The taxonomic and nomenclatural history of Cyclocephalini traces to the works of Carl Linnaeus and several of his students. The 12^th edition of Systema Naturae included the description of Scarabaeus amazonus Linnaeus, 1767, which was later designated as the type species of Cyclocephala Dejean (Linnaeus 1767, Casey 1915, Endrődi 1966). This was the only cyclocephaline species described by Linnaeus. The short Latin description of S. amazonus indicated that this beetle was from “Suriname,” was smaller than many dung beetles (with a relatively shorter pronotum), and was testaceous with longitudinal, black stripes (Linnaeus 1767). Unfortunately, the type specimen of S. amazonus is apparently lost. A serious effort to find this Linnaean type was undertaken by Sebő Endrődi and fellow Coleopterist Bengt-Oloft Landin.

Landin, an expert in Linnaean scarabaeoid types (e.g., see Landin 1956), was in correspondence with Endrődi during the early phases of the latter’s revisionary works (Endrődi 1966). They determined that the type specimen of S. amazonus was not present in any of the museums that housed parts of the Linnaeus beetle collection: The De Geer collection at Naturhistoriska Riksmuseet (Stockholm, Sweden), Uppsala University, Museum of Evolution, Zoology Section (Uppsala, Sweden), and The Natural History Museum (London, United Kingdom). In a personal correspondence with Endrődi, Landin speculated that the specimen that became the type of S. amazonus was passed from Daniel Rolander (an apostle of Linnaeus sent to Suriname), then to Baron Charles De Geer, and eventually to Linnaeus (Endrődi 1966).

Two female specimens identified as Melolontha amazona (Linnaeus) from “Jamaic” and “Columbia” were found in the Schönherr collection at Naturhistoriska Riksmuseet (Endrődi 1966). The specimen from “Jamaic” was determined to be consistent with the description of Melolontha signata Fabricius, 1781, also from Jamaica (Endrődi 1966). The specimen from “Columbia” was determined to be conspecific with the mainland species Cyclocephala detecta Bates, 1888 (a synonym of C. amazona) (Endrődi 1966). This convinced Endrődi that the names S. amazonus and M. signata referred to the same species with continental and West Indian populations, respectively. Endrődi designated a neotype for S. amazonus from Paramaribo, Suriname in his collection (now deposited at Magyar Természettudományi Múzeum Allatatara [Hungarian Natural History Museum], Budapest, Hungary).

Johan Christian Fabricius described 11 species of cyclocephaline scarabs that were ultimately classified in the genera Cyclocephala, Chalepides Casey, Dyscinetus Harold, Stenocrates Burmeister, and Ruteloryctes Arrow (Fabricius 1775, 1781, 1787, 1798, 1801). Fabricius (1798) reported the earliest floral association record for Cyclocephalini when he noted that Melolontha morio Fabricius (=Ruteloryctes morio) was found in “Nympheae floribus” in “India orientalis.” This early floral association record was later validated, and R. morio is indeed a pollinator of the water lily, Nymphaea lotus L., in Benin, Côte d’Ivoire, Nigeria, and Senegal (Ervik and Knudsen 2003, Hirthe and Porembski 2003, Krell et al. 2003). Linnaeus’ students Leonard Gyllenhal and Carl Peter Thunberg combined to describe four cyclocephaline species later classified in Cyclocephala and Stenocrates (Thunberg 1814, Gyllenhal 1817a, b).

Dejean (1821) authored the genus Cyclocephala in the first edition of the catalog of his collection. There was longstanding confusion in the literature surrounding the proper authorship of the genus Cyclocephala, with most historical workers crediting the genus to Latreille (1829) (e.g., Arrow [1937b], Blackwelder [1944], and Endrődi [1966, 1985a]). This confusion stemmed from Dejean’s practice of proposing new genera without describing them in the catalogs of his collection (Bousquet and Bouchard 2013a, b). Dejean (1821) also attributed authorship to other workers who had applied names to species in their own collections, but before the names were formally described in the literature. Thus, subsequent authors treated Dejean’s new genera and species as invalid nomina nuda. However, because Dejean (1821) included one or more available species-group names in Cyclocephala, the genus-group name became available from that work (ICZN Article 12.2.5; see Bousquet and Bouchard 2013a for further discussion).

The following originally included available names were placed in Cyclocephala by Dejean (1821): Melolontha geminata Fabricius, 1801 (=Dyscinetus dubius [Olivier, 1789]), Melolontha dubia Olivier, 1789 (=Dyscinetus dubius [Olivier]), Scarabaeus barbatus Fabricius, 1787 (=Chalepides barbatus [Fabricius]), Melolontha signata Fabricius, 1781 (=Cyclocephala amazona amazona [Linnaeus, 1767]), and Melolontha biliturata Gyllenhal, 1817 (=Cyclocephala tridentata [Fabricius, 1801]).

Dejean (1821) included five species inquirenda (indicated by a “?”) in Cyclocephala: Melolontha pallens Fabricius, 1798 (=Cyclocephala amazona amazona [Linnaeus, 1767]), Melolontha ferruginea Fabricius, 1801 (=Cyclocephala immaculata ferruginea (Fabricius, 1801), Melolontha valida Schönherr, 1817 (=Cyclocephala castanea [Olivier, 1789]), Melolontha immaculata Olivier, 1789 (=Cyclocephala immaculata immaculata [Olivier, 1789]), and Melolontha castanea Olivier, 1789 (=Cyclocephala castanea [Olivier, 1789]). These five species inquirenda were not originally included in Cyclocephala and are ineligible for type species fixation (ICZN Article 67.2.5).

The second and third editions of Dejean’s (1833, 1836b) catalog followed Latreille (1829) and recognized the genus Chalepus MacLeay. Three species previously included in CyclocephalasensuDejean (1821) were transferred into Chalepus in the second edition (Dejean 1833). Additional nomina nuda were included in these two genera: 19 nomina nuda in Cyclocephala and eight in Chalepus (Dejean 1833). Twenty-three nomina nuda were placed in Cyclocephala in the third edition of the catalog (Dejean 1836b). Many of Dejean’s (1821, 1833, 1836) nomina nuda were later validly described by subsequent authors (e.g., Ancognatha scarabaeoides Erichson and Ancognatha ustulata [Burmeister]).

Cyclocephala was first described and illustrated by Latreille (1829, 1837). Latreille’s (1829) short description of Cyclocephala utilized characters of the protarsal claws (unequal in size and cleft at the apex), labrum (visible anteriorly), body shape (ovoid with the head uncovered), elytra (weakly edged without significant lateral dilation), and mandibles (narrow, not strongly produced beyond clypeus, without a lateral sinus, and variably toothed). The genus was also considered variable enough to warrant subgeneric division into Chalepus and Cyclocephala (Latreille 1829). Figure plates illustrated a dorsal habitus of Cyclocephala frontalis Chevrolat, 1844 and the anatomy of the head, labrum, maxilla, and protarsus of Cyclocephala geminata (Fabricius) (=Dyscinetus dubius [Olivier]) (Latreille 1837). These illustrations are some of the earliest scientific depictions of the group.

Laporte (1840) was the first author to propose a tribal-level taxon for the cyclocephaline scarab beetles. This group, Cyclocephalites, was included along with Dynastites and Rutélites in the family Xylophiles (Laporte 1840). Cyclocephalites was not originally proposed in a Latinized form (see Smith 2006, Bouchard et al. 2011). However, because the name was subsequently Latinized by several authors (e.g., Cyclocephalidae by Burmeister [1847] and Imhoff [1856], and Cyclocephalinae by Bates [1888]) and was generally accepted, the family-group name is available from this work per ICZN Article 11.7.2. Cyclocephalites sensuLaporte (1840) was diagnosed by having the mandibles mostly covered by the clypeus and the labrum not extending anteriorly beyond the apex of the clypeus. Laporte included two divisions in Cyclocephalites. The first division, diagnosed by arched and hooked mandibles, included only Cyclocephala geminata (Fabricius, 1801) (=Dyscinetus dubius [Olivier, 1789]). The second division of Cyclocephala was diagnosed by having straight, truncate, or obtuse mandibular apices (Laporte 1840). This second division contained six species, and these are still classified in Cyclocephala.

