Dyscinetus Harold, 1869

Moore, Matthew R., Cave, Ronald D. & Branham, Marc A., 2018, Synopsis of the cyclocephaline scarab beetles (Coleoptera, Scarabaeidae, Dynastinae), ZooKeys 745, pp. 1-99 : 51-52

Dyscinetus Harold, 1869

Type species.

Melolontha geminata Fabricius, 1801, by monotypy.

Valid taxa.

21 species.

The genus Dyscinetus comprises 21 species distributed from North America south to Argentina and the West Indies (Fig. 58). Smooth, large, and mostly black Dyscinetus species superficially resemble hydrophilid beetles. Dyscinetus is generally not considered an aquatic or semiaquatic genus. However, some species in the genus have an intriguing association with moist, mucky soils and aquatic plants. Dyscinetus rugifrons and another Dyscinetus sp. attack water hyacinth in Uruguay ( Silveira Guido 1965, Bennett and Zwolfer 1968, Perkins 1974). Dyscinetus morator also attacks water hyacinth in Florida ( Perkins 1974, Buckingham and Bennett 1989). These species are considered scavengers and enhancers of damage started by other arthropods on water hyacinth, though they are known to attack healthy tissues ( Perkins 1974, Buckingham and Bennett 1989). Feeding damage on water hyacinth occurs inside petioles, crowns, petiole bases, and submerged roots ( Perkins 1974, Buckingham and Bennett 1989).

Experiments indicated that D. morator can survive submerged in water for up to 36 hours ( Buckingham and Bennett 1989). The mechanism allowing for this prolonged submersion is unclear. Air bubbles are visible along the elytral margin and on the metathorax in submerged individuals ( Buckingham and Bennett 1989). Dyscinetus laevipunctatus Bates was also observed submerged in association with water hyacinth in Mexico ( García-Rivera and Contreras-Ramos 2015). Unlike many other genera in the group, Dyscinetus adults are not known to visit flowers. A Brazilian Dyscinetus species was reportedly attracted to the floral odors of Annona sp., although these beetles were not encountered in any inflorescences ( Gottsberger 1989). This is the only mention of Dyscinetus floral attraction in the literature.

Dyscinetus species can be recognized by the following combination of characters: 1) dorsal coloration dark piceous to black; 2) body convex, not strongly anteroposteriorly compressed or dorsoventrally flattened; 3) clypeus trapezoidal with apex truncate in dorsal view; 4) frontoclypeal suture complete medially; 5) males with anterolateral margin of the mandibles lacking weak tooth; 6) mandibular molar area with rows of circular micropunctures; 7) mandibular molar area on proximal margin with 2 semicircular depressed pits; 8) galea of maxilla on inner surface with 2 fused basal teeth, 2 free medial teeth, and 2 fused apical teeth (2-2-2 arrangement); 9) pronotum with broadly incomplete beaded basal margin; 10) males and females with 3 protibial teeth on lateral margin, basal tooth not greatly reduced, only slightly removed from the more apical 2 teeth, and oriented laterally; 11) protibial spur straight to weakly deflexed; 12) males with inner protarsal claw enlarged and narrowly cleft at apex; 13) mesocoxae not widely separated, nearly touching; 14) metacoxae on lateral edge with transverse, depressed sulcus; 15) metacoxae with lateral edge perpendicular to ventral surface; 16) meso- and metatibiae with distal, transverse carinae; 17) anterior edge of hindwing distal to apical hinge with erect setae and lacking produced, membranous border; 18) vein RA with single row of pegs proximal to apical hinge; 19) propygidium not expanded, with propygidium and pygidium not fused.