Panstrongylus noireaui sp. nov. from Bolivia is described based on male and female specimens. Although morphologically almost indistinguishable from Panstrongylus rufotuberculatus (Champion, 1899), the new species shows remarkable chromosome and molecular features, which are very distinctive among all others Panstrongylus species. The new species is also separated by some characteristics of the processes of the endosoma of the male genitalia. An updated key for species of Panstrongylus is provided.

Chagas disease vectors, genitalia, kissing bug, taxonomy

The Triatominae are classified as a subfamily of Reduviidae (Hemiptera, Heteroptera), defined by their blood-sucking habit and morphological adaptations associated with host-finding and blood-feeding (Schofield and Galvão 2009). Currently, there are 154 extant and three fossil species distributed in 18 genera and five tribes in Triatominae (Dale et al. 2021; Galvão 2021). All of them are considered as potential vectors of the protozoan Trypanosoma cruzi (Chagas, 1909), the causative agent of Chagas disease or American trypanosomiasis, which still is a serious health problem to most Latin American countries (Arias et al. 2021). Among the five tribes included in Triatominae, the tribe Triatomini has ten genera (Galvão 2021), among which Panstrongylus Berg, 1879 has several species involved in the transmission of T. cruzi in Central and South America (Patterson et al. 2009).

Berg (1879) created the genus Panstrongylus for a single new species he was describing, P. guentheri Berg, which is the type species of this genus by monotypy. He regarded Panstrongylus as being close to Lamus Stål, 1859. Champion (1899) described Lamus rufotuberculatus based on a single male from Panama. As Lamus Stål, 1859 was a preoccupied name by Lamus Stål, 1854, a genus of Pentatomidae, Kirkaldy (1904) proposed a new name for it, Mestor Kirkaldy. The species was transferred to Panstrongylus by Pinto (1931), with the resulting new combination, P. rufotuberculatus (Champion). Pinto (1931) argued that Mestor should be considered a synonym of Panstrongylus. Usinger (1939), however, maintained these two latter genera as valid. Lent and Pifano (1940) strongly defended the synonym of Mestor under Panstrongylus as proposed by Pinto (1931), which was accepted by subsequent authors so far, with the exception of Usinger (1944), who still considered the validity of both genera. The main novelties involving species of Panstrongylus, after the classical taxonomical treatment of the group by Lent and Wygodzinsky (1979), were recently summarized by Monteiro et al. (2018), Costa et al. (2021), Galvão (2021), and Paiva et al. (2022).

Panstrongylus has been considered monophyletic based on morphological features (Lent and Wygodzinsky 1979). However, molecular studies using several nuclear (ITS-2, 18S, 28S, ultraconserved elements), and mitochondrial (16S, coI, coII, cyt b) markers demonstrated a paraphyletic status for Panstrongylus (Hypša et al. 2002; Marcilla et al. 2002; Justi et al. 2014; Monteiro et al. 2018; Kieran et al. 2021; Pita et al. 2021).

Panstrongylus rufotuberculatus has been recorded in several countries: Mexico, Panama, Costa Rica, Colombia, Venezuela, French Guiana, Suriname, Ecuador, Peru, Bolivia, Brazil, and Argentina (Galvão et al. 2003; Bérenger et al. 2009; Patterson et al. 2009; Hiwat 2014).

Beginning with the observation of Lent and Pifano (1940), several authors have recorded natural infection of P. rufotuberculatus with T. cruzi as summarized by Patterson et al. (2009). These latter authors also summarized host observation to this species, which have included different wild and domestic mammals and humans as well.

Panstrongylus rufotuberculatus has been considered as a sylvatic species, which frequently invades human dwellings as it is attracted by electric light (Lent and Wygodzinsky 1979; Salomón et al. 1999; Patterson et al. 2009; Gorla and Noireau 2010). However, truly domestic populations were reported only in some areas of southern Ecuador (Abad-Franch et al. 2001), while breeding colonies have been found inside dwellings in Bolivia and Peru too (Marín et al. 2007; Gorla and Noireau 2010). This species has been incriminated as a vector of Chagas disease in Andean and coastal foci of Ecuador, whereas its presence in the municipality of Amalfi (Antioquia, Colombia) is considered as a major epidemiological risk factor (by being the second most common triatomine caught inside buildings) (Wolff et al. 2001; Patterson et al. 2009; Gorla and Noireau 2010).

