Pachybrachis pectoralis

Barney, Robert J., 2018, Definition and Revision of the pectoralis Species-Group of Eastern North American Pachybrachis Chevrolat (Coleoptera: Chrysomelidae: Cryptocephalinae), The Coleopterists Bulletin 72 (3), pp. 471-499 : 473

pectoralis species-group

Group Diagnosis. Small beetles, males measuring 1.66–2.43 mm in length, females measuring 1.95–2.52 mm in length. Dorsum yellow, glabrous, with brown, reddish brown, or black punctures; standard maculae diffuse, often dark brown or fuscous. Eyes of male closely (IOD = 0.04–0.08 mm) to moderately (IOD = 0.18–0.26 mm) separated; front with ocular lines. Protarsal claws of males either not enlarged or greatly enlarged. Median lobe of aedeagus varying from rather basic and unadorned to moderately inflated with paired penicilli and with apicolateral angle deflexed to near 60°, creating extended, triangular DEO.

Remarks. The pectoralis species-group, as proposed here, is an artificial grouping of species with ocular lines and found in the eastern USA. Pachybrachis clarki Barney was addressed in Barney (2016a) and will not be redescribed here. The other six species may actually be three pairs of sister species, each pair representing a larger species-group also present in the western USA: P. pectoralis and Pachybrachis sobrinus Haldeman ; Pachybrachis tridens (F. E. Melsheimer) and Pachybrachis obsoletus Suffrian ; and Pachybrachis peccans Suffrian and Pachybrachis diversus Fall.

Biology. Almost nothing is known of the biology of most species of North American Pachybrachis . However, the immature stages of two species in this group, P. pectoralis and P. peccans , have been studied ( LeSage 1985; Stiefel 1993). Salix spp. (Salicaceae) , Toxicodendron radicans (L.) Kuntze ( Anacardiaceae ), Quercus spp. (Fagaceae) , Robinia pseudoacacia L. ( Fabaceae ), and Gleditsia triacanthos L. ( Fabaceae ) are among suspected host plants.

KEY TO MALES OF THE PECTORALIS SPECIES- GROUP OF PACHYBRACHIS

1. Eyes very close, almost touching (IOD = 0.04–0.11 mm) .................................... 2

1 ʹ. Eyes moderate to widely separated (IOD> 0.12 mm) ........................................... 3

2. Front tibiae sinuate on inner margin; DEO of median lobe of aedeagus entire, thickened ( Fig. 1 ) ................................................ .......... 1. P. pectoralis (F. E. Melsheimer)

2 ʹ. Front tibia unmodified on inner margin; DEO of median lobe of aedeagus with apical notch or thinning ( Fig. 2 ) ................................ ........................ 2. P. sobrinus Haldeman

3. Ocular lines fine, reduced to short lines near top of upper lobes of eyes; front claws not or only slightly enlarged; median lobe of aedeagus without penicilli .................... 4

3 ʹ. Ocular lines prominent and distinct; front claws greatly enlarged ........................... 5

4. Dorsum whitish yellow with broad, sharply contrasted, even-bordered, black maculae ( Fig. 3 ) .......... 3. P. tridens (F. E. Melsheimer)

4 ʹ. Dorsum yellow with variable, indistinct, brown/black maculae ( Fig. 4 ) .................. ......................... 4. P. obsoletus Suffrian

5. Median lobe of aedeagus with penicilli ...... 6

5 ʹ. Median lobe of aedeagus without penicilli; southern Florida .......... 7. P. clarki Barney

6. In en-face view, DEO of aedeagal median lobe gently rounded to nodule at terminus ( Fig. 5 ) ......................... 5. P. peccans Suffrian

6 ʹ. In en-face view, DEO of aedeagal median lobe narrows sharply at ALM to an extended, triangular post-orificial length that is deflexed to near 60° angle in lateral view ( Fig. 6 ) ........ ................................. 6. P. diversus Fall

Figures

Fig. 1. Pachybrachis pectoralis. 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, G) Protibia.

Fig. 2. Pachybrachis sobrinus. 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. 3. Pachybrachis tridens. 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. 4. Pachybrachis obsoletus. 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. 5. Pachybrachis peccans. 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, G) Median lobe of aedeagus, endophallus extended.

Fig. 6. Pachybrachis diversus. 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, G) Median lobe of aedeagus, endophallus extended.