Pachybrachis thoracicus Jacoby, 1889

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 : 1032-1034

9. Pachybrachis thoracicus Jacoby, 1889 ( Fig. 9 ; Map 2B)

Pachybrachys thoracicus Jacoby 1889: 136 . Fall 1915: 330 (taxonomy).

Pachybrachis thoracicus: Riley et al. 2003: 163 (catalogue).

Types. Jacoby (1889) described P. thoracicus based upon a single female from Pinos Altos, Chihuahua, Mexico (Buchan-Hepburn Collection). Fall (1915) acknowledged that the Jacoby specimen was from Pinos Altos but made no mention of having access to the beetle. A specimen labeled “ARIZ: Santa Cruz / Co., Sycamore Cyn / 5mi. SE Ruby / VII 19/20-1978 // ex: / Salix sp. // Collectors / A. J. Gilbert / M. E. Gilbert // [circular blue disc signifying dissection by RJB]” was examined, dissected, and photographed ( Fig. 9 ).

Redescription. Male. Robust, black, prothorax at base and raised basal margin of elytra orange-red, densely covered in white pubescence; L = 3.01–3.44 mm (mean = 3.21 mm, n = 10); W = 1.64–1.89 mm (mean = 1.75 mm, n = 10); L/W = 1.79–1.90 (mean = 1.84, n = 10). Head: Not distinctly wider than thoracic apex, HW = 1.02–1.22 mm (mean = 1.11 mm, n = 10); eyes moderately separated, IOD = 0.25–0.34 mm (mean = 0.31 mm, n = 10); IOD/HW = 0.23–0.30 (mean = 0.28, n = 10); face black, densely covered in white pubescence; antennae black, not reaching elytral declivity. Pronotum: Black with basal margin orange-red, densely covered in white pubescence; PL = 1.02–1.20 mm (mean = 1.12 mm, n = 10); PW = 1.53–1.81 mm (mean = 1.67 mm, n = 10); PL/PW = 0.62–0.70 (mean = 0.67, n = 10). Elytra: Black, raised basal margin orange-red, covered with white pubescence. Pygidium: Black, covered with white pubescence. Venter: Black, orange-red areas as above, with white pubescence. Legs: Black with white pubescence; front claws not enlarged. Genitalia. Median lobe in en-face view with large, oval OS, gently rounded sides to extended, prominent nodule with visible setae on each side. Base to nodule straight in lateral view, although moderately inflated. Eight males from four USA states and one Mexican state were dissected.

Female. As in male, except L = 3.07–3.95 mm (mean = 3.48 mm, n = 10); W = 1.81–2.23 mm (mean = 1.93 mm, n = 10); L/W = 1.67–1.89 (mean = 1.81, n = 10); HW = 1.05–1.33 mm (mean = 1.18 mm, n = 10); IOD = 0.37–0.47 mm (mean = 0.43 mm, n = 10); IOD/HW = 0.34–0.39 (mean = 0.37, n = 10). Some female specimens have noticeable orange-red markings on the elytra and legs.

Remarks. Pachybrachis thoracicus is instantly recognizable due to the orange-red “band” across the pronotal-elytral interface and the dense, silvery white pubescence. The aedeagal median lobe is very similar to that of P. analis and P. xanti ; however, in

P. thoracicus , the nodule is not as extended, and the shaft appears to be wider.

Distribution. Pachybrachis thoracicus is found from southern Nevada and Utah to the mid-Pacific coast of Mexico (Map 2B). Nevada and Utah are new state record s for P. thoracicus .

Biological Notes. Specimens were reported collected on A. greggii , Parkinsonia sp. , Prosopis sp. , and Salix sp. in Arizona. Four specimens were reportedly found in a boll weevil trap in Arizona.

Specimens Examined. See Appendix 9.

Figures

Fig. 9. Pachybrachis thoracicus, Gila Co., Arizona. A–B) Dorsal and lateral habitus, respectively, C) Face, D) Pygidium, E–F) Median lobe of aedeagus, lateral and en-face views, respectively.