Following the description of the male holotype by Champion (1899), Lent and Pifano (1940), Lent and Jurberg (1975) and Lent and Wygodzinsky (1979) provided thorough redescriptions of P. rufotuberculatus. These latter authors and some others, e.g., Salomón et al. (1999) and Hiwat (2014), have emphasized the morphological and chromatic variation of this species. Its male genitalia was thoroughly described and figured by Lent and Jurberg (1975), while Lent and Wygodzinsky (1979) commented on some features of it.

Although almost all species of Panstrongylus have been recorded as possessing only a paired [lateral] process in the endosoma (Lent and Jurberg 1975; Lent and Wygodzinsky 1979; Jurberg et al. 2001; Papa et al. 2003; Bérenger and Blanchet 2007; Ayala 2014, pers. comm.), P. rufotuberculatus has been recorded as the only species of the genus with two paired [lateral] process in the endosoma (Lent and Jurberg 1975; Lent and Wygodzinsky 1979). This latter feature, together with presence of body scalelike setae and an apically bilobed clypeus were all considered the three apomorphies of this species in the phylogenetic scheme proposed by Lent and Wygodzinsky (1979). These authors, however, recorded that these latter two features in P. rufotuberculatus were also present as what they considered as plesiomorphic states among Panstrongylus spp. (not scalelike setae and not bilobed [unilobed] clypeus, respectively). Salomón et al. (1999), by their turn, recorded scalelike setae but only unilobed clypeus among specimens of P. rufotuberculatus from Argentina.

The female genitalia in Triatominae was considered uniform by several authors and, by consequence, without taxonomic significance (Lent and Wygodzinsky 1979; Rodrigues et al. 2018). However, in just over the last decade several works, summarized by Rodrigues et al. (2018), have proven that the study of female genitalia is useful in many cases to the taxonomy in Triatominae, showing that in fact they present characteristics of diagnostic value. Rodrigues et al. (2018) studied, compared, and figured with SEM images the female genitalias of 26 species belonging to seven genera of Triatominae, including P. rufotuberculatus.

Pita et al. (2021) through a multidisciplinary approach suggested speciation within populations of P. rufotuberculatus. Extensive chromosomal analyses supported that the two chromosomal groups could represent different closely related species. Molecular and morphometric analyses reinforced the marked cytogenetic differences. Therefore, they proposed that Bolivian individuals constituted a new Panstrongylus species, which is herewith described as Panstrongylus noireaui sp. nov., based on male and female specimens. A detailed morphological description of the new species is provided, comparing its characteristics with extensive previous data from the literature, and examination of specimens of Panstrongylus rufotuberculatus from different countries.

All type specimens of Panstrongylus noireaui sp. nov. and non-type specimens of Panstrongylus rufotuberculatus examined here are deposited in the “Coleção de Triatomíneos do Instituto Oswaldo Cruz” (CTIOC) of the “Laboratório Nacional e Internacional de Referência em Taxonomia de Triatomíneos” (LNIRTT) at Oswaldo Cruz Institute, Rio de Janeiro, Brazil.

All the figures were produced by the first author (HRG-S). The photographs were obtained using digital cameras (Nikon D5600 with a Nikon Macro Lens 105 mm, Sony DSC-W830). Drawings were made using a camera lucida. Dissections of the male genitalia were made by first removing the pygophore from the abdomen with a pair of forceps and then clearing it in 20% NaOH solution for 24 hours. The dissected structures were studied and photographed in glycerol. Images were edited using Adobe Photoshop CS6.

