Probolomyrmex Mayr, 1901

Oliveira, Aline M. & Feitosa, Rodrigo M., 2019, Taxonomic revision of the genus Probolomyrmex Mayr, 1901 (Hymenoptera: Formicidae: Proceratiinae) for the Neotropical Region, Zootaxa 4614 (1), pp. 61-94 : 64-65

Probolomyrmex Mayr, 1901

Type-species: Probolomyrmex filiformis , by monotypy. Mayr, 1901: 2.

Probolomyrmex in Dorylinae, Dorylini: Ashmead, 1905: 381; Ashmead, 1906: 27.

Probolomyrmex in Ponerinae, Cerapachyini: Wheeler, 1910: 137.

Probolomyrmex in Ponerinae, Proceratiini: Emery, 1911: 52; Arnold, 1915: 33; Forel, 1917: 236; Wheeler, 1922: 645; Donisthorpe, 1943: 686; Chapman & Capco, 1951: 77.

Probolomyrmex in Ponerinae, Platythyreini: Brown, 1952: 1; Brown, 1975: 7 ; Dlussky & Fedoseeva, 1988: 79; Hölldobler & Wilson, 1990: 10; Jaffe, 1993: 7; Bolton, 1994: 164.

Probolomyrmex in Probolomyrmecinae: Perrault, 2000: 271.

Probolomyrmex in Proceratiinae, Probolomyrmecini : Bolton, 2003: 49, 180.

Genus diagnosis. Worker (after Taylor, 1965; Agosti, 1994; Eguchi et al. 2006; Keller, 2011; and this study): Small monomorphic ants. Body color from pale yellow to reddish brown. Integument opaque and covered by extremely fine pubescence, small punctures or foveae; foveae generally deeper and more visible on first segment of gaster.

Head foveated, interval between foveae covered by micropunctures. Antennal scapes densely punctate, with sparse small foveae. Dorsum of mesosoma and metasoma with incomplete (open posteriorly) foveae; latero-dorsal region of pronotum with micropunctures and sparse foveae.

Outer surface of mandibles with thick and short setae. Antennal funiculi with abundant pubescence and relatively long appressed hairs set in longitudinal grooves, space between hairs filled by short hairs.

Head longer than wide, with broadly convex sides. Sclerites of the anterior frons and the clypeus are highly fused and extend anteromedially beyond the clypeo-labral articulation, forming a shelflike platform that projects anteriorly covering mandibles in full-face view. Antennae with 12 segments; antennal insertions fully exposed, positioned on frontoclypeal shelflike projection and separated by narrow vertically raised carina, which is formed by the fusion of the frontal carinae. Mandibles small and triangular, hidden in frontal view by frontoclypeal shelflike projection; each mandible has a well-developed apical tooth followed by series of denticles; palpal formula 4,2; three basal maxillary palpomeres equal in size, and apical one longer; labial palpomeres equal in size. Eyes absent, except for holotype of P. brevirostris Forel , one worker of P. dentinodis sp. n., and two workers of P. kelleri sp. n.

Mesosoma slender and long in profile, with dorsum flat to weakly convex, without visible promesonotal and metanotal sutures, which are represented only by weak ventro-lateral superficial lines. Propleuron inflated, projecting ventrally. Propodeal declivity usually posteriorly emarginated on each side by low and obtuse carina, which can present an apical tooth. All tibiae with single pectinate spur; tarsal claws simple, without internal teeth.

Petiolar node narrow and strongly elevated, with uniform antero-dorsal curve in profile; posterior face high and usually concave in lateral view. Subpetiolar process present. First and second segments of gaster separated by constriction. First segment of gaster with tergite and sternite fused laterally forming tubular structure. Sting welldeveloped.

Queen (after Taylor, 1965; Agosti, 1994; Eguchi, et al. 2006; and this study): Size, color, sculpturing, structure of head, appendages, and metasoma as in workers. Additionally, queens present well-developed eyes, three ocelli similar in size and associated to dark spots. Pronotum subtriangular in lateral view. Mesoscutum and scutellum shield-shaped; transcutal suture straight; notauli absent; parapsidal lines vestigial. Mesopleural sulcus diagonal, rendering katepisternum triangular. Metanotum convex. Flight sclerites developed in most species. Wings long and narrow, venation greatly reduced. Forewings with Sc+R and M+Cu forming submedian cell; veins 2r-rs, Cu, cu-a e A not extending to external border of wing. Posterior wings with short R-Rs and A veins; three submedian hamuli present.

Male (after Eguchi et al. 2006; Yoshimura & Fisher, 2009; and this study): Head subglobose, frontoclypeal shelflike projection not as strongly projecting as in workers and queens. Antennae with 13 segments; scapes relatively long. Eyes well developed, occupying half of head lateral margins; three ocelli present. Metepisternum separated from propodeum by a strong suture. Wings as in female.

Comments. Probolomyrmex can be easily recognized from the other genera of Proceratiinae mainly by the shape of the gaster. The second gastral sternite is not reduced, so the gaster is tubular and not bent antero-ventrally as in Discothyrea and Proceratium .

In the Neotropical region it is found from northern Argentina to southern Mexico, mainly in the leaf-litter of rainforests. In the Indo-Pacific Region Probolomyrmex is divided into two species-groups ( Eguchi et al. 2006), P. greavesi group and P. longinodus group. Both species-groups occur from India east to Australia, with the greavesi group extending on to the Solomon Islands. In Australia, species can be found in habitats ranging from rainforests, Eucalyptus woodlands to spinifex grasslands ( Shattuck et al. 2012). In the Afrotropical region the genus is well distributed in sub-Saharan forests ( Hita Garcia et al. 2013). In Madagascar, species can be found in several environments, such as tropical dry forest, littoral rainforest, lowland rainforest, and montane rainforest ( Hita Garcia & Fisher, 2014).

Some species of Probolomyrmex present the postero-ventral lobe of the petiole subquadrate and lack a prora. On the other hand, species with a rounded postero-ventral lobe of the petiole often possess a prora. This could suggest a relationship between these structures, possibly involving a distinct bending mechanism of the gaster when ants are capturing (stinging) or transporting prey. The presence of a fitting mechanism between the prora and subpetiolar process could improve precision and better allow the sting to reach the mandibular region where the prey would be grasped.

Thus, when bending the gaster forwards, and engaging the prora in the subpetiolar process, the postero-ventral lobe of the petiole could serve as a support, when they are rounded; in species with a subquadrate subpetiolar process, it would be an obstacle for that fitting to occur, therefore the prora is absent. In addition, if this fitting mechanism really occurs, it is possible that it causes friction between these two structures, which could explain the small differences in the degree of development of the prora and the subpetiolar process observed in individuals of the same species, such as in P. kelleri sp. n.

This fitting mechanism between prora and subpetiolar process may occur in other genera in which these structures are present, as in Gnamptogenys , Prionopelta , Pseudoponera , and Thaumatomyrmex . In these groups, and even in the remaining proceratiine genera, the morphology of the abdomen seems to be closely related to alimentary habits ( Hölldobler & Wilson, 1990). However, more detailed observations should be made to confirm this condition.

Little is known about the feeding habits of Probolomyrmex , except for observations by Ito (1998) on the Oriental species P. dammermani Wheeler feeding on polyxenid millipedes. Different kinds of potential prey were offered to colonies of P. boliviensis kept in artificial conditions, but none were accepted ( Taylor, 1965).