Derallus Sharp, 1882

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 : 9

Derallus Sharp, 1882

Derallus Sharp, 1882: 77 .

Diagnosis. The genus is easily separated from other New World Berosini by the entirely melanic dorsum. It is also characterized by a laterally compressed, often nearly hemispherical body shape, the longitudinal carina on the metasternum, and the pubescence on the hind femora restricted to the extreme base.

Remarks. Derallus is a relatively small genus containing 15 described species ( Hansen 1999) although more await description (Short, unpublished data). Most species are found in standing water habitats with lots of vegetation, such as marshes, ponds, and swamps. They can be abundant at light traps, especially in the early dry season. Members of the genus are in general very homogenous in size and shape, making their separation difficult. No modern keys to species exist with the exception of the Argentine fauna ( Oliva, Fernández & Bachmann 2002). The larval stages have been described for four species: D. anicatus d’Orchymont, 1940 ( Bertrand 1968) , D. rudis Sharp ( Spangler 1966) , D. angustus Sharp ( Archangelsky & Durrand 1992) , and D. paranensis Oliva, 1981 ( Archangelsky & Fernández 2005) .

Characters of taxonomic importance. Dorsally, the coarseness of the ground punctation of the pronotum, the degree of impression of the elytral striae, and the distribution of punctures in the tenth elytral interstria (=interstria X) are helpful in separating species. Ventrally, the shape of the mesosternal and metasternal processes are extremely important, and frequently species-specific in the former. The aedeagus is of some value, being diagnostic in D. rudis Sharp , but generally similar in the remaining mesoamerican species.

Authoritatively identified reference material is recommended for comparison to southern Mexican and Central American material.