopsis geminata) but inordinately strong for an ant that could barely be seen! Workers are so small they cannot sting through the thicker skin of the hands.

Identification
Workers of Wasmannia auropunctata have a strongly quadrate petiolar node. The anterior face of the node is sharply differentiated from both the peduncle and the dorsal face of the node, meeting both at nearly right angles, and forming a strongly step-like profile. This is a highly distinctive feature that easily distinguishes auropunctata workers from all other Wasmannia species. (Longino & Fernández 2007)

There is considerable variation in the development of head sculpture and color.

Wetterer and Hita-Garcia (2015) - Tetramorium caldarium workers are similar in body size, proportions, and color to another tramp ant species, Wasmannia auropunctata. Wasmannia auropunctata, however, is slightly smaller, has longer setae on the face and dorsum, longer propodeal spines, and a more rectangular petiole in side view. Another important key difference is the presence of a two-segmented antennal club in W. auropunctata compared to the three segmented club of T. caldarium. The latter also has very weak frontal carinae and reduced antennal scrobes while both of these characters are strongly developed in W. auropunctata.

Distribution based on Regional Taxon Lists
Afrotropical Region: Cameroun, Gabon, Sierra Leone. Australasian Region: Australia, New Caledonia. Indo-Australian Region: Hawaii, Solomon Islands, Vanuatu. Nearctic Region: Canada, United States. Neotropical Region: Antigua and Barbuda, Argentina, Aruba, Barbados, Belize, Bermuda, Bolivia, Brazil, Colombia, Costa Rica, Cuba, Dominican Republic, Ecuador, French Guiana, Galapagos Islands, Guadeloupe, Guatemala, Haiti, Honduras, Lesser Antilles, Mexico, Netherlands Antilles, Panama, Paraguay, Peru, Puerto Rico, Saint Lucia, Uruguay, Venezuela. Palaearctic Region: Israel.



Biology
Longino & Fernández (2007) - Wasmannia auropunctata is a widespread pest ant (Clark et al., 1982; De Souza et al., 1998; Fabres & Brown, 1978; Jourdan, 1997; Lubin, 1984; Ulloa Chacon & Cherix, 1990; Williams, 1994; Wetterer & Porter, 2003). In its presumed native range it occurs from Argentina to Mexico (Kempf, 1972; Wetterer & Porter, 2003). Its introduced range includes the Galapagos Islands, West Africa (Gabon, Cameroon, and possibly the Republic of Congo and the Democratic RepubIic of Congo), Melanesia (New Caledonia, Solomon Islands, Vanuatu, and possibly Tuvalu), Polynesia (Wallis and Futuna and Hawaii), parts of the US (Florida and possibly California), and subtropical Atlantic islands (the Bahamas and Bermuda) (Wetterer & Porter, 2003). It is widespread on Caribbean islands, but it is unclear whether these are long-term native populations or recent introductions (Wetterer & Porter, 2003).

The species is remarkably catholic in its habitat preference. It is common in habitats ranging from wet to dry and from early successional to mature. In an elevational gradient of mature wet forest on the Atlantic slope of Costa Rica (the Barva Transect, from La Selva Biological Station to 2000 m elevation on the slope of Volcan Barva) it is abundant at 50 m and 500 m elevations, but nearly absent at 1070 m. In the lowland habitats where it is abundant, it occurs in leaf litter on the forest floor and at all levels in the vegetation.

Although it occurs frequently in samples from mature forest habitats in Costa Rica, it is never so abundant in those habitats that it is noticeable as a pest or appears to be displacing other native species (Tennant, 1994; McGlynn & Kirksey, 2000; pers. obs.). In contrast, in certain agricultural habitats (banana plantations) and in parts of the tropics where it has been introduced it becomes super-abundant, with negative impacts on native species and human comfort (Clark et al., 1982; Wetterer & Porter, 2003). In dry-forest fragments in Colombia there is a negative correlation between W. auropunctata abundance and overall ant diversity (Armbrecht & Ulloa Chacon, 2003). Where introduced in New Caledonia it invades dense native forest and displaces native ants (Le Breton et al., 2003). Behavioral tests and cuticular hydrocarbon analysis show that W. auropunctata is multicolonial in its native range in Brazil, unicolonial where introduced in New Caledonia (Errard et al., 2002).

