Elmidae (Coleoptera, Byrrhoidea) larvae in the state of São Paulo, Brazil: Identification key, new records and distribution

Abstract The family Elmidae Curtis, 1830 has cosmopolitan distribution and most species inhabit riffles on streams and rivers, hence the name “riffle beetle”. In recent years, this family has been featured in papers addressing the assessment and environmental monitoring of water quality. In Brazil, studies on the family remain scarce and the present investigation is a pioneering study in the state of São Paulo. This study aims to propose a taxonomic key for the identification of larvae of Elmidae genera known to occur in the State, as well as to report new records and the distribution of these genera. The material analyzed was collected from various locations in each of 15 drainage basins from 2005 to 2010. The identification key includes 12 genera (Austrolimnius Carter & Zeck, 1929, Heterelmis Sharp, 1882, Hexacylloepus Hinton, 1940, Hexanchorus Sharp, 1882, Huleechius Brown, 1981, Macrelmis Motschulsky, 1859, Microcylloepus Hinton, 1935, Neoelmis Musgrave, 1935, Phanocerus Sharp, 1882, Potamophilops Grouvelle, 1896, Stegoelmis Hinton, 1939 and Xenelmis Hinton, 1936) known in Brazil as well as three morphotypes designated herein as Genus A, Genus M and Genus X. The genus Hexanchorus is recorded for the first time in the state of São Paulo.


Introduction
Elmidae Curtis, 1830, is a truly aquatic beetle family with cosmopolitan distribution. Most species are found mainly in areas of riffles in lotic ecosystems (rivers and streams). The genera of this family are distributed in two subfamilies: Elminae Curtis, 1830 and Larainae LeConte, 1861 (Jäch and Balke 2008). Among aquatic beetles, Elmidae is the fourth most speciose family, with around 1330 species distributed in 146 genera throughout the world (Jäch and Balke 2008). In the Neotropical region, there are 330 known species in 44 genera, of which 250 species and 39 genera are recorded in South America (Manzo 2005;Passos et al. 2007;Maier and Spangler 2011). In Brazil, there are checklists for the Amazonian region and state of Rio de Janeiro, with 59 recorded species (Passos et al. 2009;Passos et al. 2010).
Elmid larvae and adults generally exploit the same habitats and obtain food by scraping the surface of rocks, wood fragments, roots and leaves, consuming periphyton and detritus (Seagle 1982) and have been included among the herbivores (Leech and Chandler 1956;Brown 1972). However, Seagle (1982) reclassified this family as detritivorousherbivorous. In terms of functional feeding groups, elmids have been described as scrapers, collectors/gatherers and/or shredders (White and Brigham 1996;Cummins 1973).
Larval development involves five to eight instars and the life cycle can last from six months (Brown 1987) to six years (Steedman and Anderson 1985), depending on temperature and quantity and quality of food available (Brown 1987). At the end of the last instar, the larvae generally migrate to the banks of lotic systems and pupate. In some cases, the larvae remain on their original substrate and pupate in situ when the water level falls (White and Jennings 1973;White 1978;Seagle 1980).
The family is used in monitoring programs and environmental assessments because of the sensitivity of most species to physical and chemical changes in the environment (Ribera and Foster 1992;Ribera 2000;Garcia-Criado and Fernandez-Aláez 2001;Compin and Céréghino 2003). However, in the Neotropical region the use of this family in environmental assessments is hindered by the lack of information on immature forms, and the availability of identification keys and reference collections.
Although a number of authors have invested effort in the collection of taxonomic data on the group, particularly the description of species (Hinton 1936(Hinton , 1937(Hinton , 1939(Hinton , 1940(Hinton , 1945(Hinton , 1971(Hinton , 1972(Hinton , 1973Brown 1970Brown , 1971Brown , 1981Spangler and Santiago 1987;Spangler 1966Spangler , 1990Costa et al. 1988) literature about the Brazilian fauna remains scarce. In recent years, some South American researchers have intensified studies on Elmidae biology (Costa et al. 1988;Passos et al. 2003a), ecology (Costa et al. 1988;Passos et al. 2003b;Segura et al. 2007a, b) and taxonomy, including the description of new species (Passos and Felix 2004a, b;Manzo 2006;Manzo 2006, 2007;Archangelsky et al. 2009;Vanin and Costa 2011) and identification keys (Passos et al. 2007;Manzo 2005;Manzo and Archangelsky 2008;Mugnai et al. 2010). However, the studies carried out by Manzo (2005) and Manzo and Archangelsky (2008) include few specimens of Elmidae from Brazil. In contrast, Passos et al. (2007) and Mugnai et al. (2010) offer taxonomic keys for the family Elmidae in Brazil, more specifically, in the state of Rio de Janeiro. Table 1 lists the genera of Elmidae recorded in South America and known genera for Brazil and the southeastern region of Brazil.
The aim of this paper is to propose an identification key for the genera of elmid larvae in the state of São Paulo, Brazil, based on the study of material from various aquatic ecosystems located in various vegetation types.

Materials and methods
The majority of specimens examined were collected from Only mature larvae (larger, well-sclerotized larvae with functional spiracles) were used to build the genus identification key. The traits used to identify the larvae were based on Hinton (1940), Santiago-Fragoso (1987, 1992), Passos et al. (2007) and Manzo and Archangelsky (2008) (Fig. 2).
The images used in the identification key were taken with a Leica DFC 280 camera coupled to a Leica MZ9 5 stereomicroscope. The images were treated with Adobe Photoshop CS4 to correct contrast, brightness and imperfections.

Results and discussion
This paper proposes an identification key for larvae of Elmidae at the genus level, encompassing 12 genera previously recorded in South America: Austrolimnius Carter & Zeck, 1929, Heterelmis Sharp, 1882, Hexacylloepus Hinton, 1940, Hexanchorus Sharp, 1882, Huleechius Brown, 1981, Macrelmis Motschulsky, 1859, Microcylloepus Hinton, 1935, Neoelmis Musgrave, 1935, Phanocerus Sharp, 1882, Potamophilops Grouvelle, 1896, Stegoelmis Hinton, 1939and Xenelmis Hinton, 1936 Passos et al. (2007), but is separated from this genus by the arrangement and number of rows of tubercles. Moreover, the mesopleura and metapleura are divided into three parts in Heterelmis, but only two parts in Genus A. Genus M is similar to but separated from Genus X, which has pleural sclerites on abdominal segments I to VII, whereas Genus M has pleural sclerites only on abdominal segments I to IV. It should be noted that young Hexanchorus larvae (Fig. 22) do not yet have the large tubercle found in mature larvae on each side of the midline on abdominal tergum VIII (Figs 19 and 20).
In general, most of the genera were distributed for all regions of State of São Paulo, such as Heterelmis, Hexacylloepus, Macrelmis e Xenelmis (Fig. 1). It is worthwhile mentioning that Heterelmis was found in both preserved and impacted areas. On the other hand, the distribution of some genera appeared to be restricted to some regions. For instance, Genus A, Genus M, and Genus X were found in streams located at eastern region state of São Paulo, Hexanchorus was recorded only in the Coast region and Stegoelmis in Central region of the state.