Biodiversity and distribution of lethaeine seed bugs (Heteroptera, Rhyparochromidae, Lethaeini) from Argentina

The tribe Lethaeini has received little attention in Argentina. In 2014, Dellapé recorded 9 genera and 15 species from this country. A comprehensive study of the Lethaeini (Heteroptera, Rhyparochromidae) from Argentina is presented. Herein three new species of Cryphula Stål, one new species of Cistalia Stål, and the male of Cryphula australis Berg are described. The genus Petissius Distant and the species Cistalia binotata Slater & Baranowski, Cistalia neotropicalis Slater & Baranowski, and Petissius spinipes Stål are reported for the first time from Argentina; also, the known distribution is extended for many of the previously recorded species. A generic key, keys to species, and distributional maps to the Argentinean species are also given. Dorsal habitus photographs of all species and the male and female genitalia of the new species are provided to facilitate identification. The Lethaeini fauna from Argentina is increased to 10 genera and 22 species. The distribution of the tribe in the country is mainly Neotropical into the Chacoan Subregion, with most of the species distributed in the Chacoan and Pampean provinces (Chacoan Domain) and Parana Forest Province (Parana Domain). Only Rhaptus quadricollis appears to be an Andean element, with most of the known records in the South American Transition Zone (Monte Province).


Background
Rhyparochromidae is the most diverse group of Lygaeoidea, with more than 2,000 species. The family contains two subfamilies, Plinthisinae and Rhyparochrominae, the latter with 14 tribes (Henry 1997). The Plinthisinae and seven tribes of Rhyparochrominae have been recorded from the Neotropical Region; among them, five have been recorded from Argentina: Antillocorini, Lethaeini, Myodochini, Ozophorini, and Udeocorini.
The tribe Lethaeini includes 38 genera and more than 160 species worldwide (Li et al. 2011) and shows its greatest diversity in the tropical and subtropical parts of the Afrotropical, Oriental, and Australian regions (Slater 1986). It is one of the most diverse tribes in the Neotropics, with 13 genera and 36 species known.
Lethaeines are recognized as monophyletic by the linear placement of trichobothria on abdominal sternum V, a rounded buccular groove joined immediately behind the labium, carinate juga, a trichobothrium at each anterior corner of the pronotum, loss of the Y chromosome, extreme modification of the sperm reservoir, immatures with a reduced scent gland between abdominal terga 5 and 6, and the presence of an iridescent area or areas on the head (Ashlock 1964;Slater and Woodward 1982;O'Donnell 1991).
Very little is known about the biology of Lethaeini; as with many other members of the family Rhyparochromidae, most species seem to be ground-litter inhabitants and seed predators (Sweet 1964; Baranowski and Slater 1979;Slater and Baranowski 1990;O'Donnell 2001;Cervantes and Gamez 2006). The tribe has received little attention in Argentina. Dellapé (2014) recorded 9 genera and 15 species from this country. In this contribution, four new Lethaeini species are described, and one genus and three species are recorded for the first time from Argentina; also, the known distribution is extended for many of the previously recorded species. A generic key, keys to species, and distributional maps to the Argentinean species are also given. Dorsal habitus photographs of all species and the male and female genitalia of the new species are provided to facilitate identification.  (Figures 3C and 4).

Cistalia parva n. sp. Diagnosis
This new species can be distinguished by its small size, females smaller than 5 mm and males smaller than 4 mm, and the thick and incrassate antenna, with a prominently fusiform pedicellus ( Figure 3D).
Abdomen: Shining below, clothed with long decumbent setae. Genitalia: Sperm reservoir as in Figure 5A; male paramere as in Figure 5B.

Female
Spermatheca as in Figure 5C.

Etymology
From the Latin 'parv-', meaning 'small', in reference to the small size of this species.

Cryphula Stål 1874
This genus comprises 11 species ranging from the northern USA and the West Indies to Argentina. Previously, three species were known from Argentina: Cryphula dubia (Berg 1883) from Buenos Aires and Corrientes provinces (Berg 1883;Melo et al. 2004;Dellapé and Carpintero 2012); C. affinis (Distant 1901) from Chaco Province , and here recorded from Buenos Aires, Córdoba, Corrientes, Entre Ríos, Formosa, Misiones, Salta, and Santiago del Estero provinces; and C. australis (Berg 1884) known from Buenos Aires Province (Berg 1884;Dellapé and Carpintero 2012), and here recorded from Córdoba, Salta, Santa Fe, and Santiago del Estero provinces. In the present contribution, we describe three new species from Argentina and the male of C. australis Berg.
Abdomen: Brown, with short recumbent setae. Genitalia: Sperm reservoir and paramere as in Figure 8A,B.

Cryphula brunnea n. sp. Diagnosis
This species can be distinguished by the uniformly dark brown pronotum and scutellum and the pale basal half of hemelytra ( Figure 6D).

Description of macropterous female holotype
Total length 4.23. General coloration dark brown ( Figure 6D). Head and pronotum shiny, scutellum dull. Head, pronotum, and scutellum with short decumbent setae; hemelytra with short decumbent and longer erect setae.

Male
Genitalia (from paratype indicated) as in Figure 8D,E.

Description of macropterous male holotype
Abdomen: Brown with short recumbent setae. Genitalia (from paratype indicated): Sperm reservoir and paramere as in Figure 8G,H.

Female
Spermatheca (from paratype indicated) as in Figure 8I.

