Identification key to the Gerridae ( Insecta : Heteroptera : Gerromorpha ) from the Amazon River floodplain , Brazil , with new records for the Brazilian Amazon

Eighteen species from seven genera are recorded from the Amazon River floodplain, Brazil. An identification key, diagnoses, drawings, and taxonomic and biological notes are given for these species. The main features used in the identification key and diagnoses are: body and leg segments proportions, coloration patterns, presence and distribution of setae, and modifications of the apical abdominal segments and external genitalia of the male. Based on material collected in the floodplain streams and lakes, Cylindrostethus bassleri Drake, 1952 is recorded for the first time from Brazil, and new municipality records are presented for Brachymetra lata Shaw, 1933, B. shawi Hungerford & Matsuda, 1957, C. erythropus (Herrich-Schäffer, 1850), C. linearis (Erichson, 1848), C. Palmaris Drake & Harris, 1934, C. regulus (White, 1879), Neogerris lotus (White, 1879), N. lubricus (White, 1879), N. visendus (Drake & Harris, 1934), Ovatametra obese Kenaga, 1942, Rheumatobates crassifemur esakii Schroeder, 1931, R. klagei Schroeder, 1931, and Trepobates taylori (Kirkaldy, 1899). Additional new records from the Brazilian Amazon are presented for B. lata and O. obesa.


MATERIAL AND METHODS
The study area included twenty-six localities in the floodplain of the Amazon River in Brazilian territory, between the municipalities of Tabatinga, state of Amazonas, and Afuá, state of Pará (Fig. 1).The examined material was collected from floating plants of the genus Eichhornia or on U.V. light traps positioned near water, and additional qualitative collections were conducted in streams (igarapés) and lakes near the sampling sites.Even with the additional collections, no Gerridae specimens have been found in some of the localities.
Specimens were deposited in the Instituto Nacional de Pesquisas da Amazônia (INPA) and Coleção Entomológica Professor José Alfredo Pinheiro Dutra, Departamento de Zoologia, Instituto de Biologia, Universidade Federal do Rio de Janeiro (DZRJ).Additional material from other regions of the Brazilian Amazon deposited in the INPA collection has been examined.
No specimens of Limnogonus recurvus Drake & Harris, 1930, Ovatametra fusca Kenaga, 1942 or Rheumatobates minutus flavidus Drake & Harris, 1942 were observed by us, but they occur in the study area and have been included in the present study.

Brachymetra lata Shaw, 1933
General color of specimens is reddish-brown, with some dark-brown areas, usually more distinct in males than in females.Macropterous individuals display forewings reddishbrown to dark-brown with yellow veins.Diagnostic features include eyes with posterior part well developed (Fig. 17), and fore femur only slightly wider than middle femur, with black peg on venter (Fig. 18).It can also be distinguished from B. shawi Hungerford & Matsuda, 1957 by the shorter pronotum of macropterous forms, which has a blunt apex (Fig. 17), and venter of male genital segment II without a notch on posterior margin.
Brachymetra lata is common in northern Brazil (PA, AM) and in Suriname, living preferably on streams (NIESER 1970).No specimen from the Amazon River floodplain was examined, but the species was recorded from the area by SHAW (1933).Several individuals from INPA were seen, most of which collected in streams and rivers.They tend to be gregarious and can be the most abundant gerrid species in lowland forest streams in Brazilian Amazon (F.F. F. Moreira personal observations), although a specimen from higher altitudes near Pico da Neblina was observed.Both apterous and macropterous forms might occur within a single population.