The German naturalist and entomologist Karl Hermann Konrad Burmeister made major contributions to dynastine scarab research in the mid-19^th century (Berg 1894). Burmeister’s (1844, 1847, 1855) Handbuch der Entomologie volumes systematically organized a large portion of Scarabaeoidea. Burmeister (1847) was one of the first authors to unite members of the subfamily Dynastinae, nearly as currently circumscribed, into a single family and recognizable tribes in the modern sense. This family, Xylophila, was subdivided into Cyclocephalidae, Phileuridae, Dynastidae, Agaocephalidae, Strategidae, Oryctidae, and Xylophila amphibola (=Scarabaeidae: Cetoniinae: Trichiini, in part) (Burmeister 1847). Seven of the genera included in Burmeister’s Cyclocephalidae are still part of Cyclocephalini (Table 1). Additionally, Burmeister described five new genera and 71 species-group taxa (56 of which are valid species or subspecies) that are still included in Cyclocephalini.

Cyclocephalidaesensu Burmeister included 13 genera placed in four divisions. Two of these divisions, Cyclocephalidaespurii and Oryctomorphidae, included genera that are all currently classified in Rutelinae and various other dynastine tribes (Table 1) (Burmeister 1847, Ohaus 1929, Endrődi 1966, 1985a, Frey 1975). Cyclocephalidaegenuini was the most species-rich of Burmeister’s divisions. This group contained three genera: Augoderia, Cyclocephala, and Harposceles. Burmeister (1847) described more than 50 new taxa in Cyclocephala and treated 70 species in the genus. Cyclocephala was further organized into eight species groups based largely on head morphology: Cyclocephalae anomalinae, Cyclocephalae acutae, Cyclocephalae parabolicae, Cyclocephalae heterocerae, Cyclocephalae reflexae, Cyclocephalae microcephalae, Cyclocephalae sinuatae, and Cyclocephalae eurycephalae. These Cyclocephala species-groups were never formalized, but they were discussed by Lacordaire (1856) and Endrődi (1966).

Famous English naturalist Henry Walter Bates treated cyclocephalines in his contributions to the scientific opus Biologia Centrali-Americana and Edward Whymper’s Travels Amongst the Great Andes of the Equator (Bates 1888, 1891). Between these two works, Bates covered over 50 cyclocephaline species-level taxa, described nearly 30 new species (20 of which are still accepted as valid), and contributed to the generic-level classification of the group. For example, he recognized the distinctiveness of Ancognatha Erichson 1847 and revalidated the genus, which had been synonymized with Cyclocephala (Erichson 1847, Lacordaire 1856, Bates 1888). He described two new cyclocephaline genera: Aspidolea Bates 1888 and the eventual junior synonym Barotheus Bates, 1891 (=Ancognatha Erichson).

Following Lacordaire’s (1856) system, Bates classified the cyclocephaline scarab beetles as a subfamily (Cyclocephalinae) within Dynastidae. He only provided diagnoses for two higher groups (what he called “subtribes” within Lamellicornia) based upon labial morphology. Thus, Bates did not propose a character-based circumscription of the cyclocephaline scarabs or dynastines more broadly. However, some of the earliest detailed discussion and comparison of generic-level diagnostic characters among cyclocephalines can be found in Biologia Centrali-Americana (Bates 1888). For example, the toothless (or nearly toothless) maxillary galeae of Aspidolea and Ancognatha were recognized as providing partial justification for accepting these genera as being distinct from Cyclocephala (Bates 1888).

Bates (1888) divided Cyclocephala into a series of informal species-groups. For example, group I, which contained C. signata Fabricius (=C. amazona) was diagnosed by: 1) an elongated or protracted clypeus; 2) the clypeal apex sometimes bent at the margin; and, 3) the apex of the ligula deeply divided and widely splayed (Bates 1888). Similar diagnoses that relied upon a combination of clypeal and labial morphology were provided for five major Cyclocephala species-groups. Sexual dimorphism of the antennal club (elongated in males) was used to further subdivide one of these species-groups (Bates 1888). Bates also covered the cyclocephaline genera Dyscinetus and Stenocrates. With less available material, he was unable to make many meaningful character comparisons for these genera. However, he did mention that the dorsoventrally flattened tibiae of Stenocrates serve to diagnose that genus (Bates 1888).

Lieutenant Colonel Thomas Casey’s major contribution to scarabaeology was the sixth volume of Memoirs on the Coleoptera (Casey 1915). This volume covered Cetoniinae, Rutelinae, and Dynastinae of Central and North America. It provided keys to tribes, genera, and species, reported distributional data, and served as an outlet for the description of many new taxa. Casey (1909, 1915) treated Cyclocephalini as a tribe of Dynastinae, and he was the first Coleopterist to propose extensive generic-level reorganization of the tribe and the genus Cyclocephala. Most of Casey’s new taxa (genera, species, and subspecies) in Cyclocephalini were not accepted as valid by subsequent workers. For example, Casey described over 60 new species and subspecies of cyclocephaline scarabs. Only seven of these taxa are currently accepted as valid. Casey (1915) proposed 16 new genera and subgenera in Cyclocephalini, among which only Chalepides Casey is currently in use (Table 2). Casey (1915) was the first author to definitively place Anoplocephalus Schaeffer, 1906 (=Coscinocephalus Prell, 1936) in Cyclocephalini.

English entomologist Gilbert Arrow was notable among early 20^th century workers for his global knowledge of Dynastinae and Rutelinae. Arrow’s work in The Natural History Museum allowed him to meaningfully compare characters between diverse New and Old World taxa. For example, the genus Peltonotus (considered by most authors to be a cyclocephaline since Burmeister) was transferred into Rutelinae based on the form of the labrum (chitinized apically and projected anteriorly beyond the apex of the clypeus), which it shares with several Asian, parastasiine-like genera (Arrow 1908, 1910). Arrow (1908) described the Afrotropical cyclocephaline genus Ruteloryctes, which he compared to the New World genus Dyscinetus.

Cyclocephalines, as currently circumscribed, were covered in 11 of Arrow’s publications (Arrow 1900, 1902, 1903, 1908, 1910, 1911, 1913, 1914, 1931, 1937a, b). Arrow described over 40 new species or subspecies of cyclocephalines, and most of these were in the genus Cyclocephala. An early critic of Casey’s (1915) genus and species concepts, Arrow (1937a) argued that many of Casey’s new dynastine taxa created unnecessary “disorder” in Cyclocephalini and the subfamily more broadly. Arrow attributed this upheaval to Casey’s ignorance of species that invalidated his generic diagnoses. For example, Arrow criticized Casey’s overreliance on geographic separation of taxa and his intolerance for intraspecific variation, specimen wear, and recognition of teratological forms as distinct taxa.

Arrow (1937b) published the first comprehensive catalog of Dynastinae since Gemminger and Harold’s Catalogus Coleopterorum (see Harold 1869b). By Arrow’s admission, incorporating Casey’s cyclocephaline taxa into this catalog was challenging. Arrow struggled to place most species within Casey’s (1915) generic and subgeneric framework or assign synonymy to many species. He generally listed Casey’s higher taxa as subgeneric-level synonyms within Cyclocephala (Arrow 1937a, b). Mimeoma was accepted by Arrow (1937b), and he included a second species in the genus. Chalepides was also accepted as valid, and he elevated the subgenus to genus status (Arrow 1937a, b). Arrow expanded the composition of Cyclocephalini (Table 3) to include several Australasian genera that were later transferred to Oryctoderini (Scarabaeidae: Dynastinae) (Endrődi 1966, 1971a). Some of these Australasian genera had been placed into Cyclocephalini at the time of their description (e.g., Chalcocrates Heller, 1903).

