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

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http://doi.org/ 10.1649/0010-065X-72.1.9

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scientific name

Pachybrachis stygicus Fall, 1915
status

 

5. Pachybrachis stygicus Fall, 1915   ( Figs. 5 View Fig , 22C View Fig , 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 View Fig )   .

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 View Fig )   .

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 View Fig ). 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.

Kingdom

Animalia

Phylum

Arthropoda

Class

Insecta

Order

Coleoptera

Family

Chrysomelidae

Genus

Pachybrachis

Loc

Pachybrachis stygicus Fall, 1915

Barney, Robert J. 2018
2018
Loc

Pachybrachis vestigialis:

Clark, S. M. & LeDoux, T. N. & Seeno, E. G. & Riley, A. J. 2004: 162
Riley, E. G. & S. M. Clark & T. N. Seeno 2003: 164
2003
Loc

Pachybrachis stygicus: Fattig 1948: 10

Ciegler, J. C. 2007: 182
Clark, S. M. & LeDoux, T. N. & Seeno, E. G. & Riley, A. J. 2004: 161
Riley, E. G. & S. M. Clark & T. N. Seeno 2003: 163
Peck, S. B. & M. C. Thomas 1998: 134
Balsbaugh, E. U. & K. L. Hays 1972: 33
Kirk, V. M. 1970: 86
Kirk, V. M. 1969: 89
Fattig, P. W. 1948: 10
1948
Loc

Pachybrachys stygicus

Blatchley, W. S. 1924: 51
Fall, H. C. 1915: 416
1915
Loc

Pachybrachys vestigialis

Fall, H. C. 1915: 415
1915