Helobata, the basics

Head of Helobata larvalis, dorsal view

The genus Helobata is restricted to the New World, with most of the species distributed in the Neotropical region. The members of this acidocerine genus are quite different in appearance to the remainder members of the subfamily: the integument is finely granulated and dull instead of smooth and shiny, and their clypeus, pronotum and elytra are laterally expanded.

The genus was originally described as Helopeltis by Horn in 1873, who designated Helopeltis larvalis as the type species. Then in 1888, Bergroth proposed the name Helobata for the hydrophilid genus because the genus name Helopeltis was already taken by a hemipteran genus (see Fernández & Bachman 1987).

From Horn 1873

The genus currently have 11 described species:
Helobata aschnakiranae Makhan, 2007 (Suriname)
Helobata bitriangulata García, 2000 (Venezuela)
Helobata confusa Fernández & Bachmann, 1987 (Argentina, Paraguay)
Helobata corumbaensis Fernández & Bachmann, 1987 (Brazil)
Helobata cossyphoides (Bruch, 1915) (Argentina)
Helobata cuivaum García, 2000 (Venezuela)
Helobata larvalis (Horn, 1873) (Argentina, Bolivia, Brazil, Paraguay, Venezuela; Guatemala, Mexico; USA; Cuba)
Helobata lilianae García, 2000 (Venezuela)
Helobata perpunctata Fernández & Bachmann, 1987 (Argentina)
Helobata quatipuru Fernández & Bachmann, 1987 (Brazil)
Helobata soesilae Makhan, 2007 (Suriname)

One of the things that constitutes the revision of this genus a challenge, is the fact that they are very similar in their external morphology: when you look at them at a certain distance, they look fairly different (also because the specimens I have on hand proceed from different countries along the continent), which makes you think you can come up with several clear characters that differentiate them; but once you get to look at them closer, those differences just vanish, because the variation of the character states is so soft and gradual, that in a certain way you could only be sure of the character state by comparing your specimen to other of a different species, which is not always what you have on hand when you are trying to identify things with a key, for example.
The good news, is that different species exhibit clear differences on the male genitalia: the shape, size and relative size of structures (among other characteristics). Actually the descriptions of Makhan species are practically limited to the description of the male genitalia.

Let's see how it goes... I'm already constructing a data matrix for the phylogenetic analysis and it will be accompanied by a database on localities for the specimens.


References

• Fernández, L. A., & Bachmann, A. O. (1987). Revisión del género Helobata Bergroth (Coleoptera: Hydrophilidae). Revista de la Sociedad Entomológica Argentina, 44(2), 1985. 
• García, M. (2000). Tres nuevas especies de Helobata Bergroth 1888 (Hydrophilidae: Hydrophilinae), de Venezuela. Boletín del Centro de Investigaciones Biológicas, 34(2): 237-246.
• Horn, G. H. (1873). Revision of the genera and species of the tribe Hydrobiini. Proceedings of the American Philosophical Society, 118-137.
• Makhan, D. (2007). Helobata soesilae sp. nov. and Helobata aschnakiranae sp. nov. from Suriname (Coleoptera: Hydrophilidae). Calodema Supplementary Paper, 14, 1-3.