American entomologist Lawrence Saylor authored five publications (Saylor 1936, 1937, 1945, 1946, 1948) that included cyclocephaline scarab beetles, especially focusing on North American species. Saylor’s publications were very important for the time because they offered high-quality diagnoses, keys, and illustrations for species of Ancognatha, Cyclocephala, Dyscinetus, and Erioscelis. Saylor’s approach and implied species concept arguably influenced Endrődi’s revision of the tribe (see Ratcliffe 2016 for further discussion). Saylor’s role was not as a describer of new species in the group, but rather as a primary reviser of many North American dynastine taxa that had been neglected since the works of John Lawrence LeConte (1854, 1861, 1862, 1863, 1866) and George Henry Horn (1871, 1875, 1894) and further obfuscated by Casey (1915). The problem of Casey’s numerous cyclocephaline synonyms also fell firmly on Saylor. Saylor (1937, 1945) synonymized over 30 of Casey’s taxa in Cyclocephala and Dyscinetus, which created more reliable and precise diagnoses of North American species in these genera.

Antonio Martínez was the most productive South American dynastine worker of the middle and late 20^th century. Martínez was the principal author or coauthor of 22 publications that covered Cyclocephalini (Martínez 1954, 1955, 1957, 1960a, b, 1964, 1965a, b, 1966, 1967, 1968a–c, 1969, 1975a, b, 1978a, b, D’Andretta and Martínez 1956, Bolívar y Pieltan et al. 1963, Martínez and Martínez 1981, Martínez and Morón 1984). These publications were outlets for the description of new taxa and distribution data from under-sampled areas of South America, especially from localities in Argentina, Bolivia, Brazil, Ecuador, Paraguay, Peru, and Venezuela. Martínez was an author of 25 cyclocephaline species and subspecies (23 of which are still valid) and four genera and subgenera. The genera Arriguttia Martínez, 1960 and Surutu Martínez, 1955 were accepted by subsequent authors. Albridarollia Bolívar y Pieltan, Jiménez-Asúa, and Martínez, 1963, which included two South American species, was synonymized with Cyclocephala (Endrődi 1964, 1966). The monotypic subgenus Paraclinidia Martínez, 1965 was also synonymized with Cyclocephala (Endrődi 1966).

The Hungarian Sebő Endrődi, a lawyer by formal training, was the most prolific and important dynastine worker of the 20^th century (Kaszab and Papp 1986). Endrődi, a scarabaeoid beetle specialist, was the principal author of over 200 scientific articles and books on beetle systematics (Kaszab and Papp 1986). In the post-World War II period, Endrődi vigorously undertook a world revision of the subfamily Dynastinae. These revisionary studies, the “Monographie der Dynastinae”, were published from 1966 through 1978 as a 22-part series. The series was later translated into English, synthesized, and published as a single volume, The Dynastinae of the World (Endrődi 1985a). Endrődi’s revisions (both the more detailed German-language series and the English-language book) are the basis of modern dynastine systematics research and identification.

Endrődi authored or coauthored 27 works that covered cyclocephaline scarabs from 1960 to 1985 (Endrődi 1960, 1963, 1964, 1966, 1967a–c, 1969a, b, 1970, 1971b, 1973a, b, 1975a–c, 1977a, b, 1979, 1980, 1981, 1985a, b, Howden and Endrődi 1966, Endrődi and Dechambre 1976, Dechambre and Endrődi 1983, 1984). In total, Endrődi named over 110 species and subspecies (>90 of these taxa are still valid) in cyclocephaline genera. The majority (~50% of valid taxa) of these new taxa were described in the speciose genus Cyclocephala. Generally, Endrődi did not describe new genera in this group (the junior synonym Surutoides Endrődi 1981 is the lone exception) and instead favored lumping species into relatively large genera (e.g., CyclocephalasensuEndrődi 1966 included over 180 taxa). The tribe Cyclocephalini was covered in the first installment of the “Monographie der Dynastinae” series (Endrődi 1966). One of the earliest modern discussions on the phylogenetic position of Cyclocephalini, and Dynastinae more broadly, was included in this first installment (Endrődi 1966). Many of the most detailed portions in the German-language monograph of Cyclocephalini (Endrődi 1966) were not included in The Dynastinae of the World and these details warrant further discussion.

Cyclocephalini was considered by Endrődi to be the most primitive tribe of Dynastinae, with many species sharing characters with Rutelinae (Endrődi 1960, 1966; Fig. 1). Endrődi’s (1966) methodology for assessing the relationships of dynastine tribes defies precise categorization within modern approaches. He attempted, with poor justification, to polarize a suite of characters into primitive and derived states within Dynastinae. Nine characters were scored as three states, which ranged from 1 (most derived) to 3 (ancestral). Character states scored as “2” indicated that both derived and ancestral states, or “partially differentiated” states, were present in each tribe (Endrődi 1966). Tribes with the highest total numerical value (numbers were summed across the matrix) were considered the most primitive overall.

This analysis suggests that Endrődi was attempting a very rudimentary cladistic approach to understanding dynastine tribal relationships. However, he did not define clear synapomorphic characters nor did he discuss homoplasy. This rudimentary approach was used only to hypothesize how “evolved” each of the eight dynastine tribes were compared to the outgroup Rutelinae. His results indicated the Cyclocephalini (score of 25) was the earliest diverging dynastine tribe, while Dynastini (score of 16) was the most derived tribe. Endrődi (1966) utilized the following characters in this analysis: 1) “body form” differentiated from Rutelinae or not; 2) presence or absence of “striking” sexual dimorphism; 3) relative length of the legs; 4) relative thickness of the protarsomeres and protarsal claws in males; 5) form of the anterior margin of the meso- and metatibia (“Hinterschienenspitze”); 6) presence or absence of stridulatory structures on the abdomen; 7) relative degree of expansion of the female elytral epipleuron; 8) presence or absence of hindwings; and 9) global distribution.

Endrődi also considered relationships among genera. A similar character polarization method was applied to cyclocephaline genera that were considered by Endrődi as valid (Endrődi 1966). Nine characters were used in this analysis: 1) clypeus short and simple to strongly differentiated; 2) lamellate club of the antennae elongated in males or not; 3) male protarsomeres thickened or not; 4) body shape vaulted, oval, or differentiated; 5) male parameres simple or differentiated; 6) prosternal peg short or elongated; 7) clypeus with or without bumps (“Höckern”); 8) elytral punctation disorganized, unistriate, or in paired striae; and 9) female elytral epipleuron strongly thickened or not. Augoderia, Arriguttia, and Ruteloryctes were thought to be the most “primitive” cyclocephaline genera, though Endrődi’s analysis provided only weak justification. By Endrődi’s (1966) own admission, this exercise did not yield clear results (“Aus diesen Wertzahlen ist deutlich zu erkennen, daß schon bei den Gattungen die Auswertung der primitiven und fortgeschritten Formen nur schwer vorgenommen werden kann”).

Endrődi’s (1966) diagnosis of Cyclocephalini is the most detailed published for the group, and it offers further discussion on the distribution of some character states among the tribe’s genera. Members of Cyclocephalini were diagnosed as being small- to medium-sized, primitive dynastines that share the oval and convex body shape of Rutelinae. The body shapes of the genera Arriguttia (anteroposteriorly compressed) and Surutu (dorsoventrally flattened) were considered exceptional in the tribe. Cyclocephaline mandibles were considered small (varying in width or broadness) for the subfamily and lacking teeth on the lateral, outer margin. Cephalic morphology in the tribe was notable for its lack of horns, tubercles, carinae, or sulci. The slightly raised frontoclypeal suture present in some Ancognatha species was a possible exception to this lack of armature on the head. These “tubercles”, however, were not considered homologous with tubercles of the head present in other dynastines (Endrődi 1966).

