Rhodnius marabaensis sp. n. was collected on 12 May 2014 in the Murumurú Environmental Reserve in the city of Marabá, Pará State, Brazil. This study was based on previous consultation of morphological descriptions of 19 Rhodnius species and compared to the identification key for the genus Rhodnius. The examination included specimens from 18 Rhodnius species held in the Brazilian National and International Triatomine Taxonomy Reference Laboratory in the Oswaldo Cruz Institute in Rio de Janeiro, Brazil. The morphological characteristics of the head, thorax, abdomen, genitalia, and eggs have been determined. Rhodnius prolixus and R. robustus were examined in more detail because the BLAST analysis of a cyt-b sequence shows they are closely related to the new species, which also occurs in the northern region of Brazil. The most notable morphological features that distinguish R. marabaensis sp. n. are the keel-shaped apex of the head, the length of the second segment of the antennae, the shapes of the prosternum, mesosternum and metasternum, the set of spots on the abdomen, the male genitalia, the posterior and ventral surfaces of the external female genitalia, and the morphological characteristics of the eggs. Rhodnius jacundaensis Serra, Serra & Von Atzingen (1980) nomen nudum specimens deposited at the Maraba Cultural Center Foundation - MCCF were examined and considered as a synonym of R. marabaensis sp. n.

Triatominae , Rhodnius marabaensis sp. n., new species, Amazon

Vectors of the protozoan Trypanosoma cruzi, the etiological agent of Chagas disease, include 151 species distributed into 18 genera belonging to the subfamily Triatominae (Galvão 2014, Mendonça et al. 2016). The genus Rhodnius includes 19 species (Alevi et al. 2015), of which six were described after the publication of the Lent and Wygodzinsky review (1979): R. stali Lent, Jurberg & Galvão, 1993; R. colombiensis Mejia, Galvão & Jurberg, 1999; R. milesi (Carcavallo, Rocha, Galvão & Jurberg, 2001); R. zeledoni Jurberg, Rocha & Galvão, 2009; R. montenegrensis Rosa et al., 2012, and R. barretti Abad-Franch, Palomeque & Monteiro, 2013. R. amazonicus Almeida, Santos & Sposina, 1973 was synonymized with R. pictipes by Lent and Wygodzinsky (1979) according a photograph of the holotype, but subsequently it was validated by Bérenger and Pluot-Sigwalt (2002) by morphological study of 19 characters with of the two species.

Among the Rhodnius species, only nine are found in the northern region of Brazil: R. amazonicus, R. brethesi, R. milesi, R. montenegrensis, R. neglectus, R. paraensis, R. pictipes, R. robustus, and R. stali (Galvão 2014, Meneguetti et al. 2015).

In May 2014, two Rhodnius spp. specimens were collected in Marabá, Pará, Brazil, and compared to the key described by Lent and Wygodzinsky (1979), as well as to previously described Rhodnius species, without success. These samples were compared and identified as the same species as Rhodnius jacundaensis Serra, Serra & Von Atzingen, 1980 which had been deposited at the Marabá Cultural Center in Pará. Rhodnius jacundaensis was mentioned in an abstract presented at the Fourth Annual Brazilian Parasitology Conference in Rio de Janeiro in 1980. According to Article 9 of the International Code of Zoological Nomenclature, however, this new species was not confirmed. As a result, Carcavallo et al. (1998) and Galvão et al. (2003) considered it to be R. jacundaensis Serra, Serra & Von Atzingen, 1980) nomen nudum. This article describes Rhodnius marabaensis sp. n. as the tenth species found in northern Brazil and the twentieth member of this genus (Abad Franch et al. 2013, Galvão 2014, Meneguetti et al. 2014, Alevi et al. 2015).

