The taxonomic status of Triatoma dimidiata (Latreille, 1811) is, by far, the most discussed within Triatominae. Molecular studies have recovered at least three independently evolving lineages in T. dimidiata across its range. The original description of T. dimidiata (as Reduvius dimidiatus) included few taxonomic characters, and no types were assigned. To define and describe the cryptic diversity within T. dimidiata sensu lato (s.l.), a neotype must be designated. For this purpose, all 199 specimens identified as T. dimidiata from the collections of the Smithsonian Institution – National Museum of Natural History and the American Museum of Natural History, ranging from Peru to Mexico, were studied. Only one specimen (from Tumbes, Peru) matched the combination of characters as listed in the original description, and it is herein formally designated as the neotype for T. dimidiata. The neotype is morphologically described and DNA sequences of its whole mitochondrial genome and the nuclear second internal transcribed spacer region (ITS2), commonly used in triatomine molecular systematics studies, are presented and compared to other publicly available sequences of T. dimidiata s.l. in GenBank. Our results suggest that T. dimidiata sensu stricto (s.s.) is somewhat rare and, therefore, unlikely to serve as a major vector of Chagas disease.

Chagas disease, Latreille, Peru, South America, vector

Triatoma dimidiata (Latreille, 1811) (Hemiptera, Reduviidae) has long been assumed to be the most widespread species of Triatominae, a reduviid subfamily of Chagas disease vectors. The long-standing discussion about its taxonomic status, however, is consequential of an original description with no type specimens defined and very few characters described by Latreille (1811).

Triatoma dimidiata was originally described as Reduvius dimidiatus by Latreille in Humboldt and Bonpland (1811), where the author only provided a drawing of the dorsal view of the described specimen (Fig. 1), a male specimen, pale yellow with body black, and no scale to size. Latreille highlighted the presence of 1+1 discal tubercles and 1+1 lateral tubercles on the pronotum, as well as 1+1 subapical “spines” on fore- and mid-femora. The locality was listed as Villa de Ybara, Peru (now Ecuador).

Figure 1. 

Original drawing presented by Latreille (1811) illustrating the description of Reduvius dimidiatus.

About 150 years after the description of T. dimidiata, two new species had been described, and later synonymized to T. dimidiata: Triatoma capitata Usinger, 1941 and Triatoma maculipennis Pinto, 1931. In their taxonomic revision of Triatominae, Lent and Wygodzinsky (1979), upon observation of 160 specimens from the whole geographic range (Mexico to Peru), highlighted the “highly variable” coloration and other morphological characters of the specimens observed. They concluded, however, that these specimens have not segregated “into clearly separable allopatric populations”; synonimizing both T. capitata and T. maculipennis with T. dimidiata.

The availability of molecular sequencing techniques led to the discovery that T. dimidiata, when comprising the recently described Triatoma mopan Dorn, Justi & Dale, 2018 and Triatoma huehuetenanguensis Lima-Cordón & Justi, 2019, is a paraphyletic species complex (Justi et al. 2014b, 2016) which includes at least three independently evolving lineages (Bargues et al. 2008; Dorn et al. 2009, 2016; Justi et al. 2018).

Here we set out to assign and describe a neotype of T. dimidiata sensu stricto (s.s.) conforming to the original description of Latreille (1811) and from as close to the original locality as possible, in order to facilitate the understanding of the systematics of T. dimidiata sensu lato (s.l.). This solid taxonomic platform allows for the conduct of future studies to facilitate better understanding of the composition and internal systematics of species comprising Triatoma dimidiata s.l.. Given that most of the diversity in T. dimidiata s.l. is reported based on molecular rather than morphological data, the whole mitochondrial genome and nuclear rDNA sequences of the second internal transcribed spacer (ITS2) of the neotype specimen are also presented.

The specific status of Triatoma dimidiata s.l., a major vector of Chagas disease in the New World, has long been debated among Triatominae systematists (Lent and Wygodzinsky 1979; Dorn et al. 2007, 2016; Bargues et al. 2008; Monteiro et al. 2013; Justi et al. 2018). Two taxa originally described as separate species and later designated as T. dimidiata subspecies-Triatoma dimidiata maculipennis (Neiva 1914) and Triatoma dimidiata capitata Usinger, 194–were synonymized with T. dimidiata by Lent and Wygodzinsky (1979). With the application of molecular approaches, it has become increasingly clear that the entity commonly described as T. dimidiata comprises several species, which may or may not differ in vector competency. Most recently, two other species-T. mopan and T. huehuetenanguensis-have been formally described within the T. dimidiata group. Adding to the incredible diversity and, at the same time, similarity of the T. dimidiata s.l. lineages, is the fact that when a cluster analysis is performed, over 50 distinct clusters are found, regardless of the marker used. However, when compared to other lineages within Triatominae, pairwise distances within T. dimidiata s.l. for both CytB and ITS2 are much lower.

