Pristomyrmex

Hita Garcia, Wiesel and Fischer (2013) - A moderately sized genus distributed in the Afrotropical, Malagasy, Oriental, and Indo-Australian regions, but also in smaller areas of the Palaearctic. The genus taxonomy is in a good state. Wang (2003) revised the genus on and provides good species keys. Most species of Pristomyrmex can be found in rainforests (Wang, 2003), although the Afrotropical representatives seem to be less restricted to this habitat and can be found in a variety of forest types and in more open woodlands (Bolton, 1981a). Their diet is most likely carnivorous and they nest in the soil, the leaf-litter, in rotten wood, or around plant roots (Taylor, 1965b; Bolton, 1981a; Wang, 2003). Some species display "faking-death" behaviour if disturbed, and some species are nocturnal.

Identification
From Wang (2003): Pristomrymrex belongs to the subfamily Myrmicinae. It possesses a raised transverse ridge or a few toothlike prominences on the dorsal labrum in all female castes, including workers, ergatoid queens, and queens. This character is also shared by the myrmicine genera Acanthomyrmex, Myrmecina, and Perissomyrmex. As a result, these four living genera are grouped together in the tribe Myrmecinini (Bolton, 1994, 1995, personal communication; Brown, 1971). Pristomyrmex is unique in the tribe because it is the only genus possessing 11 antennal segments in all three female castes and 12 segments in the male.

Pristomyrmex species groups

Distribution
From Wang (2003): Pristomymrex occurs primarily in the Oriental region, but six endemic species are present in the eastern rainforest of Australia and five endemic species in Africa. In addition, in Mauritius there are three native species, one of which also occurs on Reunion Island. Lastly, one species, Pristomyrmex punctatus, has invaded temperate China, Korea, and Japan. This species has also been detected at two entry ports in the United States and thus shows potential for spread via human commercial actions.

Biology
From Wang (2003): Most species dwell in the rainforest, foraging as predators or scavengers. An Asian species, Pristomyrmex punctatus, however, occurs in open and disturbed habitats (e.g., bare hills, agricultural areas, and beaches). These ants prefer to nest in soil, litter, or rotten wood; in rotten parts of living trees; in dead standing trees; or around plant roots.

Pristomyrmex is of great interest because it exhibits several unusual biological and evolutionary phenomena. The absence of morphologically normal queens and reproduction primarily by unmated workers in P. punctatus {=P. pungens) is a highly unusual life history in the Formicidae. Ergatoid queens, a special wingless female caste morphologically intermediate between the queen and the worker, are present in at least four species: Pristomyrmex punctatus, Pristomyrmex africanus, Pristomyrmex wheeleri, and Pristomyrmex mandibularis; two of them (P. africanus and P. wheeleri) possess both queen and ergatoid queen castes.

Simulating death, slowness of movement, and nocturnal foraging has been recorded in Pristomyrmex (Donisthorpe, 1946; Taylor, 1965; Weber, 1941). Colony size varies greatly among species, ranging from about a dozen to several thousand workers (Donisthorpe, 1946; Itow et al, 1984; Mann, 1919; Taylor, 1965, 1968).

Bolton (1981) noted the following regarding the African fauna: Most Pristomyrmex species nest in rotten wood, either in fallen twigs in the litter layer or in larger pieces of timber. Some nest in rotten parts of standing trees but most appear to prefer the ground, foraging in the leaf litter and top soil. Of the five African species three, Pristomyrmex fossulatus,Pristomyrmex cribrarius and Pristomyrmex trogor, seem fairly limited in distribution, with the first known from South Africa, the second from South Africa and Mozambique, and the latter only from Zaire. Pristomyrmex orbiceps is widely distributed throughout the wet forest zones of west and central Africa whilst the last species, Pristomyrmex africanus, has an extremely wide range and seems able to inhabit woodlands and forests virtually throughout sub-Saharan Africa.