Nests can be almost anywhere: in rolled leaves or dead sticks in the leaf litter, under stones, in rotten wood, in hollow stems suspended above the ground, in ant-plant domatia, and under epiphytes. Workers are omnivorous scavengers and predators and can rapidly recruit to food. Colonies are polygynous and it is never clear where colony boundaries are. Dozens of dealate queens may be found together in nests. Males are rare but do occasionally occur.

Surprisingly, the chemical and toxicological nature of the venom of W. auropunctata has not been investigated. Howard et al. (1982) discovered an alkylpyrazine compound in the mandibular glands, which acted as an attractant to conspecifics and a repellent to heterospecifics. They speculated that the workers might apply the mandibular gland product as an irritating secretion, augmenting the defensive properties of the venomous sting. It would be interesting to investigate whether the venom alone is the powerful agent in this small ant, or if the strong burning sensation is a synergetic effect of venom plus mandibular gland product.

Cuezzo et al. (2015) - Kusnezov (1952) hypothesized parthenogenetic reproduction by this species given the high prevalence of colonies containing only females, this was later confirmed by Fournier (et al., 2005). The LFA displays extraordinary reproductive polymorphism with both regular sexual and unusual clonal populations (Foucaud et al., 2007). This rare type of clonality was also recently reported for the invasive longhorn crazy ant Paratrechina longicornis (Pearcy et al., 2011). This unusual reproductive system is postulated to be responsible for unicoloniality, in which individuals from different nests form a large supercolony, an attribute that probably contributes to the success as an invader (Orivel et al., 2009).

Although numerous studies were conducted on the LFA in northern South America (Ulloa-Chacón & Cherix, 1990, de Souza et al., 1998, Foucaud et al., 2009, Orivel et al., 2009), little is known about populations at the southern limit of its native range (Kuznezov, 1952, Rey et al. 2012, Calcaterra et al., 2012).

Bertelsmeier et al. (2015a, b) examined elements of interspecific aggression, and food resource discovery and dominance, between this species and several other highly invasive ants. In laboratory assays Wasmannia auropunctata was the most tenacious in direct interactions. Of the group of four species that were found to be aggressive, W. auropunctata was found to be the slowest discoverer of and recruited the fewest workers to food in a laboratory arena experiment.

Foraging
Rosumek (2017) assessed trophic resource use and period of activity within the ant community in a southern Brazil Atlantic forest. For this species: A large body of knowledge describes how W. auropunctata dominate habitats and displace other ants, which often happens when the species is introduced or, within its native range, in crops and other open/disturbed areas. The species is portrayed feeding virtually on everything: scavenging; preying on small and large arthropods; collecting diversified plant parts; visiting extra-floral nectaries and tending honeydew-producing insects (Creighton, 1950; Kusnezov, 1952; Smith, 1954; Smith, 1965; Fabres & Brown, 1978; Clark et al., 1982; Deyrup et al., 2000; Wetterer & Porter, 2003; Longino & Fernández, 2007). Some of these authors suggest that honeydew is their main resource, such as Clark et al. (1982).

A comparatively small amount of information suggests that, inside forests within its native range, the species is not nearly as dominant (Majer & Delabie, 1999; Longino & Fernández, 2007). Very little is known about W. auropunctata habits in this context. Using generic baits, Orivel et al. (2009) showed a steep decline in bait use and nest density within a gradient from open areas to undisturbed forest. In Atlantic forest, ca. 1400 km north of the present study site, Santana et al. (2013) qualitatively showed it interacting with seven non- myrmecophorous diaspores on the ground.

In light of this previous work, it was really surprising to find the species to be a strict specialist in feces. In fact, it was the only species in this study that used a single resource. It was a comparatively frequent species, but appeared always in low numbers and was not collected in pitfalls. This result differs from the widespread use of fleshy diaspores found in Santana et al. (2013), and also from the use of baits in Orivel et al. (2009). The latter authors suggested that abiotic factors play a role in the ecological shift of W. auropunctata from open to forest areas. A physiological constraint related to environmental conditions (e.g. temperature) could explain why the species has a limited role inside forests, and why, in a higher latitude, it shifts to a resource less preferred by other species.

