New species of Ancistrocerus (Vespidae, Eumeninae) from the Neotropics with a checklist and key to all species south of the Rio Grande

Abstract A new species of potter wasp from South America, Ancistrocerus sur sp. n., is described. A species key and checklist for all described Ancistrocerus that occur south of the Rio Grande are provided. New synonymy includes Odynerus bolivianus Brèthes = Ancistrocerus pilosus (de Saussure), while the subspecies bustamente discopictus Bequaert, lineativentris kamloopsensis Bequaert, lineativentris sinopis Bohart, tuberculocephalussutterianus (de Saussure), and pilosus ecuadorianus Bertoni, are all sunk under their respective nominotypical taxa.


Introduction
Ancistrocerus is a genus of potter wasps with a solitary lifestyle, and belongs to the subfamily Eumeninae (Vespidae). Unlike eusocial vespid wasps, mothers nest alone and rear daughters without the aid of other females, and do not provision offspring progressively throughout their larval development. Since all Ancistrocerus presumably mass provision their progeny, their sting is specialized to paralyze and preserve prey items (Cowan 1991). They prey upon Lepidopteran, Coleopteran and Hymenopteran larvae (Iwata 1971;Yamane 1990). Ancistrocerus are typically tube renters, utilizing pre-existing cavities such as borings in twigs, stems and wood, abandoned mud-dauber cells, and old burrows of ground-nesting bees and wasps to build their nest (Cowan 1991;Iwata 1971;Krombein 1979;Yamane 1990), but some species make aerial mud nests (e. g. spilogaster Cameron, 1905, lutonidus Bohart, 1974, waldenii Viereck, 1906; see Krombein 1979). Ancistrocerus occurs worldwide (except Australia), and currently 116 species (You et al. 2013), with seven occurring in the Neotropics and 22 in North America (Bequaert 1925;Carpenter and Garcete-Barrett 2003;Carpenter and Genaro 2011;Krombein 1979), have been described. Currently, 12 species have been described that can be found south of the Rio Grande.
Eumeninae phylogeny and taxonomy is not well resolved and ~65% of vespid species belong to the subfamily (Carpenter and Cumming 1985;Hermes et al. 2014;Pickett and Carpenter 2010;Vernier 1997). Recently, Eumeninae was limited to include only the tribes Eumenini and Odynerini, and is comprised of a total of 3407 described species (Bank et al. 2017;Piekarski 2017). Ancistrocerus belongs to the tribe Odynerini in the sense of Hermes et al. (2014), but that tribe was not supported by the large-scale phylogenomic analysis by Bank et al. (2017) and Piekarski (2017). Due to their close relationship to eusocial wasps, understanding the biology and relationships among solitary potter wasps has implications for the conception of how sociality emerged (Hunt 2007). Here we present a key and checklist for Ancistrocerus that occur south of the Rio Grande, and describe a new species.

Materials and methods
The specimens used in this study are deposited at the American Museum of Natural History (New York, USA). Specimens were examined under a stereomicroscope equipped with an ocular micrometer. Body length was measured from the frons to the apex of the abdomen. Photographs were taken using a Canon 7D Mark II with a Canon MP-E 65mm 1-5× Macro Photo lens. We utilized the Canon MT-24EX Macro Twin Lite for lighting, and used a custom-made diffuser to minimize hot spots. Each image is a montage of 50 layered photos that were taken using a StackShot. Photo layers were montaged using Zerene Stacker 1.04 (Zerene Systems LLC.).
Terminology follows Carpenter and Cumming (1985), and Carpenter and Garcete-Barrett (2002). Terga are referred to as T I, T II, etc. Diagnosis. This species can be distinguished from all other Neotropical Ancistrocerus using a combination of the following characters: sternum II lacking a longitudinal basomedian furrow; sternum II in lateral view strongly truncate posterior to transverse furrow (Fig. 2a); parategula broadly flattened (Fig. 3c); humeri with angular projection (Fig. 3c); T I with carina effaced dorsally (Fig. 3g); T II with punctation ending about one puncture diameter from apex (Fig. 4c); maculations reduced, on metasoma usually at most T II with a very narrow apical yellow band (Fig. 1a, b).
Description. Female. Body length 11.50-14.00 mm. Color. Almost entirely black; small traces of yellow may be present at apex of clypeus; small yellow dot in antennocular space, interantennal space, and upper gena; usually have thin, ferruginous band at apex of T II-VI and sterna II-VI (Fig. 1b). Tarsi ferruginous (Fig. 1a).
Head. Twelve antennal articles; 1st flagellomere ~1/3 the size of scape; pedicel ~1/2 size of 1st flagellomere; vertex with pubescence as long as distance between posterior ocelli; vertex with dense coarse punctures, much less dense than on clypeus; vertex without tubercle; clypeus about as long as wide, narrowed apically with slight concavity at tip; mandibles decussate, four teeth spaced along the edge; mandibular ridges present; antennal sockets less than 1/2 socket diameter away from clypeus; palpal formula 6:4; maxillary palpomere two about same length as palpomere three; a narrow interantennal distance, approximately the diameter of a antennal socket; ocello-occipital distance greater than the length of the ocellar triangle; cephalic foveae closely spaced, set in a slight medial depression which is delimited posteriorly by a carina; dorsal occipital carina simple and complete, without fork, running to mandible; gena most wide dorsally.