Nomenclature

 *  PRISTOMYRMEX [Myrmicinae: Myrmecinini]
 * Pristomyrmex Mayr, 1866b: 903. Type-species: Pristomyrmex pungens, by monotypy.
 * Pristomyrmex senior synonym of Odontomyrmex: Mann, 1919: 341; Emery, 1924d: 233.
 * Pristomyrmex senior synonym of Hylidris: Brown, 1953c: 9.
 * Pristomyrmex senior synonym of Dodous: Brown, 1971a: 3.
 * DODOUS [junior synonym of Pristomyrmex]
 * Dodous Donisthorpe, 1946f: 145. Type-species: Dodous trispinosus, by original designation.
 * Dodous junior synonym of Pristomyrmex: Brown, 1971a: 3.
 * HYLIDRIS [junior synonym of Pristomyrmex]
 * Hylidris Weber, 1941a: 190. Type-species: Hylidris myersi (junior synonym of Pristomyrmex africanus), by original designation.
 * Hylidris junior synonym of Pristomyrmex: Brown, 1953c: 9.
 * ODONTOMYRMEX [junior synonym of Pristomyrmex]
 * Odontomyrmex André, 1905: 207. Type-species: Odontomyrmex quadridentatus, by monotypy.
 * Odontomyrmex subgenus of Pristomyrmex: Forel, 1917: 244; Wheeler, W.M. 1922a: 682.
 * Odontomyrmex junior synonym of Pristomyrmex: Mann, 1919: 341; Emery, 1924d: 233; Taylor, 1965b: 35; Bolton, 1981b: 282.

Wang (2003):

Diagnosis of worker, queen, and ergatoid queen. Combination of the following asterisked four characters (i.e., characters 2, 7, 11, and 29 in the worker caste) separating Pristomyrmex from other myrmicine genera.

Worker
Possessing the following combination of characters:

1. Small (TL 1.74, HL 0.46, HW 0.46) to large-sized (TL 7.06, HL 1.68, HW 1.74) monomorphic myrmicine ants.

2.(*) Mandible somewhat subtriangular; masticatory margin of mandible with three to five teeth, which have one or the other of the following six basic arrangements:

(1) the strongest apical + the second strongest preapical + the smallest third + the acute basal tooth, diastema lacking, as in levigatus group and in profundus group, or

(2) the strongest apical + the second strongest preapical + two smaller teeth of similar size, diastema indistinct or lacking, as in umbripennis group, or

(3) the strongest apical + the second strongest preapical + a shorter (first) diastema (sometimes the first diastema is not distinct) + a small denticle + a longer (second) diastema + a small basal denticle, as in both P. bispinosus and P. trispinosus, or

(4) the apical + the preapical + a longer diastema + a small denticle + a shorter diastema (sometimes the second diastema is indistinct) + a small basal denticle, as in P. browni, or

(5) the strongest apical + the second strongest preapical + a distinct diastema + a basal tooth (which is sometimes formed by the fusion of the two small teeth) or two (or three) small teeth of similar size, as in punctatus group, cribrarius group, and most members of the quardridens group, or

(6) the strongest apical + the second strongest preapical + an intercalary tooth + a very short diastema (or this diastema indistinct) + two small teeth of similar size, as shown in P. trachylissus.

3. Basal margin of mandible with a broad-based hiangular or an acute and prominent tooth, or only curved, not forming tooth, or almost straight.

4. Median part of clypeus shieldlike, projecting posteriorly between the bases of the antennae; lateral parts of clypeus in front of antennal insertions usually reduced to ridges but rarely (in the two Oriental species P. divisus and P. pulcher) developed so that the antennal fossae do not reach the lateral anterior margins of clypeus.

5. Anterior clypeal margin usually with a median tooth and one to three pairs of lateral denticles (or crenulate shapes) but sometimes the median tooth rudimentary (as in some species of the levigatus group) and sometimes anterior clypeal margin lacking any distinct denticles (as in P. profundus, P. divisus, and P. pulcher).

6. Ventral surface of clypeus with a median tooth or two lateral teeth, or with a transverse ridge, or without any ridge or tooth.

7.(*) Dorsal labrum with a raised transverse ridge or a few toothlike prominences, present on the anterior portion of labrum in most species.

