Pachybrachis stygicus 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 : 22-23

5. Pachybrachis stygicus Fall, 1915 ( Figs. 5 , 22C , Map 1B)

Pachybrachys stygicus Fall 1915: 416 . Blatchley 1924: 51 (taxonomy).

Pachybrachis stygicus: Fattig 1948: 10 (regional species list); Kirk 1969: 89 (regional species list); Kirk 1970: 86 (regional species list); Balsbaugh and Hays 1972: 33 (taxonomy); Peck and Thomas 1998: 134 (regional species list); Riley et al. 2003: 163 (catalogue); Clark et al. 2004: 161 (plant associations); Ciegler 2007: 182 (taxonomy).

Pachybrachys vestigialis Fall, 1915: 415 . New synonymy.

Pachybrachis vestigialis: Riley et al. 2003: 164 (catalogue); Clark et al. 2004: 162 (plant associations).

Type Material. Fall’ s male type of P. stygicus , herein designated as lectotype and labeled “6 // Enterprise / Fla. [printed, white paper] // TYPE [printed] / stygicus [hand-inked, white paper] // M.C.Z. / Type [printed] / 24979 [hand-inked, red paper] // H. C. FALL / COLLECTION [printed, white paper] // LECTOTYPE 24979 / Pachybrachys / stygicus Fall 1915 / R. J. Barney 2017 [printed, red paper]”, was examined, photographed, and dissected ( Fig. 5 ) .

Fall’ s male type of P. vestigialis , herein designated as lectotype and labeled “6 // Medora / Ks. 6/10. [hand-inked, white paper] // TYPE [printed] / vestigialis [hand-inked, white paper] // M.C.Z. / Type [printed] / 24989 [hand-inked, red paper] // H. C. FALL / COLLECTION [printed, white paper] // LECTOTYPE 24989 / Pachybrachys / vestigialis Fall 1915 / R. J. Barney 2017 [printed, red paper]”, was examined and photographed ( Fig. 22C ) .

Redescription. Male. Black, dull, with very small yellow flecks on elytra to preponderance of yellow markings on prothorax and elytra; L = 1.98–2.33 mm (mean = 2.12 mm, n = 10); W = 1.07–1.33 mm (mean = 1.17 mm, n = 10); L/ W = 1.73–1.85 (mean = 1.80, n = 10). Head: Slightly wider than thoracic apex, HW = 0.72–0.85 mm (mean = 0.78 mm, n = 10); eyes moderately separated, IOD = 0.19–0.31 mm (mean = 0.26 mm, n = 10); IOD/HW = 0.27–0.36 (mean = 0.33, n = 10); face yellow with black, W-shaped macula connecting vertex and bases of antennae, and up to base of upper lobe of eyes, often diffuse to cover entire face; punctation dense; antennae yellow-brown, not reaching elytral declivity. Pronotum: Yellow, Mshaped macula black, broadly diffuse, often reducing yellow areas to small flecks; punctation almost as dense as on elytra; PL = 0.69–0.79 mm (mean = 0.75 mm, n = 10); PW = 0.90–1.13 mm (mean = 1.02 mm, n = 10); PL/PW = 0.68–0.78 (mean = 0.73, n = 10). Elytra: Yellow, coarsely punctate with fuscous maculae often broadly diffuse to become dominant color with small, scattered yellow areas. Pygidium: Entirely black. Venter: Entirely black. Legs: Black, with standard yellow spots. Genitalia: Median lobe in en-face view rectangular, with outward swelling at midpoint; median basal plate enlarged within OS so as to appear as an inverted, movable ladle, also obvious in lateral view ( Fig. 5 ). Sixty-seven males from 14 states were dissected.

Female. As in male, except, L = 2.15–2.52 mm (mean = 2.27 mm, n = 10); W = 1.19–1.41 mm (mean = 1.29 mm, n = 10); L/W = 1.68– 1.80 (mean = 1.77, n = 10); HW = 0.79– 0.91 mm (mean = 0.85 mm, n = 10); IOD = 0.27–0.35 mm (mean = 0.30 mm, n = 10); IOD/ HW = 0.31–0.39 (mean = 0.36, n = 10).

Remarks. Fall (1915) described P. stygicus and P. vestigialis in the same publication. While his western species, P. vestigialis , was mentioned one page previous to his eastern species, P. stygicus , Fall’ s description of P. stygicus was much more detailed. Therefore, I have selected P. stygicus as the name to represent the species. Fall originally separated the species between Alabama ( P. stygicus ) and Mississippi ( P. vestigialis ).

Synonymy of P. stygicus and P. vestigialis was determined by comparison of aedeagal median lobes from nine states ranging from Florida and Georgia to Texas and Nebraska. While an examination of a matrix of these nine en-face photographs revealed some minor variation in size and DEO, the basal plate “ladle” was very distinctive and nothing even remotely similar has been found in my study.

Pre-dissection, P. stygicus is often confused with P. atomarius and P. nigricornis (Say) in the eastern United States. However, P. atomarius males have the distinctive pale yellow face and the “ carbonarius ” forms of P. nigricornis have much finer, smooth punctures on the pronotum than on the elytra, while P. stygicus has a black face and equitable punctation between pronotum and elytra.

Distribution. Pachybrachis stygicus is a common, widespread species from the mid- Atlantic Coast to the 100 th meridian (Map 1B). While virtually totally black specimens can be found from Florida to Nebraska, P. stygicus trends to a paler form in the southwestern part of its range. New state records are confirmed for three states: North Carolina, South Dakota, and Tennessee.

Biological Notes. The following potential host plants were listed on labels: Lepidium virginicum L. ( Brassicaceae ) in Florida, Quercus laevis Walter in Georgia, E. capillifolium in Georgia and North Carolina, and Coreopsis cardaminefolia DC. Torr. & A. Gray (= tinctoria Nutt.) ( Asteraceae ), Rudbeckia sp. (Asteraceae) , Englemannia sp. (Asteraceae) , Ptilimnium sp. (Apiaceae) , and Eleocharis sp. (Cyperaceae) in Texas.

Specimens Examined. See Appendix 5.

Figures

Fig. 5. Pachybrachis stygicus. 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.

Fig. 22. Pachybrachis species types, dorsal habitus. A) P. infaustus (female lectotype), B) P. atomus (female paralectotype), C) P. vestigialis (male lectotype), D) P. luctuosus (possible male syntype), E) P. carolinensis (male lectotype), F) P. tybeensis (male lectotype).