Pachybrachis pectoralis (F. E. Melsheimer, 1847 )

Barney, Robert J., 2018, Definition and Revision of the pectoralis Species-Group of Eastern North American Pachybrachis Chevrolat (Coleoptera: Chrysomelidae: Cryptocephalinae), The Coleopterists Bulletin 72 (3), pp. 471-499 : 473-475

1. Pachybrachis pectoralis (F. E. Melsheimer, 1847) ( Figs. 1 , 7A ; Map 1A)

Cryptocephalus pectoralis F. E. Melsheimer 1847: 171 .

Pachybrachys pectoralis: Fall 1915: 363 (taxonomy); LeConte 1880: 209 (taxonomy); Bowditch 1910: 53 (taxonomy); Wilcox 1954:389 (taxonomy).

Pachybrachis pectoralis: Fattig 1948: 9 (regional species list); Kirk 1970: 86 (regional species list); Balsbaugh and Hays 1972: 30 (taxonomy); Stiefel 1993: 450 (biology); Downie and Arnett 1996: 1318 (taxonomy); Barney 1984: 144 (regional species list); Riley et al. 2003: 161 (catalogue); Clark et al. 2004: 160 (plant associations); Ciegler 2007: 181 (taxonomy, plant association); Barney et al. 2011: 8 (regional species list).

Type Material. A female from the Melsheimer Collection (MCZ-MELS), here designated as lectotype of Melsheimer’ s C. pectoralis and labeled “Melsh. [printed] / pectoralis [hand-inked, white paper] // [torn red paper] // pectoralis [hand-inked, white paper with lined border] // LECTOTYPE / Cryptocephalus / pectoralis Melsh. 1847 / R. J. Barney 2017 [printed, red paper]”, was examined and photographed ( Fig. 7A ).

Seven (266 5♀♀) additional specimens ( MCZ- MELS), here designated paralectotypes, are labeled “ Pennsylvania / Melsheimer. // PARALECTOTYPE / Cryptocephalus / pectoralis Melsh. 1847 / R. J. Barney 2017 [printed, red paper]”. Two specimens (2♀♀) are labeled from Carya (Juglandaceae) in August, and two specimens (16 1♀) are labeled from white oak ( Quercus ) in July .

Redescription. Male. Yellow with diffuse brown to black maculae; L = 1.76–1.92 mm (mean = 1.84 mm, n = 10); W = 0.88–0.98 mm (mean = 0.93 mm, n = 10); L/W = 1.85–2.08 (mean = 1.99, n = 10). Head: Small, not wider than thoracic apex, HW = 0.55–0.62 mm (mean = 0.60 mm, n = 10); eyes very close, almost touching, IOD = 0.04–0.08 mm (mean = 0.06 mm, n = 10); IOD/ HW = 0.07–0.14 (mean = 0.10, n = 10); face yellow with brown to black macula descending from vertex to between eyes; ocular lines present but often fine and variable; antennae yellow/brown, not reaching elytral declivity. Pronotum: Yellow, M-shaped macula dark brown to black, broadly diffuse; lateral margins smooth; PL = 0.53–0.61 mm (mean = 0.57 mm, n = 10); PW = 0.71–0.84 mm (mean = 0.79 mm, n = 10); PL/ PW = 0.69–0.77 (mean = 0.73, n = 10). Elytra: Yellow with brown to black maculae in no discernable pattern; outer and apical striae distinctly impressed, interrupted medially. Pygidium: Mostly yellow with brown margin. Venter: Brown to black; upper sides of last ventrite yellow. Legs: Yellow with standard brown spots; protibia sinuate on inner margin ( Fig. 1G ). Genitalia: Median lobe in en-face view with shaft widest subapically; en-face outline with apicolateral margin broadly and evenly rounded, oblique to terminus, defining indistinct, broadly rounded, thickened, triangular nodule. Lateral view revealing inflated ventral surface. Beard inconspicuous with tips of longest setae visible in en-face view, consisting of apicolateral space patch; setae short, straight ( Fig. 1 ). Eighteen males from 29 states were dissected.

Female. As in male, except L = 1.98–2.24 mm (mean = 2.11 mm, n = 10); W = 1.02–1.14 mm (mean = 1.10 mm, n = 10); L/W = 1.85–1.98 (mean = 1.92, n = 10); HW = 0.62–0.72 mm (mean = 0.67 mm, n = 10); IOD = 0.09–0.15 mm (mean = 0.12 mm, n = 10); IOD/HW = 0.14–0.22 (mean = 0.18, n = 10).

Remarks. Pachybrachis pectoralis is superficially recognized by the proximate eyes with ocular lines and the enlarged foreclaws. However, separation from P. sobrinus can be achieved via the sinuation of the protibia on the inner margin beyond the middle ( Fig. 1G ), which is often difficult to detect but present in both males and females of P. pectoralis . Absolute separation of P. pectoralis and P. sobrinus males is achieved by recognition of the DEO apical notch or thinning of P. sobrinus , while P. pectoralis has a complete, thickened DEO.

Distribution. Pachybrachis pectoralis is found in virtually every state from the east coast to the 100 th meridian (Map 1A). New state records were confirmed for seven states: Kentucky, Louisiana, Minnesota, Mississippi, South Carolina, South Dakota, and Wisconsin.

Biological Notes. In one of the few studies of immatures of Pachybrachis, Stiefel (1993) found P. pectoralis larvae feeding on decaying wood in Kansas. Paralectotypes were labeled from Carya and white oak in Pennsylvania. Other specimen labels reported the following potential host plants: Quercus sp. in Alabama; Quercus ellipsoidalis E. J. Hill and Quercus muehlenbergii Englem. in Illinois; and Quercus alba L., Quercus ( borealis ) rubra L., Quercus macrocarpa Michx. , and Q. ellipsoidalis in Wisconsin. Several specimens were labeled as collected via blacklights, Malaise traps, and flight traps.

Specimens Examined. See Appendix 1.

Figures

Fig. 1. Pachybrachis pectoralis. 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, G) Protibia.

Fig. 7. Pachybrachis species, type specimens. A) P. pectoralis (female lectotype), B) P. sobrinus (female lectotype), C) P. sticticus (female lectotype), D) P. tridens (female lectotype), E) P. flavicornis (female lectotype), F) P. mollis (female lectotype), G) P. obsoletus (female designated holotypus by MNHUB), H) P. peccans (female designated syntypus by MNHUB), I) P. diversus (male lectotype).