Pachybrachis xanti Crotch, 1873

Barney, Robert J., 2019, Definition and Revision of the Pubescens Species-Group of North American Pachybrachis Chevrolat (Coleoptera: Chrysomelidae: Cryptocephalinae), Including Descriptions of Three New Species, The Coleopterists Bulletin 73 (4), pp. 1017-1048 : 1031-1032

8. Pachybrachis xanti Crotch, 1873 ( Fig. 8 ; Map 2A)

Pachybrachys xanti Crotch 1873: 32 . LeConte 1880: 205 (taxonomy).

Pachybrachys xanti: Clavareau 1913: 108 [incorrect subsequent spelling]; Fall 1915: 333 (taxonomy).

Pachybrachis xanti: Riley et al. 2003: 165 (catalogue).

Types. Crotch (1873) described P. xanti from LeConte’ s specimens from Lower California. The J. L. LeConte collection (MCZ-LEC) has four males and one female. One male, labeled “[cut silver locality disc signifying Baja California] // J. L. LeConte / Coll. // Type [printed, white paper] / 5046 [hand-inked, red paper pasted on white paper] // [circular blue disc signifying dissection by RJB] // Pachybrachys / xanti / ♂ ♀ Cr [hand-inked, white paper] // LECTOTYPE / Pachybrachys / xanti Fall 1915 / design. R. J. Barney 2019 [printed, red paper]”, was examined, dissected, and photographed is and hereby designated lectotype to stabilize the epithet ( Fig. 8 ).

Redescription. Male. Very robust, primarily yellow, sparsely covered in white pubescence; prothorax with narrow, entire or subentire, smooth median line; L = 2.18–3.17 mm (mean = 2.78 mm, n = 12); W = 1.35–1.98 mm (mean = 1.69 mm, n = 12); L/W = 1.62–1.69 (mean = 1.65, n = 12). Head: Not distinctly wider than thoracic apex, HW = 0.87–1.14 mm (mean = 1.00 mm, n = 12); eyes widely separated, IOD = 0.24–0.45 mm (mean = 0.33 mm, n = 12); IOD/HW = 0.24–0.43 (mean = 0.33, n = 12); face primarily yellow with median brown area between eyes, sparsely covered in white pubescence; antennae yellow-brown, not reaching elytral declivity. Pronotum: Primarily yellow with complete or partial, faded, orange-red, M-shaped markings, with a narrow, partial or entire, smooth median line, sparsely covered with white pubescence; PL = 0.90–1.27 mm (mean = 1.12 mm, n = 12); PW = 1.18–1.69 mm (mean = 1.49 mm, n = 12); PL/PW = 0.73–0.78 (mean = 0.75, n = 12). Elytra: Primarily yellow, strial punctures dark, sparsely covered with white pubescence. Pygidium: Yellow with white pubescence. Venter: Brown with white pubescence. Legs: Primarily yellow with white pubescence; front claws not enlarged. Genitalia. Median lobe in en-face view with large, oval OS, gently rounded sides to an extended, prominent nodule with visible setae on each side. Base to nodule straight in lateral view. Fifteen males from four USA states and two Mexican states were dissected.

Female. As in male, except L = 3.07–3.85 mm (mean = 3.49 mm, n = 10); W = 1.92–2.26 mm (mean = 2.10 mm, n = 10); L/W = 1.60–1.70 (mean = 1.66, n = 10); HW = 1.08–1.29 mm (mean = 1.21 mm, n = 10); IOD = 0.40–0.62 mm (mean = 0.51 mm, n = 10); IOD/HW = 0.35–0.49 (mean = 0.42, n = 10).

Remarks. In Fall’ s (1915) key for pubescent species, he grouped P. analis , P. desertus , P. marmoratus , and P. xanti in couplet 3 with a defining character of “Prothorax with narrow entire or subentire smooth median line”. Pachybrachis xanti and P. marmoratus were separated from P. analis and P. desertus by their “prothorax being conical, widest at base, sides less rounded”. Unfortunately, one can find gradations between the extremes of “parallel-sided, black” P. analis and the “conical, widest at base, rufo-testaceous” P. xanti .

In this present study, P. xanti specimens were separated from P. analis strictly on the following external characteristics: primarily yellow; larger; widest across humeri, narrowing to the head and elytral apices, thus creating a smaller L/W ratio; and pronotum widest at base, flaring out to the edges of the elytra. However, no appreciable difference was consistently noted between the aedeagal median lobes of these specimens and the P. analis group described previously. While future work may prove P. xanti another synonym of P. analis , I am leaving it as a separate species for now.

Distribution. Pachybrachis xanti is found on Baja California Peninsula, in northern Mexico, and north in Arizona and New Mexico (Map 2B). Arizona is a new state record for P. xanti .

Biological Notes. Labels on specimens examined reported the following possible plant associations: A. monogyra in Baja California Sur and L. tridentata in Arizona and New Mexico. Some beetles were caught by blacklight in Arizona and Mexico.

Specimens Examined. See Appendix 8.

Figures

Fig. 8. Pachybrachis xanti, lectotype. A–B) Dorsal and lateral habitus, respectively, C) Face, D) Pygidium, E–F) Median lobe of aedeagus, lateral and en-face views, respectively.