Heterocerus Fabricius, 1792

King, Jonas G. & Lago, Paul K., 2012, The variegated mud-loving beetles (Coleoptera: Heteroceridae) of Mississippi and Alabama, with discussion and keys to the species occurring in the southeastern United States, Insecta Mundi 2012 (275), pp. 1-53 : 11-12

Genus Heterocerus Fabricius

Heterocerus Fabricius, 1792: 262 .

Culmus Pacheco, 1964: 52 . (new syn.)

Dampfius Pacheco, 1964: 110 . (new syn.)

Efflagitatus Pacheco, 1964: 95 . (new syn.)

Erus Pacheco, 1964: 107 . (new syn.)

Filiolus Pacheco, 1964: 108 . (new syn.)

Gradus Pacheco, 1964: 93 . (new syn.)

Lanternarius Pacheco, 1964: 57 . (new syn.)

Lapsus Pacheco, 1964: 124 . (new syn.)

Neoheterocerus Pacheco, 1964: 69 . (new syn.)

Olmedous Pacheco, 1964: 92 . (new syn.)

Peditatus Pacheco, 1964: 119 . (new syn.)

Type species. Apate marginatus Fabricius, 1787: 33 . (by monotypy)

Discussion. Heterocerus , with approximately 200 species world-wide is what most entomologists envision upon mention of the family name: brown beetles, approximately 5 mm in length, with trifasciate elytra. A few males are hypermandibulate. They occur in a wide variety of riparian habitats on all continents except Antarctica, and have been collected from most Caribbean islands, Madagascar, New Zealand and some Pacific Islands. There are 29 species in America north of Mexico, 21 of which have been recorded from the southeastern United States. Five species recorded from the Southeast, however, are represented by single collections or otherwise dubious records.

Because of the rather extensive generic changes we have suggested, numerous new combinations have been proposed. Many of these have nothing to do with the southeastern fauna. New combinations for North American species formed as a result of these generic re-configurations, but not used in this paper, include: Heterocerus inciertus ( Pacheco 1964, Damfius), Heterocerus longilobulus ( Pacheco 1964, Neoheterocerus ), and Heterocerus sinuosus ( Pacheco 1964, Lanternarius ). New combinations for South American species suggested by our molecular data (King, et al. 2011), all originally described in the genus Efflagitatus , include: Heterocerus boliviensis ( Pacheco 1964) , Heterocerus freudei ( Pacheco 1973) , Heterocerus furmidus ( Pacheco 1964) , Heterocerus ingeniosus ( Pacheco 1964) , Heterocerus meridianus ( Pacheco 1975) , Heterocerus reticulatus ( Pacheco 1964) , Heterocerus solitarius ( Pacheco 1973) , Heterocerus splendidus ( Pacheco 1964) , Heterocerus tortuosus ( Pacheco 1973) , Heterocerus woodruffi ( Pacheco 1975) . No new combinations involving the genera Culmus , Erus , Filiolus , Gradus , Lapsus , and Olmedous were proposed because all included species were originally described as Heterocerus . Members of Heterocerus are common in the shoreline substrate of aquatic habitats. During this study, specimens of Heterocerus were collected along riverine habitats, from small streams to large rivers; lacustrian habitats such as swamps, marshes, saline ponds; oceanic beach debris, and near ponds and streams located in xeric regions. Precise habitat does seem to correlate with species composition at a given location and quite different species were often taken from separate habitats that were physically near one another. One exception, Heterocerus mollinus , was present in nearly every riparian habitat sampled. Adults emerge in late spring and cycle through two or three broods during the summer, then over-winter in flask shaped hibernacula in the substrate. Individuals of Heterocerus are prone to fly quickly when disturbed and are strongly attracted to light.

Diagnosis. Body length varies from 2.6 - 6.9 mm among the species. Eleven antennomeres are present. Varying proportions of males in about half of the species of Heterocerus are hypermandibulate. Elytral patterns vary, although the elytra are trifasciate in most species. Post-mesothoracic coxal lines are present in some species of Heterocerus , but absent in others, a trend seen in both North American and African fauna ( Pacheco 1964; Charpentier 1965). Post-metathoracic coxal lines are absent from the entire genus. As mentioned above, the male genitalia in this genus show an amazing range of structural variety. The general Heterocerus type of genitalia ( Fig. 8 ) can be described as: two basally articulated, dorsoventrally flattened, rectangular sclerotized plates, with two apical parameres attached to the ventral plate and a posteriorly extending median plate attached near the middle of the ventral plate. Members of the undatus species group ( Miller 1988a) have aberrant forms of genitalia that do not fit the above description. The genitalia in this group are more compact and the two main plates that form typical Heterocerus type genitalia seem to have been greatly reduced in exchange for an expanded median plate. Parameres are evident in most of these forms, although highly modified (see Fig. 9 ). In fact, it is difficult to homologize many structures on these types of genitalia with those seen in the typical Heterocerus type.

The lack of post-metathoracic coxal lines separates Heterocerus from Augyles . In addition, members of the latter genus are usually less pubescent and many of them have a median longitudinal pale marking on the pronotal disc that does not occur in Heterocerus . Normally, the larger body size and trifasciate elytra will separate Heterocerus from Tropicus . Species of Tropicus have either a dark central macula or solidly colored elytra and are almost always less than 2.5 mm in length. Smaller specimens of Heterocerus selanderi (Pacheco) can be difficult to separate from Tropicus macroscopically. Under magnification, however, H. selanderi has faint horizontal elytral markings reminiscent of the trifasciate pattern seen in other Heterocerus .

Figures

Figures 8-10. Male genitalia of Heterocerus spp. 8) H.pallidus exhibiting some of the characters which are important in identifying members of this genus. 8a) Ventral and 8b) dorsal aspect. Apices of genitalia face downward. 9) Heterocerus collaris, ventral. 10) Heterocerus stankerus, ventral.