Brachymetra shawi Hungerford & Matsuda, 1957
Brachymetra shawi can be distinguished from other Brachymetra by the unmarked pronotum, which reaches at least the middle of metacetabula and is narrowly rounded at apex in winged forms; forewings reddish-brown, much darker than pronotum, with yellow veins; and venter of male genital segment II with a distinct notch at middle.Eyes (Fig. 3) are not strongly produced posteriorly as in B. lata, and there are no black pegs in fore femur.Representatives of B. shawi are usually found in streams and rivers, but can also be collected in lentic environments, such as ponds (NIESER 1970), in Trinidad & Tobago, the Guyanas, Brazil (PA, AM) and Bolivia.No further details on their biology are available in the literature, but they seem to be rarer than B. lata, sometimes being found in reduced numbers among larger agglomerations of individuals of the latter species (personal observations).

Cylindrostethus bassleri Drake, 1952
This species is part of the group of Neotropical Cylindrostethus in which the mesonotum displays uniform coloration and is longitudinally impressed on sides.In addition, the last abdominal sternite of male has a deep central notch (Fig. 10), the genital segment I is dorsally large, not narrowed posteriorly, and the genital segment II bears a pair of long basal projections directed anterolaterally (Fig. 10).Individuals of C. bassleri can be differentiated from C. erythropus (Herrich-Schäffer, 1850) and C. linearis (Erichson, 1848) by the dark ferruginous brown color, and absence of a spine on posterior margin of last abdominal sternite of male (Fig. 10).Members of C. bassleri can also be separated from those species by their average larger size (15.8-18.8mm against 12.8-17.6 in other species).The depressions of male last abdominal sternites were not described by DRAKE (1952).However, in specimens examined here, the abdominal sternites are depressed from the posterior margin of IV to the base of VI, and there is a distinct longitudinal median carina on the base of sternite VI.DRAKE (1952) also stated that female connexives and connexival spines were reflexed above abdomen, with apices touching each other.In females observed, these structures were reflexed above abdomen, but apices did not touch each other.This feature is quite variable in Neotropical species of the genus, and females of the same population of a given species can display different degrees of reflection of connexives.This is the first record of C. bassleri from Brazil, and the first record of the species after its description from Peru.Biological information about this water strider is unavailable, except for its occurrence in lotic environments.The specimens examined were collected in a small stream, tributary of the Sapó River, in coexistence with a larger population of C. erythropus.The stream is shallow and narrow, probably of first order, with bottom composed of sand and litter, and slow wa-

Cylindrostethus erythropus (Herrich-Schäffer, 1850)
Differences in relation to other members of the same species group (C.linearis, C. bilobatus Kuitert, 1942, and C. bassleri) include color fuscous to black, male connexival spines large and long, slightly curved outward (Figs 4 and 5), last two or three male abdominal sternites longitudinally impressed on center, and projections of male genital segment II wide (Figs 4  and 5).Females display connexival spines much shorter than in males, last abdominal sternite with a triangular projection on middle of posterior margin, and genital segment I dorsally as long as wide, narrowed posteriorly, with rounded apex.
Most of the previous records of the species were made based on material collected from large rivers (DRAKE & HARRIS 1934, KUITERT 1942, NIESER 1970), at altitudes up to 350 m (MOLANO- RENDÓN et al. 2005) in Colombia, Brazil (PA, AM, RO), Ecuador and Peru.MOLANO-RENDÓN et al. (2008) stated that individuals prefer living on the margins of fast running, small streams in Colombia.On the water surface of the lakes and streams sampled, members of the species were found in large numbers, showing a tendency to gregarism.They also displayed the behavior of resting above the water line on tree trunks, as previously mentioned by ROBACK (1966).
Examined material from the Amazon River floodplain.BRA-

Cylindrostethus linearis (Erichson, 1848)
Members of this species share the uniformly colored mesonotum and general aspect of male external genitalia with C. erythropus, C. bilobatus and C. bassleri.Cylindrostethus linearis, and can be diagnosed by the orange-brown to reddish-brown color, relatively short and narrow male connexival spines (Figs 8 and 9), last male abdominal sternite depressed near anterior margin, with central spine on posterior margin short and reflexed downward (Fig. 8), and projections of male genital segment II curved and slender (Figs 8 and 9).
Considering the few records that provided habitat information, previous collections of C. linearis were made exclusively in rivers (DRAKE & HARRIS 1934, KUITERT 1942, NIESER 1970).Speci-mens examined here were collected in only two of the lakes studied, co-existing with C. erythropus in both cases.DRAKE & HARRIS (1941) mentioned that the species occurs in the state of Rio de Janeiro, but there is no evidence that its distribution extends that far south.The current distributional range of the species extends from Guyana to Peru and Bolivia, including the Brazilian states of Pará, Amazonas and Rondônia.

