Pseudoplisus willcoxi, Ohl, Michael, 2009

Ohl, Michael, 2009, A colorful new species of the digger wasp genus Pseudoplisus Ashmead from the Southwestern United States (Hymenoptera: Apoidea, Crabronidae), Zootaxa 2009, pp. 27-34 : 28-33

Pseudoplisus willcoxi sp. nov.

Etymology. The new species epithet, willcoxi , refers to the collecting locality of the holotype and most of the paratypes, the sandy area southeast of the city of Willcox, Cochise County, Arizona.

Diagnosis. Within Pseudoplisus , the new species is unique in its spectacular color pattern ( Figs 1–2 ): the metasoma is bright yellow and markedly contrasts with a largely black thorax and head and the dark infumate wings. Pseudoplisus willcoxi can be readily identified based on this character alone and cannot be confused with any other apoid wasp in the southwestern United States known to me.

Pseudoplisus willcoxi belongs in the assemblage of New World species with the metapleural-propodeal suture simple above the upper fossa ( Fig. 6 ). Besides the unique coloration, it differs from both possible species groups (the P. montanus and the P. abdominalis species groups) by having the lateral sulcus of the propodeal enclosure indistinctly pitted. This character state is intermediate between the two groups: in the P. montanus species group, the lateral propodeal sulcus is markedly coarsely pitted, whereas in the P. abdominalis species group the sulcus is simple or seamlike.

Description of female.

Measurements. Total body length (without appendages) 9.4–10.0 mm; maximum head width (including eyes, in frontal view) 2.38–2.45 mm; interocular ratio (maximum upper distance between eyes divided by minimum lower distance) 1.8; forewing length 8.0– 8.4 mm; hindwing length 6.4–6.9 mm.

Coloration (as in Figs. 1–3 ). Head and mesosoma black except the following. Narrow stripe along inner eye margin above and below antennal socket bright yellow. The following are reddish yellow in most specimens but distinctly yellow in some: mandibular base and antennal base to a varying extent, markings on pronotal collar, and labial and maxillary palps. Otherwise red are: most of lower portion of clypeus, pronotal lobe, one marking each on mesopleuron below and above scrobal sulcus and on metapleuron, posterolateral corner of mesoscutum, most of scutellum (except for narrow, sharply delimited anterior black band), most of metanotum, two indistinct markings on propodeal enclosure, most of propodeal side and declivity behind spiracular groove, legs completely (except narrowly black at extreme base of coxa).

Metasoma largely bright yellow, with reddish tinge on sterna I–II to a varying extent. Black are: extreme metasomal base, narrow and irregular basal markings on terga II–IV, all of tergum V except for median yellow spot, pygidial plate except for indistinct reddish marking, sterna III–VI except for some indistinct reddish markings.

Stigma and costal vein pale brown, distinctly contrasting with totally infumate wings.

Head ( Fig. 3 ). With sparse, shallow macropunctures, several puncture diameters apart, somewhat coarser on clypeus. Frontal sulcus complete from midocellus to antennal socket level. Ocelli forming low triangle. Distance between hindocelli about equal to ocellocular distance. Inner eye margins converging strongly below; minimum distance (at upper tentorial pits) about half maximum distance (across ocellar triangle). Distances between antennal sockets and between antennal socket and inner eye margin 0.5 × socket diameter each. Antennal socket placed above clypeus by slightly less than one socket diameter. Subantennal triangle about as long as broad. Scape about twice as broad as flagellomere I. Flagellomeres I–V longer than broad, VI–X broader than long. Flagellomere I 1.3–1.5 × as long as flagellomere II. Clypeal length 0.5 × maximum width. Clypeal lip with three shallow emarginations. Mandible with two median teeth on inner margin.

Mesosoma ( Figs 1–2 , 5–6 ). Virtually polished throughout. Pronotal collar narrow, evenly rounded. Pronotum coarsely but shallowly pitted at base of collar, particularly laterally. Acetabular carina reduced to tiny ventromedian elevation. Omaulus continued by sternaulus to form distinct curve from scrobal sulcus to mesopleural pit, sharply edged ventrally. Episternal sulcus weakly developed, not reaching scrobal sulcus ventrally. Scrobal sulcus distinct, continued beyond omaulus but not reaching ventral portion of pronotal lobe. Metapleural-propodeal suture indistinct above upper fossa, not pitted. Posterolateral corner of scutum somewhat translucent behind oblique scutal carina. Prescutellar sulcus pitted. Lateral and median propodeal sulci indistinctly pitted. Spiracular groove distinct, not pitted.

Base of forewing with markedly bulging costal lobe.