Cyclocephaline antennae are comprised of 8–10 antennomeres with the lamellate club always three-segmented and occasionally elongated in males (Endrődi 1966). The pronotum is convex and only dorsoventrally flattened in Surutu, while the scutellum is triangular. The elytra are usually 1.5 times longer than wide and are rarely shorter (e.g., Arriguttia). Elytral punctation is regularly spaced and paired when punctures form striae (except for Augoderia and Surutu). The females of many species have pronounced expansions of the elytral epipleural margin with or without produced lateral flanges (Endrődi 1966).

The propygidium of cyclocephalines lacks a stridulatory apparatus (Endrődi 1966). Pygidial morphology varies between the group’s genera. The pygidium is reduced in Chalepides, while it is a large segment in all other cyclocephaline genera. The prosternal process is relatively long and generally rounded at the apex, but has a variably present or absent button-like folding of the cuticle (Endrődi 1966). Protibial morphology in the tribe is also highly variable. The outer lateral margins of the protibia in males have 1–3 produced teeth, while most genera have no teeth on the inner lateral margin of the protibia. Harposceles is the lone exception for the tribe, having a small tooth on the inner margin of the protibia (Endrődi 1966).

Three genera included in CyclocephalinisensuEndrődi (1966) lack thickened, foreshortened protarsomeres and enlarged (and sometimes cleft) protarsal claws in males: Erioscelis, Stenocrates, and Coscinocephalus. The meso- and metatarsomeres are not thickened and foreshortened in any cyclocephaline genera (though metatarsomeres are reduced in females of some Cyclocephala species). The apical margins of the meso- and metatibia are simple in cyclocephalines, lacking crenulated extensions (“Hinterschienenspitze fast immer gefingert”) (Endrődi 1966). CyclocephalinisensuEndrődi (1966, 1985a) included 14 genera and was a strictly New World tribe, except for the Afrotropical genus Ruteloryctes (Table 4).

Endrődi (1966) considered the criteria for defining genera like those used to define families. Within this concept, genera were phylogenetic units that needed to show several characteristics in a “constant state” to be valid (Endrődi 1966). This line of argumentation was extended into a criticism of several genera and subgenera proposed within Cyclocephalini. Casey’s generic-level hypotheses in Cyclocephalini were especially in violation of this guiding principle. Endrődi considered most of Casey’s genera as based upon only a single character and were thus invalid within his paradigm. It was also argued that Casey’s subgenera were based upon species-level characters and not applicable to higher-level classification schemes (Endrődi 1966). This led to the synonymy of nearly all of Casey’s higher-level cyclocephaline groups, some of which were tentatively adopted by other authors in the intervening period (e.g., Arrow 1937a, b, Saylor 1937, 1945, and Buchanan 1927) (Casey 1915, Endrődi 1966). The subgenus Cyclocephala (Paraclinidia) was ambiguously synonymized within Cyclocephala, and Endrődi (1966) commented that the group could “at most be considered a subgenus.”

An explanation of some aspects of Endrődi’s (1966) morphological approach to his revision of Cyclocephalini was provided in a section entitled “Morphologie der Tribus.” Three types of coloration schemes are found in the tribe: 1) species that are all black or dark brown, except in teneral specimens (e.g., Surutu, Harposceles, Coscinocephalus, Erioscelis, Ruteloryctes, Stenocrates, Dyscinetus, Chalepides, and occasionally other genera); 2) species that are monotoned and light in color, sometimes with darkened legs and head, and lacking dorsal maculae (e.g., Cyclocephala and Aspidolea); and 3) species with red or black dorsal maculae (e.g., Augoderia, Ancognatha, and Cyclocephala) (Endrődi 1966). Among species with dorsal maculae, Endrődi considered these characteristics to be highly variable within a “system” of patterning that displayed some species-level specificity. Some species vary from having elaborate dorsal maculae to being nearly free of patterning, and these species were the most challenging for precise identification (Endrődi 1966).

Short or long setae on the head and thorax were useful characters for diagnosing species. Endrődi thought that setae on the frons and anterolateral margins of the pronotum were particularly easy to observe (even when eroded) because they were erect and in obvious punctures. The shape of the clypeus, important since Burmeister (1847), was considered diagnostic in Mimeoma, Ancognatha, Stenocrates, and Aspidolea (Endrődi 1966). However, clypeal shape was considered too variable among species for diagnosing groups in other genera such as Cyclocephala (Endrődi 1966). Sculpturing and rugosity of the frons, interocular distance, and shape of the frontoclypeal suture were considered stable characters within species (Endrődi 1966). He noted that there is significant variation of the mouthparts (labrum, ligula, maxillae, and mandibles) among cyclocephalines and observed this variation mostly from dissected Burmeister type specimens. Due to the number of species and specimens he needed to examine, Endrődi eschewed characters that required dissection (except for male genitalia) to observe. Thus, he generally did not use mouthpart or hindwing characters in his diagnoses for genera or species. The usefulness of mouthpart and hindwing characters for circumscribing groups remains largely unevaluated in Cyclocephalini and Dynastinae.

Dynastine scarab enthusiast Roger-Paul Dechambre, a former curator of Coleoptera at Museum National d’Histoire Naturelle in Paris, published 21 papers or book chapters on Cyclocephalini (Dechambre 1979a–c, 1980, 1982, 1985, 1991a, b, 1992, 1995, 1997, 1999, 2000, 2006a, b, Dechambre and Duranton 2005, Dechambre and Endrődi 1983, 1984, Dechambre and Hardy 2004, Dupuis and Dechambre 1995, Ponchel and Dechambre 2003). Dechambre was a prolific describer of cyclocephaline taxa, having authored or coauthored over 80 species and subspecies in the group (only five of which are currently junior synonyms). Most of these taxa were described in Cyclocephala (65 species and subspecies) and Stenocrates Burmeister (15 species). Beyond his Cyclocephala expertise, he described the second species of the African genus Ruteloryctes (Dechambre 2006b), a species of Chalepides (Ponchel and Dechambre 2003), a species of Ancognatha (Dechambre 2000), and three species of Aspidolea (Dechambre 1992). Nearly all of Dechambre’s new cyclocephaline taxa are South American, which highlights the need for continued work on that fauna.

Dechambre’s treatment of cyclocephaline genera was conservative. Dechambre did not describe any new cyclocephaline genera, and he synonymized Surutoides with Cyclocephala (Dechambre 1991a). Dechambre seems to have favored treating “species groups” in lieu of upsetting the classification of Cyclocephala. For example, Dechambre (1997) revised the “Cyclocephala cribrata species group” which included the relatively large, black species of Cyclocephala previously included in Mononidia and Surutoides.

Fortuné Chalumeau worked on revising the West Indian scarabaeoids, especially on islands under French sovereignty. Chalumeau’s articles provided identification keys and diagnoses for Cyclocephala, Chalepides, and Dyscinetus species found across the Lesser Antilles (Chalumeau and Gruner 1977, Cartwright and Chalumeau 1978, Chalumeau 1982, 1983, Dutrillaux et al. 2013). Fabien Dupuis described 16 cyclocephaline species in Aspidolea, Cyclocephala, Dyscinetus, and Stenocrates (Dupuis and Dechambre 1995, Dupuis 1996, 1999, 2006, 2008, 2009, 2014, 2017, 2018). All of Dupuis cyclocephaline taxa were described from Ecuador, French Guiana, Peru, Bolivia, Venezuela, and Colombia.

Brett Ratcliffe, Curator of Entomology at the University of Nebraska State Museum, greatly expanded upon Endrődi’s dynastine research in the Nearctic and Neotropical realms. Ratcliffe has authored or coauthored 39 publications that cover cyclocephaline scarabs, and many of these are monographic in scope (Ratcliffe 1977, 1978, 1981, 1985, 1986, 1989, 1991, 1992a–d, 2002a, b, 2003, 2008, 2014, 2015, Ratcliffe and Cave 2002, 2006, 2008, 2009, 2010, 2015, 2017, Ratcliffe et al. 2013, 2015, Ratcliffe and Delgado-Castillo 1990, Ratcliffe and Hoffman 2011, Ratcliffe and Morón 1997, Ratcliffe and Paulsen 2008, Figueroa and Ratcliffe 2016, Gasca-Álvarez et al. 2014, Jameson et al. 2002, 2009, Maes and Ratcliffe 1996, Maes et al. 1997, Neita-Moreno et al. 2006, 2007, Saltin and Ratcliffe 2012).