Cylindrostethus palmaris Drake & Harris, 1934
Specimens of C. palmaris display a conspicuous longitudinal dark stripe on each side of mesonotum, last male abdominal sternite concavous, without deep central notch (Fig. 6), male genital segment I dorsally narrowed posteriorly (Fig. 7), and base of male genital segment II with a pair of short plate-like projections (Figs 6 and 7).They can be separated from other Neotropical species with same features by antennomere I distinctly longer than head width across eyes, antennomeres I-II black, and male connexival spines reaching middle of genital segment I (Fig. 7).In females, connexival spines are long and genital segment I ends in an acute apex.
Representatives of C. palmaris are quite common and have been collected in streams, large rivers and lakes, up to 460 m above sea level (KUITERT 1942, SAMPAIO & PY-DANIEL 1993, MOLANO-RENDÓN et al. 2005).They have gregarious behavior, living preferably in non-turbulent shaded areas of streams and rivers (HYNES 1948, NIESER & MELO 1997).In Brazil, they occur in the North, Central-West and Southeast regions (PA, AM, MT, RO, MG).

Cylindrostethus regulus (White, 1879)
This species shares the mesonotum with lateral stripes and the structure of male genitalia with C. palmaris, C. hungerfordi and C. podargus Drake, 1958.Males of C. regulus can be separated from them by the antennomere I longer than width of head through eyes, antennomeres I-II brown, male connexival spines not reaching middle of genital segment I (Fig. 11), female connexival spines relatively short, and female genital segment I rounded on posterior margin.In the studied specimens, mesonotal stripes are brownish-black, lighter than those of C. palmaris, and slightly fainted before posterior third of segment.Stripes are wide and continue over metanotum, differently from C. hungerfordi, which possesses narrow stripes and only elongate spots on metanotum.Specimens of C. regulus have been collected only from rivers in the state of Amazonas (DRAKE & HARRIS 1930, KUITERT 1942), and only one male was collected in the lakes studied.Examined material from the Amazon River floodplain.BRAZIL, Amazonas: Tefé! (São Francisco da Boca do Capivara, Botão Lake,-3.26539/-64.62745), 1 apterous male, 09.IX.2003,N. Hamada & J.L. Nessimian leg., INPA.

Limnogonus aduncus aduncus Drake & Harris, 1933
Males of this species can be identified by the mesosternum with a shallow wide depression, and by the venter of genital segment I without keels or gibbosities, with a small curved spine on apex (Fig. 24).Females display connexival spines moderately long and last abdominal sternite sharply produced at middle behind.In both sexes antennomere I is longer than width of head through eyes and dorsalmost part of the mesopleura is dark-brown to black with a lighter central stripe of variable size.
Representatives of the species are common throughout South America, being found in streams and rivers, stagnant water bodies with emergent vegetation, and pools of various sizes (ROBACK 1966, NIESER 1970, NIESER & MELO 1997, MELO & NIESER 2004).In Argentina they generally inhabit the margins of small streams in forested mountain areas, but can also be found in dryer areas dominated by savannas on the Chaco Plain.In the last case, the species is uncommon and probably not gregarious, with few individuals obtained in each collection (MAZZUCCONI & BACHMANN 1995).Even though we have found no specimens in the lakes sampled, L. aduncus had been previously recorded from the area by DRAKE & HARRIS (1935).In Brazil, the species is distributed through the North, Central-West and Southeast regions (PA, AM, MT, MG, ES, SP, RJ).
The first author of the present work recently went to INPA and had the opportunity to examine its dried Gerridae collection.He noticed that a long series collected by Dr. B.M. Mascarenhas at INPA, Manaus, and identified by him as L. recurvus Drake & Harris, 1930, like specimens cited in MASCARENHAS (1979), were in fact representatives of L. a. aduncus.Some specimens had been identified and labeled as L. aduncus by Dr. J. T. Polhemus.Therefore, the records of L. recurvus in MASCARENHAS (1979) should be instead referred to L. a. aduncus.