General morphological terminology and particularly those of the male genitalia portions used here follows mostly Lent and Wygodzinsky (1979), while to female genitalia Rodrigues et al. (2018) is followed. However, some portions of head terminology follow Schuh and Weirauch (2020), in which “rostrum” is named labium. In this particular, the [visible] segments of the labium are numbered II to IV, given that the first segment is said to be lost or fused to the head capsule (Weirauch 2008). In addition, according to Schuh et al. (2009), for the convention of numbering labial segments in the Reduviidae, the apical segment should be considered as number four and then counted backwards towards the base. Jugum (pl. juga) sensu Lent and Wygodzinsky (1979) is named mandibular plate. In male genitalia, “vesica” as recognized by Lent and Jurberg (1975) and Lent and Wygodzinsky (1979) has been considered to be absent in reduviids. The assumed equivalent structure in reduviids is a somewhat sclerotized appendage of the phallosoma or the endosoma (Forero and Weirauch 2012), but not the homologous vesica that occurs in other heteropterans such as Pentatomomorpha (Rédei and Tsai 2011). Thus, this term is not used here for the median process of endosoma, which is named as such.

When describing label data, a slash (/) separates different labels.

It is noteworthy that P. rufotuberculatus has been considered the only species of Panstrongylus to have two paired [lateral] endosoma process (Lent and Jurberg 1975; Lent and Wygodzinsky 1979; Jurberg et al. 2001; Papa et al. 2003; Bérenger and Blanchet 2005; Ayala, pers. comm., 2014). However, as recorded here, the second alleged paired endosoma process described by Lent and Jurberg (1975) was in fact a misinterpretation of the flap like prominence of the dorsal phallothecal plate as well as a moderately elongate ventral process of it. A similar structure was observed in P. noireaui sp. nov. Therefore, as in all species of Panstrongylus the processes of endosoma have shown to possess only a paired lateral process, it seems that this is a constant feature in this genus. Thus, the consideration of two paired endosoma process as an apomorphy of P. rufotuberculatus as proposed by Lent and Wygodzinsky (1979) is not sustainable when confronted with the evidence obtained here. On the other hand, two other apomorphies attributed to P. rufotuberculatus by these authors, i.e. presence of body scalelike setae and an apically bilobed clypeus, would need to be confirmed in future more extensive works, given they have been shown not only to be variable but commonly absent (Lent and Wygodzinsky 1979; Salomón et al. 1999; present work).

Because the dissection of the male genitalia is usually carried out on only one specimen of each species (Lent and Jurberg 1985), the variability of these structures may remain unrecorded. Among predatory Reduviidae (Gil-Santana et al. 2013) and particularly Triatominae (Lent and Jurberg 1985; Pires et al. 1998) qualitative differences in some phallic structures of male genitalia have been recorded when more than a male specimen of the same species had its genitalia dissected (e.g., Costa et al. 1997). Therefore, despite not being the main objective of this work, four males of P. rufotuberculatus with diverse dimensions and from different localities as well as two males of P. noireaui sp. nov. (out of three) were dissected in order to perform a preliminary evaluation of a possible male genitalia variability. While the male genitalia structures of P. noireaui sp. nov. were shown to be very similar, in P. rufotuberculatus the median process of endosoma (“vesica” sensu auths.) was shown to be increasingly larger how much bigger was the male examined. It was strikingly diverse from many previous observations (Lent and Jurberg 1985; Pires et al. 1998; Gil-Santana et al. 2013), which have recorded variations in shape or number of phallic structures but not in their size. Costa et al. (1997), although have recorded that the “vesica” of Triatoma brasiliensis Neiva, 1911 was variable in size, did not provide any additional information about other characteristics of the males examined by them possibly related to this variable, such as variation of their body size. The variation in size of the median process of endosoma also contradicts the current evidence to insects in general, which suggests that the allometric slopes of genitalia are lower than those of other body parts, giving rise to the “one size fits all” hypothesis (Eberhard et al. 1998; Schulte-Hostedde and Alarie 2006). Therefore, future studies, possibly including morphometry and dissection of more specimens of P. rufotuberculatus and other triatomine species, should be carried out to clarify the preliminary observations recorded here.