This species showed no preference in its time of foraging.

Argentina
Cuezzo et al. (2015) - W. auropunctata is widely distributed in Argentina; however, it is common only in anthropic habitats, mostly in northeastern Argentina (Rey et al., 2012; L.A.C, unpublished data). Nests are usually found in urban areas under stones, around or inside tree trunks, and under sidewalks. W. auropunctata was found in Lozano (34º51´S, 59º03´W, 45m, Francisco Sola coll.) in Buenos Aires province, representing the southernmost record reported so far for this species. Unexpectedly, it was also found for the first time in the arid desert of the Monte ecoregion from Salta province to the locality of Anillaco (28°49’S, 66°56’W, Adriana Aranda coll.) in La Rioja province, and up to 2125 m elevation in the locality of Tumbaya (23º51’S, 65º28’W), Puna ecoregion, Jujuy province. Wasmannia auropunctata is uncommon in minimally disturbed native habitats where ant assemblages are typically more diverse compared with anthropic habitats (L.A.C., unpublished data). Though scarce in native forests in northern Argentina (L.A.C., unpublished data). W. auropunctata was only common in one type of agricultural habitat (banana plantations) in the Jujuy (Yungas) and Formosa (Chaco) provinces.

Two specimens of gynandromorphs were found in a nest of W. auropunctata with putatively sexual castes reproducing clonally, in Colón (32º14´S, 58º08´W), Entre Ríos province, Argentina. This is the first record of gynandromorphs occurring naturally in a LFA colony, however, additional gynandromorphs have been found recently in natural populations of W. auropunctata in São Sebastian, Brazil (LAC, unpublished data) and also found by F. Cuezzo in series of W. auropunctata collected by N. Kusnezov and deposited in IFML. Gynandromorphs previously have been found in clonal LFA colonies that were exposed to temperatures of more than 40°C in the laboratory (Olivier Rey, personal communication). They could have been induced in the laboratory during embryonic development by the effect of the extremely high rearing temperature. Gynandromorphism is common in Hymenoptera (ants: Jones & Phillips, 1985; bees: Wcislo et al., 2004). These sexual mosaics have been reported in more than 40 ant species (Jones &Phillips, 1985) but, to date, their production has only been explained in two cases: sub-lethally high breeding temperature in the pharaoh’s ant, Monomorium pharaonis (L.) (Berndt & Kremer, 1982), and Wolbachia infections in the isopod Armadillidium vulgare (Rigaud & Juchault, 1993).

The wide distribution and relatively high abundance of W. auropunctata could be explained by the fact it has the largest and most fecund queen within the genus (Kusnezov, 1952; Longino & Fernández, 2007). However, the higher abundance of W. auropunctata in disturbed habitats, mostly in central-eastern Argentina, seems to be more related with the fact that sexual castes are produced almost exclusively by clonal reproduction (clonal populations) in this region (Rey et al. 2012, LAC, unpublished data).

Clonal populations of W. auropunctata were found up to 2125 m elevation in the locality of Tumbaya, Jujuy. This was surprising because it had been previously found only up to approximately 1070 m elevation (Wetterer & Porter, 2003). The discovery of W. auropunctata in the Puna ecosystem (Tumbaya, Jujuy) under extremely cold and dry conditions (annual rainfall 179 mm and mean and minimum temperatures of 8.1ºC and -8ºC in July, the coldest month, De Fina, 1992) was unexpected. According to Kusnezov (1952), W. auropunctata was not able to resist prolonged drought. However, our finding supports laboratory evidence that clonal populations present in Argentina are strongly adapted to very low temperatures and probably also to low levels of humidity in environments such as the Puna. This record represents both the highest altitude and the most severe natural environmental conditions reported so far for this species.

