Isonychus Mannerheim, 1829

Katovich, Kerry, 2008, A generic-level phylogenetic review of the Macrodactylini (Coleoptera: Scarabaeidae: Melolonthinae), Insecta Mundi 2008 (23), pp. 1-78 : 47-49

Isonychus Mannerheim, 1829

( Figure 110-114 )

Isonychus Mannerheim, 1829: 69 . Type species Isonychus sulphureus Mannerheim, 1829 , by original designation. Colporhina Curtis, 1844: 200 . Type species Colporhina bifoveolata Curtis, 1844 , by monotypy. Synonymized by Dalla Torre (1913).

Taxonomic Notes

The following generic diagnosis is based on a single dissected specimen of the generic type species, I. sulphureus . Specimens were authoritatively identified by Moser, Arrow, and the author with the aid of the original description. The type was not seen during this study.

Generic diagnosis

This genus is characterized by its ovate, rotund body shape; body often covered with scale-like hairs; prementum elongate, ventral surface medially grooved; pronotum oblong, transverse, anterior angles acute, appearing toothed; pygidium subtriangular, width equal to length.

Generic redescription

Measurements: Prothorax at widest point 3.6 mm, elytra widest point 4.8 mm, length 9.3 mm.

Color and vestiture: Head and pronotum black, legs reddish brown, body with a vestiture consisting of sulphur-colored scales.

Head: Clypeus coplanar with frons; frons angled at 60 o; labrum in frontal view narrow, ovate, slightly emarginate medially, labrum coplanar with clypeus; labium with prementum rectangular, elongate, ventral surface medially grooved ( Fig. 112 ); mandibles in dorsal view broadly rectangular, anterior margin broadly rounded, scissorial area reduced to a membrane, molar region prominent, well sclerotized; maxillary palpi with apical palpus ovate, elongate, equal to length of 2 nd and 3 rd segments combined, thin in lateral profile, blunt apically; antennae with 9 antennomeres, antennomeres 7-9 forming the club, equal to length of antennomeres 2-6 combined.

Prothorax: Pronotum oblong, transverse, widest medially, anterior angles acute, lateral margin convex, posterior 1/4 of margin straight, posterior angles acute, posterior margin weakly concave, medially with a broad lobe ( Fig. 113 ); prothoracic leg with coxa elongate; tibia dentate, ventral margin with spur present in distal 3/4; pretarsus with claws divergent, equal in length, both claws narrowly split, upper lobe narrow, lower lobe broad on individual claw, base of claw toothed.

Mesothorax: Scutellum subtriangular; elytra slightly longer than wide, widest in anterior 1/2 ( Fig. 114 ), elytral epipleuron absent, membrane lining lateral margin, dorsal surface with seven weak sutural striae present, surface covered with dense, sulfur colored scales anterior umbone moderately prominent, posterior umbone weak; pretarsus similar to prothoracic pretarsus.

Metathorax: Metathoracic leg with coxa contiguous; femur elongate, ovate, narrow proximally, widest medially; tibia vase-shaped, proximally narrowed, widest medially, narrowing in distal 1/4, posteroventral margin with two long, stout spurs, ventral spur slightly shorter than posterior spur, arising from same plane as tarsal articulation joint, posterior margin with a deep, U-shaped grooved; pretarsus with claws similar to claws of prothoracic and mesothoracic legs.

Abdomen: Ventrites 2-4 equal in length, 5 th ventrite (= propygidium) equal to length of ventrites 2-4 combined, posterior margin membranous, below plane of sclerotized 5 th ventrite, ventrite and sternite of 5 th abdominal segment lacking a suture, spiracle located in the posterior 1/4, 6 th ventrite triangular, glabrous, posterior margin appearing membranous, surface of all ventrites covered with dense, sulfur colored scales; pygidium subtriangular, width equal to length, posterior margin rounded.

Diversity and Geographic Distribution

Isonychus comprises 147 species, distributed from Argentina, Bolivia, Brazil, Colombia, Costa Rica, Ecuador, French Guiana, Guatemala, Guyana, Honduras, Mexico, Nicaragua, Panama, Peru, Surinam, United States, Uruguay, and Venezuela. Regional keys are provided by Frey (1964, 1965, 1970) and Morón (1994).

Figures

Figure 110-114. Isonychus sulphureus Mannerheim. 110) Dorsal habitus. 111) Left lateral view.112) Prementum, ligula and labial palpi, ventral view. 113) Pronotum, dorsal view. 114) Elytra, propygidium and pygidium, dorsal view.