Limnogonus recurvus Drake & Harris, 1930
Limnogonus recurvus differs from L. aduncus aduncus by the presence of a rounded gibbosity on male genital segment I, besides the posterior spine-like curved projection.The two species can also be separated based on the color of the mesopleura, which is brown with a light transversal stripe in L. recurvus, and usually black with a transversal light stripe in L. aduncus aduncus.
No representatives of L. recurvus were examined in the present study, but the species had been recorded from the Amazon River floodplain by KUITERT (1942), specifically from Lago Grande [do Curuai], Santarém, Pará.Limnogonus recurvus is also known from Bolivia and the Brazilian states of Mato Grosso, Rondônia, Goiás and Minas Gerais.Another representative of the genus, L. hyalinus (Fabricius, 1803), had been recorded from Manaus by WHITE ( 1879), but no records of the species specifically from the Amazon River have been found.For this reason, we have not included L. hyalinus in this study.(White, 1879) This species can be distinguished from other Neotropical Neogerris by the pronotum of apterous forms relatively short, usually reaching slightly beyond half length of mesonotum (Fig. 14), and the pronotum of alate forms constricted between anterior and posterior lobes.Other features that might allow its identification are the globose eyes (Fig. 15) and the fore femur displaying an ovate spot on its outer surface, just before the apical third.In some apterous specimens, the pronotum can be longer, leaving only a small strip of the mesonotum exposed or completely covering it, as was noticed by NIESER (1994) for specimens from Mato Grosso and Trinidad and Tobago.

Neogerris lotus
Members of N. lotus are distributed in a wide area, occurring in lowlands (up to 200 m above sea level) from the Guyanas to North and Central-West Brazil (PA, AM, MT, DF) (NIESER 1970, MOLANO-RENDÓN et al. 2005).Its representatives have been recorded from pools, ponds, and low current streams and rivers (NIESER 1994), and not much is known about their biology.Only one specimen was collected in the lakes of the Amazon River we studied.Members of this species either have a preference for habitats different from those sampled, or are associated with other hydrophyte species.

Neogerris lubricus (White, 1879)
The pronotum of apterous specimens of N. lubricus is always long, almost reaching the metanotum (Fig. 16), and that of alate forms does not show central constriction.Eyes are long, not globose; and the male abdominal tergite I is narrow, tapering to the apex, with posterior margin with very faint central notch or without notch.
Members of N. lubricus show the widest geographic distribution among Neotropical representatives of this genus, occurring in streams, rivers, permanent or semi-permanent pools and ponds, up to 400 m above sea level (NIESER 1970, MAZZUCCONI & BACHMANN 1995, NIESER & MELO 1997, MOLANO-RENDÓN et al. 2005).In Brazil, the species occurs in the North, Central-West and Southeast regions (PA, AM, MT, RO, MG).
Macropterous and apterous individuals are equally common, and gregarism is not evident in the populations studied in Argentina (MAZZUCCONI & BACHMANN 1995).According to NIESER (1994), representatives of the species occur in the same habitats as N. lotus, and both are more abundant in sites rich in emergent vegetation (NIESER 1970, MAZZUCCONI & BACHMANN 1995).As cited above for N. lotus, only one specimen of N. lubricus has been collected in the lakes studied, confirming their presence in the Amazon River floodplain, but probably indicating preference for mesohabitats or hydrophytes different from those sampled.Based on literature data, N. lubricus is associated with hydrophyte species of Salvinia, Azolla, and Equisetum, among other genera (MELO & NIESER 2004), but not Eichhornia.