The designation of a neotype was critical to fix the identity of T. dimidiata s.s. and better understand the component members of this very diverse and epidemiologically important group moving forward. In this study, our goal was to find a specimen as close as possible as the one Latreille described in 1811. With Latreille’s original specimens untraceable, we re-examined all USNM and AMNH T. dimidiata specimens used by Lent and Wygodzinky (1979) in their work, searching for the optimal specimen fitting the original description, to assign as the neotype. We noted that, while all exhibit a similar overall morphology, specimens markedly differed in several important taxonomic features from one locality to another, suggesting that the specimens used by Lent and Wygodzinsky (1979) in fact comprised several closely related taxa within T. dimidiata s.l.. These findings go some way to explaining the wide diversity of taxonomic characters, bionomics, and distribution currently attributed to T. dimidiata in the literature.

The most recent example of how deeper knowledge of T. dimidiata s.l. taxonomy is necessary, is the great effort by Rengifo-Correa et al. (2021). In this study, the authors performed a morphological review and published a long overdue diagnostic key to the species of the T. phyllosoma species group. Unfortunately, however, the taxonomic uncertainty regarding the status of T. dimidiata led the authors to include, as such, what seems to be at least three distinct lineages [see fig. 3D-F of Rengifo-Correa et al. (2021)]. Upon comparison of the diagnosis for T. dimidiata provided there, and the neotype, several disparities were found: (1) the anteocular region of the neotype is 2× the length of the postocular region, not 2.5–3× as stated by Rengifo-Correa et al., (2) the first antennal segment does not reach the apex of the clypeus on the neotype, (3) comparison of the images [fig. 3D-F of Rengifo-Correa et al. (2021)] shows disparities in the shape and coloration of the anterolateral angles; shape, color, and rugosity of the pronotum; and shape, color, and location of the wing spots, in relation to the neotype.

Despite examining all 199 available specimens housed in the AMNH and USNM collections, we found only one specimen that exactly matched Latreille’s (1811) original description of T. dimidata. Similarly, only one of over 100+ publicly available mtDNA CytB sequences clustered with the neotype. Clustering analyses of ITS-2 sequences, however, showed the neotype sequence to be grouped with 14 other publicly available samples.

These observations are consistent with the hypothesis previously raised that T. dimidiata s.s. would have originated in northern Central America and been, somehow, introduced to South America (Bargues et al. 2008). Combined with the young age (<10 My) of the T. dimidiata s.l. lineage (Justi et al. 2016), these results show that the radiation of the group likely occurred very quickly and recently, like the radiation of south American Triatoma (Justi et al. 2016) that comprise several morphologically differentiable species, but for which current widely used molecular markers cannot be used for reliable species identification (Justi et al. 2014a).

With ITS-2 being a more conserved genetic marker, it is cautious to rely on CytB for the most accurate identification of such a young lineage, which lead us to conclude that true T. dimidiata is a rare species, with a seemingly limited range; contradicting current opinion that it is one of the most widespread species of the genus Triatoma, and consequently casting doubt on its perceived role as the major vector of Chagas’ disease in the New World. Efforts are urgently needed to better assess the taxonomic status of the genetically diverse entities within the T. dimidiata s.l. and assess which of the component taxa are truly involved in transmission of this increasingly important disease in the New World.

We thank Thomas Henry (NMNH), Randall T. Schuh and Ruth Salas (AMNH) for unrestricted access to the archive specimens, and Yvonne-Marie Linton for her comments and suggestions on the original manuscript. This study was conducted while S.A.J. held a National Research Council Research Associateship at the Walter Reed Biosystematics Unit (WRBU) and Walter Reed Army Institute of Research (WRAIR). The study was funded by the Armed Forces Health Surveillance Division (AFHSD) – Global Emerging Infections Surveillance (GEIS) Branch core support to WRBU (P0030_21_WR to Yvonne-Marie Linton). The material published reflects the views of the authors and should not be misconstrued to represent those of the Department of the Army or the Department of Defense. The funders had no role in study design.