Etymology
The specific epithet refers to the pale pronotal humeral angles. This species can be distinguished by the particular coloration pattern of pronotum, scutellum, and hemelytra: Pronotum brown except middle anterior margin, lateral margins, and most of posterior lobe paler; posterior lobe at middle and two small maculae on humeral angles darker; scutellum brown, with two pale spots laterally and slightly paler apically; and hemelytron mostly light brown with two large maculae medially. Scutellum with three small and diffuse spots; meso-and metafemur light brown ( Figure 6H).

Description of male holotype
Total length 3.43 ( Figure 6H).
Abdomen: Brown, with abundant short recumbent setae. Genitalia (from paratype indicated): Sperm reservoir as in Figure 8J, paramere as in Figure 8K.

Female
Spermatheca (from paratype indicated) as in Figure 8L.

Etymology
The specific epithet refers to the collector of most of the specimens known of this new species, Hermes A. Riviére.

Type material Esuris Stål 1874
This monotypic genus is known from Brazil and Argentina. Esuris terginus Stål 1874 is known from Buenos Aires Province (Dellapé and Carpintero 2012) and is here recorded from Córdoba, Chubut, and La Pampa provinces (Figure 2).

Remarks
The specimens from Chubut Province show a V-shaped iridescent spot on the head ( Figure 9C), which is different from the sub-quadrangular spot ( Figure 9D) present in the rest of the studied specimens (also present in the type material); nevertheless, all the specimens share the external morphology and exhibit the particular highly modified paramere characteristic of the species (O'Donnell 1991).

Neopetissius O'Donnell 2001
This genus comprises six species ranging from Mexico and the West Indies to Argentina. The only species recorded from Argentina, Neopetissius perplexus O'Donnell 2001, is known from Buenos Aires, Corrientes, and Entre Ríos provinces (Carpintero et al. 2006), and herein is also recorded from Santa Fe and Santiago del Estero provinces ( Figure 12).

Neopetissius perplexus O'Donnell 2001
This species can be recognized by its most allied species, Neopetissius froeschneri O'Donnell, by the presence of fine punctures on the pronotal calli that are absent in the former species and the different sperm reservoir (O'Donnell 2001) ( Figure 10D).

Petissius Distant 1893 first country record
This genus comprises two species mostly known from Central to northern South America. Herein we record the genus and species P. spinipes Stål 1874 from Argentina for the first time ( Figure 12).

Petissius spinipes Stål 1874
This species can be distinguished by the profemur of the male with a field of tuberculate hairs postero-ventrally and the presence of four distal femoral spines (Baranowski and Slater 2005, following O'Donnell 1986) ( Figure 10E).

Rhaptus Stål 1874
This genus comprises only one species, Rhaptus quadricollis (Spinola 1852), from Argentina and Chile. In Argentina, it had been recorded from Corrientes and Mendoza provinces (Berg 1880), but at least the record from Corrientes Province is doubtful. Herein we record R. quadricollis from Chubut, Neuquén, and San Luis provinces (Figure 12).
Comparing the specimens from Argentina with two male specimens from Chile, we noticed that Chilean specimens are larger with a more quadrangular pronotum, a shorter rostrum (barely exceeding the procoxa in one specimen), and a darker general coloration. The specimens from Argentina show a trapezoidal pronotum, a longer rostrum, most of the time reaching the mesocoxae, and a lighter coloration, especially on the hemelytra. This last feature is absent in the specimens from western Chubut (near Esquel). Despite these differences, the male genitalia are conspecific with the specimens examined and, therefore, we consider all material R. quadricollis.
Nothing is known about the biology of this species; the specimens found near Esquel (Chubut Province) were collected under rocks in an herbaceous steppe (60% to 70% coverage) affected by sheep grazing.  (Beeskow et al. 1987).

Discussion
Previous works have reported 9 genera and 15 species of Lethaeini from Argentina, with the addition of the genus and the species Petissius, Cistalia binotata, and C. neotropicalis as new records and four new species, Cistalia parva, Cryphula brunnea, C. humeralis, and C. rivierei; the lethaeine fauna of Argentina is increased to 10 genera and 22 species.
The distribution of the tribe in the country is mainly Neotropical into the Chacoan Subregion, with most of the species distributed in the Chacoan and Pampean provinces (Chacoan Domain) and Parana Forest Province (Parana Domain) (Morrone 2014). The most common species in central Argentina is Stictolethaeus inerme, with its distribution extending to the South American Transition Zone (Monte Province). The entomofauna of this area shows an overlap of Neotropical and Andean insect taxa, and according to Morrone (2006), Monte Province fauna is basically of Chacoan origin with some elements from the Patagonian, Prepunan, and Subantarctic areas. As it has been suggested, the Monte represents an impoverished Chaco (Willink 1988). Only Rhaptus quadricollis appears to be an Andean element, with most of the known records from the South American Transition Zone (Monte Province).
The Patagonian records of S. inerme, Esuris terginus, and Petissius spinipes suggest that the lethaeine fauna from southern Argentina, an area scarcely explored, could be more diverse than we currently know. The only two records of P. spinipes, one from Iguazú National Park (Paranaense forest) and the other from Cerro Bayo (Nothophagus forest), are 2,300 km away from each other and show a big gap between records; this can be explained by the geophilous habits of the lethaeines that require a specific collecting method.

Conclusions
The knowledge about the diversity and distribution of this group of seldom collected rhyparochromids in Argentina is far from complete, and more thorough explorations are needed to improve the understanding of this tribe.