EMILIO BALLETTO, LUIGI A. CASSULO , SIMONA BONELLI : An annotated Checklist of the Italian Butterflies and Skippers (Papilionoidea, Hesperiioidea) -pag.101-
"It has long been known that Melitaea athalia and M. nevadensis (often referred to as M. celadussa) are separate taxa. Their male genitalia, however, demonstrate that they form a 20–100 miles broad hybridisation area, spanning roghly West to East, across France, Switzerland and N.E. Italy (Higgins 1932. Entomologist, 65: 217). M. athalia inhabits areas north of this belt, while M. nevadensis occurs in C.S. France and most of Italy. Extensive DNA sequencing by Leneveu et al. (2009. Biol. J. Linn. Soc., 97:346–361) have demonstrated that M. nevadensis is not, as previously expected, sister taxon to M. athalia, The latter taxon, in fact, is genetically closer to some Asiatic species such as M. ambigua (ranging from the Altai to Japan) than it is to M. nevadensis. We are faced therefore, with the alternative of either considering a paraphyletic Melitaea athalia (s. l.), or two separate species (i.e. M. athalia and M. nevadensis), many specimens of which, having hybrid origin, cannot be assigned to any of the two. As concerns Italy, M. athalia (s. str.) occupies only the extreme N.E. (i.e. E. Trentino-Alto Adige, E. Veneto and Friaul), while only M. nevadensis is found in the rest of the country. The Italian hybridization area is about 80 km broad and extends along the Resia (Reschsen) Pass to Venice line.