This body of research includes the description of over 60 new cyclocephaline species, only eight of which are in synonymy. These publications are mostly focused on Central or Mesoamerican taxa, but they also enhance knowledge of the poorly known South American genera Surutu and Harposceles. Ratcliffe, with collaborators Ronald Cave and Enio Cano, have systematically treated Dynastinae north of Panama, including the West Indies (Ratcliffe 2003, Ratcliffe and Cave 2006, 2015, 2017, Ratcliffe et al. 2013). These monumental works provide the most comprehensive, authoritative taxonomic treatment (synonymy and consistent species concept), identification tools, distribution data, and synthesized biological information ever produced for the subfamily in the New World. Venezuelan scarabaeologist Luis Joly, along with collaborator Hermes Escalona, advanced understanding of the group in South America, having revised Chalepides and the Dyscinetus of Venezuela (Joly and Escalona 2002, 2010). Joly has also described several new species of Cyclocephala from across South America and the West Indies.

Recent publications have generally been conservative regarding the generic composition of Cyclocephalini. Morón and Ratcliffe (1996) transferred the genus Coscinocephalus from Cyclocephalini to Pentodontini based on characters of the head, mouthparts, and parameres shared with Orizabus Fairmaire, 1878. The work of Mary Liz Jameson, while focused mainly on the subfamily Rutelinae, has altered the concept of Cyclocephalini (Jameson 1998, Jameson et al. 2002, Jameson and Wada 2004, 2009, Jameson and Jákl 2010, Jameson and Drumont 2013). Two genera, Acrobolbia Ohaus, 1912 and Peltonotus, previously classified in Rutelinae were transferred into Cyclocephalini based on morphological phylogenetic analyses (Jameson 1998, Jameson et al. 2002, Jameson and Wada 2004).

Several species of wetland birds, reptiles, and amphibians prey on Chalepides, Cyclocephala, and Dyscinetus species in mucky habitats. White-faced ibis (Plegadis chihi (Vieillot)), white ibis (Eudocimus albus (Linnaeus)), and scarlet ibis (E. ruber (Linnaeus)) eat adult Dyscinetus and Chalepides in Argentina and Venezuela (Aguilera et al. 1993, Soave et al. 2006.). Common terns (Sterna hirundo Linnaeus), white-browed blackbird (Sturnella superciliaris (Bonaparte)), yellow-winged blackbird (Agelaius thilius (Molina)), Olrog’s gull (Larus atlanticus Olrog), and brown-hooded gull (L. maculipennis Lichtenstein) eat Dyscinetus spp. and C. signaticollis in Argentinian marshes, grasslands, lagoons, and riparian areas (Darrieu et al. 2001, Mauco and Favero 2004, Camperi et al. 2004, Ghys and Favero 2004, Berón and Favero 2010). Clapper rails (Rallus crepitans Gmelin) hunt D. morator in Louisiana marshes (Roth et al. 1972). Wattled Jacana (Jacana jacana (Linnaeus)) have been observed to catch and eat Cyclocephala species associated with Amazonian water lilies (Prance and Arias 1975). Lizards and birds will quickly eat Cyclocephala if they are knocked out of Cyclanthus spathes during the day (Beach 1982).

Juvenile brown caimans (Caiman crocodilus fuscus (Cope)) in Costa Rica feed primarily on insects, especially Dyscinetus (Allsteadt and Vaughan-Dickhaut 1994). The invasive cane toad (Rhinella marina (Linnaeus)) eats C. barbatus in Puerto Rico (Wolcott 1937). In the American southwest, Couch’s spadefoot toad (Scaphiopus couchii Baird) will readily eat A. manca and Cyclocephala species (Dimmitt and Ruibal 1980). Mammal predation on cyclocephalines has rarely been documented, but it is suspected that fossorial mammals, such as armadillos, would consume larvae (Tashiro 1987). Mountain coati, Nasuella olivacea (Gray), dig up and eat A. scarabaeoides larvae in the Eastern and Central Colombian Cordilleras (Apolinar Maria 1946). Several species of bat are known to eat Cyclocephala seasonally or opportunistically (Goldman and Henson 1977, Johnston and Fenton 2001, Lenoble et al. 2014).

Cyclocephaline scarab beetle larvae are subject to parasitism by ecto- and endoparasitoid flies and wasps. The fly Mallophora ruficauda Wiedemann (Diptera: Asilidae) is a koinobiont parasitoid of C. signaticollis (Barrantes and Castelo 2014). Mallophora ruficauda can also attack C. putrida and C. modesta, but the fly does not complete its development on these hosts or the adult flies are stunted and deformed (Barrantes and Castelo 2014). Two other asilid flies, M. sylverii Macquart and Diogmites vulgaris Carrera, parasitize Dyscinetus rugifrons in Brazil (Dennis and Knutson 1988). Dyscinetus species are parasitized by Tiphia parallela Smith (Hymenoptera: Tiphiidae) in Guyana (Box 1925). Tiphia pygidialis Allen parasitizes C. borealis, C. lurida lurida, and C. pasadenae (Rogers and Potter 2004). Cyclocephala pasadenae was demonstrated to be toxic to spiders of several families when eaten, though the mechanism of this toxicity remains unexplained (Cokendolpher 1993). Ants can be significant egg and larval predators of C. lurida lurida in turfgrass (Zenger and Gibb 2001). The parasitoid larvae of Plega banksi Rehn (Neuroptera: Mantispidae: Symphrasinae) attack Cyclocephala pupae in Arizona (Werner and Butler 1965).

Cyclocephalines, like many relatively large beetles, are hosts of phoretic mites. Acarid and macrochelid mites have been reported from Cyclocephala (Goldwasser 1987, Crocker et al. 1992). Phoretic macrochelid mites on Cyclocephala are common in aroid inflorescences visited by the beetles, and the mites appear to feed on floral exudates (Goldwasser 1987). The mesostigmatid Dyscinetonyssus hystricosus Moss and Funk is hypothesized to be a parasite of D. morator (Moss and Funk 1965). This conclusion was based on morphological features of the mites consistent with parasitic habits and the observation that all life-stages and sexes of the mites are present on D. morator (Moss and Funk 1965).

Entomopathogenic nematodes are remarkable for their ability to attack and kill numerous insect pests. Their flexibility of use, combinability with other chemical and biological controls, and safety has led to their use in IPM strategies for control of C. borealis, C. pasadenae, C. lurida lurida, and C. hirta grubs (Kaya et al. 1995, Koppenhöffer and Kaya 1997, 1998, Converse and Grewal 1998, Koppenhöffer and Fuzy 2003, Koppenhöffer et al. 1999, 2002, 2004). Many species and strains of Steinernema Travassos (Nematoda: Steinernematidae) and Heterorhabditis Poinar (Heterorhabditidae) infect these Cyclocephala species, though C. pasadenae appears to have the most natural resistance to nematode infection among examined North American Cyclocephala (Koppenhöffer and Kaya 1996, Koppenhöffer et al. 2004).

Nematode infections of South American cyclocephalines have received some attention. The Argentinian pest grub C. signaticollis is naturally infected by two rhabditid and two thelastomatid nematodes (Reboredo and Camino 2000, Camino and Reboredo 2005, Camino and Achinelly 2012). Cyclocephala modesta hosts a thelastomatid parasitic nematode in its alimentary canal (Achinelly and Camino 2008). Ancognatha scarabaeoides, a major grub pest in Colombia, can be readily infected by Steinernema nematodes (Lucero Malfa et al. 2006). Dyscinetus morator can be an intermediate host of the swine parasite, thick stomach worm (Ascarops strongylina [Rudolphi]; Nematoda: Spirocercidae) (Fincher et al. 1969). Beyond nematodes, information regarding the infection of cyclocephalines by other worms is lacking. The only known example is that of D. gagates adults, which are suitable intermediate hosts of the rat tapeworm (Hymenolepis diminuta [Rudolphi]; Cestoda: Hymenolepididae) under laboratory conditions (Bacigalupo 1939).

