obscurus Bruner , 1900 , Distrito de los Campos , Misiones , Northeastern Argentina : historical occurrence

Dichroplus obscurus Bruner, 1900 is closely allied to other eight species (D. conspersus, D. maculipennis, D. pratensis, D. porteri, D. robustulus, D. silveiraguidoi, D. vittatus and D. vittiger) that conform the Maculipennis group (Cigliano and Otte, 2003), widely distributed in Argentina, with a strong presence of some species in the Pampas, mainly in pastures, and also in Patagonia and the biogeographical regions of Monte and Espinal (Cigliano and Otte, 2003). Some of them also occur in Uruguay and Southern Brazil, and some have been cited for Bolivia, Chile and Paraguay (D. maculipennis: Brazil, Chile and Uruguay; D. pratensis: Bolivia, Brazil and Urguay; D. porteri: Chile; D. conspersus: Brazil, Chile; D. robustulus: Brazil, Uruguay, D. vittiger: Chile, D. silveiraguidoi: Brazil, Uruguay).

Dichroplus obscurus Bruner, 1900 is closely allied to other eight species (D. conspersus, D. maculipennis, D. pratensis, D. porteri, D. robustulus, D. silveiraguidoi, D. vittatus and D. vittiger) that conform the Maculipennis group (Cigliano and Otte, 2003), widely distributed in Argentina, with a strong presence of some species in the Pampas, mainly in pastures, and also in Patagonia and the biogeographical regions of Monte and Espinal (Cigliano and Otte, 2003).Some of them also occur in Uruguay and Southern Brazil, and  Nevertheless, the former record is doubtful because the species has not since been recorded from that locality that, in addition is a forest area in which the presence of D. obscurus is highly improbable.We consider that the D. obscurus record by Jorgensen (1911) for Misiones, may be due to erroneous labelling of the specimen.
In this paper we communicate the finding of a marginal and unstable D. obscurus population in Southern Misiones province, belonging to the phytogeographic Distrito de los Campos.This district extends from southern Misiones to the northeastern part of the neighboring province of Corrientes, and forms a gradual transition between the Paraná and Chaco biogeographic provinces (Cabrera, 1976;Giraudo et al. 2003), characterized by savannas which alternate with woodlands and forests of urunday trees (Astronium balansae).
The location of the population analyzed during the summers of 1999 through 2006 (27º26´30,7´´ S 55º52´49,7´´ W -113 meters above sea level), is indicated in Figure 1.A total of 18 individuals (10 males and 8 females) were studied.The scarcity of specimens is attributed by us to the marginal (thus, unstable) nature of the population.Morphometric measurements were obtained using high precision calipers (0.01 mm) and karyotyping was performed following Bidau and Martí (2001).Voucher specimens are deposited in the Laboratorio de Genética Evolutiva of the Facultad de Ciencias Exactas Químicas y Naturales, Universidad Nacional de Misiones.In some have been cited for Bolivia, Chile and Paraguay (D. maculipennis: Brazil, Chile and Uruguay; D. pratensis: Bolivia, Brazil and Urguay; D. porteri: Chile; D. conspersus: Brazil, Chile; D. robustulus: Brazil, Uruguay, D. vittiger: Chile, D. silveiraguidoi: Brazil, Uruguay).According to Cigliano and Otte (2003), D. obscurus occurs in Argentina (Santa Fe and Buenos Aires provinces), Brazil (Southern Rio Grande do Sul state), and Uruguay.However, they indicate that a specimen of D. obscurus deposited in the Academy of Natural Sciences of Philadelphia, was collected in Misiones province (Argentina) in January of 1911, by Jorgensen.

Figure 1 .
Figure 1.Map of Argentina emphasizing the province of Misiones.The red circle indicates the location of the Posadas population of Dichroplus obscurus (27º26´30, 7´´ S 55º52´49,7´´ W), and the white circle indicates the population cited by Jorgensen (Cigliano and Otte, 2003).
2 4.70 ± 0.1The presence of D. obscurus (Figure2) in Posadas was first reported and fully documented for the first time for Misiones province, byBidau and  Marti (2001)  who collected several individuals which were karyotyped and showed the unique D. obscurus chromosome complement described bySáez (1963)  that includes an autosomal fixed centric fusion and a neo-XY pair of sex chromosomes.D. obscurus and the closely related D. pratensis are very similar morphologically in external characters but may be identified through careful analysis of genitalia; however, they have been confused in the past, and many of the D. pratensis records for Corrientes province in Argentina byLiebermann (1963)  possibly belongs to D. obscurus.Thus, karyotyping is the simplest way to identify both species due to the uniqueness of their chromosome complements.

Finally
, we should mention the reference to the presence of D. obscurus in Misiones made byCigliano and Otte (2003)  and based in a single labeled specimen collected by Jorgenssen in 1911.Although the locality of the specimen is not specified in their publication, according to the maps showed (see their Figures) it would correspond to "San Javier-San José, Pindapoy" (Figure1, white circle in the map) where also a specimen of D. vittatus (another species of the Maculipennis group) was apparently collected.However, D. vittatus is a typical dweller of dry and arid environments, contrary to the Misiones location indicated inCigliano and Otte (2003), which may suggest that Jorgensen erroneously cited this specimen's location.It also suggests that this may be the case for the Misiones specimen of D. obscurus.

Table 1 .
Measurements (± Standard Error)in mm of six morphometric characters of Dichroplus obscurus from the Posadas population Number of individuals examined (N), Total body length (BL), length of left hind femur (F3L), length of left hind tibia (T3L), length of tegmina (TeL), mid-dorsal length of pronotum (PL) and height of pronotum (PH).