In epidemiological terms (i.e., considering the role of the species as vectors of T. cruzi), the three main Triatominae genera are Panstrongylus, Rhodnius, and Triatoma. Distinguishing among these three genera is not difficult because they can be characterized macroscopically based on the format of the head and the position of the antenniferous tubercle, as described by Pinto (1931). However, distinguishing among Rhodnius species requires a more detailed examination through optical microscopy. The difficulty in identifying Rhodnius species was first noted by Neiva and Pinto (1923). At the time, there were five known species: R. nasutus, R. prolixus, R. pictipes, R. brethesi, and R. domesticus (Lent and Wygodzinsky 1979). Including this description of R. marabaensis sp. n., there are currently 20 species (Rosa et al 2012, Abad Franch 2013); therefore, specific distinction is even more difficult and requires more characteristics to be considered. As a result, the characterization of R. marabaensis sp. n. is discussed comparatively using R. prolixus and R. robustus. R. marabaensis is closely related to R. robustus and R. prolixus (until 99% and 94% of identity, respectively). In view of this and of the fact that all three species occur in Northern Brazil (Galvão 2014), R. robustus and R. prolixus were morphologically examined and compared in more detail (Table 3).

Rhodnius marabaensis sp. n. is predominantly yellow, whereas R. prolixus is black and R. robustus is brown. The legs of the three species are also consistent in these color schemes (Fig. 2). Another very clear characteristic of R. marabaensis sp. n. is that it is larger than R. prolixus and R. robustus (Figs 3–5 and Table 1).

The head of R. marabaensis sp. n. has four very clear characteristics that help to distinguish it from the others:

1. It possesses a keel-shaped longitudinal dorsal portion (apex) running from the clypeus to the ocelli. This feature is not accentuated in R. prolixus or R. robustus (Fig. 3);

2. It possesses a rounded anteclypeus. In R. prolixus and R. robustus, the anteclypeus is flat (Fig. 3);

3. It possesses an indistinguishable clypeus. In R. prolixus, it is narrow in the anterior portion and wide in the posterior one. In R. robustus it is wide in the anterior portion, narrow in the medial portion, and wide in the posterior one (Fig. 3);

4. The second segment of the antenna is significantly larger than the other three, with the following length ratio among the four antennal segments: 2nd > 3rd > 4th > 1st. This relative length pattern of the four antennal segments is the same as the pattern observed by Rosa et al. (2010) in R. neglectus and R. prolixus adults; however, the differences in size between the largest and the smallest segments are distinct: the second antennal segment of R. marabaensis sp. n. is 10.3 times larger than the first; in R. prolixus, it is 6.2 times larger, and in R. robustus it is 8.3 times larger (Table 1).

For the description of R. marabaensis sp. n. five features of the thorax allow for its distinction:

1. The scutellum is larger and includes two prominent internal lateral carinae. It is therefore distinct from R. prolixus and R. robustus, which present smaller scutellum and whose carinae are not pronounced (Fig. 4);

2. The first urotergite has a pronounced transverse groove and inferior fringe consisting of long and straight filaments. In R. prolixus, the transverse groove does not appear and the fringe possesses short and irregular filaments. On the other hand, in R. robustus the transverse groove is not accentuated, and the fringe possesses short and straight filaments, as shown in (Fig. 5).

3. It possesses a longer and more clearly shaped stridulatory sulcus relative to those of R. prolixus and R. robustus (Fig. 5). This specific differentiation among these three Rhodnius species adds to the observations by Lent and Wygodzinsky (1979), who verified that the stridulatory sulcus in six species from different genera presented characteristics that allowed for species identification;

4. The transverse carinae that border the mesosternum and the metasternum differ among the three species. In R. marabaensis sp. n., they are elevated and prominent, and possess convex curvature in the central portion. In R. prolixus, they are less elevated and prominent, and in R. robustus they are interrupted in the central portion (Fig. 6);

5. The metasternum is slightly rectangular in shape in R. marabaensis sp. n., whereas in R. prolixus and R. robustus they are slightly triangular (Fig. 6).

From the view of the ventral surface, the abdomen of R. marabaensis sp. n. is distinct because of its yellow colouring; this area is brown in R. prolixus and black in R. robustus (Fig. 11). The set of dark brown spots does not appear in R. prolixus or R. robustus, and the ventral connective is also distinct among the three species: the black spots are smaller and, on the sixth segment, much smaller in R. marabaensis sp. n. (Fig. 2).

