Melolonthinae

Evans, Arthur V. & Smith, Andrew B. T., 2020, On the tribal classification of the Nearctic Melolonthinae (Coleoptera: Scarabaeidae), with descriptions of new species of Acoma Casey, 1889, Zootaxa 4748 (1), pp. 51-77 : 52-54

Subfamily Melolonthinae

Our diagnosis of the Melolonthinae below is based largely on Evans (2002).

Diagnosis. Scarabaeidae . Adults 3–60 mm in length. Dorsal surface glabrous, setose or scaled; sometimes setae or scales forming distinct patches or lines; color testaceous to reddish brown or black, occasionally with metallic blue, green, coppery, or brassy luster. Head usually unarmed, never with frontal extensions or horns. Eyes only partially divided by ocular canthus. Antennae with 7–10 antennomeres, rarely more, and insertions not visible from above; lamellate club usually consisting of 3–7 antennomeres; lamellae glabrous or with only a few setae, often longer in males. Mandibles sclerotized, usually well developed, and concealed in dorsal view. Transverse, narrowed, or conical labrum free or fused beneath clypeus, sometimes extending beyond or fused to apical clypeal margin. Thorax with pronotal disc more-or-less convex, never concave or with raised carinae; scutellum exposed. Elytra with lateral margins more-or-less straight behind humerus, with mesepimeron usually covered by elytral bases. Metathoracic wings fully developed or reduced. Metepimeron rectangular or triangular. Legs with procoxae transverse or conical; protibiae usually with apical spurs; mesotibiae and metatibiae usually with a pair of apical spurs located below or set on either side of tarsal articulation, or with upper spur adjacent to tarsal articulation; opposing mesotarsal and metatarsal claws equal in thickness (except Hoplia , which have a single, enlarged metatarsal claw; see comments below on female Acoma ) and length and simple, cleft, bifid, toothed, or pectinate. Abdomen often concave medially in males, flat or slightly convex in females; sternites imbricate or smooth, narrowed medially or not, with sutures visible or completely effaced medially; sternite and propygidium fused or not with or without trace of suture; sixth sternite partially or completely retracted beneath fifth; pygidium exposed; 7 or fewer pairs of abdominal spiracles scarcely or not divergent posteriorly, with 1–3 posterior abdominal spiracles located in sternites or tergites. Male genitalia without sclerotized median lobe.

Evans & Smith (2009) considered the Nearctic genera Acoma , Chaunocolus , and Chnaunanthus as incertae sedis, while following the traditional placement of both Phobetus and Warwickia in tribe Tanyproctini . The tribal placement of all these genera is reconsidered below. During the course of our investigations, all worldwide Melolonthinae tribes (see Table 1 for a complete list) were studied and we found no compelling morphological characters indicating that Acoma , Chaunocolus , Chnaunanthus , Phobetus , or Warwickia belong to any of them.

Excluded taxa. Oncerinae new status and Podolasiinae new status. Evans (2002, 2003), Smith (2006), and Bouchard et al. (2011) all considered Oncerini and Podolasiini as tribes within the Melolonthinae . With regards to Oncerini , we now follow Saylor (1938), who considered both Oncerus LeConte, 1856 and Nefoncerus Saylor, 1938 in the subfamily Oncerinae on the basis of the placement of all abdominal spiracles within the pleural membrane. Ritcher (1969) confirmed Saylor’s findings for the placement of abdominal spiracles in Oncerus , but apparently did not examine the more rarely collected Nefoncerus . In addition to the placement of their abdominal spiracles, both of these monotypic genera are characterized by having hidden mandibles, labrum fused and coplanar with the clypeus, small and moderately setose lamellate clubs, and abdominal sutures that are distinct or not.

Howden (1997) erected the tribe Podolasiini for Podolasia Harold, 1869 and his new genus, Podostena Howden, 1997 , and stated that its position within the Melolonthinae is “problematical” and “remains debatable since some characters are not typical for the subfamily”. Ritcher (1969) found Podolasia to have seven pairs of functional spiracles and a vestigial eighth pair, all located in the pleural membrane. Lacroix (2007) considered the Podolasiinae ( Podolasiini ), along with the Palaearctic Chasmatopterinae (Chasmatopterini) to be in the Chasmatopteridae without discussion or justification. As mentioned previously, this presumed relationship is untenable given that Chasmatopterus Dejean, 1821 and Podolasia have very different abdominal spiracle configurations. The lack of any posterior abdominal spiracles in the tergites or sternites, and the small, nearly globose, and densely setose lamellate antennal clubs, combined with the cephalic armature and genital capsule characters found in recently described Podolasia (see Smith & Paulsen 2017), and an undescribed Podostena species (Evans, personal observation) from Mexico precludes the inclusion of Podolasiini within the Melolothinae, thus requiring its elevation to the subfamily rank of Podolasiinae. The phylogenetic position of this new subfamily with relation to the Melolonthinae needs further study and it will likely occupy a branch basal to the phytophagous scarab clade (see Smith et al. 2006).