Florida
Deyrup, Davis & Cover (2000): A common species in south Florida, occurring sporadically as far north as Marion County. Nests are in leaf litter, in rotten wood or hollow twigs on the ground, at the bases of trees, and frequently in flower pots. Habitats that are wet or dry, shaded or open, are ail acceptable. On some sites the populations are huge, the massed workers forming golden patches on the underside of any object that has been left on the ground, but it is generally a minor species in the fauna. Where it is most abundant, it is easy to see how this ant could become a major pest (because of its powerful sting) and reduce populations of native species, as it has in the Galapagos (Clark et al. 1982, Lubin 1984). We have recently found sites on the island of New Providence, Bahamas, with huge concentrations of W. auropunctata. The factors that trigger or support these outbreaks are unknown. At two outbreak sites in south Florida there are unusual concentrations of plants that produce large amounts of extra-floral nectar, and are visited day and night by hordes of W. auropunctata. It may be that this resource has tipped the balance in favor of W. auropunctata and caused these very local outbreaks.

This species is a general scavenger, and seems quite dependent on extra-floral nectaries. Pest status: this species packs a sting out of all proportion to its size, and humans are frequently stung by ants that have fallen out of trees, or are foraging across lawn chairs, or floating on the surface of swimming pools. Foraging columns often move for many yards, and may invade homes, where stray ants sting the occupants. First published Florida record: Smith 1929; earlier specimens: 1924.

Castes
Longino & Fernández (2007) - There appear to be two size classes of queens. Queens with smaller heads include ten from various sites in Costa Rica, including La Selva Biological Station and the Penas Blancas Valley, one from Jamaica, and one from Venezuela. Queens with large heads are all from the Atlantic slope of Costa Rica. Three are from La Selva (two from different Winkler samples of sifted leaf litter from the forest floor, one from a small nest under an epiphyte mat in an old treefall) and one is an alate queen found in a Cecropia sapling near Volcan Arenal. Thus the small-headed and big-headed forms are broadly sympatric in Costa Rica. Among the small-headed queens four are definitively associated with workers from the same colony, and among the big-headed queens one is associated with workers. Others have workers doubtfully associated (together in the same Winkler sample). We can discern no differences in workers associated with the two types of queens. The cause of the two size classes of queens is unknown, but could reflect either differences between cryptic species or intraspecific polymorphism.

An aberrant worker form is frequently encountered in large samples of W. auropunctata. These aberrant workers have the head grossly swollen. The entire head is more spherical than normal, as if the head were inflated like a balloon. The rest of the body is little different from a normal worker. These aberrant workers are occasionally encountered in Winkler samples that contain hundreds or thousands of auropunctata workers.

Cuezzo and Calcaterra (2015) - Two sympatric sizes of gynes were described in Costa Rica on the basis of their head size (Longino & Fernández, 2007) and could represent either differences between cryptic species or intraspecific polymorphisms. Gyne variation in head size was not observed in Argentina. Argentinean queens were most similar to the small headed form found in Costa Rica, Jamaica, and Venezuela (Longino & Fernández, 2007). According to Kusnezov (1952), the worker size of populations of W. auropunctata from Misiones province differ from the size of workers found in other populations elsewhere in Argentina; however, we have not observed such variation.

