4. Pachybrachis immaculatus Jacoby, 1889

(Figs. 3, 5c, Map 1)

Pachybrachys immaculatus Jacoby 1889: 148; Fall 1915: 339 (taxonomy).

Pachybrachis immaculatus: Riley et al. 2003: 158 (catalog).

Type. Jacoby (1889) described P. immaculatus from three Mexican specimens. Only one of these specimens is currently present in MCZ. This specimen, hereby designated lectotype, is a female labeled “H. H. S. [hand-inked] / Mexico City [printed, white paper] // 1 st Jacoby / Coll. [printed, white paper] // P. immaculatus / Jac. [hand-inked, blue paper] // Type [printed] / 8785 [hand-inked, red paper] // LECTOTYPE / Pachybrachys / immaculatus Jacoby / R. J. Barney 2020 [printed, red paper]”. This specimen was examined and photographed (Fig. 5c).

Redescription. Male. Dull yellow with brown punctures (Fig. 3); L = 1.87–2.56 mm (mean = 2.12 mm, n = 9); W = 1.04–1.36 mm (mean = 1.15 mm, n = 9); L/W = 1.79–1.91 (mean = 1.84, n = 9). Head: Wider than thoracic apex, HW = 0.69–0.92 mm (mean = 0.79 mm, n = 9); eyes moderately separated with ocular lines, IOD = 0.20–0.28 mm (mean = 0.23 mm, n = 9); IOD/HW = 0.25–0.33 (mean = 0.30, n = 9); face dull yellow, densely punctate, ocular lines close to upper lobes of eyes; antennae not reaching elytral declivity. Pronotum: Dull yellow, densely punctate, less so at margins, with feeble and obscure M-shaped brown macula; PL = 0.76–0.88 mm (mean = 0.70 mm, n = 9); PW = 0.92–1.24 mm (mean = 1.04 mm, n = 9); PL/PW = 0.65–0.71 (mean = 0.68, n = 9). Elytra: Dull yellow, submarginal stria fairly regular, marginal interspace devoid of punctures in apical half. Pygidium: Yellow, brown at base. Venter: Brown with yellow side and apical margins. Legs: Yellow with brown spots, front claws of male not enlarged. Genitalia: Median lobe in en-face view rounded with large orificial space resulting in much-reduced POL and small nodule. Lateral view shows ridge-like keel extending from mid-lobe to nodule. Six males from three USA states and Mexico were dissected.

Female. As in male, except L = 2.20–2.95 mm (mean = 2.58 mm, n = 7); W = 1.23–1.65 mm (mean = 1.39 mm, n = 7); L/W = 1.77–1.99 (mean = 1.85, n = 7); HW = 0.77–1.07 mm (mean = 0.94 mm, n = 7); IOD = 0.27–0.39 mm (mean = 0.31, n = 7); IOD/HW = 0.28–0.37 (mean = 0.66, n = 7).

Remarks. Pachybrachis immaculatus keys out to couplet 7 in Fall’ s (1915) Group B key with P. jacobyi, P. densus, and now P. americanus. However, P. immaculatus differs from the other species by the fairly regular submarginal elytral stria and marginal interspace devoid of punctures in apical half.

Distribution. This species is most likely a primarily Mexican species with a northern range extending into extreme southwestern border areas of USA (Map 1).

Biological Notes. McClay et al. (1995) reported larval and adult stages of P. immaculatus feeding on Parthenium hysterophorus L. (Asteraceae) in areas of Mexico and Texas. The following plants were reported on labels and probably represent incidental adult associations only: Domesticated jojoba, Simmondsia chinensis (Link) C.K. Schneid. (Simmondsiaceae); corn, Zea mays L. (Poaceae); cotton, Gossypium hirsutum L. (Malvaceae) in Mexico; carrot, Daucus carota L. (Apiaceae) in California.

Specimens Examined. Lectotype + 16 specimens. MEXICO: Mexico City, H. H. Smith, 1 st Jacoby Collection [1♀, LECTOTYPE, MCZ-BOW]; Sonora, Ciana Casta Hillo, 5.v.1978, ex. domesticated jojoba, F. Gonzalez [1♂, BYUC]; same data, except 31.viii.1975, ex. Gossypium hirsutum [1♂, BYUC]; same data, except 25.ix.1975, ex. corn [1♀, BYUC]. USA: ARIZONA: Cochise Co., San Bernardino Ranch, 3.vii [1♂, det. H. C. Fall, USNM]. CALIFORNIA: Orange Co., Tustin, 15.xii.1943, ex. carrot, D. H. Byers [1♂ 1♀, BYUC]. TEXAS: Cameron Co., Brownsville, 1.v.1904, H. S. Barber [1♂, Fall 1915 Rev., USNM]; vicinity of Sabal Palm Grove, 5-6.v.1989, A. J. Gilbert [1♂ 6♀♀, AJGC]; Resaca de las Palmas State Park, 26.ix.1996, S. M. Clark [1♂, BYUC]; Kenedy Co., 6 mi S Sarita, 8.v.1999, S. M. Clark [1♂, BYUC].