Neogerris visendus (Drake & Harris, 1934)
Males of this species can be readily identified by the genital segment II bearing a distinct pair of tufts of setae (Fig. 13) on each side.In addition, antennomere I is slightly longer than head width plus an eye, the pronotum of apterous forms has no posterior lobe, being larger than longer (Fig. 12), and the pronotum of alates has no central constriction.
This species ranges from Colombia to Peru, including the North Region of Brazil (RR, PA, AM).Its representatives are commonly recorded from streams and lakes.Previous records include localities shared with N. lotus, but they most likely inhabit distinct microhabitats (NIESER 1970, MOLANO-RENDÓN et al. 2005).Several specimens of N. visendus were collected in association with Eichhornia sp. in the lakes and nearby streams sampled, but only one exemplar of N. lotus.Our findings corroborate the hypothesis that the two species have different habitat preference.Another representative of the genus, N. genticus (Drake & Harris, 1934), was described from Santarém, but not specifically from the Amazon River floodplain.Since there have been no further records of N. genticus since its description, the species has not been included in the present study.

Ovatametra fusca Kenaga, 1942
Ovatametra fusca differs from O. minima Kenaga, 1942 andO. parvula (Drake &Harris, 1935) by its length greater than 2.50 mm and by the color pattern of mesonotum.Specimens of O. fusca do not possess a tuft of black setae on the posterior margin of abdominal tergite VII, which is present in O. obesa Kenaga, 1942.The only information available on the biology of O. fusca is the occurrence in rivers.Just its type-series, from Solimões River (Manacapuru, Brazil) and Supuruni Creek (British Guiana) has been collected so far.Kenaga, 1942 Representatives of O. obesa are known from the states of Pará and Amazonas.Individuals from different populations vary in coloration, but specimens from the same population are relatively uniform.Specimens examined from the Anavilhanas Archipelago have mesonotal markings similar to those of O. parvula and, according to NIESER (1970), the color pattern of some individuals is very similar to that of O. fusca.Ovatametra obesa can be separated from O. fusca by a tuft of black setae present on the posterior margin of abdominal tergite VII.Despite being cited only for females by NIESER (1970), this feature has also been observed in males.

Ovatametra obesa
NIESER (1970) examined specimens collected both in lentic and lotic environments, but material studied here was collected exclusively from lakes.The alate form of O. obesa has not yet been recorded in the literature, and in the only macropterous specimen examined the wings were broken off along a suture line near base, a feature that was observed by TORRE-BUENO (1908) in other Halobatinae.A third representative of the genus, O. parvula (Drake & Harris, 1935), was described from "Amazon, Manaos", without further details.As only the type-series of the species is known, and there is no evidence of its occurrence in the Amazon River floodplain, O. parvula was not included in the present study.

Rheumatobates crassifemur esakii Schroeder, 1931
Males of the three subspecies of Rheumatobates crassifemur Esaki, 1926 have strongly modified antennae and legs, and the hind femur is connected subbasally to the trochanter, without basal anteriorly directed tuft of setae (Fig. 20).Rheumatobates c. esakii can be distinguished from R. c. crassifemur Esaki, 1926 andR. c. schroederi Hungerford, 1954 by the male antennomere IV with a tuft of about five long erect black setae (Fig. 21).
Both adults and nymphs of R. c. esakii are found in lentic environments in Northern South America, including the Brazilian states of Pará and Amazonas (NIESER 1970), and occasionally occur in sympatry with R. klagei Schroeder, 1931.In the present study, males and females were collected associated with Eichhornia sp. and by use of U.V. light traps, which

Figure 1 .
Figure 1.Map showing the location of the Amazon River floodplain and the collecting localities along the river course.