8. Palp formula 1,2, 1,3, 2,2, 2,3, 4,3, or 5,3.

9. Frontal lobes absent in punctatus and trispinosus groups or weak, as in levigatus, profundus, and quadridens groups, or somewhat expanded, as in umbripennis group; as a result, the articulations of the antennae are mostly or entirely exposed in full-face view.

10. Frontal carinae usually developed, extending to the level of the posterior margins of eyes, but sometimes frontal carinae absent or very short, as in the trispinosus group, in P. trogor, and in P. longispinus.

11.(*) Antennae with 11 segments; apical three segments forming a distinct club.

12. Base of each antennal scape encircled by a narrow lamella, except in P. profundus; this lamella usually with a broad and deep notch on the center of dorsal surface in the umbripennis group but entire in the other species groups.

13. Antennal scrobes usually absent or weakly developed, but in P. profundus, the scrobes are deep and well developed.

14. Eyes present in all known species, situated approximately at the midlength of the sides of the head; usually moderatesized, but small in the several species (P. boltoni, P. coggii, P. longus, P. eduardi, P. picteti, and P. pollux).

15. Alitrunk usually lacking dorsal sutures, but in the three species of the trispinosus group, a promesonotal suture or impression present.

16. Pronotum unarmed, or armed with a pair of tubercles, teeth, or spines of varying sizes.

17. Mesonotum usually unarmed, but with a pair of thick, blunt, and digitlike short prominences in P. trispinosus, and sometimes weakly tuberculated in P. bispinosus and P. browni.

18. Propodeum armed with a pair of teeth or spines, except in P. inermis.

19. Metapleural lobes usually subtriangular, or each with a blunt-rounded to semicircular apex, but indistinct in P. profundus.

20. Fore tibial spurs pectinate. Middle and hind tibiae sometimes without any spur, sometimes with either simple or hairlike spurs.

21. Propodeal spiracles circular and high-positioned on the lateral surfaces of the propodeum.

22. Metapleural gland bullae large, separated from the propodeal spiracles, and positioned above the posterior lower corners of propodeum.

23. Petiole in profile nodiform or wedge-shaped, pedunculate, usually with a long anterior peduncle.

24. Subpetiole sometimes without a ventral process, sometimes bearing a narrow semitranslucent lamella. In P. acerosus, a pinlike process is present.

25. Postpetiole in profile nodiform, usually rounded dorsally.

26. Petiole spiracle, postpetiole spiracle, and first gastral spiracle visible.

27. Dorsal surfaces of head and alitrunk smooth, or possessing either scattered foveolate punctures, or foveolate-reticulate sculpture, or developed rugoreticulum, or regular striate sculpture. Gaster unsculptured.

28. Dorsal surfaces of head and alitrunk usually with numerous hairs, but only a few hairs present on the dorsal alitrunk in P. fosslilatus, P. orbiceps, and P. trogor. Petiole and postpetiole each usually with one to three pairs of hairs, but sometimes more pairs of hairs present; sometimes petiole and postpetiole lacking hairs. First gastral tergite usually without hairs or with a few sparse hairs, but sometimes first gastral tergite covered with numerous, evenly distributed, erect or suberect hairs.

29. (*) Anterior clypeal margin lacking a median seta at the midpoint of the margin, instead usually having two to three pairs of long, forward-projecting hairs flanking the midpoint of margin.

30. Sting slender and long.

Queen
Usually alate, but in some species (P. punctatus, P. mandibulans), only ergatoid queens have been found. In some species (P. wheeleri, P. africanus), both alate and ergatoid queens exist.