Legs ( Fig. 4 ). Foretarsal rake distinct, distal rake setae of tarsomeres I–III significantly longer than length of following tarsomere, respectively. Outer face of midtibia with several strong, stout setae, particularly distally. With two long midtibial spurs. Midtarsomere I with single, markedly enlarged, blade-like seta anterodistally. Outer face of hindtibia with several stout setae, which are markedly less pronounced than on midtibia. Size of arolia subequal, slightly larger on foreleg.

Metasoma. Metasomal segments I–V virtually impunctate, polished. Terga I–IV virtually asetose, fine setae dense and distinct on tergum V, setae strong on apex of pygidial plate. Metasomal sternum with dense micropubescence. Tergum I slightly longer than broad distally. Pygidial plate sharply edged, forming sharp angle apically.

Description of male ( Figs 1–6 ). As in the female, except for the following:

Measurements. Total body length (without appendages) 7.5–10.6 mm; maximum head width (including eyes, in frontal view) 1.9–2.4 mm; interocular ratio 2.1–2.3; forewing length 6.6–8.6 mm; hindwing length 5.6–6.9 mm.

Coloration. Males have significantly fewer markings on head and mesosoma, but these are yellow and markedly brighter (in some specimens markings have reddish margins). Legs generally becoming darker from fore- to hindlegs; coxae and trochanters almost completely black, femora yellow but tinged with reddish in some specimens, tibiae and tarsi mostly yellow. In most specimens, mesosoma only with narrow yellow stripe on pronotal collar and with small marking on pronotal lobe, otherwise black. Three males have one or more of the following markings: one or two tiny yellow spots on mesopleuron, tiny reddish markings on posterolateral corners of mesoscutum, and transverse reddish marking posteriorly on scutellum. Propodeal enclosure black, most of propodeal side and declivity behind spiracular groove reddish, but surrounded by distinct black.

Metasomal segments I–II completely bright yellow (except for black extreme base of I and some indistinct reddish markings). Visible part of tergites III–V and sternite III (if not exserted) bright yellow, if exserted in many dry specimens, base broadly black. Sternites IV–V with tiny yellow spots on posterior corners. Segments VI–VII black.

Head. Virtually impunctate. Antennal sockets placed above clypeus by slightly more than one socket diameter. Subantennal triangle 1.2–1.4 × as high as broad at base. Flagellomeres longer than wide, median flagellomeres indistinctly so in some specimens. Flagellomere I not or indistinctly longer than flagellomere II. Flagellomeres IV–XI externoventrally each with indistinct placoid. Clypeus about as long as wide. Clypeal lip with two small projections, bordering shallow emargination. Mandible with one subapical tooth on inner margin.

Mesosoma. Episternal sulcus not reaching scrobal sulcus below, indistinct, in some specimens virtually absent.

Legs. Foretarsal rake absent. Midtarsomere I without modified seta.

Metasoma. Terga I–III virtually asetose. Sternum IV and segments V–VII densely covered by fine, whitish pubescence. Pygidial plate absent. Sternum VIII narrowly blade-like apically, straight.

Material examined. Holotype. Male. USA: Arizona: Cochise County. 5 km SE Willcox, N32°13.011’ W109°46.917’, 9 Aug 2007, on Wislizenia refracta Engelmann, D. Linde and M. Ohl collectors ( ZMB).

Paratypes (6 Ƥ, 28 3) (duplicate paratypes will be deposited in BMNH).

USA: Arizona: Cochise County. Willcox, 28 Aug 1974, R.M. Bohart (1 3, CAS); 6 mi SE Willcox, 9 Aug 2001, M. Ohl, D. Linde, I. Maier, S. Saueracker (1 3, ZMB); same data, but 13 Aug 2001 (2 3, ZMB); same data, but 15 Aug 2001 (3 3, ZMB); 5 km SE Willcox, N32°13.011’ W109°46.917’, 17 Aug 2007, on Wislizenia refracta , V. L o h r m a n n (2 3, ZMB); same data, but 18 Aug 2007 (2 3, ZMB); same data, but 27 Aug 2007 (3 Ƥ, 2 3, ZMB); same data, but 27 Aug 2008, S. Krause (1 Ƥ, 9 3, ZMB); same data, but 28 Aug 2007 (1 Ƥ, ZMB); same data, but 17 Aug 2008, S. Krause (1 3, ZMB); same data, but 27 Aug 2008, D. Zimmermann (1 Ƥ, 3 3, NHMW); same data, but 13 Aug 2007, D. Linde, M. Ohl (1 3, ZMB). New Mexico: Hidalgo County. Animas, Bee Course 2003, L. Packer (2 3, PYU). Colorado: Huerfano County. 24 km NW Walsenburg, 15 Aug 1995, H.E. Evans (1 Ƥ, CAS).