When the male genitalia was examined from the dorsal surface, the apex of the endosoma of R. marabaensis sp. n. was found to be long and straight; in R. prolixus, the apex is long and convex, and in R. robustus it is shorter, wide, and convex (Lent and Jurberg 1969) (Fig. 7). The analysis also revealed that the two final portions of the basal piece are turned to the side in R. marabaensis sp. n., whereas in R. robustus they face the posterior region. From the ventral surface, the phallosoma of R. marabaensis sp. n. is rounded, whereas in R. prolixus the anterior portion is convex and in R. robustus it is square (Fig. 7). The pygophore of R. marabaensis sp. n., R. prolixus, and R. robustus are all in the shape of an isosceles triangle. However, the sides of the pygophores are straight in R. robustus and curved in R. prolixus and R. marabaensis sp. n. The pygophore of R. marabaensis sp. n. is also larger at the tip, thicker, and circular (Fig. 8).

The external female genitalia was also considered. From the dorsal surface, R. marabaensis sp. n. and R. robustus show no differences; however, the format of the ninth segment of the dorsal surface in R. prolixus presents different characteristics (Fig. 9). The posterior surface and the ventral surface of the ninth and tenth segments are distinct in the three species (Fig. 10). These characteristics are also distinct from 12 other Rhodnius species, as described by Rosa et al. (2014).

Rhodnius marabaensis sp. n. eggs possess chorion rims, whereas those of R. prolixus and R. robustus do not. The diameter of the follicular tubes of the exochorion cells in R. prolixus are larger than those of R. marabaensis sp. n. and R. robustus; however, they are regular in R. marabaensis sp. n. and varied in R. robustus (Figs 12, 13 and Table 2).

The data obtained corroborate the status of R. marabaensis sp. n. as a new species and indicates that the use of morphology for the description of Triatominae species offers phenotypic information (morphological and morphometric) to define the status of species. It is also important to note that molecular analysis generates data that can help phylogenetic relationships and taxonomic studies of Triatominae (Abad-Franch and Monteiro 2005, Justi et al. 2014). BLAST analysis of cyt-b sequence shows R. marabaensis sp. n. as closely related to R. robustus and R. prolixus, so this new species must be included in the R. prolixus complex (Carcavallo et al. 2000). Complementary approaches using molecular data must be encouraged to establish the phylogenetic placement of this new species based on the evaluation of other gene fragments and a more robust assessment.

We want to thank Dr. Oswaldo Pinto Serra and Raquel Guglielmetti Serra (in memoriam), who briefly characterized R. jacundaensis [nomen nudum] in 1980. We also want to thank Nelson Papavero from the Zoological Museum of USP and Cleber Galvão from the Oswaldo Cruz Institute for suggesting the scientific name of the new species. We are grateful to José Jurberg, who allowed us to observe the Herman Lent and Rodolfo Carcavallo collection at the Oswaldo Cruz Institute. We thank Marcelo Ornaghi Orlandi, Mario Cilense, Juan Carlos Guerrero Barreto, and Sebastião Dameto from the Institute of Chemistry at São Paulo State University, Araraquara, for their help with the electronic microscope, as well as Danila Blanco de Carvalho, Aline Ribeiro Rimoldi, and Felipe Fatobene from the School of Pharmaceutical Sciences at São Paulo State University, Araraquara, for their collaboration. Special thanks are given to Marcos Takashi Obara from the University of Brasília (UnB) and to Mara Cristina Pinto from the School of Pharmaceutical Sciences at São Paulo State University, Araraquara, for their suggestions, and finally, to Davi Antonio da Rosa for the photos and drawings. Financial Support: São Paulo Research Foundation (FAPESP) grant process number 2010/15386-3; Brazilian Federal Agency for the Support and Evaluation of Graduate Education (CAPES), grant process number 23038-005285/2011-2012, Program for the Improvement and Scientific Development of the Pharmaceutical Sciences, School of Pharmaceutical Sciences at São Paulo State University, Araraquara - PADC/FCF/UNESP; Brazilian National Council for Scientific Technological Development (CNPq).