Nomenclature

 *  auropunctata. Tetramorium auropunctatum Roger, 1863a: 182 (w.q.m.) CUBA. Wheeler, G.C. & Wheeler, J. 1954d: 444 (l.). Combination in Ochetomyrmex: Forel, 1886b: xlix; in Wasmannia: Forel, 1893g: 383. Senior synonym of atomum: Wheeler, W.M. 1922a: 912; of glabra: Kempf, 1964e: 66; of panamana: Brown, 1948d: 102; of australis, laevifrons, nigricans, obscura, pulla, rugosa: Longino & Fernández, 2007: 276.
 * rugosa. Ochetomyrmex auropunctatus var. rugosus Forel, 1886b: xlix (w.) GUATEMALA. Santschi, 1929d: 299 (q.m.). Combination in Wasmannia: Forel, 1901c: 128. Subspecies of auropunctata: Emery, 1888c: 353. Junior synonym of auropunctata: Longino & Fernández, 2007: 276.
 * australis. Wasmannia auropunctata var. australis Emery, 1894c: 193 (w.) BRAZIL. Junior synonym of auropunctata: Longino & Fernández, 2007: 276.
 * laevifrons. Wasmannia auropunctata var. laevifrons Emery, 1894c: 193 (w.) BOLIVIA. Wheeler, W.M. 1925a: 36 (q.). Junior synonym of auropunctata: Longino & Fernández, 2007: 276.
 * nigricans. Wasmannia auropunctata var. nigricans Emery, 1906c: 160 (w.) PARAGUAY. Junior synonym of auropunctata: Longino & Fernández, 2007: 276.
 * obscura. Wasmannia auropunctata var. obscura Forel, 1912g: 1 (w.) COLOMBIA. Junior synonym of auropunctata: Longino & Fernández, 2007: 276.
 * atomum. Xiphomyrmex atomum Santschi, 1914d: 370 (w.) GABON. Combination in Wasmannia: Santschi, 1916b: 504. Subspecies of auropunctata: Santschi, 1916b: 504. Junior synonym of auropunctata: Wheeler, W.M. 1922a: 912.
 * weiseri. Wasmannia sulcaticeps var. weiseri Forel, 1914d: 281 (q.m.) ARGENTINA. Junior synonym of auropunctata: Longino & Fernández, 2007: 281.
 * glabra. Wasmannia glabra Santschi, 1931c: 272 (q.) FRENCH GUIANA. Junior synonym of auropunctata: Kempf, 1964e: 66.
 * pulla. Wasmannia auropunctata st. pulla Santschi, 1931c: 272 (w.) PANAMA. Junior synonym of auropunctata: Longino & Fernández, 2007: 277.
 * panamana. Hercynia panamana Enzmann, J. 1947a: 44, pl. 5 (w.q.) PANAMA. Junior synonym of auropunctata: Brown, 1948d: 102.

Worker
Cuezzo et al.(2015) - (n=10): HL: 0.55-0.61; HW: 0.42-0.48; EL: 0.11-0.13; SL: 0.35-0.40; AD: 0.20-0.27; PSL: 0.13-0.20; WL: 0.51-0.55; PD: 0.10-0.12; PTL: 0.12-0.15; PPTL: 0.10-0.12; PTW: 0.10; PPTW: 0.15-0.17; CI: 0.91-0.93; OI: 0.20-0.21.

Color reddish-yellow to orange brown, variable. Frons between frontal carinae punctate, covered with irregular striae. Only 5-6 striae reach vertexal margin of head. Occipital margin of head with short, curved setae. One curved and long seta present at posterior end of frontal carinae. There are three long hairs on each frontal carina, arranged longitudinally and curved inwards. Antenna with 11 segments. Shallow antennal scrobe, with sculpture similar to rest of head. Preocular carina runs along ventral margin of scrobe. Disc of clypeus striate. Clypeal striae weakly developed, running longitudinally. Masticatory margin of mandible with five teeth, no denticles and basal margin without teeth or denticles. Compound eye well developed, protruding from lateral margin of headin full face view. Malar space with 4-5 longitudinal irregular carinae. Vertexal margin straight. Promesonotum with 3-4 pairs of long, simple, and curved setae (length approx. 0.1 mm). Humeral angle well developed, without hairs. Mesosomal dorsum reticulate-punctuate. Propodeum with one pair of straight setae shorter than promesonotal setae. Long propodeal spines weakly curved inwards in dorsal view. In lateral view, propodeal spines shorter than or equal to length of petiole and posteriorly directed. Petiole rectangular, with 1-2 pairs of setae, similar in longitude to those of propodeum, anterior face well differentiated, forming a well defined angle with dorsal face. Mesosoma, petiole, and postpetiole, in lateral view, strongly spotted. Metapleural gland strongly developed, bulky. Posteropropodeal lobe rounded and well developed. Petiolar peduncle approximately of same length as petiole in lateral view. Very short acute spine present in anterior ventral face of peduncle. In dorsal view, petiole is long with rounded anterior edge, tapering towards apex. Postpetiole quadrate and wider than long, in dorsal view. Gaster weakly punctuate, with long, curved setae, scattered along each segment.