Bacterial and fungal pathogens have proven useful for IPM of injurious scarab grubs, especially Japanese beetle (Popillia japonica Newman). Several of the most important pathogens for P. japonica control have been explored for use on Cyclocephala species. The fungal parasites Beauveria bassiana (Bals.-Criv.) Vuill and Metarhizium anisopliae (Metchnikoff) Sorokin (both Sordariomycetes: Hypocreales) have been evaluated for pathogenicity and virulence in C. signaticollis, C. borealis, and C. lurida lurida (Berón and Diaz 2005, Redmond and Potter 2010). Experiments demonstrated that one Brazilian strain of B. bassiana caused significant mortality against C. signaticollis, while native strains of M. anisopliae were not pathogenic in this species (Berón and Diaz 2005). This relatively low mortality caused by B. bassiana and M. anisopliae was also observed in C. lurida lurida, but both fungal pathogens display synergism with entomopathogenic nematodes (Wu et al. 2014). Cyclocephala borealis and C. lurida lurida larvae surveyed from Kentucky golf courses also showed low infection rates by M. anisopliae (Redmond and Potter 2010). Cyclocephala parallela can also be naturally infected by M. anisopliae in sugarcane fields (Boucias et al. 1986). Metarhizium anisopliae – based control measures of A. scarabaeoides may have promise in Colombia, as at least one identified strain causes high mortality in this species (Marino et al. 2004).

Milky disease, caused by the bacterium Paenibacillus popilliae Dutky (Bacillales: Paenibacillaceae), is the only registered biological control specifically for P. japonica (Koppenhöfer et al. 2000). Infections of the disease are chronic in populations, but infection rates grow slowly (Klein 1992). Thus, milky disease is effective for inoculative, long-term treatments rather than as an emergency control measure (Klein 1992). Several Cyclocephala species can be infected by P. popilliae. Cyclocephala parallela larvae infected by P. popilliae show significantly higher mortality than healthy larvae (Boucias et al. 1986, Cherry and Boucias 1989, Cherry and Klein 1997).

Bacillus thuringiensis Berliner (Bt) is the most important bacterial biological control agent of insects, but there is a lack of information about infectivity in cyclocephalines. What is known about Bt in Cyclocephala suggests that infections enhance other biological control methods. Like fungal infections, bacterial infections by B. t. subspecies japonensis Buiui and P. popilliae cause additive or synergistic mortality with entomopathogenic nematodes in C. hirta and C. pasadenae (Thurston et al. 1993, 1994, Koppenhöfer and Kaya 1997, Koppenhöfer et al. 1999). Bt isolated from C. signaticollis in Argentina caused 100% mortality in inoculated larvae (Consolo et al. 2010).

Based on the most specific available data, about 97 cyclocephaline scarab beetle species have been reported from the flowers of at least 58 plant genera representing 17 families and 15 orders (Moore and Jameson 2013), though new data are being published often. The preponderance of data suggests that tropical cyclocephaline species are involved in a pollination mutualism with species in the early-diverging angiosperm families Nymphaeaceae, Annonaceae, Magnoliaceae, Araceae, Cyclanthaceae, and Arecaceae (Moore and Jameson 2013). More sporadic data suggests that cyclocephaline floral visitation of more derived angiosperm groups is opportunistic and not adequately explained. However, based on the observations of Prance (1976), Cyclocephala species may be unrecognized pollinators of some Neotropical genera of the Brazil nut family (Lecythidaceae).

The mutualism between cyclocephaline scarab beetles and these early-diverging angiosperms has resulted in a cantharophilous floral syndrome in these groups. This floral syndrome is the result of the convergent evolution of several floral traits that accommodate “mess-and-spoil” beetle pollination (Faegri and van der Pijl 1979). Among the families Nymphaeaceae, Annonaceae, Magnoliaceae, Araceae, Cyclanthaceae, and Arecaceae these convergent floral traits include: 1) bisexuality of flowers or inflorescences; 2) protogyny; 3) nocturnal flower activity; 4) relatively large flowers or inflorescences that provide a “pollination chamber” and are sturdy enough to withstand beetle damage; 5) thermogenesis during anthesis; 6) production of excess pollen, floral exudates, or sterile floral parts as a food reward; 7) coordination of timing between beetle behavior, thermogenesis, and floral sexual stages; 8) large pollen grains; 9) sticky floral exudates; 10) strong floral scents and; 11) pale colored flowers or inflorescences (Bawa and Beach 1981, Bernhardt 2000, Silberbauer-Gottsberger et al. 2001, Davis et al. 2008, Thien et al. 2009, Gibernau et al. 2010). Excellent observational and experimental evidence indicates that cyclocephaline scarab beetles are primary or secondary pollinators of these plant groups (Cramer et al. 1975, Beach 1982, 1984, Young 1986, 1988a, b, Gottsberger 1989, Dieringer et al. 1999, Hirthe and Porembski 2003, Maia et al. 2012). Cyclocephalines are offered rewards for their pollination of these families. These rewards include access to aggregation and mating sites, food, and metabolic boosts associated with floral thermogenicity.

Facultative endothermy (sustained increase in thoracic muscle temperature) during rest, terrestrial activity, and preparation for flight has been documented in Coleoptera and Scarabaeidae more narrowly, including Cyclocephala species (Bartholomew and Casey 1977a, b). Among some examined dung beetles, changes in thermoregulation and behavior are associated with high levels of intra- and interspecific competition for rapidly depleting dung resources (Heinrich and Bartholomew 1979, Ybarrondo and Heinrich 1996). Cyclocephala colasi Endrődi experience sporadic bouts of endothermy during the early evening when these beetles fly between inflorescences (Seymour et al. 2009). These bouts of endothermy are more intense at lower ambient temperatures and continue throughout the night, when they may be associated with feeding, mating, or escape behaviors (Seymour et al. 2009). The host plant, Philodendron solimoesense A.C.Sm. (Araceae), continues thermogenesis even after floral scent compounds have been volatilized (Seymour et al. 2003). This suggests that the increased temperature of the inflorescences serves as a thermal reward to the beetles, lowering the amount of energy spent achieving sporadic endothermy (Seymour et al. 2003, 2009). Thermal rewards of this nature are predicted to be more important in montane forest habitats with much lower average ambient temperatures than lowland rainforests (Seymour et al. 2009).

Cyclocephaline scarab beetles have been observed to mate within the inflorescences or flowers of many families: 1) Nymphaeaceae (Prance and Arias 1975; Hirthe and Porembski 2003); 2) Annonaceae (Gottsberger 1990, Murray 1993, Costa et al. 2017); 3) Magnoliaceae (Gibbs et al. 1977, Dieringer and Espinosa 1994, Dieringer et al. 1999); 4) Cyclanthaceae (Beach 1982); 5) Araceae (Young 1986, 1988a, b, Maia and Schlindwein 2006, Grimm 2009, Seymour et al. 2009, Moore 2012); 5) Arecaceae (Beach 1984, Rickson et al. 1990, Voeks 2002); 6) Solanaceae (Ratcliffe and Cave 2017); and possibly 7) Cactaceae (B. Schlumpberger in litt. 2011). Large, chamber-like flowers also serve to protect the beetles from predation (Prance and Arias 1975, Beach 1982).