Metasoma.
Thin white or yellowish hairs on metasoma, longest on T I; T I carina effaced dorsally (Fig. 3g); width of T1 at least twice as long as wide; T1 without apical lamella; T II with very thin apical lamella; T II with punctation ending about one puncture diameter from apex (Fig. 4c); T I and T II punctation equally dense, but T II punctures slightly smaller; apices of terga not more punctate than rest of terga; bottom of basal sulcus with longitudinal ridges; sternum II in lateral view strongly truncate posterior to transverse furrow (Fig. 2a); sternum II without basomedian longitudinal sulcus; sterna with similar puncture size and density as corresponding terga.
Male. Body length 10.00-13.00 mm. Color. Almost entirely black; clypeus usually entirely yellow (Fig. 5b); scape may be yellow ventrally; mandible may have yellow traces; small yellow dot present on upper gena but typically absent in antennocular and interantennal space; usually have ferruginous band at apex of T II-VII and sterna II-VII (Fig. 5b). Tarsi ferruginous. Head. Identical to female, except for: 13 antennal articles; apex of antennae hooked; clypeus longer than wide, narrowed apically with slight concavity at tip; mandibles decussate, four (five on allotype) teeth spaced along the edge; cephalic foveae absent.

11
Punctation coarse on mesosoma; T II and III with punctation dense, coarser near apices than on rest of surface, apices slightly thickened or reflexed (Fig. 4f ); pubescence consisting of long hairs (Fig. 4f )  T I and II dull, with fine punctation (Fig. 4g); T I carina sharp, thin (Fig. 4g

Discussion
Color variability is usually a poor character to demarcate species due to large variability within and between closely related species, and because distantly related species occupying the same area share similar coloration patterns (Richards 1978). However, all described neotropical species, except Ancistrocerus sur, have distinct colored maculations on the mesosoma and/or metasoma. A darker gestalt is always in combination with the proposed diagnostic characters of Ancistrocerus sur, including sternum II strongly truncate posterior to transverse furrow, an effaced dorsal carina on tergum I and a projecting acute humeral angle. Although, the extent of coloration in the female clypeus varied, the lack of colored maculations on the mesosoma and metasoma is consistent across Bolivian and Argentine representatives. Thus, a lack of coloration on the metasoma and mesosoma is a reliable diagnostic character for Ancistrocerus sur.
There exists sexual dimorphism in clypeus color between males and females of Ancistrocerus sur, as well as presence/absence of yellow spots in the antennocular and interantennal space. Males lack a T2 with a reflexed apex, suggesting that the sexual dimorphism in this species may be less than in other Ancistrocerus. Typically, male vespids either have the same number of teeth as conspecific females, or fewer (Carpenter 1988b;c;Carpenter and Cumming 1985). Unusually, based on our examined material, it seems that females of A. sur have four mandibular teeth, while males tend to have five (some appearing to have four). Within Ancistrocerus there is variability as to what characters are sexually dimorphic across species. Thus, this genus may be an exceptional group for studying how traits diverge across sexes. Diagnosis. Male antenna hooked apically; female cephalic foveae closely spaced, sometimes in slight depression, nearer occipital margin than posterior ocelli, but not in distinct area of differentiated cuticle; anterior face of pronotum without medial pits or foveae (cf. Parancistrocerus); pronotal carina weak or absent dorsally, but well developed laterally; pronotum without oblique humeral carina (cf. Pachodynerus); pretegular carina present; tegula tapered posteriorly, reaching slightly beyond the parategula; axillary fossa oval, broader than long; epicnemial carina absent; midtibia with one spur; metanotum somewhat flat, without tubercles; dorsal face of propodeum short or lacking, and sloped; propodeal concavity divided by well-developed median longitudinal carina; propodeal valvula not enlarged; metasoma sessile, not petiolate; T1 with width more than half that of T2 in dorsal view, and T1 less than twice as long as wide; T1 with single transverse carina near summit; T1 without broad longitudinal median groove posterior to carina (c.f. Symmorphus); sternum II with basal transverse furrow; prestigma length < one-third stigma; second recurrent vein received by second submarginal cell; second submarginal cell not petiolate. Note: The subspecies discopictus is a minor color variant, like other cases in Eumeninae discussed by Carpenter (1988aCarpenter ( , 2003 and Carpenter and van der Vecht (1991). In its description Bequaert (1944: 269) mentioned that both it and the nominotypical form occurred in the same locality, and were connected by transitional specimens. Bequaert stated that "It may, nevertheless, be useful to distinguish the variety by name, as it parallels similar color forms of other species of Ancistrocerus in the same area" but we disagree; formal nomina are a poor way to deal with continuous variation. We therefore synonymize it. Note: The subspecies kamloopsensis and sinopis are both minor color variants, which are known to intergrade with the nominotypical form (Bequaert, 1944: 280), and we therefore synonymize them.  Bequaert, 1944, Entomol. Amer Note: The subspecies sutterianus is a minor color variant, which is known to intergrade and to co-occur with the nominotypical form (Bequaert 1944: 283), and we therefore synonymize it.