Queen
Cuezzo et al. (2015) - (n = 17): HL: 0.69-0.74; HW: 0.77-0.84; EL: 0.21-0.26; WL: 1.47-1.57.

Color and pilosity similar to worker. Head wider behind compound eyes. Scape barely reaches vertexal margin. Frontal carina separated by 10-12 longitudinal, poorly developed and irregular striae. Antennal scrobe deep and reticulate, with longitudinal carina that starts atventral margin of antennal torulus and almost reaches posterior margin of compound eye. Preocular carina runs along ventral margin of scrobe almost to occipital angle of head. Compound eye well-developed, located close to anterior margin of head, and protruding. Antena with 11 segments; apical club with two antennomeres. Mandibular dorsum with longitudinal, thin striae. Masticatory margin of mandible with five teeth. Malar space with three to four longitudinal striae. Disc of clypeus with more than 10 well developed, longitudinal striae. Pronotum poorly developed anterodorsally scutum encompasses more than half of mesosoma in dorsal view. Humeral angle rounded. Mesonotum dorsally striate, with thin, irregular striae and poorly developed. Axilla well developed, almost triangular and continuous in midline by narrow strip of integument. Middle area of scutellum with a deep, longitudinal groove. Anapleural sulcus completely divides anepisternum from the katepisternum. Anepisternum, katepisternum and metakatepisternum finely striate. Propodeal spine thick at its base. Propodeal lobe rounded. Fore and hind wings infuscate. Fore wing with three closed cells: costal, radial (=basal) and cubital (=subbasal). No closed discal cell. Hind wing with a closed radial cell and cubital cell, almost entirely delimited by veins. Hamuli composed by five hooks. Cinctus 1 and 2 well-developed. Petiolar peduncle longer than petiolar node in lateral view. Sterno-postpetiolar process sharp and short. Metasoma III weakly punctuate, covered with sparse, subdecumbent and thin setae.

Male
Cuezzo et al. (2015) - (n = 10): HL: 0.6-0.68; HW: 0.55-0.62; EL: 0.27-0.32; WL: 1.32-1.57.

Head oval in full face view. Mandible falcate with four teeth. Antenna with 13 segments, last antennomere of funicle longer than the rest. Scape not reaching frontovertexal margin of head. Compound eye well developed, covering more than half of lateral side of head. Three well developed ocelli are present; lateral ocellus reaches frontovertexal margin of head. Area between ocellicarinulate. Several diagonal carinae present in malar space and clypeal disc. Clypeal disc covered with parallel longitudinal carinae. Axillae medially compressed on middle of mesonotum; anterior and posterior margins nearly parallel. Fore and hind wing venation similar to queen. Petiolar node quadrate in profile, but with angles (anterior and posterior) not as strongly marked as worker. Postpetiole narrowly attached to abdominal segment III. Abdominal sternum IX (=subgenital plate) medially projected as a triangle and distally rounded. Pygostyles well developed, one segmented. Telomere elongated, finger like, ventrally curved, longer than basimere, distal width 0.05 mm. Digitus and cuspis poorly developed. Digitus stout and strongly curved ventrally. Ventral margin of aedeagus denticulate.

Gynandromorphs
Cuezzo et al. (2015) - (n = 2): HL: 0.70-0.75; HW: 0.70 (measured only in the specimen with a head shape similar to a normal male); EL: 0.32; SL (right scape): 0.50, (left scape): 0.25; WL: 1.60-1.62.

These are unusual sexual caste specimens because the left side of their head and antennae are similar to those of a normal male, but the right side has the characteristics of a queen. In one specimen, both compound eyes are less developed than in a normal male, but larger than a queen´s eyes (EL: 0.325). In the second specimen the left side of the head, including eyes and antennae, is similar to a male, while the right side is similar to a queen. In this specimen both antenna scrobes are well developed. In this last specimen, the left antenna is similar to a male and the right one has the same shape of the queen antenna. In both specimens, meso and metasoma are similar to a normal male, with similar wing venation and a male external genitalia. The only difference noted in the genitalia is referred to the development of the telomere. In both gynandromorphs the telomere is more stout (distal width: 0.1 mm) than in a normal male. Pygostyle is also longer than in a normal male.