Floral food rewards for these scarab beetles are diverse and include sterile staminate or staminode tissue (Prance 1976, 1980, Young 1986, Maia et al. 2010, Maldonado et al. 2015), carpellary appendages (Prance and Arias 1975, Hirthe and Porembski 2003), stamens (Dieringer and Espinosa 1994, Hirthe and Porembski 2003, Costa et al. 2017), petal tissue (Gibbs et al. 1977, Gottsberger 1989, Dieringer and Espinosa 1994, Dieringer et al. 1999, Voeks 1992), specialized adaxial food tissue of bracts (Beach 1982), and pollen (Rickson et al. 1990). Cyclocephala amazona was observed consuming epidermal trichomes from the stalk of Bactris gasipaes Kunth (Arecaceae) inflorescences before feeding on pollen (Rickson et al. 1990). These trichomes are hypothesized to serve as non-nutritional gastroliths that aid in the piercing of pollen grains in the beetles’ gut (Rickson et al. 1990). Some Cyclocephala species may be destructively florivorous and detrimental to the reproductive success of the plants they visit. For example, Cyclocephala species are known to destructively feed on flowers of some crop plants (Remillet 1988, Posada Ochoa 1989) and the cactus species Echinopsis ancistrophora Speg. (Schlumpberger et al. 2009) and Opuntia monocantha Haw (Lenzi and Orth 2011).

Cyclocephaline attraction to their floral hosts is hypothesized to be driven by both long-distance chemical cues and short-distance visual stimuli. In the case of Philodendron bipinnatifidum Schott ex Endl. (Araceae), Erioscelis emarginata (Mannerheim) will not land on inflorescences covered in black cloth (obscuring visual stimuli associated with the scent releasing plant) (Gottsberger and Silberbauer-Gottsberger 1991). Furthermore, experiments demonstrated that these beetles were differentially attracted to P. bipinnatifidum spathes covered in yellow paper, indicating that contrasting colors play a role in close range attraction (Gottsberger and Silberbauer-Gottsberger 1991). Slight differences in spathe color and scent have also been hypothesized to influence the community of Cyclocephala spp. visiting Dieffenbachia spp. inflorescences in Costa Rica and Panama (Beath 1999). The white flowers of Victoria amazonica (Poepp.) J.C. Sowerby (Nymphaeaceae) have been hypothesized to aid in the attraction of cyclocephalines, along with their heavy floral scent (Prance and Arias 1975). Contrasting colors have also been suggested to play a role in the attraction of Cyclocephala species to Cyclanthus (Beach 1982).

The chemical composition of the floral scents attractive to cyclocephalines has received some research attention. These heavy scents are generally only volatile at elevated temperatures during floral thermogenesis. For example, protogynous P. bipinnatifidum inflorescences can reach an astonishing 46˚C during the female phase of anthesis (Gottsberger and Silberbauer-Gottsberger 1991). Research on these floral scents reveals that while they are complex chemical mixtures, a single dominant scent compound is sufficient for cyclocephaline attraction. In Brazil, the nitrogen and sulfur containing compound 4-methyl-5-vinylthiazole is the dominant floral scent constituent in four Annona spp. (Annonaceae) and Caladium bicolor (Aiton) Vent. (Araceae) pollinated by Cyclocephala species (Maia et al. 2012). Scent trap experiments confirmed that this compound alone was sufficient to attract these beetles (Maia et al. 2012).

Dötterl et al. (2012) identified three main compounds present in the P. bipinnatifidum floral scent that are attractive to E. emarginata. The dominant compound alone, 4-vinylanisole (also called 4-methoxystyrene), was sufficient to attract E. emarginata and various mixtures of the three scents also served to attract the beetles (Dötterl et al. 2012). A mixture of dihydro-β-ionone and methyl jasmonate was synergistically attractive to E. emarginata, which pollinates Philodendron adamantium Mart. ex Schott (Araceae) (Pereira et al. 2014). Among Nymphaea spp. (Nymphaeaceae) pollinated by Cyclocephala, floral scents are dominated by aromatic ethers and aliphatic esters (Maia et al. 2014). 4-vinylanisole is also present in Nymphaea species pollinated by Cyclocephala, suggesting that some Nymphaea spp. and P. bipinnatifidum may have converged on a similar floral scent for attracting these beetles. The ester methyl-2-methylbutanoate is the dominant floral scent compound in Magnolia ovata (A.St.-Hil.) Spreng. (Magnoliaceae) and is sufficient to attract C. literata Burmeister (Gottsberger et al. 2012). (S)-2-hydroxy-5-methyl-3-hexanone is one of the dominant compounds in the floral scent of Taccarum ulei Engl. & K.Krause and is sufficient to attract its Cyclocephala pollinators (Maia et al. 2013).

The mechanisms of attraction of cyclocephalines to other flower groups is poorly understood. The phytelephantoid palms (Arecaceae) Phytelephas aequatorialis Spruce, P. macrocarpa Ruiz & Pav., P. seemannii O.F. Cook, and Aphandra natalia (Balslev & A.J. Hend.) Barfod, all visited by Cyclocephala, have floral scents that are dominated by 4-methylanisole and 2-methoxy-3-sec-butyl pyrazine (Ervik et al. 1999). The presence of anisoles in the floral scents of phytelephantoid palms, Nymphaeaceae, and Araceae suggests that this class of compounds may have convergently evolved in these groups for attraction of cyclocephalines. Cyclanthus bipartitus Poit., visited by several Cyclocephala species, has a floral scent dominated by a unique compound called (E)-cyclanthone (Schultz et al. 1999). Heavy floral scents are likely to play a role in cyclocephaline attraction in every case. For example, C. melanocephala has been collected in the flowers of Datura and related genera (Solanaceae) from across its range (Moore and Jameson 2013). The dominant floral scent compounds found in these flowers are very different from those in early diverging angiosperms described above, and are comprised mostly of terpenes, terpenoids, and aromatic alcohols (Raguso et al. 2003).

Some authors have speculated that floral scent compounds are serving as surrogate sex pheromones for cyclocephalines (Schatz 1990, Dieringer et al. 1999). No specific Cyclocephala-derived sex pheromones have been chemically identified (Leal 1996), though some North American Cyclocephala species appear to use volatile pheromones. For example, C. lurida and C. borealis females use pheromones to attract males, and these pheromones are cross-attractive to males of both species (Potter 1980). Further experiments demonstrated that C. lurida larvae produce a similar male-attracting compound that elicits attempted mating (Haynes et al. 1992). These pheromones are present in all three instars and pupae (Haynes and Potter 1995). Cross-attractiveness of C. lurida pheromone extracts are limited to C. borealis, as C. pasadenae and C. longula are not attracted to these scents (Bauernfeind et al. 1999).

In cases of cross-attractive pheromones, it can be predicted that some other mechanism (temporal or behavioral) maintains species boundaries. For sympatric C. lurida and C. borealis in Kentucky, differences in peak flight time and mating periods throughout the night serve to temporally isolate these species (Potter 1980). If attractive floral scents are serving as sex pheromones for tropical cyclocephalines, then the mechanisms isolating species remain unexplained. Only one case of interspecific copulation has been documented for cyclocephalines. The South American species C. putrida was observed mating at light traps, and several male C. putrida copulated with females of a Tomarus sp. (Dynastinae: Pentodontini) (Bosq 1936). Because these tropical cyclocephalines often mate within their host inflorescences, it is unclear how sexual isolation is maintained when congenerics are present. Diagnostic secondary sexual characters of the elytral epipleuron in females and protarsal and paramere morphology in males may be involved in the sexual isolation of cyclocephaline species (Moore 2012).

Many different cyclocephaline species can be found associated with a floral host at a specific time or throughout a season. There is little evidence for monophagy in the group, and available data indicate that tropical cyclocephalines are predominantly oligophagous or polyphagous floral feeders (Moore and Jameson 2013). For example, C. bipartitus inflorescences can contain up to three Cyclocephala species at one time (Beach 1982). Parsing out how redundant cyclocephalines are in their pollinator functions has been assessed in a few cases. Detailed studies on Dieffenbachia Schott (Araceae) indicate that among a group of cyclocephaline floral visitors, some species are relatively more effective pollinators (Young 1988a). Seasonal abundance of cyclocephalines at a specific locality, along with floral phenology, may also determine which species are primary or secondary pollinators (Maia et al. 2010, Costa et al. 2017).

