Hemiosus Sharp

Short, Andrew Edward Z. & Torres, Phillip J., 2006, Review of the Hemiosus Sharp and Derallus Sharp of North America, Central America, and the Caribbean (Coleoptera: Hydrophilidae: Berosini), Zootaxa 1369, pp. 1-17 : 3-4

Genus Hemiosus Sharp

Hemiosus Sharp, 1882: 84 .

Diagnosis. Hemiosus can be distinguished from Derallus by the dorsum being at least partially testaceous, and by being convex but not as laterally compressed and globular. Hemiosus most resembles a small Berosus , from which it can be separated by the extremely fine and dense pubescence of the hind femora, the low and wide mesosternal keel (linear in most Berosus ), and the 5 -segmented male protarsi (4 -segmented in Berosus ). Smaller body (less than 3.0 mm) separates Hemiosus from many (but not all) species of Central American Berosus .

Remarks. With the description of H. selva , the genus Hemiosus now contains 32 species ( Hansen 1999). The South American fauna was recently revised by Oliva (1991, 1994), which covered all previously known species of the genus except the mesoamerican H. exilis (LeConte) . d'Orchymont (1940) split the genus into two groups according to pronotal coloration: the dejeanii-group for species with a totally or partially testaceous pronotum, and the maculatus-group for species possessing a completely melanic (and often metallic) pronotum. These informal groupings were retained by Oliva (1994). One species in the maculatus-group ( H. maculatus ) and two species in the dejeanii-group are found outside of South America, and easily distinguished by pronotal coloration.

Most species of the genus are associated with streams and rivers with sandy substrate ( Oliva 1994), which seems to be true for the Central American species. The larvae of H. bruchi Knisch, 1924 , H. dejeanii ( Solier, 1849) and H. multimaculatus ( Jensen-Haarup, 1910) were recently described by Archangelsky (2000, 2002) and Archangelsky & Fernández (2005).

Characters of taxonomic importance. All three Mesoamerican species have a diagnostically colored pronotum, and this character alone was sufficient to separate all material examined for this study. Additionally, the male protarsi are expanded in some species and not in others. The aedeagi are also frequently diagnostic, as is the median process of the mesoventrite.