Pachybrachis vigilans Fall, 1915

Barney, Robert J., 2019, Definition and Revision of the Pubescens Species-Group of North American Pachybrachis Chevrolat (Coleoptera: Chrysomelidae: Cryptocephalinae), Including Descriptions of Three New Species, The Coleopterists Bulletin 73 (4), pp. 1017-1048 : 1025-1026

4. Pachybrachis vigilans Fall, 1915 ( Fig. 4 ; Map 1A)

Pachybrachys vigilans Fall 1915: 329 .

Type. Fall’ s male P. vigilans , labeled “101 // San Felipe / Low, Cal. // ♂ // TYPE [printed] / vigilans [hand-inked, white paper] // H. C. FALL / COL- LECTION // M.C.Z. / Type [printed] / 24990 [handinked, red paper] // [circular blue disc signifying dissection by RJB]”, was examined, dissected, and photographed ( Fig. 4 ) .

Redescription. Male. Pale yellow with fuscous markings, sparse white pubescence; L = 2.43–2.94 mm (mean = 2.64 mm, n = 10); W = 1.25–1.48 mm (mean = 1.36 mm, n = 10); L/W = 1.88–2.00 (mean = 1.94, n = 10). Head: Slightly wider than thoracic apex, HW = 0.85–0.96 mm (mean = 0.90 mm, n = 10); eyes contiguous or nearly so, IOD = 0.00– 0.08 mm (mean = 0.02 mm, n = 10); IOD/HW = 0.00–0.08 (mean = 0.02, n = 10); face yellow without markings, evenly punctate; antennae yellow-brown, not reaching elytral declivity. Pronotum: Yellow-brown, widest at basal third, strongly arcuate, punctures to margins, Mshaped macula imperfect; PL = 0.78–0.91 mm (mean = 0.84 mm, n = 10); PW = 1.06–1.40 mm (mean = 1.18 mm, n = 10); PL/PW = 0.65–0.74 (mean = 0.71, n = 10). Elytra: Yellow with fuscous postscutellar, subapical sutural, humeral knob, and median and subapical marginal spots all quite irregular. Pygidium: Yellow-brown. Venter: Yellow-brown. Legs: Yellow; front claws not enlarged. Genitalia: Median lobe in en-face view with extended PRL with thickened sides, culminating in triangular OS, no protruding nodule, visible setae at ALM; MLW = 0.16–0.22 mm (mean = 0.19 mm, n = 9). Median lobe very wide in lateral view, without distinct ridge or keel; MLL = 0.39–0.50 mm (mean = 0.43 mm, n = 9). Twentyeight males from three USA states and one Mexican state were dissected.

Female. As in male, except L = 2.85–3.64 mm (mean = 3.23 mm, n = 10); W = 1.50–2.03 mm (mean = 1.72 mm, n = 10); L/W = 1.75–1.92 (mean = 1.88, n = 10); HW = 0.92–1.22 mm (mean = 1.06 mm, n = 10); IOD = 0.00– 0.22 mm (mean = 0.14 mm, n = 10); IOD/HW = 0.00–0.23 (mean = 0.14, n = 10).

Remarks. Pachybrachis vigilans was described by Fall (1915) based upon a single male specimen, and neither Fall’ s personal collection nor the national collection contain any additional examples (personal communication, Rachel L. Hawkins, MCZ; Alex Konstantinov, USNM). Fall noted that P. vigilans is much like P. integratus , speculating that additional specimens may prove them to be the same. Dissection of 32 males from Arizona, California, Texas and Utah revealed two very similar, but distinct median lobes. The median lobes matching the P. vigilans holotype were decidedly shorter and narrower, with no ridge or nodule, as compared to a second cohort, which had a distinct ridge and nodule. Unfortunately, Fall’ s description of P. integratus was based upon a female, thereby eliminating the absolute confirmation of the second cohort as P. integratus . While future research may prove otherwise, I am working under the assumption that cohort two is P. integratus . Interestingly, P. vigilans was not listed by Riley et al. (2003).

Fall (1915) characterized P. vigilans as the “only species in our fauna, thus far known, with absolutely contiguous eyes”. However, this is based upon a single specimen. Pachybrachis vigilans and P. integratus , as I have redescribed them here, have interocular distance ranges of 0.00– 0.08 mm and 0.05–0.08 mm, respectively. Also, I have seen at least one example of contiguous eyes in a Pachybrachis specimen most assuredly not P. vigilans nor P. integratus , possibly Pachybrachis bullatus Fall from Pima County, Arizona.

Distribution. This species is found in the southwestern USA and northern Mexico (Map 1A). Arizona, California, and Utah are new state records.

Biological Notes. One specimen from California is labeled as from Salix sp. (Salicaceae) . Several specimens were caught via Malaise and blacklight traps in Arizona, California, and Mexico.

Specimens Examined. See Appendix 4.

Figures

Fig. 4. Pachybrachis vigilans, lectotype. A–B) Dorsal and lateral habitus, respectively, C) Face, D) Pygidium, E–F) Median lobe of aedeagus, lateral and en-face views, respectively.