Erioscelis Burmeister, 1847

Moore, Matthew R., Cave, Ronald D. & Branham, Marc A., 2018, Synopsis of the cyclocephaline scarab beetles (Coleoptera, Scarabaeidae, Dynastinae), ZooKeys 745, pp. 1-99 : 53-55

Erioscelis Burmeister, 1847

Type species.

Apogonia emarginata Mannerheim, 1829, by monotypy.

Valid taxa.

Five species.

The five species of Erioscelis are distributed in South America north to Nicaragua (Fig. 59). Erioscelis species are remarkable among cyclocephalines for their well-characterized floral visitation syndromes. Erioscelis species are associated with nocturnally blooming genera in the family Araceae . Three Erioscelis species have been reported from the spathes of Dieffenbachia , Philodendron Schott, Syngonium Schott, Montrichardia Crueg., and possibly Xanthosoma Schott ( Schrottky 1910, Gottsberger and Amaral 1984, Young 1986, Grayum 1996, Croat 1997, Morón 1997, Beath 1998, 1999, Gibernau et al. 2003). While the association between Erioscelis species and aroid flowers is firmly established, there is little evidence of species- or genus-level specificity in this pollination mutualism. For example, Erioscelis columbica Endrődi has been collected from the spathes of nine different Philodendron species in Heredia, Costa Rica ( Grayum 1996, Croat 1997, Morón 1997, Moore and Jameson 2013). Based on feeding damage to Philodendron inflorescences by Erioscelis , it was hypothesized that this genus may be an interloper on the cyclocephaline/aroid mutualism ( Goldwasser 1987). Other observations seem to indicate that Erioscelis species are part of this mutualism.

The descriptions of Erioscelis spp. visitation of Dieffenbachia and Philodendron inflorescences are some the most detailed available for Cyclocephalini . In Costa Rica, E. columbica is a pollinator of Dieffenbachia nitidipetiolata Croat & Grayum ( Young 1986, 1988a, 1988b, 1990). Erioscelis columbica arrive at receptive female-phase inflorescences during nightfall, where they feed on staminodia and mate ( Young 1986). The beetles exit the spathe after 24 hours when the spadix is in the male-phase and shedding pollen ( Young 1986). Erioscelis columbica are covered in sticky pollen grains while exiting the spathe, and they may also feed on some of the pollen ( Young 1986). Erioscelis proba (Sharp) displays similar behavior in the inflorescences of two other Dieffenbachia species in French Guiana (Gibernau 2015a).

Observational and experimental evidence suggests that Erioscelis emarginata (Mannerheim) prefers to feed upon sterile staminate flowers on the spadix in two Philodendron species ( Maldonado et al. 2015). Furthermore, analyses of nutritional and defensive compound (calcium oxalate) content of sterile and fertile flowers in these Philodendron species suggested that sterile staminate flowers have lower amounts of defensive compounds ( Maldonado et al. 2015). Erioscelis species are seemingly attracted to the strong floral scents that are volatilized during thermogenesis and receptivity of the staminate flowers in these aroids. The dynamics of floral scent attraction are mostly unexplored for Erioscelis . In the case of Philodendron adamantium Mart. ex Schott, a single dominant flower scent compound (Dihydro-β-ionone) extracted from this species was sufficient to attract E. emarginata to scent traps ( Pereira et al. 2014).

Erioscelis was first revised by Saylor (1946) and again by Endrődi (1966, 1985a). These works provide a strong foundation for species-level identification, but characters that separate Erioscelis from other cyclocephalines are largely undiscussed. For example, Saylor (1946) commented, "When compared with such species as Cyclocephala (Stigmalia) mafaffa Burmeister, or C. (Aclinidia) castanea (Fabricius), the only character definitely to separate Erioscelis is the unenlarged front tarsal claws of both sexes". Unique protibial (2 teeth on the lateral margin in both sexes, subapical position of reduced protibial spur) and abdominal (bisinuate margin of 6th abdominal sternite, terminal spiracle not positioned on pleural suture) characters of Erioscelis emarginata also complicate recognition of the genus and may be reasons to doubt the monophyly of the group. These characters (except for the bisinuate margin of 6th abdominal sternite) are associated with Anomalini ( Rutelinae) and are absent in all other members of Erioscelis and Cyclocephalini more broadly. Sister-relationships of Erioscelis have not been hypothesized and the immature stages are unknown for the genus.

Erioscelis species can be recognized by the following combination of characters: 1) dorsal coloration castaneous, rufocastaneous, or piceous; 2) body not dorsoventrally flattened nor anteroposteriorly compressed; 3) clypeal apex truncate, weakly emarginate, or deeply emarginate in dorsal view; 4) frontoclypeal suture complete medially; 5) apical margin of mentum shallowly emarginate; 6) anterolateral margin of mandible lacking tooth; 7) mandibular molar area with rows of circular micropunctures; 8) galea of maxilla not dorsoventrally flattened; 9) galea of maxilla on inner surface with 6 teeth in 2-2-2 arrangement (each pair shares a base); 10) pronotum with apical bead complete medially; 11) basal bead of pronotum incomplete medially; 12) anterior membrane of pronotum straight at middle, not projected anteriorly; 13) anterior membrane of the pronotum extending laterally to apicolateral margins of the pronotum; 14) protibia with 2 or 3 lateral teeth in both sexes; 15) when protibia tridentate, basal tooth not greatly reduced, only slightly removed from the apical 2 teeth, and oriented laterally; 16) protibial spur subapical or apically positioned; 17) protibial spur straight to weakly reflexed; 18) males and females with protarsal claws simple, not enlarged; 19) males and females with inner protarsal claws with apex entire, not cleft; 20) mesocoxae not widely separated, nearly touching; 21) metacoxae with lateral edge perpendicular to ventral surface; 22) anterior edge of hindwing distal to apical hinge simple (lacking setae or membrane) or with row of long, erect setae extending along vein; 23) vein RA with double row of pegs proximal to apical hinge; 24) terminal abdominal spiracle situated on pleural suture or not.