Pachybrachis dixianus Fall, 1915

Barney, Robert J., 2018, Definition and Revision of the Atomarius Species-Group of North American Pachybrachis Chevrolat (Coleoptera: Chrysomelidae: Cryptocephalinae), Including Descriptions of Nine New Species, The Coleopterists Bulletin 72 (1), pp. 9-74 : 32

12. Pachybrachis dixianus Fall, 1915 ( Fig. 12 , Map 2B)

Pachybrachys cephalicus, var. dixianus Fall 1915: 419 . New status.

Pachybrachis cephalicus, var. dixianus: Kirk 1970: 86 (regional species list); Balsbaugh and Hays 1972: 33 (taxonomy); Riley et al. 2003: 156 (catalogue).

Type Material. Fall’ s male type, herein designated as lectotype and labeled “Tumblin Gap Ala / June 3-8 ’11 / H.P.Löding // 6 // TYPE / var- [printed, white paper] / dixianus [hand-written] // M.C.Z. / Type [printed] / 24933 [hand-written, red paper] // H.C. FALL / COLLECTION // LECTOTYPE 24933 / Pachybrachys / dixianus Fall 1915 / R. J. Barney 2017 [printed, red paper]”, was examined, photographed, and dissected ( Fig. 12 ) .

Redescription. Male. Yellow with fuscous punctures, standard maculae diffuse; L = 1.91– 2.16 mm (mean = 2.02 mm, n = 11); W = 1.01–1.15 mm (mean = 1.08 mm, n = 11); L/W = 1.83–1.97 (mean = 1.86, n = 11). Head: Slightly wider than thoracic apex, HW = 0.71–0.83 mm (mean = 0.77 mm, n = 11); eyes moderately separated, IOD = 0.19–0.25 mm (mean = 0.22 mm, n = 11), IOD/HW = 0.24–0.33 (mean = 0.22, n = 11); face yellow with black, median line extending down from vertex between eyes, forming paired, yellow, inverted triangular maculae. Pronotum: Yellow, black, M-shaped macula broadly diffuse, often only leaving small, scattered yellow spots, punctate to lateral margins, PL = 0.62–0.75 mm (mean = 0.69 mm, n = 11); PW = 0.89–1.03 mm (mean = 0.96 mm, n = 11); PL/PW = 0.67–0.80 (mean = 0.72, n = 11). Elytra: Confused punctures in baso-sutural region, striae irregular and distinctly impressed, marginal interspace mostly impunctate. Pygidium: Black with 2 small, oval, yellow maculae. Venter: Black. Legs: Black with standard yellow spots. Genitalia: Median lobe in en-face view with wide, parallelsided shaft, gently rounding to terminus, with sclerotized, lateral basal plates and reduced PRL. POL, best seen in the lateral view, with ALA near 70°. Base wide, with mid-keel or ridge eventually narrowing at ALA. Long setae present along edges of deflexation, but no denticles present at ALM ( Fig. 12 ). One hundred and ten males from nine states were dissected.

Female. As in male, except L = 2.10–2.25 mm (mean = 2.19 mm, n = 9); W = 1.13–1.27 mm (mean = 1.21 mm, n = 9); L/W = 1.76–1.86 (mean = 1.81, n = 9); HW = 0.80–0.93 mm (mean = 0.85 mm, n = 9); IOD = 0.25–0.29 mm (mean = 0.26 mm, n = 9).

Remarks. Fall (1915) described P. dixianus as a variation of P.cephalicus . Dissection of the P. dixianus and P. cephalicus lectotypes revealed P. dixianus to be quite distinct. Therefore, I am elevating it to full species status.This species could possibly be confused with several other primarily yellow and black mottled species like P. gibsoni , P. atomarius , P. stygicus , and P. confusus Bowditch. Pachybrachis confusus is much larger with enlarged foreclaws, and the other species can be separated using the key.

Distribution. This species is found from the south-Atlantic coastal states, northwest to Illinois and Missouri (Map 2B). New state records are confirmed for three states that were not reported for P. cephalicus ( Riley et al. 2003) : Indiana, Kentucky, and Virginia.

Biological Notes. A label cited a potential host plant as Desmodium sp. and Hypericum sp. in Illinois.

Specimens Examined. See Appendix 12.

Figures

Fig. 12. Pachybrachis dixianus, lectotype. A) Dorsal habitus, B) Lateral habitus, C) Face, D) Pygidium, E) Median lobe of aedeagus, lateral view, F) Median lobe of aedeagus, en-face view.