Pachybrachis atomarius (F. E. Melsheimer), 1847

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 : 21-22

4. Pachybrachis atomarius (F. E. Melsheimer), 1847 ( Figs. 4 , 22A–B , Map 1B)

Cryptocephalus atomarius F. E. Melsheimer 1847: 170 .

Pachybrachys atomarius: Blatchley 1910: 1126 (taxonomy); Dozier 1922: 117 (regional species list); Blatchley 1924: 51 (taxonomy); Hughes 1944: 131 (regional species list); Wilcox 1954: 390 (taxonomy).

Pachybrachis atomarius: Melsheimer 1853: 127 (catalogue); Fattig 1948: 9 (regional species list); Downie and Arnett 1996: 1316 (catalogue); Kirk 1969: 89 (regional species list); Kirk 1970: 86 (regional species list); Balsbaugh and Hays 1972: 32 (taxonomy); Barney 1984: 137 (regional species list); Peck and Thomas 1998: 133 (regional species list); Riley et al. 2003: 155 (catalogue); Clark et al. 2004: 155 (plant associations); Ciegler 2007: 177 (taxonomy); Barney et al. 2011: 6 (taxonomy); Barney et al. 2013: 113 (taxonomy).

Pachybrachis infaustus Haldeman 1849: 262 . Melsheimer 1853: 127 (catalogue); Blatchley 1910: 1127 (taxonomy).

Pachybrachys atomus Bowditch 1909: 319 .

Type Material. A male from the MCZ-MELS, here designated as lectotype and labeled “Melsh. [printed] / atomarius [hand-inked, white paper] // [torn red paper] // atomarius [hand-inked, white paper with lined border] // LECTOTYPE / Cryptocephalus / atomarius Melsh. 1847 / R. J. Barney 2017 [printed, red paper]”, was examined, photographed, and dissected ( Fig. 4 ). Melsheimer described the type from Pennsylvania. An additional specimen in the Melsheimer Collection, labeled “[blue round disc] // Ziegler. [printed, white paper] // atoma / rius M. / Pa. [hand-inked, white paper with lined border], is likely a syntype .

A female from the MCZ-LEC, here designated as lectotype of Haldeman’ s P. infaustus and labeled “[orange round disc] // Type [printed] / 8405 [handinked, red paper] // P. infaustus / Hald. [hand-inked, white paper] // LECTOTYPE 8405 / Pachybrachis / infaustus Haldeman 1849 / R. J. Barney 2017 [printed, red paper]”, was examined and photographed ( Fig. 22A ). The orange disc is LeConte’ s locality disc, believed to represent the southern and Gulf States .

A male from the MCZ-BOW, here designated as lectotype of Bowditch’ s P. atomus and labeled “6 // Douglas Co. / Kan. 900 ft. / F. H. Snow [printed, white paper] // atomus / Type 6 [hand-inked, white paper] // Type / F. C. B. Collection [printed, pink paper] // LECTOTYPE / Pachybrachys / atomus Bowditch 1909 / R. J. Barney 2017 [printed, red paper]”, was examined and photographed ( Fig. 22B ). A female labeled “ ♀ // Douglas Co. Kan / 900 ft. / F. H. Snow [printed, white paper] // atomus / Type ♀ [hand-inked, white paper] // Type / F. C. B. Collection [printed, pink paper] // Type [printed] / 8781 [hand-inked, red paper] // PARAL- ECTOTYPE 8781 / Pachybrachys / atomus Bowditch 1909 / R. J. Barney 2017 [printed, red paper] ” and two specimens (16 1♀) with identical Douglas Co., Kansas labels as the male lectotype above are herein designated as paralectotypes [PARAL- ECTOTYPE / Pachybrachys / atomus Bowditch 1909 / R. J. Barney 2017 [printed, red paper]”. Specimens from Iowa City (366, MCZ-BOW) and Pennsylvania (16, MCZ-BOW) were also examined.

Redescription. Male. Yellow with fuscous maculae to almost black; L = 1.82–2.03 mm (mean = 1.86 mm, n = 10); W = 0.93–1.11 mm (mean = 1.02 mm, n = 10); L/W = 1.74– 1.88 (mean = 1.83, n = 10). Head: Not wider than thoracic apex, HW = 0.65–0.73 mm (mean = 0.69 mm, n = 10); eyes moderately separated, IOD = 0.20–0.24 mm (mean = 0.22 mm, n = 10); IOD/HW = 0.29–0.35 (mean = 0.32, n = 10); face pale yellow with sparse brown to black punctures, antennae yellow to brown-black, not reaching elytral declivity. Pronotum: Yellow, Mshaped macula dark brown to black, broadly diffuse; incomplete punctation to lateral margins; PL = 0.54–0.63 mm (mean = 0.59 mm, n = 10); PW = 0.80–0.95 mm (mean = 0.87 mm, n = 10); PL/PW = 0.65–0.71 (mean = 0.68, n = 10). Elytra: Yellow, coarsely punctate with fuscous maculae often broadly diffuse to become general color with small, scattered yellow areas; outer striae distinctly impressed. Pygidium: Entirely black, convex extended. Venter: Entirely black. Legs: Dark brown to black, with standard yellow spots. Genitalia: Median lobe in en-face view parallel-sided, abruptly narrowing at ALM to rounded extended tip; in lateral view, ALA 40° with setae along edges. Fifty-six males from 30 states and provinces were dissected.

Female. Generally larger and darker than males, with definitively extended black pygidium, L = 2.04–2.25 mm (mean = 2.16 mm, n = 10); W = 1.09–1.27 mm (mean = 1.18 mm, n = 10); L/W = 1.75–1.87 (mean = 1.83, n = 10); HW = 0.70–0.81 mm (mean = 0.77 mm, n = 10); IOD = 0.24–0.33 mm (mean = 0.28 mm, n = 10); IOD/ HW = 0.31–0.40 (mean = 0.36, n = 10).

Remarks. Historically, there has been much misperception concerning P. atomarius . Fall (1915) documented confusion by Suffrian, Haldeman, and LeConte and presented a key to separate P. atomarius from his new species Pachybrachis obfuscates Fall , P. cephalicus , Pachybrachis vestigialis Fall , and P. stygicus . I found the pale yellow face of the male, and the extended convex entirely black pygidium of males and females, to make P. atomarius easily distinguishable from these and other eastern USA species. Additionally, we now have knowledge of the aedeagal median lobes of these species. Pachybrachis infaustus and P. atomus are confirmed as synonymies.

Distribution. This species is widespread in the eastern USA, being found from the Atlantic Coast to the 100 th meridian. New state records are confirmed for five states: Maryland, Minnesota, North Dakota, Tennessee, and Wisconsin (Map 1B). Specimens were darker in the East and progressively lighter in the western part of its range.

Biological Notes. Despite being one of the most widespread species in the eastern USA, only one instance of a potential host plant ( Rhus glabra L., Anacardiaceae in Illinois) and no trapping methods were documented on labels of over 1,000 specimens of P. atomarius . Clark et al. (2004) reported many potential plant associations, but they cannot be confirmed.

Specimens Examined. See Appendix 4.

Figures

Fig. 4. Pachybrachis atomarius. 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).