Other species of New World Pseudoplisus and Saygorytes studied for comparison:

Pseudoplisus aequalis (Handlirsch) (Ƥ syntype of Gorytes handlirschi Cameron , BMNH); P. d i v i s u s (F. Smith) (holotype, 3, BMNH; 1 3, ZMB); P. montanus ( Cameron) (holotype, 3, BMNH; 1 Ƥ, 1 3, UCD); P. samiatus Bohart (1 Ƥ, 1 3, both syntypes, UCD; 4 Ƥ, 1 3, BMNH); P. smithii smithii (Cresson) (1 Ƥ, ZMB); P. smithii floridanus (Fox) (1 3, BMNH); P. venustus (Cresson) (1 3, BMNH; 1 3 ZMB).

Saygorytes apicalis (F. Smith) (holotype, 3, BMNH); S. oraclensis (Bohart) (1 Ƥ, 1 3, ZMB); S.

phaleratus (Say) (several specimens of both sexes, BMNH, ZMB; syntypes of Gorytes alpestris Cameron and Gorytes alticola Cameron ; BMNH).

Distribution and abundance ( Fig. 7 ). The distribution of Pseudoplisus willcoxi ranges from southeastern Arizona, southwestern New Mexico to southern Colorado. Only three specimens are currently known from localities outside of the Willcox area in Arizona. Two specimens have been collected in New Mexico by Laurence Packer in 2003. One specimen is known from Walsenburg in southern Colorado. Fig. 7 shows all collecting sites of P. willcoxi including a hypothetical distribution range based on similar patterns known for other aculeate Hymenoptera . An example is the bee Oreopasites favreauae Rozen, 1992 . This hypothetical distribution corresponds with arid and semi-arid areas at relatively low altitude, bordering the southern foothills of the Sangre de Cristo Mountains northwest of the suggested area.

We collected a relatively large series of this species in the Willcox area between 2001 and 2007, but only a single specimen is known from this area prior to this time period, collected by Richard Bohart in 1974. This is an unusual finding for two reasons. Pseudoplisus is a spectacularly coloured, relatively slow flying wasp, which immediately attracts attention when visiting flowers or flying above sandy ground. The arid and semiarid regions of southeastern Arizona and particularly the sandy areas southeast of Willcox have been exceptionally well collected for decades and have regularly been visited by sphecid wasp collectors like Richard M. Bohart, Howard, E. Evans, Arnold S. Menke, myself, and many others. It is hard to imagine that it can regularly be overlooked by collectors. Also students and instructors of the Bee Course held at the Southwestern Research Station have regularly visited this collecting site for years, but have revealed only a few specimens.

The paucity of P. willcoxi in historical collections and its relatively high abundance in recent years is difficult to explain. Population density might be very low, which would result in low collecting rates. Very short flight periods also minimize the probability of being caught in the field. Both scenarios imply that the population structure and distribution pattern of P. willcoxi has not been significantly changed and that the observed shift in specimen numbers in collections is an artifact. As implied above, I consider this very unlikely because the species is so conspicuous and the collecting locality so intensively worked on. The other explanation is that the shifted collecting rates reflect a true increase of the population density, which is hard to prove based on the available data.

Pseudoplisus willcoxi was rather common in the Willcox area in mid–late August 2007. Without exception, all specimens have been collected on the jackass-clover, Wislizenia refracta (Engelm.) , a native annul dicot, which is a common plant of alkali sink communities of the southwestern U.S. Precipitation was high until mid August 2007, so that the Willcox area was partly flooded at that time. Wislizenia refracta was fully in bloom in mid August and started to diminish in late August. With respect to apoid wasps, species diversity and specimen numbers were unusually high when blooming flowers of W. refracta were abundant. We collected the specimens of P. w i l l c o x i on flowers, which densely covered a narrow strip of a few hundred meters along the soft shoulders of an unpaved road. Towards the end of August, blooming W. refracta and the general diversity of apoid wasps appreciably decreased, whereas the population density of P. willcoxi apparently reached its seasonal peak.

Figures

FIGURE 7. Collecting localities of Pseudoplisus willcoxi sp. nov. in the southwestern United States (black dots). The shaded area represents an estimation of the minimum distribution range of this species.

FIGURES 1 – 4. Pseudoplisus willcoxi sp. nov. 1 – 3. male (holotype). 1. Body laterally. 2. Right wings. 3. Head in frontal view. 4. Right midbasitarsus, female, paratype (arrow indicates position of modified anterodistal seta).

FIGURES 5 – 6. Pseudoplisus willcoxi sp. nov., male (holotype). 5. Mesosoma in lateral view from left. 6. Illustration of major landmarks and sutures. Details explained in the text. Abbreviations: cl—costal lobe of forewing base; es—episternal sulcus; mp—upper portion of metapleural-propodeal suture; om—omaulus; pl—pronotal lobe; sc—scrobal sulcus; sg—spiracular groove; st—sternaulus; tg—tegula.