Pachybrachis chester Riley and Barney

Riley, Edward G. & Barney, Robert J., 2015, Definition And Revision Of The Viduatus Species- Group Of North American Pachybrachis Chevrolat (Coleoptera: Chrysomelidae: Cryptocephalinae), The Coleopterists Bulletin 69 (1), pp. 25-59 : 42

6. Pachybrachis chester Riley and Barney , new speices ( Figs. 16 , 20 ; Map 3)

Pachybrachis viduatus: Ciegler 2007: 183 (misidentification, partim).

Holotype. Male ( Figs. 16 , 20 ), labeled “CHESTER / GEORGIA / 6 – 1 – 04 // GEOR. STATE / COLLECTION [printed, black on tan] // Collection / FKnab [printed, black on tan] // [circular blue disc signifying dissection by RJB] // HOLOTYPE / Pachybrachis / chester / Riley & Barney [printed, black on red].” Deposited in USNM. The specimen is point-mounted and dissected, with abdomen and genitalia affixed to the point. It is in excellent condition, with all appendages intact.

Paratypes. 3♂♂, 3♀♀ (Appendix 2).

Description. Male: As described for P. bloxham , except length 2.62–2.92 mm (mean = 2.74 mm, n = 4); width across humeri 1.40–1.62 mm (mean = 1.48 mm, n = 4); L/ W 1.81 –1.92 mm (mean = 1.86 mm, n = 4). Head: Width 0.95– 1.03 mm (mean = 0.99 mm, n = 4); eyes widely separated, IOD 0.42–0.49 mm (mean = 0.46 mm, n = 4); IOD/HW 0.44–0.48 (mean = 0.46, n = 4). Pronotum: Length 0.90–1.09 mm (mean = 0.96 mm, n = 4), width 1.28–1.44 mm (mean = 1.33 mm, n = 4), PL/PW 0.69–0.76 (mean = 0.73, n = 4). Elytra: Lateral vitta on elytra reduced to an elongate spot, or extended from humerus to elytral mid-length, with or without a small, detached, apical macula. Pygidium: Black with lower half occupied by two large, more-or-less confluent yellow spots. Genitalia: Median lobe in en-face view of near equal width throughout, side margins of shaft broadly, very feebly emarginate behind apicolateral curvature ( Fig. 20 ); length of postorificial space short, ca. 2 times width of marginal spaces; lateral basal plates well-pigmented, median plate weakly pigmented, broad basally, narrowed distally. En-face outline with apicolateral margin rounded; distal en-face outline oblique to terminus, weakly emarginate before indistinct, broadly triangular nodule. Beard conspicuous, consisting of apicolateral wisp on each side; setae of wisp dense, long, weakly graded in length with longest medial in serial position, curved mesad. Ventral surface evenly swollen, without keel, evenly arched to base of nodule; distal profile abruptly narrowed before terminus.

Female. As described for P. bloxham , except length 2.94–3.32 mm (mean = 3.09 mm, n = 3); width across humeri 1.61–1.77 mm (mean = 1.67 mm, n = 3); head width 1.09–1.19 mm (mean = 1.14 mm, n = 3); interocular distance 0.53–0.60 mm (mean = 0.56 mm, n = 3); IOD/HW 0.48–0.50 (mean = 0.49, n = 3).

Etymology. This species is named for the type locality, and the name is used as a noun in apposition.

Remarks. The viduatus species-group characters, together with the heavy median elytral vittae, and the distinctive male genitalia distinguish the species. It is externally inseparable from some members of the viduatus complex ( P. bloxham , P. kentuckyensis , and P. viduatus ), but it may be separated from P. picturatus by its heavy black maculation and dense, coarse dorsal punctation. Males are distinguished by their genitalia, with the ventral surface inflated but lacking a keel, and with the curvature in profile evenly arched to the base of the nodule. We have been unable to find definitive external characters to distinguish females, but the lateral vitta is reduced in comparison with most specimens of the similar species. One of the specimens from Chester, Georgia in the Fall Collection (MCZ) was identified as P. viduatus by Fall, but was not cited in his work (1915).

Distribution. Known only from one locality in Georgia and one locality in South Carolina (Map 3).

Biological Notes. Nothing known.

Specimens Examined. See Appendix 2.

Figures

Figs. 15–18. Pachybrachis species, dorsal and lateral habitus, face and pygidium. 15) P. bloxham, holotype;

Figs. 19–22. Pachybrachis species, median lobe, en-face and lateral views. 19) P. bloxham, holotype; 20) P. chester, holotype; 21) P. kentuckyensis; 22) P. viduatus.