Alate. Characters similar to those of worker in the structure and shape of mandible, palp formula, clypeus, frontal lobes, frontal carinae, antennae, metapleural lobes, tibial spurs, petiole node, postpetiole, and sting as well as in the sculpture of body. But larger, with slightly or much larger eyes, than in the conspecific worker; three ocelli present. The alitrunk with wings and flight sclerites; well-marked dorsal sutures present. Pronotal spines usually absent, but in some species, the pronotum is armed with a pair of teeth that are much shorter than in conspecific worker; propodeal teeth or spines usually shorter than those of conspecific worker. Wing venation as shown in Figure. On the forewings, the marginal cell (see Holldobler and Wilson, 1990: 9) is always open; R + Sc thick (for the explanation of symbols used, see Brown and Nutting, 1950); A short, far from the anal angle; A, Cu-A, Mf2+3 usually reduced to vestigial lines distally; cross-vein m-cu and r-m absent; cross-vein Cu-a usually present but sometimes broken in larger species (such as P. picteti, P. umbripennis) and sometimes rudimentary or very weak in some samples of a few smaller species (e.g., P. orbiceps, P. lucidus); 1r absent; anal lobe usually indistinct in smaller species but present in larger species. Hind wings without anal lobe. (Note: The venation of the both fore and hind wings of alates, in Pristomyrmex, is rather stable, with only slight variations within the different species. For example, on the forewings, Mf2+3, sometimes becomes an almost entirely vestigial line, but sometimes it is distinct and rather long; Rsf4 + Rsj5 is rather thick and long in some larger species but thin and short in some smaller species).

Ergatoid. General characters, including the pronotal prominences and size of body, similar to those of the conspecific worker. Ocellus present (one ocellus in P. mandibularis but three ocelli in P. punctatus, P. wlteeleri, and P. africanus); apterous, but mesonotum more convex than in conspecific worker; pro-mesonotal suture present in P. mandibularis but represented by an impression in P. punctatus, P. wheeleri, and P. africanus''.

Male
Possessing the following combination of characters (summarized according to 54 specimens falling into at least 17 species):

1. Small to moderate size (TL 2.40-6.04, HL 0.48-0.94, HW 0.51-0.98, HWE 0.62- 1.10), usually smaller than the conspecific queen.

2. Head, in full-face view, across and including the eyes, usually broader than long.

3. Mandibles vestigial, very small, rounded or toothlike, far from meeting.

4. Anterior margin of labrum broadly concave at center; dorsum of labrum without any transverse ridge or toothlike prominences.

5. Eyes very large, well developed, and convex, situated at the sides of head.

6. Antennae filiform, 12 segments, lacking a lamella encircling the base. Scapes short, usually distinct shorter than the maximum length of eye; of the other 11 funicular segments, the first segment shortest, the apical segment longest, the remaining nine segments much longer than their broad.

7. Three ocelli conspicuous and well developed, situated on the vertex of the head.

8. Antennal sockets set back from the posterior margin of the clypeus.

9. Antennal scrobes absent.

10. Frontal carinae absent or very short and weak.

21. Venation as in alate queen.

22. Legs slender; fore tibial spurs pectinate; middle and hind tibiae usually lacking any spurs but sometimes simple spurs are present.

23. Petiole with a long or a rather long anterior peduncle. In dorsal view, sides of petiole subparallel. Petiole node low, lower than in the conspecific worker and queen; subpetiole lacking any lamella or toothlike projection.

24. Postpetiole node rather low, lower than in the con specific worker and queen. In profile, subpostpetiole usually lacking any projections, but sometimes bearing a small tooth.

25. Positions of spiracles on propodeum, petiole, postpetiole, and first gastral segment similar to those in the con specific worker and queen.

26. Usually much less sculptured than conspecific worker and queen.

27. Numerous hairs present on the entire dorsal surfaces of body.

Larva
According to Wheeler and Wheeler's (1954, 1960, 1973, 1976) studies, the larva of Pristomyrmex has the following combination of characters:

1. Stout and rather short.

2. Head extremely long and narrow.

3. Thorax more slender than abdomen and forming a neck, which is curved ventrally. Diameter greatest near middle of abdomen, decreasing gradually toward head; posterior end rounded.

4. Body without tubercles.

5. Mandible s subtriangular, without medial blade; apical tooth curved medially and usually acute; subapical medial tooth small.

6. Body hairs numerous, with five or six types, including anchor-tipped hairs. Head hair few, short to moderately long.

7. Gula spinulose.

8. Anterior surface of labium densely spinulose.

9. Palps lateral.

Pupa. Not enclosed in cocoons (Wheeler and Wheeler, 1976).