The only known cyclocephaline fossil is from the extant South American species C. signaticollis. A fossilized elytron and pronotum of an unsexed C. signaticollis individual were discovered in Buenos Aires Province, Argentina (Ramírez and Alonso 2016). The fossil is from the Late Pleistocene (Tarantian Stage) and the sediments containing the fossil dated between 12,100 ± 100 BP and 13,400 ± 200 BP (Ramírez and Alonso 2016). Neoichnological experiments demonstrated that C. borealis and C. lurida lurida larvae create diagnostic backfilled meniscate burrows and ellipsoidal chambers as they burrow through soil, while adults create poorly organized backfilled burrows (Counts and Hasiotis 2009). The diagnostic features of these burrows may allow for the future detection of cyclocephaline scarab beetle ichnofossils.

Very little is known about the phylogeny of Dynastinae, and the monophyly of its tribes is in doubt. The lack of phylogenetic framework for the subfamily has limited the ability to hypothesize sister relationships among tribes and reconstruct the evolution of ecological (e.g., the floral feeding syndromes in Cyclocephalini) and morphological (e.g., such as thoracic and cephalic armature in Oryctini and Dynastini) traits. Indeed, the most meaningful comparison of characters for Dynastinae in the literature has centered around the subfamily’s relationship to Rutelinae, especially among cyclocephalines (Jameson 1998, Jameson et al. 2002, Jameson and Wada 2004). Several studies have begun to address this gap in knowledge.

The morphological phylogenetic analysis (128 characters) of Rutelina (Rutelinae: Rutelini) (Jameson 1998) was the first empirical study to suggest that the monobasic ruteline tribal- and subtribal-groups Peltonotini and Acrobolbiina were more closely related to Cyclocephalini than Rutelini. This analysis, however, did not include enough exemplar taxa from Dynastinae to conclude anything about tribal relationships in the subfamily. Schiestl and Dötterl (2012) used an analysis of 18S sequence data to examine the evolution of olfactory preferences in scarabaeoids. This analysis suggested a sister relationship between Dynastinae and Rutelinae, but it did not resolve intrasubfamilial relationships of the included genera nor did it report statistical support for recovered nodes (Schiestl and Dötterl 2012). A Cyclocephala exemplar species was included in this analysis, and this species fell within the dynastine clade (Schiestl and Dötterl 2012). Rowland and Miller (2012) performed a four-gene phylogenetic analysis of Dynastini (Dynastinae) that included one Cyclocephala exemplar. This analysis was useful for recovering subtribal relationships within Dynastini, but the relationship of Dynastini to Cyclocephalini (Cyclocephala) and Pentodontini (Orizabus) was unresolved (Rowland and Miller 2012, see also Jin et al. 2016).

The most informative molecular phylogenetic analyses of phytophagous scarabs to date were conducted by McKenna et al. (2014) and Gunter et al. (2016). Both studies represent huge leaps forward in our understanding of subfamilial relationships in Scarabaeidae due to their resolution, statistical support, and taxa sampling. Despite their strengths, these studies are difficult to compare because of differences in gene selection and small (but significant for interpretation) differences in taxa sampling. McKenna et al. (2014) utilized 28S and CAD to phylogenetically analyze staphyliniform beetle (Histeroidea, Hydrophiloidea, and Staphylinoidea) relationships while using Scarabaeiformia as an outgroup. The most derived group of Scarabaeidae recovered from this analysis was a clade that included Cetoniinae + (Dynastinae and Rutelinae) (McKenna et al. 2014) (Fig. 2). Rutelinae was recovered as polyphyletic (McKenna et al. 2014) (Fig. 2). Three orthochilous (labrum vertically produced from clypeus and fused to clypeus) and three homalochilous (labrum horizontally produced relative to the clypeus and separated from the clypeus by a suture) rutelines from four total tribes were included in the analysis (McKenna et al. 2014). The included orthochilous rutelines (Anoplognathini and Anatistini) were recovered in the same clade, but the group was not monophyletic (McKenna et al. 2014) (Fig. 2).

The homalochilous Rutelinae (Anomalini and Rutelini) were polyphyletic, with Oryctomorphus (Rutelini) falling into a clade including Anatistini and Anoplognathini(McKenna et al. 2014). Three dynastines were included: Dynastes, Cyclocephala, and Peltonotus (McKenna et al. 2014). Cyclocephala was recovered in a clade along with Dynastes (McKenna et al. 2014) (Fig. 2). However, Peltonotus was recovered in a sister clade that included the remaining homalochilous rutelines (Popillia and Parastasia) (McKenna et al. 2014) (Fig. 2). These results suggest that Cyclocephalini is correctly classified in Dynastinae, but that the tribe is polyphyletic if it includes Peltonotus. This phylogenetic analysis is more in line with the placement of Peltonotus near the Asian parastasiine rutelines by Arrow (1908, 1910) than the hypotheses of Jameson (1998).

Gunter et al. (2016), building on the datasets of Ahrens et al. (2011, 2014), utilized 16S, 12S, CO1, and 28S to conduct a phylogenetic analysis of Scarabaeoidea that included over 400 taxa. A clade including Cetoniinae + (Dynastinae and Rutelinae) was recovered, but the node uniting these subfamilies was only weakly supported (0.89 posterior probability) (Gunter et al. 2016) (Fig. 3). These three analyses, built from similar datasets, together suggest that Rutelinae is a paraphyletic grade of tribes (Ahrens et al. 2011, 2014, Gunter et al. 2016). The subfamily Dynastinae in these analyses was consistently recovered as the most derived of all scarabaeoids (Ahrens et al. 2011, 2014, Gunter et al. 2016). Gunter et al. (2016) recovered a strongly supported node that suggests that the Asian orthochilous ruteline tribe Adoretini is sister to a monophyletic Dynastinae. This node had been similarly recovered by Ahrens et al. (2011). However, this relationship between Adoretini and Dynastini was weakly supported and interrupted by Pachydemini (Melolonthinae) in Ahrens et al. (2014). McKenna et al. (2014) did not include exemplars from Adoretini, making this relationship difficult to evaluate.

The analysis by Gunter et al. (2016) included 22 dynastine species from 18 genera in 5 tribes. Nodes were generally poorly supported within Dynastinae, making it difficult to assess relationships among tribes (Gunter et al. 2016) (Fig. 4). The study included one Cyclocephala species, which was recovered as sister to Onychionyx (Oryctoderini), but this relationship was weakly supported (0.83 posterior probability). These results suggest future analyses of Cyclocephalini should include oryctoderine genera (nearly all of which were at some point previously included in Cyclocephalini) to assess the boundaries of the two tribes. Additionally, these analyses do not support the monophyly of the tribes Oryctoderini, Pentodontini, and Phileurini (Gunter et al. 2016).

Taken together, these studies demonstrate that the position of Cyclocephalini in the broader phylogeny of Dynastinae and Rutelinae is not resolved. In addition, very little is known about the relationships among cyclocephaline genera and species. Breeschoten et al. (2013) presented a morphological phylogeny of cyclocephaline genera, but few details of the analysis were provided and the support for recovered relationships were not reported. Moore et al. (2015) suggested that Mimeoma species were nested among a clade of Cyclocephala that included the type species of the genus, C. amazona. These data also provided evidence of two major clades of Cyclocephala based on morphological and molecular evidence (Moore et al. 2015). However, the relationship of Cyclocephala to the other cyclocephaline genera is completely unevaluated.

Males: Protarsomeres and inner protarsal claws enlarged except for in the genera Stenocrates and Erioscelis (Fig. 5). Last abdominal sternite emarginate (Fig. 7).

Females: Protarsomeres and inner protarsal claws simple, not enlarged (Fig. 6). Last abdominal sternite entire, not emarginate (Fig. 8).