American trypanosomiasis, or Chagas disease, is an infectious illness caused by the protozoan parasite Trypanosoma cruzi Chagas 1909, which is transmitted by triatomines (Hemiptera, Reduviidae, Triatominae)1. In Brazil, the Triatominae is represented by ten genera, including Alberprosenia, Belminus, Cavernicola, Eratyrus, Microtriatoma, Panstrongylus, Parabelminus, Psammolestes, Rhodnius, and Triatoma2. However, only four genera (seven species: Rhodnius montenegrensis2, Rhodnius robustus3, Rhodnius stali1, Rhodnius pictipes4, Panstrongylus geniculatus4, Eratyrus mucronatus5, and Triatoma sordida6) have been reported to occur in the State of Acre. The aim of the present study is to report, for the first time, the occurrence of an additional species, Rhodnius neglectus, in the State of Acre and in the Brazilian Western Amazon Region.
An adult male R. neglectus (Figure 1) and seven R. robustus specimens were collected from the Catuaba Experimental Reserve, which is located in the municipality of Senador Guiomard, State of Acre, Brazil (10° 09′ 03″ S; 67° 44′ 09″ W), and belongs to the Universidade Federal do Acre (UFAC). Triatomines were collected from palm (Attalea sp.) trees during June 2016 by individually removing most of the palm bracts, and the identities of the collected triatomines were confirmed at the Insectarium of the Department of Biological Sciences, Faculty of Pharmaceutical Sciences, Universidade Estadual Paulista Júlio de Mesquita Filho (UNESP), Araraquara, State of São Paulo, Brazil, according to genital morphology7,8 (Figure 2).
Feces and urine from the specimen were diluted in saline solution, prepared on microscope slides, and then examined using an optical microscope (640× magnification), for analysis of trypanosomatid infection.
Rhodnius neglectus (Figure 1) is 17.5 to 20.5 mm in length, dark brown in color, lacking a mottled appearance, and possesses a head that is substantially longer than the pronotum, a third antennal segment (with dark basal portion and clear apical portion) that is shorter than the second, a second frontal segment that does not reach the posterior margin of the head, anteriorly projected pronotal anterolateral angles, a posterior pronotal lobe with two dark longitudinal bands and a single clear band between the submedial carenas, legs with no spots or dark rings, trochanters that are more clear than the femurs, slender previous femurs, and a clear connexivum with well-defined dark rectangular spots9. In addition, the species’ genital morphology is characterized by a median pygophore process that is short and triangular with a rounded tip, hairy and thin-tipped parameres, and a phallosome with a broad plaque and rounded upper region.
The internal genitalia of the putative male R. neglectus specimen presented were consistent with the morphological description of Lent & Jurberg8. However, no trypanosomatids were detected.
Despite the lack of infection in the collected specimen, R. neglectus is frequently infected by T. cruzi and T. rangeli10 and is the most common Rhodnius species to invade houses in Brazil. Recent data also indicate that R. neglectus plays an important role in maintaining the enzootic circulation of T. cruzi and T. rangeli in the Brazilian savanna11. This study increases the number of triatomine species reported from the State of Acre to eight and is also the first report of R. neglectus from the Brazilian Western Amazon Region. The occurrence of R. neglectus is alarming because, even though the species is wild, it can invade and colonize human dwellings and peridomiciles12,13, with colonies even reported from the tenth floor of a building in Araçatuba, State of São Paulo, Brazil14. The present study also confirms the findings of Gurgel-Gonçalves et al.15, who reported that R. neglectus occurs in human environments in the Brazilian the States of Mato Grosso, Mato Grosso do Sul, Goiás, Minas Gerais, and Tocantins, among others, and predicted that R. neglectus was also present in the State of Acre. Another alarming issue regarding the occurrence of R. neglectus in the State of Acre is that the species is often observed to colonize homes with palm thatch roofs14, which are common among homes in the Amazon region and may facilitate the domiciliation of R. neglectus.
Further studies should investigate the ecology and distribution of R. neglectus in the State of Acre, with the purpose of a future georeferencing and prophylaxis of vector transmission for this and other species that have been registered in this region.