When considering all the morphological and chromatic variation recorded to P. rufotuberculatus (Lent and Wygodzinsky 1979; Salomón et al. 1999; Hiwat 2014; this work) (Table 5), almost all features of P. noireaui sp. nov. lie within part of all variation observed to the former species (Table 6). Yet, while measurements of males of P. noireaui sp. nov. are comparable to those of smaller males of P. rufotuberculatus, females of the new species have been shown to be distinctly smaller (Table 6). However, until more specimens can be examined in order to confirm (or not) possible differences and/or reach a minimal number to allow statistical inference of data, these differences will not be considered to separate these species from each other.

Besides the difference between the ventral process of flap like prominence of phallothecal plate (Figs 9, 14), the smooth lateral endosoma process of P. noireaui sp. nov. (Fig. 10) in comparison with the finely and densely denticulate lateral endosoma process of P. rufotuberculatus (Figs 15, 16) is an objective and reliable morphological feature to separate these species. It is noteworthy that analogous taxonomic situations occur among other species of Triatomini as follows. Triatoma maculata (Erichson, 1848) and T. pseudomaculata Corrêa & Spínola, 1964 are extremely similar and cannot be easily distinguished from each other based on external characters alone; only the striking structural differences of the endosomal processes of the phallus [lacking apical teeth, with ribbon-shape sclerotizations in T. maculata and delicately striate and denticulate in T. pseudomaculata] allow secure identification (Lent and Wygodzinsky 1979). Similarly, Triatoma arthurneivai Lent & Martins, 1940 and T. wygodzinskyi Lent, 1951 are very similar chromatically and in their external morphology, with minor color differences, which may be subject of slight variation. However, the structure of endosoma processes (with ~ 100 teeth in the first species and ~ 20 in the latter) is sufficient to differentiate these species (Lent and Wygodzinsky 1979).

Thereby, although P. noireaui sp. nov. has proved to be morphologically very similar to P. rufotuberculatus, the differences observed in male genitalia are analogous to other cases of close morphological species included in Triatomini as referred just above. Therefore, their separation based in differences of the male genitalia, even if considered by themselves alone, would have good grounds in the taxonomy of Triatominae. At the genetic level, P. noireaui sp. nov. presents very different chromosomal and molecular characteristics compared to the other Panstrongylus species studied so far (Pita et al. 2021) (Table 7). Out of the eight Panstrongylus species cytogenetically described, P. noireaui sp. nov. is the only one that has a simple sex male mechanism (XY), while the other Panstrongylus have multiple sex chromosomes (X₁X₂Y or X₁X₂X₃Y) (Panzera et al. 2021). In addition, the chromosomal location of the 45S ribosomal DNA clusters is distinctive character of this new species. In P. rufotuberculatus, like all Panstrongylus species analyzed hitherto, the rDNA clusters are localized on an autosomal pair, while in P. noireaui sp. nov. are localized in both sex chromosomes (X and Y). Both chromosomal markers (sex chromosome system and location of ribosomal clusters) are species-specific characters, being their variation within the same species an exceptional event (Pita et al. 2021, 2022). Moreover, mitochondrial DNA markers showed a remarkable genetic diversity between this new species with all others Panstrongylus species, higher than the expected for conspecific populations (Pita et al. 2021). Sequence analyses of cyt b and coI fragments revealed high nucleotide divergence between P. noireaui sp. nov. with P. rufotuberculatus samples from Colombia, Ecuador, and Mexico, showing Kimura 2-parameter distances higher than 10% (10.7–18.7% for cyt b and 10.6–15.8% for coI) (Pita et al. 2021). Therefore, the morphological evidence presented here is in agreement with previously published genetic data, which reveals that P. noireaui sp. nov. represents a new species of Panstrongylus, morphological and evolutionarily very close to P. rufotuberculatus.

We thank José Manuel Ayala L. who kindly reexamined the male genitalia of Panstrongylus martinezorum by the request of first author (HRG-S) and provided crucial information about the endosoma processes of this species. We are also grateful to an anonymous reviewer, Jane Costa, Jean-Michel Bérenger, and Jader de Oliveira, for their valuable comments and suggestions.